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GFDL Past Events & Seminars - 2017

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Date Speaker Affiliation Title of Presentation
Jan. 11Alexis BergGFDL/Princeton UniversityGlobal warming, continental drying
In this talk we will discuss whether global warming implies an overall more arid climate over land (as is most commonly argued in the literature), or a wetter one. I will review some elements of the literature in favor of the different perspectives, and present recent results based on CMIP5 climate model projections regarding changes in aridity over land which shed some light on this discussion.
Jan. 12Adrian JenkinsCambridge, UKOcean forcing of Marine Ice Sheet Change in the Amundsen Sea Sector of Antarctica
Mass loss from the West Antarctic Ice Sheet is driven by changes at the marine margins, which have been particularly prominent in the Amundsen Sea. Thinning of the ice shelves has allowed many outlet glaciers to accelerate and thin, resulting in inland migration of their grounding lines. Observations of water properties at the front of Dotson Ice Shelf have been made eight times in the past 17 years, sampling a cycle of warming and cooling and allowing estimates to be made of the changing meltwater flux from the ice shelf. Depth-averaged temperatures in front of the ice shelf changed by approximately 1 deg C and drove a factor three change in melting at the base of the ice shelf. High melting during the late 2000s drove grounding line retreat, but readvance has occurred in places during the subsequent cool phase. Similar variability has been reported at Pine Island Glacier, but the glacier response has been subtly different as a result of differing bed geometry near the grounding line. The picture that emerges is one of step-wise grounding line retreat between localised high points in the bed, forced by a decadal cycle of warming and cooling in the waters of the continental shelf. This process is particularly prominent in the Amundsen Sea because: the warm waters on the continental shelf increase the sensitivity of ice shelf melting to temperature change; the amount of warm water on the shelf is sensitive to atmospheric forcing; the regional atmospheric circulation is highly variable, at least in part because of the impact of tropical variability.
Feb. 1GFDL Poster ExpoWinter 2017 GFDL Poster Expo
Winter 2017 GFDL Poster Expo
Feb. 8Levi SilversGFDLDecadal variations of cloud feedback in long-AMIP experiments with three GFDL climate models
Feb. 10Erik van SebilleImperial College LondonChasing Water: Lagrangian tracking of tracers, plastic and plankton through the global ocean
The ocean is in constant motion, with water circulating within and flowing between basins. As the water moves around, it caries heat and nutrients, as well as larger objects like planktonic organisms and litter around the globe. The most natural way to study the pathways of water and the connections between ocean basins is using particle trajectories. The trajectories can come from either computing of virtual floats in high-resolution ocean models, or from the paths of free-flowing observational drifters (surface buoys or Argo floats) in the real ocean. In this seminar, I'll give an overview of some recent work with Lagrangian particles. I will show applications to dynamical oceanography, marine ecology, palaeoclimatology and marine plastic pollution. Central to each of these studies is the question on how connected the different ocean basins are, and on what time scales water flows between the different regions of the ocean.
Feb. 10Jack Scheff Lamont-Doherty Earth Observatory, Columbia UniversityWhat we mean when we talk about wetting and drying under climate change: perspectives from models and paleo-evidence.TBD
Postdoc/visiting scientist lecture The expected response of Earth's water cycle to CO2-driven warming has been described as anything from amplification of extremes, to poleward shifts of features, to widespread drought, depending on the metric and domain chosen. I will argue that the water-linked responses we ultimately care about are regional photosynthesis on land and regional P-E on land, that these responses are ill-described by the above frameworks, and that evidence from the last ice age supports comprehensive land-model projections of these quantities over common heuristic metrics. I will also argue that the direct responses of vegetation to CO2 and warming represent 0th-order uncertainties in these projections.
Feb. 13Geroge MellorOn theories dealing and with the interaction of ocean surface waves and ocean circulation
The first derivation of the effect of surface gravity waves on ocean circulation was by Longuet Higgins and Stewart in the 1960's followed closely by the book by Phillips. The derivation began and ended with the vertically integrated equations of motion. It took forty year more before vertically dependent equations - which could be applied to three-dimensional, ocean calculations - were derived first by McWilliams and Retrepo* (1999) and then by (Mellor 2003). The two resulting equations were very different however; they have been labelled the "vortex force theory" and the "radiation stress theory". Whereas the radiation stress equations, when vertically integrated, reduce to those of Longuet Higgins and Stewart, the vortex force equations theory do not. Nevertheless, the vortex force theory has gained considerable traction in the ocean community and there are applications not only to ocean modelling per se, but also to Longmuir circulation, LES turbulence simulations and surface boundary layer theories. Two disparate theories for the same process is not useful for physical oceanography moving forward so that the talk will present arguments in favor of the radiation stress theory. * Leibovich (1980) actually derived vorticity equations in a quest to explain Langmuir circulation which were then "uncurled" by McWilliams and Retrepo for application to ocean circulation.
Feb. 14Noah BrenowitzNew York UniversityImproving cumulus convective parameterizations using non-local stochastic processes
Postdoc/visiting scientist lecture
Feb. 15Nathaniel W. ChaneyGFDL/Princeton UniversityUsing Big Data to Rethink Spatial Heterogeneity in the GFDL Land Model
The terrestrial water, energy, and biogeochemical cycles play a pivotal role in the Earth system; they have a profound impact on the global climate, food and energy production, freshwater resources, and biodiversity. The processes that govern these cycles operate at spatial scales far below the spatial resolution of existing Earth System models leading to oversimplifications of terrestrial ecosystems. This presentation will illustrate how this persistent challenge is being addressed by harnessing Big Data to explicitly represent sub-100 meter spatial scales in the GFDL land model. The potential benefits that this approach can have for both model validation and application in numerical weather prediction, precision agriculture, seasonal forecasting, and Earth system modeling will be discussed.
Feb. 16Eric MaloneyColorado State UniversityThe Madden-Julian Oscillation and its Teleconnections in a Warmer World
Two simulations of the uperparameterized Community Earth System Model (SP-CESM) are examined, one with pre-industrial (PI) levels of CO2 and one where CO2 levels have been quadrupled (4xCO2). Diagnostics based on the dominant thermodynamic energy balance for the tropics under weak temperature gradient scaling indicate the importance of radiative feedbacks for destabilizing the MJO in pre-industrial climate. While MJO convective variability increases considerably in the 4xCO2 simulation, the dynamical response to this convective variability decreases. Increased MJO convective variability is shown to be a robust response to the steepening vertical moisture gradient. The decreased dynamical response to MJO convective variability is shown to be a consequence of increased static stability, which allows weaker variations in large-scale vertical velocity to produce sufficient adiabatic cooling to balance variations in MJO convective heating. This weakened dynamical response results in a considerable reduction of the MJO's ability to influence the extratropics, which is closely tied to the strength of its associated divergence. A linear baroclinic model is used to verify the impact of increased static stability on the extratropical circulation in a warmer climate. These results suggest that while MJO convective variability may increase in a warming climate, the MJO's role in bridging weather and climate in the extratropics may not.
Feb. 17Feiyu Lu University of WisconsinUnderstanding Extratropical Control on Tropical Variability and Climatology Using Regional Coupled Data Assimilation
Postdoc/visiting scientist lecture. Tropical variability (e.g. El Nino-Southern Oscillation or ENSO) and climatology (e.g. asymmetric Inter-Tropical Convergence Zone or ITCZ) were initially thought to be determined mostly by local forcing and ocean-atmosphere interaction in the tropics. In the last 20 years or so, numerous studies have showed that extratropical forcing could affect, or even determine some aspects of the tropical climate. Due to the coupled nature of the climate system, it remains a challenge to determine and further quantify the impact of extratropical forcing on tropical climate. In this talk , I'll introduce a new approach to study the extratropical influence on tropical climate, using coupled data assimilation (CDA) in a coupled GCM. A perfect-model framework is first used to demonstrate the significant extratropical control on ENSO variability in the model. Then real world reanalysis data are assimilated to determine and quantify the impact of constraining extratropical climate in the model on its tropical climatology and variability.
Feb. 17Scott BachmanCambridge University (UK)Muddied waters: Large-scale ocean eddy closures for CMIP6 and beyond
Postdoc/visiting scientist lecture. Many ocean simulations being conducted as part of OMIP and CMIP6 will utilize a grid fine enough to permit mesoscale eddies throughout much of the world ocean. These eddy-permitting models offer potential for realism and novel dynamics but also require greater care. The title of this talk, "muddied waters", alludes to a variety of new eddy parameterizations which have been developed for these models (known as mesoscale ocean large eddy simulations, or MOLES), and the general uncertainty about which of these offers the best way forward. Here I will discuss two such parameterizations which show promise. The first of these is inspired by techniques traditionally used in LES for the forward energy cascade in 3D, homogeneous, isotropic tubulence, but are here applied to the forward QG potential enstrophy cascade. The resulting "QG Leith" parameterization is shown to be successful at cleanly truncating the cascades in idealized models, with the added bonus that it specifies the Gent-McWilliams (GM) transport coefficient as well. Results are also shown from a successful 0.1 degree global simulation using QG Leith in the POP model. The second parameterization I will present utilizes the geometric framework of Marshall et al. (2012) to write the GM coefficient as a function of the eddy energy. To test the skill of this technique, an ensemble of passive tracers is used to directly diagnose the GM coefficient in a baroclinic spindown simulation. Excellent agreement is found between the diagnosed coefficient and the prediction from the geometric framework. Lastly, the problem of developing skillful eddy closures applies to submesoscale turbulence as well. To this end, I conclude with new results from a realistic, submesoscale-resolving simulation of the Drake Passage region, which is used to inform how a submesoscale parameterization might depend on the mesoscale flow.
Feb. 22Cenlin HeUCLABlack Carbon-Snow-Radiation Interactions and Albedo Effects over the Tibetan Plateau
Postdoc/visiting scientist lecture. Black carbon (BC), commonly known as soot, has been identified as the second most important anthropogenic emissions in terms of global climate forcing in the current atmosphere. Its regional warming effect can be even stronger over snow-covered areas due to BC-snow albedo effects. Observations have shown that BC deposition on snow is an important driver of rapid snow melting and glacier retreat over high mountains such as the Tibetan Plateau, which can further affect hydrological cycle and water availability. However, BC-snow-radiation interactions and associated albedo effects have not been thoroughly studied in such a manner as to understand, quantify, and reduce large uncertainties in the estimate of radiative and hydrological effects. Thus, this study seeks to improve our understanding and estimates of BC-snow albedo effect by developing a new snow model and BC-snow parameterizations for several important features in BC-snow-radiation-mountain interactions, including realistic snow grain shape, stochastic multiple aerosol-snow internal mixing, snow close packing, and 3-D radiative transfer over complex terrain, which have not been accounted for in previous studies. We particularly focus on the Tibetan Plateau regions. Additional efforts have also been given to investigate BC atmospheric aging, a key process representing hydrophobic-to-hydrophilic conversion, which affects BC optical properties and deposition on snow and hence BC-snow albedo effects.
Feb. 23Sloan CoatsUniversity of ColoradoPaleoclimate constraints on the spatio-temporal character of past and future drought in climate models
Drought is a spatio-temporal phenomenon; however, due to limitations of traditional statistical techniques it is often analyzed solely temporally—for instance, by taking the hydroclimate average over a spatial area to produce a timeseries. Herein, we use machine learning based Markov Random Field methods that identify drought in three-dimensional space-time. Critically, the joint space-time character of this technique allows both the temporal and spatial characteristics of drought to be analyzed. We apply these methods to climate model output from the Coupled Model Intercomparison Project phase 5 and tree-ring based reconstructions of hydroclimate over the full Northern Hemisphere for the past 1000 years. Analyzing reconstructed and simulated drought in this context provides a paleoclimate constraint on the spatio-temporal character of past and future droughts, with some surprising and important insights into future drought projections. Climate models, for instance, suggest large increases in the severity and length of future droughts but little change in their width (latitudinal and longitudinal extent). These models, however, exhibit biases in the mean width of drought over large parts of the Northern Hemisphere, which may undermine their usefulness for future projections. Despite these limitations, and in contrast to previous high-profile claims, there are no fundamental differences in the spatio-temporal character of simulated and reconstructed drought during the historical interval (1850-present), with critical implications for our confidence in future projections derived from climate models.
Feb. 24Julius BuseckeColumbia UniversityTemporal variability in surface eddy mixing
Lateral mixing by mesoscale eddies is widely recognized as a crucial mechanism for the global ocean circulation and the associated heat/salt/tracer transports. The Salinity in the Upper Ocean Processes Study (SPURS) confirmed the importance of eddy mixing for the surface salinity fields even in the center of the subtropical gyre of the North Atlantic. We focus on the global salinity maxima due to their role as indicators for global changes in the hydrological cycle as well as providing the source water masses for the shallow overturning circulation. A suite of observationally driven model experiments is used to investigate the contribution of near-surface lateral eddy mixing to the subtropical surface salinity maxima in the global ocean. Surface fields of salinity are treated as a passive tracer and stirred by surface velocities derived from altimetry, leading to irreversible water mass transformation. In the absence of surface forcing and vertical processes, the transformation rate can be directly related to the integrated diffusion across tracer contours, which is determined by the observed velocities. The destruction rates of the salinity maxima by lateral mixing can be compared to the production rates by surface forcing, which act to strengthen the maxima. The ratio of destruction by eddy mixing in the surface layer versus the surface forcing exhibits regional differences in the mean - from 10% in the South Pacific up to 25% in the South Indian. Furthermore, the regional basins show seasonal and interannual variability in eddy mixing. The dominant mechanism for this temporal variability varies regionally. Most notably, the North Pacific shows large sensitivity to the background salinity fields and a weak sensitivity to the velocity fields while the North Atlantic exhibits the opposite behavior. The different mechanism for temporal variability could have impacts on the manifestation of a changing hydrological cycle in the SSS field specifically in the North Pacific. We find evidence for large scale interannual changes of eddy diffusivity in several ocean basins that could be related to large scale climate forcing.
Mar. 1Minjin LeeGFDLNitrogen sequestration in land biospheres buffers atmospheric and oceanic pollution
Mar. 2William CollinsLBL and UC BerkeleyMethane's Shortwave Climate Forcing: Big Enough to Matter?
Although the primary well-mixed greenhouse gases (WMGHGs) absorb both shortwave and longwave radiation, to date assessments of the effects from human-induced increases in atmospheric concentrations of WMGHGs have focused almost exclusively on quantifying the longwave radiative forcing of these gases. However, earlier studies have shown that the shortwave effects of WMGHGs are comparable to many less important longwave forcing agents routinely in these assessments. These earlier studies include the Radiative Transfer Model Intercomparison Project (RTMIP) conducted by Collins and Ramaswamy in 2006. In this talk, we preview the first global estimates of the shortwave radiative forcing by methane due to the anthropogenic increase in CH4 between pre-industrial and present-day conditions. This forcing is a balance between reduced heating due to absorption of downwelling sunlight in the stratosphere and increased heating due to absorption of upwelling sunlight reflected from the surface as well clouds and aerosols in the troposphere. We show how these estimates are likely to be quite stable despite the considerable uncertainty and large gaps in the laboratory-measured near-infrared spectroscopy of methane. We show that our results are insensitive even to including much more complete empirical absorption spectra collected for methane-dominated Jovian atmospheres. We conclude by suggesting that these forcings be included in future assessments of climate change, in particular the upcoming Sixth Assessment Report (AR6) by the Intergovernmental Panel on Climate Change (IPCC).
Mar. 6Yujin ZengChinese Academy of ScienceEffects of anthropogenic water exploitation and groundwater lateral flow on land surface and climate
Mar. 7Katarzyna TokarskaUniversity of VictoriaCarbon budgets aspects of the low warming climate targets
The cumulative emissions framework identifies a total amount of carbon that can be emitted, referred to as a carbon budget, compatible with stabilization of the global mean temperature at a desired level. Carbon budgets consistent with remaining below 1.5°C global mean warming, reported in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5), are directly based on responses from comprehensive Earth System Models (CMIP5), which, on average, tend to warm more than observations for the current amount of carbon emitted. In this talk, I will present a screening approach of the available CMIP5 models, based on whether or not they simulate consistent fossil fuel emissions with those that have occurred for the observed level of present warming. The 1.5°C carbon budgets based on the CMIP5 models which are consistent with observations show a higher median remaining amount of carbon that can be emitted than that inferred from the IPCC AR5. I will also address the effects of non-CO2 greenhouse gases on carbon budgets. Using simulations from comprehensive Earth System Models, I will present a consistent approach of comparing carbon budgets compatible with not exceeding 1.5°C and 2.0°C warming due to CO2 alone, and in simulations that also include non-CO2 forcings.
Mar. 8Hiroyuki "Hiro" MurakamiGFDLSimulation, Prediction, and Attribution Study for Tropical Cyclones using GFDL FLOR and HiFLOR
Extremely intense tropical cyclones (TCs), such as categories 4 and 5 (C45) hurricanes, have marked socio-economic impacts. Therefore, developing a climate global model that has skill in predicting/simulating intense TCs is central to NOAA's mission and highly relevant to society. In order to tackle the problem of understanding and predicting the variations and changes in regional hydrometeorological conditions and extreme events (particularly C45 hurricanes) on timescales of weeks to centuries, we have developed a new high-resolution 25-km mesh coupled model (HiFLOR). The presentation consists of three topics: 1) performance of TC simulation by HiFLOR, 2) seasonal prediction skill for TCs and development of statistical-dynamical model, and 3) attribution study of the recent extreme TC events using HiFLOR.
Mar. 9Dargan FriersonUniversity of WashingtonHow the sea, land, ice, and mountains move the rain
I'll talk about research using idealized GCMs to pick apart the role of various factors in setting the rainfall distribution on Earth, including simple continents, mountain ranges, the ocean circulation, ice sheets, and vegetation. The use of simple diffusive closures in the atmospheric energy budget is a common thread in this work. These results highlight interconnections within the Earth system, including some new and unexpected long-range teleconnections.
Mar. 15Angel MunozGFDLCross-Time Scale Diagnostics of Coupled Circulation Models
Approaches to diagnose numerical circulation models generally involve metrics that provide an overall summary of the performance of the model in reproducing the particular variables of interest, normally tied to specific spatial and temporal scales. Nonetheless, the evaluation of the goodness of a model is not always linked to the understanding of physical processes that may be correctly represented, distorted or even ab- sent in the model universe. As physical mechanisms are frequently related to interactions at multiple temporal and spatial scales, cross-scale model diagnostic tools are not only desirable but required. This study proposes an integrated diagnostic framework based on weather type spatial patterns and frequencies of occurrence to facilitate the identification of model biases across multiple timescales. To illustrate the approach, three sets of 32-year-long simulations are analyzed for Northeastern North America and for the March-May season. The numerical experiments were produced by the LOAR and FLOR models, coupled Global Circulation Models developed by the Geophysical Fluid Dynamics Laboratory (GFDL) with 2-degree and 0.5-degree horizontal resolution in the atmosphere, respectively, and with nudging approaches designed to reproduce key aspects of the observed climate variability. It is found that both models exhibit a fair representation of the observed circulation regime's spatial patterns and frequencies of occurrence, although some biases are present inde- pendently of the horizontal resolution of the models used. Overall, inter-experiment differences in the mean frequencies of occurrence of the simulated weather types, and their variability across multiple timescales, tend to be negligible. It is proposed that low-resolution models could be of potential use to diagnose and predict physical variables (e.g., rainfall and surface temperature), via their simulated weather type characteristics.
Mar. 16Johannes QuaasUniversity of LeipzigOn the magnitude of the aerosol effective radiative forcing
There were arguments in the recent literature that the effective radiative forcing due to anthropogenic aerosols might be relatively small. One suggests that part of the forcing in the solar spectrum might be offset by a adjustments acting in the terrestrial spectrum. Another argument postulated that the fact that the Earth warmed also in the early industrial period might preclude a strong aerosol forcing. I'll present an analysis of the CMIP5 ensemble that calls into question both hypotheses. Two "emergent constraint" approaches, in turn, suggest an aerosol forcing around -1.2 W m-2 and I'll discuss these arguments. Besides these model-tied arguments, satellite data may be exploited to shed light on the effective forcing due to aerosol-cloud interactions. I will present some progress along this axis of research as well, in which we propose ways to overcome shortcomings in previous studies. The implied global forcing is consistent with a moderately strong forcing of -1.2 W m-2. The talk will also briefly discuss a perspective for CMIP6 analyses.
Mar. 16Oliver WildLancaster University, UKQuantifying Uncertainty in Models of Atmospheric Chemistry and Climate
Projections of future atmospheric composition change and its impacts on air quality and climate are heavily dependent on chemistry-climate models that allow us to investigate the effects of changing emissions and meteorology. These models are imperfect, based on our incomplete understanding of the chemical, physical and dynamical processes governing atmospheric composition, on the approximations needed to represent these numerically, and on the limitations of the observations required to constrain them. Model intercomparison studies show a great diversity in results that reflects these underlying uncertainties, but little progress has been made over the past decade in identifying the weaknesses in process understanding or representation that might lead to improved models and to better scientific understanding. Model emulation and uncertainty analysis provide a new method of identifying and quantifying the main sources of uncertainty in current models. We apply this approach to quantify the sensitivity of ozone and OH to important climate-relevant variables, poorly-characterized processes and uncertain anthropogenic emissions, using two independent global chemistry transport models, the FRSGC/UCI CTM and the GISS GCM. The models show a similar sensitivity in tropospheric ozone to atmospheric humidity and precursor emissions, but a surprisingly large difference in sensitivity for tropospheric OH which has major implications for the simulated response of methane to climate change. We demonstrate that the approach applied here has great potential for identifying model weaknesses and providing valuable new insight into the processes driving tropospheric composition change.
Mar. 21Laure ResplandyPrinceton UniversityOcean controls on climate: challenging heat and carbon budgets
Mar. 22Jie HeQuantifying Air-sea Interactions in the Tropics
It is well accepted that tropical atmospheric variability is largely regulated by variations in sea surface temperature (SST). Studies based on this knowledge have yielded some interesting but not necessarily intuitive results. For example, early research based on the observed SST-convection relationships suggested that convection starts to respond strongly to SST variability when the SST reaches approximately 27.5oC but further increases in SST somehow appear to have little impact on convection. On the other hand, it has been long recognized that atmospheric variability also feedbacks on SST. As a result, air-sea relationships in any coupled system, including observations, reflect a complex combination of SST forcing and atmospheric feedback, and should not be used to interpret SST forcing alone. In this talk, I will show that using coupled air-sea relationships to study the atmospheric response to SST forcing has led to some biased understanding in the past. The atmospheric response needs to be studied in an uncoupled system where the atmospheric feedback is turned off. To that end, a suite of atmosphere-only simulations was performed and will be discussed with a focus on precipitation and evaporation responses to SST variability. These uncoupled simulations should be taken as the first step towards understanding the full air-sea relationships in coupled systems.
Mar. 23Josep PenuelasUniversity of BarcelonaShifting from a fertilization-dominated to a warming-dominated period in terrestrial biosphere
Carbon dioxide and nitrogen fertilization effects on ecosystem carbon sequestration are prone to slow down in the future because of nutrient constraints, climate change, land use change and land management and disturbances. At the same time, rapid warming is leading to negative impacts on ecosystems productivity. We will discuss that, together, these two phenomena might drive a shift from an Anthropocene period dominated by the positive effects of fertilization to another period characterized by the saturation of fertilization positive effects on carbon sinks and the rise of climate change related negative effects. We will walk through these issues revisiting field, remote sensing and modeling data.
Mar. 29Jess AdkinsCalifornia Institute of TechnologyThe record of Pacific Warm Pool climate change from stalagmites in Borneo
Mar. 30Anna MichalakCarnegie Institute-Stanford, CAMoving from quantity to quality: Exploring climate impacts on inland and coastal waters
Questions surrounding water sustainability are most commonly framed in terms of quantity, whether too much or too little. The same is true for discussions of climate change and extreme events. Water is useful (usable) only if it is of sufficient quality for its intended use, however, whether directly by humans or by the broader ecosystem. The last two years alone have provided a host of compelling examples, with unprecedented harmful algal blooms developing along the West coast, in Utah Lake, in Lake Erie, and off the Florida coast. Several factors explain the lack of understanding of climate impacts on water quality impairments, including the relative complexity of underlying processes, the spatial and temporal scale mismatch between hydrologists and climatologists, and the difficulty in assessing historical conditions. The need to understand linkages is clear, however. Focusing on eutrophication, harmful algal blooms, and hypoxic dead zones, this talk will frame challenges and opportunities related to characterizing water quality, bridging from local to global scales, identifying key drivers, and understanding the role of climate. Specific examples will include the development of statistical tools for mapping hypoxia, remote-sensing algorithms for tracking phytoplankton blooms, and empirical approaches for identifying common drivers of eutrophication across landscapes. In each case, the availability of these new tools makes it possible to develop and test novel hypotheses about the role of climate and what the future may hold.
Apr. 5Qinjian JinMassachusetts Institute of TechnologyClimatic impacts of international shipping emissions in a general circulation model
International shipping contributes about 0.5% to 3.5% to the global sulfur emission. It is well known that sulfate particles in the atmosphere can not only modulate Earth's radiation budget but also sever as cloud and ice nuclei. In this work, a general circulation model (i.e. CESM) coupled with a sophisticated, multi-mode aerosol model (MARC) that explicitly treats the aerosol-cloud interactions are used to quantify the radiative forcing of international shipping emissions as well as their impacts on climate by interacting with clouds. The preliminary model results show that the shipping emissions can increase the total cloud water path and the droplet number concentration by about 50% and up to 100% in the regions of frequent shipping tracks (i.e. in the northern Pacific Ocean and Atlantic Ocean), respectively. The cloud shortwave radiative forcing due to shipping emissions is much larger than the direct shortwave radiative forcing. Preliminary results regarding the climate response to shipping emissions mainly through aerosol indirect effects will also be discussed.
Apr. 6Kevin BowmanNASA JPLThe potential of satellites and assimilation to quantify climate forcing, feedbacks, and prediction in the Earth System: application to atmospheric chemistry and the carbon cycle
Anthropogenic activities since the industrial revolution have led to profound changes in atmospheric composition (e.g., carbon dioxide, methane and tropospheric ozone) and consequently the trajectory of our climate. However, the coupling of these constituents must be quantified in order to assess the efficacy of climate mitigation strategies against the backdrop of natural variability and climate feedbacks. The last decade has witnessed the launch of satellite constellations that measure Earth's atmosphere, land, and oceans with a concomitant advance in data assimilation approaches to link these data to Earth System processes. Using these approaches, we have attributed ozone and methane radiative forcing to global emissions at large urban scales. By incorporating both methane emissions and chemical losses, we show that the top 10% of locations with positive net methane RF are responsible for 50% of the global positive RF and the top 10% of locations with negative RF cause 60% of the global negative RF based upon an RCP 6.0 trajectory through 2050. To understand the role of the carbon cycle in controlling the most important greenhouse gas, the NASA Carbon Monitoring System Flux (CMS-Flux) project was initiated as a coordinated effort between land surface, ocean, fossil fuel, and atmospheric scientists to develop a comprehensive a carbon cycle data assimilation system. Based upon this system, we attribute the historic atmospheric CO2 growth rate during the 2015 El Nino to spatially-resolved fluxes. We show how tropical productivity and respiration processes related to anomalously high climate variability, i.e., "extreme"events, are responsible for this growth rate and their implications for carbon-climate feedbacks. Emergent constraints have been become an active area of research that use contemporary observations to constrain climate projections. We have developed a Bayesian formulation of this approach that explicitly accounts for the uncertainty in observations and the uncertainty between the future and present state. We explore the potential of this framework for tropospheric ozone radiative forcing and the carbon cycle. Taken together, these advances in observations, modeling, and the methodologies to link them point to a scientifically rigorous and policy-relevant framework critically needed for the international community to address climate change. Dr. Kevin Bowman is the Principal Investigator of the EOS Aura Tropospheric Emission Spectrometer and the NASA Carbon Monitoring System (CMS-Flux) project. He received a BEE from Auburn University in 1991, a Diplôme de Spécialisation en Traitement et Transmission des Informations at L'Ecole Supérieure d'Electricité (SUPELEC), Metz, FRANCE in 1993, and a Phd in Electrical Engineering from the Georgia Institute of Technology in 1996. He subsequently continued his career at the Jet Propulsion Laboratory in 1997. His research is centered on understanding the processes controlling atmospheric composition and their impact on climate using satellite observations, modeling, and data assimilation techniques. Dr. Bowman's broad interests have led to publications in diverse fields including air quality, carbon cycle, chemistry-climate, atmospheric hydrology, and remote sensing science. An avid musician and guitarist, Dr. Bowman is a founding member of the JPL Jazz Propulsion Band.
Apr. 12Andrew HazeltonEvaluation of Tropical Cyclone Structure Forecasts in a High-Resolution Version of the fvGFS Model
The FV3 dynamical core has been developed at GFDL for a wide range of applications in models ranging from climate to convective scale. A nested version of the FV3 core with GFS physics and initial conditions (fvGFS) allows for simulation of features such as tropical cyclones (TCs) at high resolution. Here, a version of the model with 2 km resolution is evaluated for its ability to simulate TC track, intensity, and structure. The 2 km nest covers most of the North Atlantic. The current version of fvGFS features a new microphysics scheme developed at GFDL to replace the current GFS microphysics. TC structure is evaluated through comparison of model forecasts with 3-dimensional Doppler radar from NOAA P-3 flights by NOAA's Hurricane Research Division (HRD). Structural metrics evaluated include the 2-km radius of maximum wind (RMW), slope of the RMW, depth of the TC vortex, and vortex decay rate. 7 TCs from the 2010-2016 seasons are evaluated: Earl (2010), Irene (2011), Edouard (2014), Gonzalo (2014), Danny (2015), Hermine (2016), and Matthew (2016). In total, this includes 10 separate model runs and 38 individual flights into the 7 TCs. From the intensity verification, it is found the model had some success in producing rapid intensification (RI) forecasts for Earl, Edouard, and Matthew, although it did struggle with the inner-core structure and intensity of Matthew in the Caribbean. Looking at structure verifications, the model does a good job of capturing RMW in the 25-50 km range, but tends to have a small bias at very large radii and a large bias at very small radii. The wind peak also tends to be somewhat too sharp, and the vortex depth occasionally has a high bias, especially for storms that are observed to be shallow. Composite radial wind shows that the boundary layer tends to be too deep, although the outflow structure aloft is relatively consistent with observations. Detailed examination of several cases highlights details of the structural features that the model is capable of predicting.
Apr. 13Yoshihide Wada, Dr.IASA Vienna Austria /NASA Goddard Institute for Space Studies, New York, USASustainability of global water use: An integrated water resources modeling framework to assess surface water and groundwater overuse
Water scarcity, caused by an existing regional imbalance of water availability and water use, poses a serious environmental issue to the global society. Soaring human water use worsens water scarcity condition already prevalent in semi-arid and arid regions, where available surface water is limited due to lower precipitation, casting significant doubt on the sustainable water supply, economic development, and food production. Over these regions, the water demand often exceeds the available surface water resources due to intense irrigation which requires large volumes of water during crop growing seasons. Groundwater resources serve as a main source of such intense irrigation. Excessive groundwater pumping, however, often leads to overexploitation, causing groundwater depletion. To assess overexploitation of surface freshwater and groundwater resources, a state-of-the-art global hydrological model and global water demand model were developed. Eventually, to simulate more realistically human water use behavior and associated impacts on terrestrial water fluxes, the two models were coupled to realize an integrated water resources modeling framework. The relative impact of climate and human water use on global water resources was investigated by contrasting two simulation runs including: 1) pristine conditions or natural climate variability only, and 2) human-induced change (human water use and reservoir regulation). Demographic, socio-economic, technological, and irrigated area changes were reflected in growing human water use over time. Substantial regional variations were observed for the human and climate impacts on surface freshwater and groundwater resources, with humans having by far the largest impact on terrestrial water system in various regions (e.g., India, Pakistan, China, USA, and the Middle East). Since the 1990s, people have increasingly relied on groundwater resources as surface water has been extensively exploited during past decades and the construction of new reservoirs has been tapering off. Over the Middle East and Northern Africa, more than half of irrigation water comes from depleting groundwater resources. Over major irrigated countries, the contribution of fossil groundwater to irrigation is equally substantial: 20% for India, 15% for China, and 25% for the USA and Pakistan. Globally, groundwater depletion sustains 20% to irrigation water supply and has more than tripled in size over the last 50 years. Most of the groundwater released from storage due to groundwater depletion will end up in the ocean, the depleting groundwater resources were found to be an important contributor to global sea-level rise. Groundwater depletion currently contributes a considerable amount of 0.27 (±0.04) mm yr−1 to sea-level rise. An increasing trend of water used from non-sustainable water resources over the historical period (30%) is projected to continue further towards the end of this century (40%). ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Yoshihide Wada, Dr. International Institute for Applied Systems Analysis, Laxenburg, Austria NASA Goddard Institute for Space Studies, New York, USA Center for Climate Systems Research, Columbia University, New York, USA Department of Physical Geography, Utrecht University, Utrecht, The Netherlands (
Apr. 19Honghai ZhangGFDLDecadal Detectability of Anthropogenic Hydroclimate Changes over North America
Future changes in hydroclimate consist of shifts in mean state resulting from anthropogenic forcing and contributions from natural climate variability. Considering the limited predictability of natural climate variability owing to the chaotic nature of the climate system, our confidence in projections of hydroclimate changes relies on a faithful assessment of anthropogenic shifts in mean state. Assessment of anthropogenic forcing in near-term hydroclimate projections is challenging because of the very low signal to noise ratio; however, this ratio can be greatly improved in a model that undergoes the same forcing but initializes from different conditions to form a large ensemble. Here using three large ensembles from two state-of-the-art climate models along with millennial preindustrial simulations, we assess the near-term (2000~2050) decadal shifts in hydroclimate (precipitation minus evaporation) mean state caused by anthropogenic forcing over North America. In both models, anthropogenic forcing will cause significant shifts in hydroclimate mean state over large parts (50~70%) of North America by 2050 relative to the 1950~1999 mean state, with early shifts towards moistening in high latitudes and drying in subtropics. During cold seasons, northeastern and southwestern North America will experience the earliest significant anthropogenic moistening and drying, respectively; during warm seasons, central North America will experience the earliest significant drying that however is mostly not attributable between anthropogenic and natural forcing. Changes in submonthly transient eddies account for the northeastern winter moistening and central summer drying while changes in monthly atmospheric circulation explain the southwestern winter drying. In few regions without significant shifts in hydroclimate mean state, the lack of detectability is due to a combination of weak hydroclimate changes and large uncertainties from low-frequency internal variability, the latter of which arises mostly from unpredictable atmospheric dynamics. Note in regions with detectable anthropogenic signal, large irreducible spread remains in projected hydroclimate changes and should be fully accounted in policy planning and efforts of mitigation and adaptation.
Apr. 20Noah DiffenbaughStanford UniversityQuantifying the influence of global warming on the probability of historically unprecedented extreme climate events
Effective climate risk management requires robust quantification of the probability of different kinds of hazards, such as heat waves, droughts, floods, and severe storms. As a result, there has been increasing interest in the extent to which historical global warming has influenced the occurrence and severity of individual extreme climate events. However, although trends in the extremes of the seasonal- and daily-scale distributions of climate records have been analyzed for many years, quantifying the contribution of observed global warming to individual events that are unprecedented in the observed record presents a particular scientific challenge. I will describe a framework for leveraging observations and large climate model ensembles to quantify the influence of observed global warming on the probability of unprecedented extreme events. This approach is grounded on three tenets: (1) Focus on understanding the physical causes of the individual event; (2) Use formal uncertainty quantification to test the probability of those physical conditions occurring in the current climate; and (3) Use formal hypothesis testing to compare the probability of those physical conditions occurring in the current climate and a climate without human influence. My group has applied our analysis to a number of different climate variables from a number of individual events, including temperature, precipitation, soil moisture, and atmospheric circulation patterns. Together, this work has shown that global warming can influence the risk of extreme events that are unprecedented in historical experience, particularly by altering the probability of the physical conditions that are responsible for the event. In addition, given the widespread public interest in "real time"attribution, the prospects for operational attribution analysis will also be discussed.
Apr. 21Singh BrarGeorge Mason UniversitySeasonality of the tropical interaseasonal oscillations
Lecture will take place at Sayre Hall in Lecture Room 312.
Apr. 26Christian HovyUniversität HamburgTesting in computational science & engineering
Testing in computational science & engineering is considered to be difficult. One major problems is the lack of test oracles for algorithms for which correct solutions are unknown due to the approximative character of numerical models such as climate models. However, scientists have developed and run climate models successfully since decades. But while one can find publications in the geoscience literature about model validation and evaluation from a high-level scientific point of view, there is lack on publications about model testing from the software engineering perspective (with a few exceptions). Even if the applied practices in climate science are not as rigor as described in the software engineering literature, there must be be some test processes established to enable concurrent development in large teams and to keep the model running. In the study I am conducting at GFDL and other climate modeling centers, I want to collect and describe such software testing methods, processes, tools and environments being used in every day development of coupled climate models. In this talk, I will give an introduction to my study and present some of my previous findings from the ICON model developed at the Max Planck Institute for Meteorology and the German Weather Service.
Apr. 27Yaoxian HuangYale UniversityImpacts of global residential biofuel emissions on air quality and climate
The residential biofuel sector is defined as fuelwood, agricultural residues and dung used for household cooking and heating. Aerosol emissions from this human activity play an important role affecting local, regional and global air quality, climate and public health. However, there are only few studies available that evaluate the net impacts and large uncertainties persist. Here we use the Community Atmosphere Model version 5.3 (CAM v5.3) within the Community Earth System Model version 1.2.2, to quantify the impacts of cook-stove biofuel emissions on air quality and climate. The model incorporates a novel advanced treatment of black carbon (BC) effects on ice clouds. We update the global anthropogenic emission inventory in CAM v5.3 to a state-of-the-art emission inventory from the Greenhouse Gas-Air Pollution Interactions and Synergies integrated assessment model. Global in-situ and aircraft campaign observations for BC and organic carbon are used to evaluate and validate the model performance. Sensitivity simulations are employed to assess the impacts of residential biofuel emissions on regional and global direct and indirect radiative forcings in the contemporary world. We focus the analyses on several key regions including India, China and Sub-Saharan Africa.
May. 2GFDL Hurricane Science SymposiumGFDL Hurricane Science Symposium
GFDL Hurricane Science Symposium. For more information, see New Meeting Tue, May 2, 2017 9:00 AM - 5:00 PM EDT Please join my meeting from your computer, tablet or smartphone. You can also dial in using your phone. United States: +1 (872) 240-3212 Access Code: 884-347-445
May. 3Andrew ShaoOffline Tracer Modelling in MOM6
The inclusion of passive tracers into ocean general circulation models can represent a significant computational cost because they are often transported along at the same timestep as the thermodynamics (on the order of hours). Offline tracer methods reduce the computational requirements required to simulate tracers in two ways: 1) by saving diagnosed mass transports from a previous 'online' integration, only the tracer advection equation needs to be integrated and 2) longer tracer advective timesteps can be used (on the order of days or months) in most regions of the ocean. This seminar presents how we have implemented this idea into MOM6 and some initial evaluations of the differences in simulating ideal age and boundary impulse tracers between offline and online integrations of the half-degree version of OM4. Additionally, potential applications of this capability will be discussed including how external groups can take advantage of GFDL output, tracer sensitivity studies, and spinning up ocean biogeochemistry (with some early demonstrations using the BLING biogeochemical model).
May. 4Rich NealeNCARA History of Bias in the Community Earth System Model (CESM): 20-years of Successes, Tough Choices and Persistent Problems
This 'paleo-climate' talk will present a selection of results showing the evolution of skill metrics and diagnostics from simulations through six generations of the NCAR atmosphere model (CCM3 to CAM6) and five generations of the NCAR coupled model (CCSM2 to CESM2) spanning more than 20 years. During this time the complexity of the models have increased dramatically in almost every facet possible. These increases in complexity aim to target missing or poorly represented processes and interactions in models, but an improved simulation, where new representations are thought to play a substantial role, is frequently not guaranteed. Although advances from early model versions are undeniable, they are not monotonic in nature, and certain degradations often come at the expense of including these new processes, a result of the inevitable trade offs that come with model development. Precipitation is often a main target of model validation and the tropical double ITCZ crucial to model performance. The NCAR model has certainly had problems in the past, but in atmosphere-only simulations this was a minor problem prior to CAM4, became significant through CAM5 and was mostly remedied in CAM6. This recent degradation was the result of a trade off due to the improved variability, ENSO and regional precipitation characteristics with the inclusion of deep convection modifications in CAM4. Cloud radiative fields are important components of the global energy budget used to balance a fully coupled system. There is a stark contrast between short-wave cloud forcing, which has seen a 50% reduction in error, and long wave cloud forcing, which has seen virtually no improvement. This is somewhat surprising give that these fields are often addressed together as part of the model development process. Variability at timescales shorter than monthly have until relatively recently been a more secondary consideration. Since CAM3 tropical variability in particular has improved, but this has not been even when different models of variability are considered e.g., Kelvin Waves and the Madden Julian Oscillation (MJO). However, other improvements such as blocking statistics show more robust improvement over time. Finally we present a brief overview of the recent development process for CAM6, the need to continually consider the whole coupled system and its, at times, ad-hoc nature. -Evolution from CCSM2 and CCM2 -Mean climate -Coupled versus non-coupled -Non monotonic -Release variability -Paradigms for development (fully coupled) -A recent development exercise CAM6
May. 10Marianne HaseloffGFDL/Princeton UniversityThe effect of buttressing on marine ice sheet dynamics
The effect of buttressing on marine ice sheet dynamics A marine ice sheet rests on a bed that is below sea level. At the grounding line, the ice becomes thin enough to float and the ice sheet forms an ice shelf. Ice shelves transmit changes in oceanic forcings (e.g. variations in basal melt rates) inland to the grounding line, influencing the grounding line's position and stability. The loss of grounded ice contributes to sea level, and so determining the position and evolution of the grounding line is crucial for predictions of future sea level rise. However, determining forcing mechanisms and quantifying their effects on marine ice sheet dynamics remains a major challenge for ice sheet models, and the conclusions drawn from these models often depend on the type of model used. For example, recent simulations with laterally-confined, two-dimensional ice flow models suggest that ice shelves can change the stability of grounding lines through a process called buttressing. In contrast, unconfined ice shelves can be excluded from the momentum balance in computationally efficient flowline models. To investigate the role of buttressing in grounding line dynamics, we extend a recently developed boundary layer approach to laterally integrated models with parameterized buttressing. This approach allows us to determine the backstress at the grounding line as a function of ice shelf properties such as shelf width and length, and to calculate how the ice flux at the grounding line changes with different ice shelf properties and forcings. We find that the steady state position and stability properties of marine ice sheets are governed by the properties of the ice shelf, and compare the effects of different calving laws on grounding line dynamics. We illustrate how buttressing and an assumed constant calving front position can lead to multivalued flux-ice thickness relationships and stable grounding lines on retrograde slopes. In contrast, a thickness-based calving law can lead to both stable and unstable grounding line positions on downward sloping beds. Our results highlight the need for a better understanding of the effects of oceanic forcings on ice shelf mass balance. We will conclude with a discussion of the implications for current ice sheet models and avenues for future research.
May. 12Alex HaumannSwiss Federal Institute of Technology, ZurichSouthern Ocean response to recent changes in surface freshwater fluxes
Earth's climate bears a close relation to the vertical exchange of water masses in the Southern Ocean. This connection originates from the transport of heat, carbon, and nutrients with the subduction and upwelling of water masses in this region. To date, the mechanisms that control long-term changes in this exchange between deep and surface waters are not firmly established. In this presentation, I will present observational and modeling studies to make the case that increased freshwater fluxes from sea ice are a major driver of observed changes in the Southern Ocean over recent decades by changing its surface density stratification in the upwelling region. An analysis of satellite and reanalysis data over the period 1982 to 2008 suggests that sea ice provides the dominant surface freshwater flux in the seasonally ice-covered region of the Southern Ocean compared to the available data of the atmospheric and land-ice freshwater fluxes. I will argue that the coastal formation, northward transport, and melting of sea ice is mainly responsible for observed meridional and vertical salinity gradient in the underlying ocean. This northward transport of freshwater through sea ice has increased by about 20% over the observational period, which explains the majority of the observed freshening of the open-ocean waters. Sensitivity studies with a regional ocean model suggest that this sea-ice induced freshening strongly increased the surface density stratification in the upwelling region and reduced the strength and depth of deep wintertime mixing. As a consequence, the surface ocean in these simulations cools with a spatial pattern and magnitude that is consistent with the satellite observed surface cooling over this period. Additionally, both the surface cooling and reduced vertical exchange considerably strengthen the net uptake of CO2 in the model, providing a potential explanation why the Southern Ocean carbon sink strengthened over recent decades despite an increase in westerly winds. In conclusion, the insights gained from the presented studies point towards much higher sensitivity of the upwelling in the Southern Ocean to changes in the sea-ice freshwater fluxes than previously thought and suggested by global climate models. Therefore, surface freshwater fluxes in the Southern Ocean could play a fundamental role in modifying the surface heat and CO2 exchange with the atmosphere during past and future changes in the global climate system.
May. 16Daniel GilfordMITStratospheric Influences on the Seasonality of Tropical Cyclone Potential Intensity
Understanding the variability of tropical cyclone (TC) potential intensity (PI), sometimes called the TC "speed limit", is important because it scales with the variability of observed TC intensity. While previous studies have examined TC PI trends or interannual variability, relatively few have examined TC PI seasonality and its controlling environmental factors. Potential intensity is a function of the thermodynamic atmosphere-ocean disequilibrium and the TC thermodynamic efficiency"i.e. the difference between sea surface temperatures and the TC outflow temperatures" and consequently it varies across ocean basins with different ambient conditions. This work analyzes the climatological seasonal cycles of TC PI in each main TC development basin using reanalysis data over the past 30 years. We find that TC outflow in the Western North Pacific basin is above the tropopause throughout the seasonal cycle. Consequently, Western North Pacific TC PI is strongly influenced by the seasonal cycle of lower stratospheric temperatures, which act to damp its seasonal variability and permit powerful Typhoons any time during the year. In contrast, the other main development basins (such as the North Atlantic) exhibit outflow levels in stratosphere only briefly during their peak-seasons. Strong linkages between sea surface temperatures and TC PI in these basins result in thermodynamic support for powerful TCs during only a few months a year. Our results suggest that accounting for lower stratospheric temperature seasonality is important for capturing the phase/amplitude of TC PI seasonal cycles, particularly in the Western North Pacific.
May. 17Angel AdamesGFDLPrecipitation equation of the MJO
May. 22Anna Trugman - Final Public OralAnna Trugman - Final Public Oral
Understanding The Roles Of Climate, Disturbance, And Functional Diversity In The Terrestrial Carbon Cycle: Linking Mechanisms From Regional To Global Scales
May. 24Xi ChenBeyond second-order centered differencing: An alternative view on grid staggering
Traditionally, linear Von Neumann analysis is used to examine dispersive and dissipative properties of numerical schemes. However, linear analysis on state-of-art dynamical cores is difficult because high-order accurate schemes result in extremely complicated analytical solutions to the linear analysis. Diffusion (implicit or explicit) makes the solutions even more complicated, as does the effects of time discretization and upwinding. Moreover, a dynamical core's ability to handle discontinuities is critical in real-world applications, and the solutions to the linearized analysis must consider this context. This work will examine the dispersion properties of high-order staggered and unstaggered non-diffusive numerical schemes for linearized shallow water equations. The first part of this presentation will demonstrate a numerical approach to the high-order linear analysis, challenging the traditional perception that "the non-staggered scheme has poor dispersion properties." The linear analysis is also extended to our Riemann-solver based unstaggered extension to the GFDL FV3 dynamical core, showing that the dispersion and dissipation properties are optimal. Due to the limitation of applying the linear analysis to high-order schemes, in the second part of this presentation, a set of 1D tests is constructed to validate the dispersion and dissipation relations to any numerical scheme. The tests will verify the computed group speed and dissipative properties from the linear analysis, and reveal the discontinuity handling of the numerical schemes. These tests will show the staggered schemes may introduce undesired numerical aliasing to the short wave noises. Even with the recognizable limitations of these linear analyses, our results challenge the conclusions drawn from traditional linear centered-difference, second-order, inviscid analyses of grid staggering methods.
May. 26Samantha SiedleckiUniversity of WashingtonModeling ocean acidification and hypoxia
The coastal ocean is important to global biogeochemical cycling in many ways - high productivity and carbon burial, source for iron to the open ocean, and through making global change issues relevant locally. Ocean acidification and hypoxia of coastal waters are of increasing concern to local fisheries. Many economically or ecologically important species (oysters, crabs, phytoplankton, zooplankton) in the Pacific Northwest (PNW) are expected to feel direct effects of ocean acidification. Direct effects have been observed on the $100 million shellfish industry, and additional indirect economic impacts are possible on the finfish industry due to a loss of prey species. The ability to predict the degree of hypoxia and acidification as well as relevant indices of impact for species of interest could be of considerable benefit to managers. Through the design of biogeochemically relevant tracers and implementation in high-resolution models, regional simulations can improve our understanding of processes difficult to observe, investigate relationships between the ecology of marine organisms and ocean health, and generate forecasts and projections of changes to the region. For example, through realistic simulations of oxygen variability on the Washington and Oregon shelves, the seasonal oxygen decline observed on the Washington shelf was determined to be dominated by local respiration of biomass, which experiences a lot of spatial and temporal variability (Siedlecki et al, 2015). That model was extended into a seasonal forecasting project for the same region (JISAO's Seasonal Coastal Ocean Prediction of the Ecosystem, J-SCOPE) with applications for fisheries management (Siedlecki et al, 2016), as well as a short term (days), state funded forecasting system to inform the shellfish industry (LiveOcean). The model now includes ocean acidification variables, whose design elucidated the importance of regional freshwater variability in determining local OA variability. These results showcase the increasingly stressful conditions over most of the water column for biota in the coastal ocean. While the PNW waters are experiencing this earlier than other coastal regions, the tools developed and lessons learned there can be applied to other regions to equip local stakeholders with the knowledge necessary to manage the risk to their species of interest.
May. 31Davide FarandaLaboratorie des Sciences du Climate (LSCE) of the University of Paris-SaclayPredicting and characterizing atmospheric states from local dynamical properties of the underlying attractor
Mid-latitude flows are characterized by a chaotic dynamics and recurring patterns hinting to the existence of an atmospheric attractor. In 1963 Lorenz described this object as: "the collection of all states that the system can assume or approach again and again, as opposed to those that it will ultimately avoid" and analyzed a low dimensional system describing a convective dynamics whose attractor has the shape of a butterfly. Since then, many studies try to find equivalent of the Lorenz butterfly in the complex atmospheric dynamics. Most of the studies where focused to determine the average dimension D of the attractor i.e. the number of degrees of freedom sufficient to describe the atmospheric circulation. However, obtaining reliable estimates of D has proved challenging. Moreover, D does not provide information on transient atmospheric motions, such as those leading to weather extremes. Using recent developments in dynamical systems theory, we show that such motions can be classified through instantaneous rather than average properties of the attractor. The instantaneous properties are uniquely determined by instantaneous dimension and stability. Their extreme values correspond to specific atmospheric patterns, and match extreme weather occurrences. We further show the existence of a significant correlation between the time series of instantaneous stability and dimension and the mean spread of sea-level pressure fields in an operational ensemble weather forecast at lead times of over two weeks. Instantaneous properties of the attractor therefore provide an efficient way of evaluating and informing operational weather forecasts
Jun. 1Nicholas Lutsko - FPOPrinceton UniversityAspects of Eddy Momentum Fluxes in the General Circulation of the Troposphere
New Meeting Thu, Jun 1, 2017 9:45 AM - 11:45 AM EDT Please join my meeting from your computer, tablet or smartphone. You can also dial in using your phone. United States: +1 (872) 240-3212 Access Code: 630-214-909 First GoToMeeting? Try a test session:
Jun. 9Michael L. BannerUniversity of New South Wales Sydney, AustraliaRecent progress on predicting breaking onset for water waves and modeling wave breaking influence in sea state forecast models
Breaking waves have challenged mariners since the earliest days of seafaring, with scientific and engineering interest in this topic increasing rapidly following the publication of Stokes' remarkable mathematical theory of water waves in 1847. Yet despite transformative advances in computational capabilities, wave breaking has resisted a compelling understanding of what actually underpins its onset and whether it is generic across the diverse scenarios of breaking onset - group-mediated, bottom-induced, opposing current, amongst others. In this talk I will highlight our exciting recent progress on elucidating key aspects of this historically elusive topic, which likely have broader application to other natural dispersive wave systems. Of particular interest are refinements to present understanding of wave geometry/kinematics in unsteady 2D and 3D wave packet evolution, involving crest (and trough) leaning modes which can appreciably modify wave crest (and trough) speeds. This has led to new insights on wave breaking onset, including development of a unified breaking threshold for 2D and 3D wave packets for a wide range of depth/wavelength conditions which is closely supported by observations. I will also overview recent advances we have made on the allied topic of representing wave breaking in spectral ocean wave forecast models to model the turbulent kinetic energy dissipation rate from breaking. This enables forecasting key properties of geophysical importance from standard sea state forecasts that depend on wave breaking as well as the wind speed, including whitecap cover and sea spray flux.
Jun. 14Bing PuPrinceton UniversityDustier United States in the late 21st century due to climate change?
Mineral dust is one of the most abundant atmospheric aerosols by mass and plays an important role in the climate system. Severe dust storms have far-reaching socioeconomic impacts. Climate models project rising drought risks over the southwestern and central U.S. in the twenty-first century due to increasing greenhouse gases. The projected drier regions largely overlay the major dust sources in the United States. However, whether dust activity in U.S. will increase in the future is not clear, due to the large uncertainty in dust modeling. This study found that changes of dust activity in the U.S. in the recent decade are largely associated with the variations of precipitation, soil bareness, and surface winds speed. Using multi-model output under the Representative Concentration Pathways 8.5 scenario, we project that climate change will increase dust activity in the southern Great Plains from spring to fall in the late half of the twenty-first century - largely due to reduced precipitation, enhanced land surface bareness, and increased surface wind speed. Over the northern Great Plains, less dusty days are expected in spring due to increased precipitation and reduced bareness. Given the large negative economic and societal consequences of severe dust storms, this study complements the multi-model projection on future dust variations and may help improve risk management and resource planning.
Jun. 20Steven D. AllisonUniversity of California, IrvinePredicting the future of soil carbon with Earth system models
Scientific investment in predictive power must be commensurate with the crucial role of Earth system models in crafting environmental policy. In these models, biological feedbacks are a major source of uncertainty in simulations of global temperature and ecosystem resilience. Soils play a key role in this uncertainty, and current biogeochemical models diverge widely in their soil carbon projections. For example, current models simulate global carbon stocks of 510 to 3040 Pg C compared to observations of 890 to 1660 Pg C. Going forward, these models project changes in global soil carbon ranging from losses of 72 Pg C to gains of 253 Pg C over the 21st century. Importantly, all of these models omit microbial processes. New models that account for microbial physiology and enzyme kinetics can explain up to half of the spatial variation in contemporary soil carbon stocks, roughly double the variance explained by the best conventional models. Still, newer microbial models are relatively unproven. They project a wide range of soil carbon responses to 21st century global change, and they are surprisingly insensitive to changes in carbon inputs. New analyses are required to parameterize microbial models and scale up microbial physiology. Small-scale models that account for microbial diversity and functional traits are promising tools for addressing this challenge.
Jun. 21Hayley DosserGFDLLateral eddy fluxes and circulation in the deep Arctic Ocean from an inverse method
The intermediate and deep waters of the Canada Basin in the Arctic Ocean have a complex and slowly evolving temperature and salinity structure, characterized by thermohaline intrusions and double-diffusion. We use EOF analysis of observational hydrographic data coupled with a novel inverse method to determine the relative importance of the Beaufort Gyre circulation and lateral along-isopycnal diffusion to water mass evolution in this region. We provide rough estimates of parameterized horizontal eddy diffusivity and the geostrophic flow field.
Jun. 22Ning LinPrinceton UniversityRisk analysis of hurricane storm surge in a changing climate
Hurricanes, with their strong winds, heavy rainfall, and storm surges, cause much damage and loss of life worldwide. The impacts of these storms may worsen in the coming decades because of rapid coastal development coupled with sea-level rise and possibly increasing hurricane activity due to climate change. We develop an integrated framework to assess hurricane hazard risk in a changing environment; in this talk, we focus on hurricane storm surge risk. We first couple a General Circulation Model (GCM)-driven statistical/deterministic hurricane model with hydrodynamic model ADCIRC to simulate large numbers of synthetic storm surge events and project future surge climatology. We then propose an integrated dynamic risk analysis for flooding task (iDraft) framework to assess coastal flood risk at regional scales, considering integrated dynamic effects of projected surge climatology change, sea-level rise, and economic/population growth. Temporally-varying risk measures such as the return period of various damage levels and the mean and variance of annual damage as well as temporally-integrated measures such as present value of future losses are derived to support probabilistic benefit-cost analysis for risk mitigation strategies. The application of the risk analysis framework to hurricane wind, rainfall, and eventually the joint multi-hazards is under development. Ning Lin is an Assistant Professor of Civil and Environmental Engineering at Princeton University. She integrates science, engineering, and policy to study hurricane hazards, how they change with the climate, and how to better mitigate their impact on the society. She has published in high-impact journals including Science, Nature Climate Change, and Proceeding of the National Academy of Sciences. Lin received her Ph.D. in Civil and Environmental Engineering from Princeton University in 2010. She also received a certificate in Science, Technology and Environmental Policy in 2010 from Princeton's Woodrow Wilson School of Public and International Affairs. Before rejoining Princeton as an assistant professor in 2012, she conducted research in the Department of Earth, Atmospheric and Planetary Sciences at MIT as a NOAA Climate and Global Change Postdoctoral Fellow.
Jun. 22Ning LinRoundtable Discussion
After Action Review - Roundatable Discussion
Jul. 5Kun GaoGFDL/Princeton UniversityToward Skillful Subseasonal Prediction of North Atlantic Hurricanes
Skillful prediction of hurricane activity on the subseasonal scale (from two weeks to less than a season) is important for reducing the hurricane damage in coastal regions. In this talk, I will present a synthetic summary of the recent efforts on the subseasonal prediction of North Atlantic hurricanes based on the non-hydrostatic two-way-nested version of GFDL HiRAM. Key results are 1) the HiRAM not only well captures the impact of Madden-Julian Oscillation (MJO) on global tropical cyclone genesis, but also faithfully reproduces the modulation of MJO on regional hurricane activity, especially in the Gulf of Mexico and Caribbean Sea region; 2) The two-way-nested grid with 8-km resolution realistically simulates the hurricane size distribution and inner-core structure, which leads to significant improvement in the subseasonal prediction of major hurricanes in North Atlantic.
Jul. 19Riccardo Farneti Climate Processes and Sensitivity GroupPacific interdecadal variability: tropical-extratropical interactions, subtropical cells and the recent global warming slow-down
To estimate the anthropogenic contribution to climate signals in the recent past and future decades implies a certain degree of confidence in both understanding and simulating natural internal variability at interdecadal timescales. In this talk I will examine interactions between the tropical and subtropical Pacific at decadal time scales using a hierarchy of models, configurations and forcing in uncoupled oceanic and atmospheric simulations. It is found that Pacific subtropical cells (STC) provide the connection between subtropical wind stress anomalies and tropical SSTs. Tropical atmospheric anomalies do not have much influence at these timescales. Our simulations are also able to capture recent trends in observed STC transport, convergence, and equatorial SST anomalies. We argue that tropical SST decadal variability partly stems from the forcing of the Pacific subtropical gyre through the atmospheric response to ENSO. The resulting Ekman pumping anomaly alters the STC and oceanic heat transport, providing a negative feedback on the SST. We thus suggest that extratropical atmospheric responses to tropical forcing have feedbacks onto ocean dynamics that lead to a time-delayed response of the tropical oceans, giving rise to a possible mechanism for multidecadal ocean-atmosphere coupled variability. Subtropically-forced STC variability is identified as a major player in the generation of equatorial Pacific decadal SST anomalies, pacing tropical Pacific natural climate variability on inter-decadal time scales, as observed in historical records. The natural mode of variability has implications for the evolution of equatorial SST in the coming decades under the concomitant effects of climate change. Dr. Riccardo Farneti ICTP, Trieste, Italy
Jul. 24Dr. Zhan SuClimate Processes and Sensitivity GroupImpact of ocean submesoscale turbulence on global climate
For the first time, we explicitly resolve ocean turbulence down to ~5km on a global scale using a new high-resolution global model (1/48º horizontally). Results highlight strong submesoscale turbulence (defined here as scales ~50km) in most mid and high latitude oceans. These submesoscale structures are found to cause strong upward heat fluxes up to ~1000 W/m2 in the upper ocean. Our results show that submesoscale processes are critical to setting the rate, timing and location of heat exchange between the interior ocean, the surface ocean, and the atmosphere, and are therefore a key component of the global heat budget. Furthermore, submesoscale dynamics is found to provide a significant kinetic energy source that powers the global large-scale ocean circulation. Dr. Zhan Su, California Institute of Technology. POC at GFDL is Stephen Griffies, 609-452-6672.
Jul. 25Geeta Persad Carnegie InstitutionThe Influence of Aerosol Emissions' Geographic Location on the Magnitude and Spatial Distribution of Climate Effects
The global distribution of anthropogenic aerosol emissions has evolved continuously since the preindustrial era - from 20th century North American and Western European emissions hotspots to present-day South and East Asian ones. With this comes a relocation of the regional radiative, dynamical, and hydrological impacts of aerosol emissions, which may influence global climate differently depending on where they occur. A lack of understanding of this relationship between aerosol emissions' location and their global climate effects, however, obscures the potential influence that aerosols' evolving geographic distribution may have on global and regional climate change - a gap which we address in this work. Using a novel suite of experiments in the CESM CAM5 atmospheric general circulation model coupled to a slab ocean, we systematically test and analyze mechanisms behind the relative climate impact of identical black carbon and sulfate aerosol emissions located in each of 8 past, present, or projected future major emissions regions. Results indicate that historically high emissions regions, such as North America and Western Europe, produce a stronger cooling effect than current and projected future high emissions regions. Aerosol emissions located in Western Europe produce 3 times the global mean cooling (-0.34 °C) as those located in East Africa or India (-0.11 °C). The aerosols' in-situ radiative effects remain relatively confined near the emissions region, but large distal cooling results from remote feedback processes - such as ice albedo and cloud changes - that are excited more strongly by emissions from certain regions than others. Results suggest that aerosol emissions from different countries should not be considered equal in the context of climate mitigation accounting, and that the evolving geographic distribution of aerosol emissions may have a substantial impact on the magnitude and spatial distribution of global climate change. POC at GFDL is Yi Ming, 609-452-5338.
Jul. 25Haylie Mikulak, Manon Vignes, Bridgette BefortExamining the impact of temperature on shipping days for corn, soy beans and wheat
30 minute Intern Presentations - HAYLIE MIKULAK: Examining the impact of temperature on shipping days for corn, soy beans and wheat. MANON VIGNES: HiFLOR model projections of North Atlantic tropical cyclone activity under late 21st century warming conditions. BRIDGETTE BEFORT: Evaluation of intra-seasonal variability of the Asian Monsoon in GFDL's latest climate model.
Jul. 25Manon VignesHiFLOR model projections of North Atlantic tropical cyclone activity under late 21st century warming conditions
30 minute Intern Presentations
Jul. 25Bridgette BefortEvaluation of intra-seasonal variability of the Asian Monsoon in GFDL's latest climate model
30 minute Intern Presentation
Jul. 28Rebecca Barber, Elise Penn, Katie Boaggio, Hannah TandyModel based evaluation of bubble injection in air-sea gas exchange parameterizations
30 minute Intern Presentation - REBECCA BARBER: Model based evaluation of bubble injection in air-sea gas exchange parameterizations. ELISE PENN: Evaluation of GFDL-AM4 simulations of nitrogen oxides with OMI satellite observations. KATIE BOAGGIO: Tracking and analyzing extratropical cyclones with fvGFS. HANNAH TANDY: ESM2Mb sensitivities to Paleoclimate forcings of the Paleocene/Eocene thermal maximum.
Aug. 4Intern PresentationIntern Presentation
Intern Presentation
Aug. 9Jordan SchnellGFDLExploring the relationship between meteorology and surface PM2.5 in Northern India
Northern India is one of the most polluted and densely populated regions in world. Accurately modeling pollution in the region is difficult due to the extreme conditions with respect to emissions, meteorology, and topography, but it is paramount in order to understand how future changes in emissions and climate may alter the region's pollution regime. We evaluate a developmental version of the new-generation NOAA GFDL Atmospheric Model, version 4 (AM4) in its ability to simulate observed wintertime PM2.5 and its relationship to meteorology over the Northern India (23°N-31°N, 68°E-90°E). We perform two simulations of the GFDL-AM4 nudged to observed meteorology for the period (1980-2016) with two emission inventories developed for CMIP5 and CMIP6 and compare results with observations from India's Central Pollution Control Board (CPCB) for the period 1 October 2015 - 31 March 2016. Overall, our results indicate that the simulation with CMIP6 emissions has substantially reduced the low model bias in the region. The AM4, albeit biased low, generally simulates the magnitude and daily variability in observed total PM2.5. Ammonium nitrate and ammonium sulfate are the primary components of PM2.5 in the model, and although not directly observed, correlations of total observed PM2.5 and meteorology with the modeled individual PM2.5 components suggest the same for the observations. The model correctly reproduces the shape and magnitude of the seasonal cycle of PM2.5; but for the diurnal cycle, it misses the early evening rise and secondary maximum found in the observations. Observed PM2.5 abundances within the densely populated Indo-Gangetic Plain are by far the highest and are closely related to boundary layer meteorology, specifically relative humidity, wind speed, boundary layer height, and inversion strength. The GFDL-AM4 reproduces the observed pollution gradient over Northern India as well as the strength of the meteorology-PM2.5 relationship in most locations.
Aug. 11Intern PresentationGFDLIntern Presentation
Intern Presentation
Aug. 23Andrew RossPenn StateModeling the impacts of climate variability and change on Chesapeake and Delaware Bays
In this talk, I discuss two key questions on the use of numerical models to understand the impacts of climate variability and change on the Chesapeake and Delaware Bays and other estuarine ecosystems. First, are numerical ocean models capable of accurately simulating the effects of climate change that have already been observed? Using model simulations of changes in tides in response to past sea-level rise, I show that the model successfully reproduced some of the observed sensitivity of tidal amplitudes to mean sea level. Notably, sea-level rise produces a shifting of the amphidromic system in the Chesapeake Bay and increased amplification of the tides in the Delaware Bay. Second, how can we use numerical models to simulate the effects of uncertain future climate change? Top-down strategies are often employed, which involve a computationally expensive chain of models to translate global climate change into local impacts. However, to reduce the computational costs, modelers often must restrict their simulations to use boundary conditions from only a few emissions scenarios and global climate models. My work examines how to optimally select a limited number of boundary condition models using a test case of simulating runoff in the Susquehanna River Basin. I show that only one model selection strategy was satisfactory. However, regardless of the selection strategy used, simulations with only a few model scenarios neglected a large range of actual uncertainty. Therefore, complex numerical models may be better used in idealized sensitivity experiments or as compliments to other modeling approaches. POC at GFDL is Charles Stock, 609-452-5331.
Aug. 28Climate EngineeringClimate Engineering
Climate Engineering
Aug. 29Climate EngineeringClimate Engineering
Climate Engineering
Aug. 30Climate EngineeringClimate Engineering
Climate Engineering
Sep. 6MATLAB Exploratory SessionMATLAB Exploratory Session
MATLAB Exploratory Session
Sep. 6Yi MingGFDLSahel rainfall response to a uniform oceanic warming
Coupled climate models project future changes to rainfall in the African Sahel ranging from severe drying to severe wettening. Atmosphere-only models perturbed with uniform ocean surface warming span a similar range, motivating study of the simpler latter problem in order to constrain the more societally relevant former one. We analyze four comprehensive atmospheric models developed at the NOAA Geophysical Fluid Dynamics Laboratory, which respond to uniform ocean surface warming of 2 K with Sahel wet season rainfall changes ranging from -38 to +15%. A detailed MSE budget analysis reveals the relative importance of different processes in determining the response.
Sep. 14 Prof. Raffael Ferrari, MITA new theory of the abyssal ocean circulation
It has been long been recognized that the large-scale circulation of the abyssal ocean is enabled by small-scale diapycnal mixing. Theories developed in the fifties and sixties posited that the diapycnal mixing drives widespread upwelling of abyssal waters and broad poleward meridional flows. We will argue that these predictions need to be revised in view of observations collected over the last twenty years which suggest that mixing is strongly enhanced towards the ocean bottom, where the breaking of internal tides and lee waves is most vigorous. The bottom-intensified mixing induces a a pattern of near-bottom up- and downwelling that is quite different from the traditionally-assumed widespread upwelling. The up- and downwelling flows result in a horizontal circulation characterized by zonal flows, while the meridional flows are confined along the ocean's western boundaries. We will discuss the implications of these circulation patterns for the residency time of abyssal waters in the ocean and for the role of the abyssal ocean on Earth's climate.
Sep. 14Stephen Griffies & CompanyGroup Meeting
Sep. 20Yohai KaspiDept. of Earth and Planetary Sciences Weizmann Institute of Science, IsraelThe spatial structure of midlatitude storm tracks and its dependence on climate change
The spatial structure of midlatitude storm tracks is analyzed by tracking transient cyclonic eddies in an idealized GCM with several levels of complexity and in CMIP5 simulations. The localized atmospheric response is decomposed in terms of a time-zonal mean background flow, a stationary wave and a transient eddy field. The Lagrangian tracks are used to construct cyclone composites and perform a spatially varying PV budget. Three distinct mechanisms that contribute to the spatial structure emerge: transient nonlinear advection, latent heat release and stationary advection. The downstream evolution of the PV composites shows the different role of these mechanisms as the storm tracks evolve downstream. We demonstrate that the poleward motion of individual cyclones increases with increasing global mean temperatures, and by this provide an alternate quantitative explanation to the poleward shift of storm tracks under climate change.
Sep. 27Harvey & Irma, Part One: Attribution, Precipitation & FloodingHarvey & Irma, Part One: Attribution, Precipitation & Flooding
Harvey & Irma, Part One: Attribution, Precipitation & Flooding
Sep. 28Harvey & Irma Part Two: Prediction Across TimescalesHarvey & Irma Part Two: Prediction Across Timescales
Harvey & Irma Part Two: Prediction Across Timescales
Oct. 11Alexandra JonesGFDLClimate Impacts of Radiative Parameterization Errors Using a Global Line-by-Line Framework
A novel framework has been developed to quantify instantaneous radiative effect error on a global scale. It combines line-by-line spectral variation of gaseous optical properties with a multi-stream solver to create benchmark calculations of radiative transfer on a given global distribution of meteorological variables. Comparing the benchmark fluxes to fluxes computed by a GCM radiative parameterization allows for quantification of parameterization errors, sampled across a wide variety of conditions. Prior attempts at understanding radiative parameterization error have been constrained by computational expense to only a handful of cases, inadequate to understand the mean, variability, and source of the error. In contrast, the benchmark results can be visualized on a map, which provides spatial context to the error. The large range of conditions also allows for visualization of the error as uni- or multi-variate functions of meteorological properties of interest. Both aid in hypothesis formulation and testing about the sources of error. The utility of the framework and the resulting benchmark calculations will be demonstrated with implications for climate relevant variables. It is applied to instantaneous radiative effect of aerosol to quantify the global average parameterization error, spatial variability of error, and variability of error as a function of aerosol optical properties, resulting in hypotheses about sources of the error. Then it is used to test a hypothesis in the literature that links radiative parameterization error to the intermodel spread in global mean precipitation.
Oct. 16Suki ManabeAOS Program at Princeton UniversityInterhemispheric Asymmetry in Global Warming
As the concentration of greenhouse gas increases in the atmosphere, temperature increases at the earth surface. In the Northern Hemisphere, the magnitude of the warming increases with increasing latitude and is at a maximum over the Arctic Ocean and its immediate vicinity. In the Southern Hemisphere, on the other hand, the polar amplification of the global warming is absent in the Antarctic Ocean. This is what happened in the numerical experiment conducted at GFDL almost 30 years ago. The geographical pattern of global warming described above appears to be broadly consistent with the pattern of surface temperature change that have been observed during the last several decades, when the rate of increase of greenhouse gas is pronounced. In this talk, I would like to discuss the role of ocean in delaying global warming particularly in the circumpolar ocean of the Southern Hemisphere.
Oct. 17Angel Adames GFDLIndian Monsoon Depressions: New insights from GFDL's AGCM and Linear Theory
The mechanisms that lead to the propagation of moisture and moist static energy in monsoon low and high-pressure systems collectively referred to as synoptic-scale monsoonal disturbances (SMDs), are investigated using daily output fields from GFDL's Atmospheric Model 4 (AM4). Propagation of the moisture anomalies is dominated by vertical moisture advection while the MSE anomalies propagate due to horizontal advection of low-frequency dry static energy by the SMD winds. By combining the budgets, we interpret the propagation of the precipitation anomalies in terms of lifting that is forced by horizontal dry static energy advection. This process moistens the lower free troposphere, producing an environment that is conducive for deep convection. The precipitation anomalies are, in turn, largely maintained by longwave radiative heating. Based on these results, we propose a linear framework where the evolution of moisture plays a central role in SMDs. In this framework, warm air advection by the anomalous northerly winds induces vertical moisture advection, which moistens and destabilizes the column. The moistened lowered troposphere enhances convection which, in turn, causes the low pressure system to intensify through vortex stretching. This instability only occurs if the vorticity tendency from dry processes (such as horizontal vorticity advection) and moist processes (vortex stretching from convection) are of the same polarity.
Oct. 18Veronica ChanBritish Antarctic SurveyThe impact of nitrogen chemistry in snow on atmospheric oxidising capacity in the polar boundary layer
Snow surfaces do not only influence the albedo feedback on Earth but also have a significant impact on the chemistry of the overlying air. Light-induced chemical reactions take place in the snow leading to emissions of reactive chemical species such as nitrogen oxides, an ozone precursor, which can alter ozone concentration in the lower atmosphere. Tropospheric ozone is a pollutant and a greenhouse gas that can influence the regional energy balance and climate. This project aims at developing a model to quantify the emissions of nitrogen species from snow for the following reasons: 1) In the Arctic, there is strong interest in near-term mitigation of the current warming by controlling tropospheric ozone precursors as the level of nitrogen oxide has doubled since the mid-twentieth century due to fossil fuel burning from the shipping industries. To provide an accurate assessment of how effective the adopted mitigation measures are it is necessary to understand the natural background air chemistry and take into account the chemical snow source. 2) Climate models predict the largest temperature rise in the polar regions which would certainly change the chemical snow source. The consequences of the changing climate on nitrogen emission from snow and the feedback via tropospheric ozone level will be constrained. 3) Ice cores are powerful archives of past climate and environmental conditions, from seasonal to multi-millennial timescales. However, photoreactions and physical processes within the snowpack do influence nitrate concentrations and currently prevent a quantitative interpretation of the polar ice core record of nitrate.
Oct. 19Formal Seminar - Mingfang TingColumbia UniversityThe Role of Aerosol and Greenhouse Gas Forcing in CMIP5 Models: Impacts on Atlantic Hurricane Intensity and Asian Monsoon
In this talk, I will discuss our recent work on the regional climate changes in the historical period due to both the aerosol and greenhouse gas forcing, in particular how these anthropogenic forcing may have impacted the Asian monsoon and the Atlantic hurricane intensity. While aerosols and greenhouse gases tend to produce opposite sign changes in terms of surface temperature and precipitation as previously discussed, the mechanisms by which these changes occur are not entirely symmetric between the two forcing cases. For example, aerosols tend to produce largely dynamical responses in Asian monsoon circulation changes, while greenhouse gas forcing tends to be dominated by the thermodynamic impact through changes in atmospheric moisture content. For their impact on the Atlantic hurricane intensity, aerosols are more effective in causing changes in hurricane intensity than greenhouse gases, due to differences in surface energy balances. Future changes in Asian monsoon and hurricane intensity as simulated by the CMIP5 models will also be discussed as a comparison to that during the historical period.
Oct. 25Kieran BhatiaGFDLUnderstanding How Tropical Cyclone Intensification Rates Could Increase with Climate Change
Recent studies have showed that tropical cyclone (TC) intensification rates control forecast performance, the magnitude of financial losses, as well as the lifetime maximum intensity of a storm. As one of the first global coupled climate models to simulate and predict category 4 and 5 (Saffir-Simpson scale) TCs and their interannual variations, the High-Resolution Forecast-Oriented Low Ocean Resolution (HiFLOR) model at the Geophysical Fluid Dynamics Laboratory (GFDL) is uniquely able to provide insight on how the entire TC intensification distribution could be transformed due to climate change. In this study, three 70-year HiFLOR experiments are performed to identify the effects of radiative forcing on TC intensity change. For each of the experiments, sea surface temperature (SST) and atmospheric radiative forcing are nudged to different targets, allowing us to explore the sensitivity of TCs to these conditions. First, a control experiment, which uses prescribed ocean and atmospheric forcing observed during the years 1986-2005, is compared to two observational records and evaluated for its ability to capture the mean TC intensity behavior during these years. The simulated intensification distribution as well as the percentage of TCs that become major hurricanes agrees well with observations. The control experiment is then compared to two climate change experiments, which use the same climatological SSTs from the control experiment plus mean SST anomalies and atmospheric radiative forcing from either 2016-2035 or 2081-2100. The frequency, intensity, and intensification distribution of TCs all shift to higher values as the 21st century progresses. Several synoptic variables are investigated as possible pathways for a warming climate to affect TC intensification.
Oct. 26Formal Seminar - John AbatzoglouUniversity of IdahoHow much has human-caused climate change influenced wildfire extent across western US forests?
Wildfire activity across western US forests has seen substantial variability over the past century with changes in human settlement, fire management policies, and climate variability. Since the mid 1980s, the amount of fire across western US forests has increased 8-fold leading to a cascade of impacts including widespread forest mortality, carbon emissions, periods of degraded air quality, and substantial fire suppression expenditures. Although numerous factors aided the recent rise in fire activity, observed warming and drying have significantly increased fire-season fuel aridity, fostering a more favorable fire environment across forested systems. Human-caused climate change was responsible for half of the documented increases in fuel aridity since the 1970s and contributed to a substantial increase in forest fire extent over the past three decades.
Oct. 31Luc DeikePrinceton UniversityWave breaking in ocean-atmosphere interactions
Breaking waves at the water surface is a striking example of turbulent mixing across a fluid interface. The impact of the jet generates turbulence, entrains air into the water and ejects droplets into the air. A fundamental understanding of the general multi-scale properties of the resulting multiphase turbulent flow is necessary to develop more accurate gas transfer or spray generation parameterizations. In this talk, I will discuss a general framework to account for the effect of breaking waves on ocean-atmosphere interaction, such as dissipation, momentum flux, air entrainment or Lagrangian drift. I will start by a model for air entrainment by breaking waves in the ocean, based on laboratory experiments and direct numerical simulations at the wave and bubble scale. This model is then up-scaled to the ocean using measurements of the wave and wave breaking statistics. This leads to semi-empirical formulas relating wind and wave variable, such as wind speed and significant wave height, to air entrainment by breaking. I will discuss how this approach can be used to compute other key exchanged variables, such as energy dissipation, Lagrangian drift or sea spray. Point of Contact: Dr. Stephen Griffies, 609-452-6672.
Nov. 1Nadir JeevanjeeGFDLConvection, climate, and their sensitivities in cloud-resolving FV3
We present cloud-resolving FV3 simulations and explore their sensitivity to resolution, the hydrostatic approximation, and numerical damping parameters. We find that O(100 m) resolutions are required for convective vertical velocities to converge, and that the hydrostatic solver overestimates these by a factor of 2 - 3 in this regime. We develop analytic theory to explain these results. We also find a striking sensitivity of the mean climate to `divergence damping', a commonly used form of explicit diffusion on the wind fields. This sensitivity appears to be tied to the width of convective updrafts, which increases with increased damping and acts as kind of convective organization, dramatically drying out the troposphere, reducing cloudiness, and increasing the OLR by up to 35 W/m^2.
Nov. 2GFDL 2017 Fall Science SymposiumGFDL Science Symposium
GFDL 2017 Fall Science Symposium takes place at Frick Hall in Taylor Auditorium
Nov. 13Rick RussottoUniversity of WashingtonEffects of Solar Geoengineering on Clouds, Energy Transport and the ITCZ
The polar amplification of warming and the ability of the inter-tropical convergence zone (ITCZ) to shift to the north or south are two very important problems in climate science. Examining these behaviors in global climate models (GCMs) running solar geoengineering experiments is helpful not only for predicting the effects of solar geoengineering, but also for understanding how these processes work under increased CO2. Both polar amplification and ITCZ shifts are closely related to the meridional transport of moist static energy (MSE) by the atmosphere. This study examines changes in MSE transport in 10 fully coupled GCMs in Experiment G1 of the Geoengineering Model Intercomparison Project, in which the solar constant is reduced to compensate for abruptly quadrupled CO2 concentrations. In this experiment, poleward MSE transport decreases relative to preindustrial conditions in all models, in contrast to the CMIP5 abrupt4xCO2 experiment, in which poleward MSE transport increases. This reduction in poleward energy transport likely plays a role in limiting the polar warming in G1. The seasonal migration of the ITCZ is dampened in G1 relative to abrupt4xCO2 due to preferential cooling of the summer hemisphere by the solar reduction. The ITCZ shifts northward in G1 by 0.14 degrees in the annual, multi-model mean, with an inter-model range of -0.33 to 0.89 degrees. These shifts are anticorrelated with changes in cross-equatorial MSE transport. An attribution study with a moist energy balance model shows that cloud feedbacks are the largest source of uncertainty regarding changes in cross-equatorial energy transport under solar geoengineering. Analysis of cloud changes in G1 has so far shown a robust reduction in low cloud fraction, which over the ocean is likely connected with reductions in the strength of the marine boundary layer inversion. This reduction in low cloud fraction increases the amount of solar reduction required to compensate for the increased CO2. Changes in mid-level and high clouds reflect an annual mean narrowing of the ITCZ. Outside the tropics, high cloud fraction is enhanced in most models.
Nov. 14Gan ZhangUniv of IllinoisExtratropical Impacts on Atlantic Tropical Cyclone Activity: from Theory to Practice
My work points toward possible extratropical influences on seasonal hurricane activity in the Atlantic basin, which may help explain why seasonal forecasts of the 2013 season were generally biased high compared to observations.
Nov. 15Laure ZannaGFDL Ocean Heat Uptake and Dynamical Sea Level Rise: Past and Future Uncertainty
The ocean absorbs a large portion of the anthropogenic heat released in the climate system, leading to an increase in global mean sea level rise. The magnitude, pattern and rate of ocean heat uptake are governed by several processes such as deep water formation, Southern Ocean Ekman pumping, and air-sea interaction. The spatial patterns of heat uptake and storage are further impacted by heat redistribution via changes in the ocean circulation, induced by natural variability and anthropogenic forcing. We use observations, theory and a hierarchy of models to estimate the heat storage and thermosteric sea level rise in the Atlantic due to changes in circulation during the observational period and in future projections. We will show that about 2/3 of the thermosteric sea level rise at the latitude of NYC in the past 50 years is attributed to ocean circulation changes and traced back to surface forcing. We will further explore the link between air-sea forcing, ocean circulation and heat and carbon uptake in future projections. Our findings highlight high-latitude forcing as the cause for the large uncertainty in regional sea level projections, and provide a way forward to constrain regional projections of ocean heat uptake and sea level rise, including the use of anthropogenic carbon to infer circulation changes.
Nov. 22Hailey ShinEvaluation of PBL simulation in GFDL AGCMs: Improvement by a refined vertical grid resolution and a revised PBL parameterization scheme
This study describes the performance of Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric general circulation models (AGCMs) in simulating the climatologies of planetary boundary layer (PBL) parameters, with a particular focus on their diurnal cycles. Two GFDL models, which differ solely in the PBL parameterization, are evaluated through the comparison to the reanalysis datasets. The overall patterns of the near-surface parameters (near-surface temperature and wind speed, and PBL height) in the models agree well with those in the reanalysis, but several systematic biases are identified. To understand the link between the systematic biases and the turbulent mixing in PBL, a detailed analysis of surface turbulent fluxes and vertical profiles is performed for the Sahara region, which is suitable for focusing on the role of vertical mixing in dry PBLs. Based on the evaluation results, the models are modified to better simulate the PBL climatologies; the vertical grid resolution is refined with an additional layer near the surface, and the PBL parameterization scheme is revised by implementing non-local heat and momentum transport terms.
Nov. 27Manvendra DubeyLos Alamos National Laboratory, DOECarbonaceous Gas and Aerosol Measurements to Validate Models and Verify Emissions
Earth system models rely on accurate representations of processes and emissions that are evaluated using observations. Iterative refinements are crucial for robust assessments, as I will illustrate with our recent research findings as follows: Carbonaceous aerosol (CA) forcing in current models is prescribed as a balance between the warming by black carbon and the cooling by organic aerosol. However, data show that some organic aerosols called brown carbon absorb sunlight. Furthermore, transparent coatings on black carbon amplify their light absorbing potency by lensing. Such coatings could make black carbon more hydrophilic thereby reducing their lifetime and burden. I will use field and laboratory studies to uncover the fundamental chemistry controlling the optical properties and water affinity of CAs as they age to enable prognostic treatments. Atmospheric carbon dioxide (CO2) accumulation is moderated by its uptake by forests and oceans that soak up 25% each of the human emissions. How carbon sinks will respond to future climate change is uncertain. I will present observations of daily and seasonal variations of column CO2 and CO over the Amazon rainforest. I will show that both biomass burning and net ecosystem exchange that are out of phase control the seasonal CO2 cycle and are captured well by models. However, the daily CO2 drop driven by photosynthesis is biased low in models, a problem that needs to be fixed. Atmospheric Methane (CH4) that accounts for ~25% of anthropogenic forcing is rising again after a hiatus. Potential causes include leaks from shale gas growth, intensive agriculture, permafrost thaw, expanded wetlands and/or shorter lifetime from increased Hydroxyl radicals. I will review recent findings and focus on our discovery of the methane hot spot over Four Corners, attributed it to fossil sector and show that reported emissions are low by a factor of 3. I will close with our development of an automated neural network CH4 leak detection system for well pads that is fast, cheap and profitable.
Nov. 28Heather ArchambaultGFDL Associate DirectorDiabatic Influence of Recurving Tropical Cyclones on the Midlatitude Atmospheric Circulation
Tropical cyclones (TCs) frequently cause flooding and high winds as they recurve poleward and undergo extratropical transition (ET). Along with causing local hazards, the interaction of a recurving TC with the extratropical flow can excite or amplify a Rossby wave packet that induces large-scale circulation anomalies and extreme weather thousands of kilometers downstream. In this work, composite analysis and a case study are used to highlight the importance of moist dynamics in TC-extratropical flow interactions that induce downstream circulation anomalies following western North Pacific (WNP) TC recurvature and ET. Prior findings from idealized modeling studies of TC-extratropical flow interactions indicate that diabatically driven divergent outflow impinging on an potential vorticity (PV) gradient (Rossby waveguide) is critical to ridge amplification and jet intensification during TC recurvature and ET. Motivated by these findings, the magnitude of upper-tropospheric negative PV advection by the irrotational wind associated with a recurving TC is used as a metric for the strength of a TC-extratropical flow interaction. Composite analyses of objectively identified strong and weak interactions (i.e., top and bottom quintiles of negative PV advection by the irrotational wind, respectively) over the WNP during 1979-2009 are constructed from NCEP-NCAR reanalysis. It will be shown in a comparison of the two sets of composites that strong TC-extratropical flow interactions tend to amplify long-lived Rossby wave packets that induce circulation anomalies over North America, whereas weak interactions tend to excite short-lived Rossby wave packets that fail to reach North America. Thus, the influence of recurving WNP TCs on the downstream atmospheric circulation apparently is sensitive to the magnitude of diabatic forcing of the Rossby waveguide during TC recurvature. This result stands in contrast to prior results indicating that the downstream influence of a recurving WNP TC is relatively insensitive to the size or intensity of the recurving TC. Additionally, a case study of recurving WNP TC Malakas (2010) will be used to elucidate the dynamical chain of events linking a TC-extratropical flow interaction over the WNP to extreme heat and flooding over North America. This case also will be presented as an example of how the inability of NWP models to capture a TC-extratropical flow interaction can lead to a major forecast failure at even short lead times.
Nov. 29David GoodrichChesapeake Climate Action NetworkA Hole in the Wind: A Bicycle Journey Across the US, Looking at Climate
A Hole in the Wind: A Bicycle Journey Across the US, Looking at Climate After retiring from NOAA in 2011, the speaker rode 4200 miles from Delaware to Oregon, looking at the effects of climate change up close and talking with people along the way. He came across fragmented barrier islands on the coast, drought and expanding wind farms in Kansas, beetle-killed forest in Colorado and fire in Idaho. Along the way, he encountered a toddler's beauty pageant in Maryland, the landscape of fracking in Pennsylvania, a tornado party in Missouri, and a ghost town in Wyoming. His book, A Hole in the Wind, was released by Pegasus Books this summer.
Nov. 29Galen A. McKinleyLamont Doherty Earth Observatory of Columbia UniversityVariability in the ocean carbon sink: Drivers and challenges to detection of change
Cumulatively since preindustrial times, the ocean has absorbed 41% of all fossil fuel emissions; the remaining emissions have almost entirely remained in the atmosphere. Variability in the ocean carbon sink is substantial and poorly understood. Improved understanding of the driving physical and biogeochemical mechanisms is critical, and has increasingly important international policy implications. In this talk, I will present three studies using models and observations that elucidate the drivers and consequences of this variability. First, using a North Atlantic regional model, we show that decadal timescale circulation changes associated with the Atlantic Multidecadal Oscillation (AMO) have significant impacts on the natural component of surface ocean pCO2. With positive AMO, a slowing subpolar gyre and associated reduced mixed layer depths leads to more carbon being retained at depth. AMO-related warming only partially compensates by increasing pCO2. Second, we address the degree to which the biological pump may be a first-order driver of CO2 flux variability. Using co-located observations of surface ocean pCO2 and satellite chlorophyll, our global analysis supports the long-held assumption that the carbon cycle is most strongly driven by the biological pump at high latitudes, particularly in the Southern Ocean. Third, we note that detection of expected long-term growth in the ocean carbon sink will require filtering out variability. Large ensemble climate model simulations indicate that the forced trend in carbon uptake should be largest, and thus most quickly detectable, in the high latitudes. Surface ocean pCO2 observations over the past 35 years indicate a pattern consistent with this prediction in the North Pacific; but elsewhere, variability continues to be the dominant signal. POC: John Dunne, (609) 452-6596.
Dec. 6Lorenzo PolvaniColumbia UniversityWhy has the tropical lower stratosphere stopped cooling for the last 20 years?
Dec. 7Formal Seminar - Amilcare PorporatoPrinceton UniversityImpact of hydrologic fluctuations on soil formation and runoff production
The space-time distribution of soil moisture fluctuations exerts a crucial control on a multitude of ecohydrological and biogeochemical processes. In the first part of the talk, we link the intermittent pulsing of deep percolation events to soil formation and rock weathering. We couple subsurface water and chemical molar balance equations to analyze the roles of hydrology and dissolved organic carbon (DIC) transport on chemical weathering. Three weathering regimes are elucidated. For very small or large values of transit time, the weathering is limited by reaction kinetics or transport, respectively. For intermediate values, the system is transport controlled and is sensitive to transit time. We apply the model to a series of watersheds for which we estimate transit times and identify the type of weathering regime. The results suggest that hydrologic transport of DIC may be as important as reaction kinetics and dilution in determining chemical weathering rates. In the second part of the talk we outline a theory of rainfall, soil moisture and runoff production, starting from a probabilistic, event-based framework that allows us to unify and extend existing semi-distributed models such as SCS-CN, VIC, and TOPMODEL. The resulting runoff curves are interpreted as ‘mean-field assumptions' for the statistical mechanics of watersheds and their antecedent conditions are linked consistently to the temporal dynamics of soil moisture at a point. We conclude by extending the theory to include analytical solutions of Bousinnesq equation to account for physical processes at the hillslope scale in the rainfall-runoff response of watersheds. POC/HOST: Elena S.
Dec. 8RDML Tim Gallaudet Town Hall MeetingRDML Tim Gallaudet Town Hall Meeting
RDML Tim Gallaudet Town Hall Meeting
Dec. 18FPO - Robert NazarianFPO - Robert Nazarian
FPO - Robert Nazarian Sponsor: Sonya Legg
Dec. 20Prof. Jianjun YinUniv of ArizonaRecord warm global mean surface temperatures in 2014-2016 linked to large ocean heat releases from the western tropical Pacific
A 0.24°C increase of record warm global mean surface temperature (GMST) over the past three consecutive years (2014-2016) was highly unusual and largely a consequence of an El Niño that released unusually large amounts of ocean heat from the subsurface layer of the northwestern tropical Pacific. This heat had built up since the 1990s mainly due to greenhouse-gas forcing (GHG) and possible remote oceanic effects. Model simulations and projections suggest that the fundamental cause, and robust predictor of large record-breaking events of GMST in the 21st century is GHG forcing. Climate models project that such events will increase in the future under elevated GHG forcing. Point of Contact: Stephen Griffies, tel: 452-6672