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GFDL Past Events & Seminars - 2018

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Date Speaker Affiliation Title of Presentation
Jan. 3Lunchtime Seminar Series - Yongfei ZhangArctic sea ice data assimilation: State and parameter estimations
Simulating Arctic sea ice conditions up to the present and predicting them several months in advance has high stakeholder value, yet remains challenging. Advanced data assimilation (DA) methods combine real observations with model forecasts to produce sea ice reanalyses and accurate initial conditions for sea ice prediction. This study introduces a sea ice DA framework for a sea ice model with a parameterization of the ice-thickness distribution by resolving multiple thickness categories. Specifically, the Los Alamos sea ice model version 5 (CICE5) is integrated with the Data Assimilation Research Testbed (DART). A series of perfect model Observing System Simulation Experiments (OSSEs) are designed to explore DA algorithms within the ensemble Kalman filter (EnKF) and the relative importance of different observation types. In addition, we extend the DA framework to have the ability to update model parameters. A series of OSSEs with selected parameters are designed to explore the feasibility of parameter estimation through DA. POC/Host: Mike Winton & Mitch Bushuk
Jan. 4Formal Seminar - Claire MonteleoniUniversity of Paris-Saclay and George Washington UniversityAdvances in Climate Informatics: Machine Learning Algorithms for Climate Science
The threat of climate change is one of the greatest challenges currently facing society. Given the profound impact machine learning has made on the natural sciences to which it has been applied, such as the field of Bioinformatics, machine learning is poised to accelerate discovery in climate science. Our recent progress on Climate Informatics reveals that collaborations with climate scientists also open interesting new problems for machine learning. I will give an overview of challenge problems in climate informatics, and survey work from my research group in this nascent field. I will center the discussion on machine learning algorithms for combining the projections of the multi-model ensemble of global climate models that inform the Intergovernmental Panel on Climate Change (IPCC). POC/Host: V. Balaji
Jan. 10Lunchtime Seminar - Robbie ToggweilerGFDLHow Cool Water is Drawn Up to the Ocean's Surface in the Tropics
No Abstract provided.
Jan. 17Lunchtime Seminar Series - Lori SentmanHow the Central American Seaway Alters Large-Scale Ocean Circulation, Climate, and Marine Biogeochemistry
The study of past climates using climate models and paleoclimate proxy records is helpful for understanding how the Earth system responds to external natural forcing on time scales longer than the current instrumental records. The Central American Seaway (CAS) was an important ocean gateway connecting the Pacific and Atlantic Oceans until its gradual shoaling and final closure near the end of the Pliocene (5.3-2.6 Ma), when paleoclimate proxy records indicate a major reorganization in large-scale ocean circulation and shifting spatial patterns in global climate and marine biogeochemistry. Climate models are inconsistent on the impact of the CAS on global deep-water circulation, tropical Pacific and Southern Hemisphere physical mean state, and interannual tropical Pacific climate variability, and have not explored the coupled impacts on ocean biogeochemistry or sediment calcium carbonate (CaCO3) long-term burial. A suite of four idealized experiments, including a very narrow (109 km-wide) channel, are performed for multi-millennial scale simulations using the Geophysical Fluid Dynamics Laboratory Earth System Model, GFDL-ESM2G, to explore the various stages of CAS constriction and shoaling on global ocean circulation, climate and marine biogeochemistry. The CAS in GFDL-ESM2G provides a shortcut for southern sourced Pacific water mass transport that warms the South Atlantic, reduces Indonesian Throughflow mass transport by 59- 82%, suppresses Antarctic Bottom Water northward extent, and allows North Atlantic Deep Water to deepen ~500 m and slightly strengthen (~2Sv). In response to the global ocean reorganization associated with the CAS opened to various shoaling stages, global mean surface air temperatures warm 0.4-0.7°C with a bipolar, asymmetric response of Northern Hemisphere cooling up to ~2°C in the northwest Pacific and Southern Hemisphere warming up to ~8°C near the Ross Sea, in contrast to global mean cooling in previous CAS climate modeling studies. Opening the CAS also leads to larger El Niño-Southern Oscillation (ENSO) amplitude with more La Niña or cold events, a weaker annual cycle, and ~3 months earlier development. Opening the CAS results in stronger ventilation and a reduction in the sequestration efficiency of the biological pump, allowing respired CO2 to escape to the atmosphere via increased ocean CO2 outgassing, a short-term (< 500 kyr) increase in global sediment CaCO3 (~200 PgC over 105 years), and an additional release of 238 ppmv (507 PgC) to the atmosphere from the partitioning of carbonspecies implying short-term warming of 0.4-1.0 K in the Pliocene with a very narrow CAS. Overall, this paleoclimate application has broad implications for the sensitivity of coupled ocean-atmosphere dynamics and ocean biogeochemistry to changing ocean circulation with farreaching, long-term climate, ENSO, marine ecosystem, ocean biogeochemical, and atmosphere pCO2 impacts.
Jan. 23FPO - Anna FitzmauriceParameterizing the Melting of Icebergs in Global Climate Models
Final Public Oral Examination (FPO) for Anna Fitzmaurice Sponsor: Robert Hallberg
Jan. 30Informal Seminar - Chao-Yuan YangUniversity at Albany, State University of New YorkArctic Sea Ice Predictability and Prediction
Arctic sea ice has experienced a dramatic change for the past few decades. This drastic change and its associated impacts have led to increasing demands on sea ice predictions to a wide scope of stakeholders from seasonal to decadal timescales. This talk will focus on Arctic sea ice predictability in CMIP5 decadal hindcasts and seasonal Arctic sea ice prediction using a newly-developed regional coupled model in combination with the assimilation of satellite-based sea ice data. First, we examined to what extent present-day coupled climate models can predict Arctic sea ice at longer timescales by analyzing CMIP5 decadal hindcast/prediction simulations. The results show that for most models, the areas showing significant predictive skill become broader associated with increasing lead times. Sea ice in the Atlantic side has lower predictability than that of the Pacific side, particularly at a lead time of 3-7 years, but the Atlantic side show reemerging predictive skill at a lead time of 6-8 years. Our analysis also suggested that initialized decadal hindcasts show improved predictive skill compared to uninitialized simulations. Second, we have developed a regional coupled atmosphere-sea ice-ocean model by coupling the Los Alamos Sea Ice Model (CICE) into the framework of the Coupled-Ocean-Atmosphere-Wave-Sediment Transport system (COAWST) for seasonal sea ice prediction. To better predict sea ice at seasonal timescale, accurate sea ice initialization is required. Here we implement the Parallel Data Assimilation Framework (PDAF) into the new model and use the localized error subspace transform ensemble Kalman filter to assimilate SSMIS sea ice concentration and CyroSat-2 and SMOS sea ice thickness to improve sea ice initial conditions. The sea ice prediction results during the melting season in 2017 will be discussed.
Jan. 31GFDL 2018 Poster ExpoGFDL Poster Expo Setup
GFDL is hosting its 5th Poster Expo Event on January 31 2018 from 1-4pm. Colleagues in the GFDL/AOS/CICS communities will be showcasing their research at the event. Additional details including a list of posters will be available at the Poster Expo webpage: http://www.gfdl.noaa.gov/poster-expo This event is open to the public, but please note the visitor access requirements on the webpage.
Feb. 1Formal Seminar - Tapio SchneiderCalifornia Technical InstituteExpectations and surprises about climate feedbacks from low clouds
Uncertainties in how tropical low clouds respond to climate change continue to dominate uncertainties in climate projections. They have resisted reduction for decades. But because of recent computational and observational advances, substantial progress on the low-cloud problem is now within reach. In this talk, I will describe recent progress in (a) constraining the low-cloud response to climate change observationally, (b) understanding how the large-scale energy balance controls the low-cloud response, and (c) in simulating the low-cloud response with large-eddy simulations that are driven in a way that respects the large-scale energy balance. The results consistently indicate a positive feedback from tropical low clouds on global warming, and they point to potential surprises from stratocumulus clouds.
Feb. 6Informal Seminar - Huang YangJohns HopkinsUncertainty of midlatitudes-to-Arctic transport
Transport from midlatitudes to Arctic is critical in determining the abundance and spatial distribution for a suite of anthropogenic trace species that may have substantial impacts on the Arctic and global climate. For both real tracer CO and idealized tracers (simplified chemistry, focus on transport) that have the primary emissions in the NH midlatitudes, we found a ~20% multi-model spread of their Arctic concentrations in boreal winter and ~30% in summer among models participating the Chemistry-Climate Model Initiative (CCMI) phase 1. The uncertainty of trace species concentration in Arctic due to midelaitutde-to-Arctic transport is well correlated with the multi-model spread of midlatitude convection in winter but relates more to the spread in jet location during summer. Generally, simulations with more southern midlatitude jets are accompanied by stronger midlaitude-to-Arcitic transport. It is further suggested that this correlation is more due to the meridional mean transport varying with the width of Hadley Cell and simultaneously varying with the jet location instead of the eddy transport induced by the jet-associated Rossby Wave breaking.
Feb. 7Lunchtime Seminar Series - Jong-Yeon ParkGFDLToward seasonal to multi-annual marine biogeochemical prediction using GFDL's Earth System Model
While physical ocean prediction systems routinely assimilate observations and produce seasonal to decadal forecasts, ocean biogeochemical (BGC) prediction systems are less mature due to additional challenges. These include insufficient global-scale BGC observations to inform model initialization, uncertainties from both physical and BGC processes in earth system models, and properties of BGC variables that challenge data assimilation approaches (e.g., non-Gaussian, complex patterns of cross-correlation). A first impediment, however, is the high BGC sensitivity to transient momentum imbalances that arise during physical data assimilation. In this study, we develop a strategy to robustly integrate the GFDL's ocean BGC model (i.e. COBALT) with the ensemble coupled-climate data assimilation (ECDA) system used for GFDL's seasonal to decadal global climate predictions. The ocean and atmosphere data constraints in the assimilation system are optimally modified to reduce BGC biases caused by momentum imbalances while retaining the information of observed physical states. We then performed retrospective prediction runs by initializing the model with the output from our ECDA run coupled with BGC model and investigated seasonal to multi-annual prediction skills of nutrient anomalies, oxygen, phytoplankton and zooplankton over 1991 to 2016. We found that BGC variables generally show a higher and longer-term predictability than sea surface temperature although predictability varies regionally and with initialization month. While the predictability results here suggest a promising strategy of using earth system models for future operational BGC prediction systems, assessment of BGC predictions against satellite datasets shows a considerable gap between potential predictability and achieved prediction skills. Opportunities to close this gap will be also discussed.
Feb. 14Lunchtime Seminar - Spencer HillCalTech/UCLAWhat limits the ITCZ's poleward movement into the summer hemisphere?
In the solsticial seasons, insolation maximizes on the summer pole, yet Earth's ITCZ only extends roughly 10 degrees into the summer hemisphere. On Titan --- a moon of Saturn with a hydrological cycle not unlike our own (but with methane instead of water) --- the ITCZ spans from pole-to-pole over its annual cycle. So what are the salient differences between these two planetary bodies? In this talk, I use classical theory of angular momentum conserving Hadley cells, in particular as articulated by Emanuel (1995), to address this question. Insofar as it is valid, the theory implies that the cross-equatorial Hadley cell (and with it the ITCZ) can extend to any latitude, provided it is radiatively forced as to be "supercritical" at all latitudes equatorward. After presenting a slight modification to Emanuel's original critical surface potential temperature profile to account for latitudinally varying static stability, I present results from simulations in an idealized dry GCM forced with explicitly sub- or super-critical Newtonian cooling profiles, for various (rotation rate, forcing maximum latitude) combinations. I describe the results of these simulations, compare them to simulations with more commonly used "sine-squared" profiles, and discuss the implications for the real world ITCZ.
Feb. 22Formal Seminar - Lori BruhwilerESRL/GMDTracking Carbon in The Global Atmosphere: What Have We Learned from Sustained Atmospheric Observations?
A major uncertainty in projections of future climate is how the carbon cycle will respond to changing climate. Also, human activities have a significant effect on the global land and ocean biospheres, resulting in further impacts on atmospheric composition. Long term atmospheric observations can play a critical role in understanding the sensitivity of the carbon cycle to changing climate and human activities. Sustained observations also can play an important role in evaluating attempts to mitigate greenhouse gas emissions, and spatially distributed observations are essential for attributing emissions to specific regions and economic sectors. Observations from the NOAA Greenhouse Gas Reference Network operated by the NOAA Global Monitoring Division are fundamental to our current understanding of the carbon cycle, and an overview of its operation and findings from analysis of network observations will be discussed. Attribution of changes in atmospheric greenhouse gases to specific regions and processes requires the use of atmospheric models, ranging in complexity from global box models to complex data assimilation/flux estimation systems such as the NOAA GMD CarbonTrackers. Findings from carbon data assimilation systems will be discussed, as well as the challenges of using these systems and the potential for future development.
Mar. 8Formal Seminar - Jane MulcahyUK MET Office, Exeter, UKConstraining the aerosol ERF in UKESM1 through in-depth process-based assessment of underlying physical model parameterizations and aerosol processes
The latest generation UK Earth System model, UKESM1, is built on top of core physical climate model, HadGEM3-GC3.1. Simulations from both the physical and ES models will be submitted to CMIP6. In this seminar I will briefly introduce these models and the synergistic model development approach of the Met Office and wider UK academic community as well as CMIP6 plans. Aerosol processes and, in particular, aerosol-cloud interactions cut across the traditional physical-Earth system boundary of coupled Earth system models and remain one of the key uncertainties in estimating anthropogenic radiative forcing on climate. An improved representation of tropospheric chemistry-aerosol processes was therefore an integral part of the development of UKESM1 which incorporates the UKCA stratospheric-tropospheric chemistry (Telford et al. 2014) and GLOMAP-mode aerosol microphysics (Mann et al. 2010, 2012) schemes. We quantify the effective radiative forcing (ERF) due to aerosols in the prototype physical and ES models. The aerosol ERF was found to be large and negative due to underlying assumptions in both the physical model and aerosol parameterizations - the result is an unrealistically weak total anthropogenic forcing over the 20th century. A number of model improvements are investigated to assess their impact on the aerosol ERF. These include; an improved representation of cloud droplet spectral dispersion, updates to the aerosol activation scheme and black carbon optical properties. Furthermore we examine the role of the largely unconstrained preindustrial aerosol climate by evaluating the contribution of uncertainties in the natural marine emissions of dimethyl sulphide (DMS) and organic aerosol to the ERF. The combination of model improvements derived from these studies weaken the aerosol ERF by more than 40% of the original value but more importantly do not degrade the present-day climate model performance. The improvements are expected to lead to a total anthropogenic historical forcing more in-line with assessed values.
Mar. 13Informal Seminar - Sarah KapnickSnowpack Prediction
NIDIS Brownbag Seminar Webinars: SeriePacific NW Drought and Climate Outlook
Mar. 14Lunchtime Seminar - Alex TurnerUniversity of California, BerkeleyAtmospheric methane: where did you come from, where did you go?
Methane is the second strongest anthropogenic greenhouse gas and its atmospheric burden has more than doubled since 1850. Methane concentrations stabilized in the early 2000s and began increasing again in 2007. Neither the stabilization nor the recent growth are well understood, as evidenced by multiple competing hypotheses in the literature over the past 12 months. Hypotheses in the literature include: Asian livestock, tropical wetlands, US oil and gas. This talk will address three main questions: 1) What are the drivers of the decadal trends in atmospheric methane?, 2) Why do so many, apparently, plausible explanations disagree with each other?, and 3) What is the role of ENSO in modulating the methane sink (OH)?
Mar. 15Formal Seminar - Cecilia BitzUniversity of WashingtonA Year of extreme low Antarctic sea ice extent after decades of expansion
Throughout the Satellite record, Antarctic sea ice extent had been increasing until the 2016 austral spring. An extreme low extent developed with anomalously warm surface waters surrounding most of Antarctica. Two distinct processes contributed to this event. First, the extreme El Niño event peaking in December-February 2015/2016 contributed to pronounced SST and sea ice extent anomalies in the Pacific sector of the Southern Ocean that persisted far longer than normal. Second, internal atmospheric variability yielded a negative phase of the Southern Annular Mode added to the Southern Ocean anomalies. These results suggest that a combination of tropical forcing and internal atmospheric variability contributed to the unprecedented sea ice extreme event. I'll update what we have learned in the year following the onset of these extraordinary conditions, and place the recent year in the context of the last century.
Mar. 20Dave ThompsonColorado State UniversityWhat controls the height of the extratropical tropopause?
Host is Gabriel Vecchi.
Mar. 20Informal Seminar - Kai-Yuan ChengUniversity of Wisconsin at Madison"Modeling cloud physics on different scales: hydrometeors and thunderstorms."
The proper representation of cloud processes in models has been one of the biggest challenges faced by the weather/climate modeling community. One way to tackle the challenge is to improve our comprehension of cloud physics. My talk will address recent findings in cloud physics on two different scales. One is hydrometeor growth (of order 1 mm) and the other is storm top infrared features (of order 1 km). For the study of hydrometeor, I will show the simulations of flow fields around falling hydrometeors and discuss characteristics of these flow fields while analyzing their impact on the growth of hydrometeors. For the study of storm, I will show the simulations of storm top temperature distribution, which closely resembles the storm top infrared features observed by satellites. I will discuss the mechanisms accounting for the features and their applications on the satellite retrieval of stratospheric wind profile and stability.
Mar. 29Formal Seminar - Norman G. LoebNASARecent Science Highlights from the Clouds and the Earth's Radiant Energy System (CERES)
Earth's climate is determined by the exchange of radiant energy between the Sun, Earth and space. The absorbed solar radiation at the top-of-atmosphere (TOA) fuels the climate system, providing the energy needed for atmospheric and oceanic motions. Earth's radiation budget (ERB) involves a balance between how much solar energy Earth absorbs and how much terrestrial thermal infrared radiation is emitted to space. Because of its critical role in climate, continuous monitoring of the ERB is necessary for improved understanding and prediction of climate variability and change. The Clouds and the Earth's Radiant Energy System (CERES) project provides the only truly global satellite-based record of TOA and surface ERB along with the associated atmospheric and surface properties. CERES data are vital for quantifying changes in Earth's heat uptake, constraining climate feedback, and climate model evaluation.
Apr. 5Formal Seminar - Linus MagnussonECMWFMulti-scale predictability of extreme weather
Predicting high-impact weather events is a crucial task for forecasting centres and is clearly a multi-scale issue. On the subseasonal time-scale, the aim is to predict flow-regimes that have higher likelihood of extreme events. In the medium-range the challenge is to predict the timing, position and duration of the event. However, for some types of extreme weather it is still difficult for current models to capture the intensity even at the shortest scales. As extreme events by nature are rare, and each case is unique, a statistical evaluation is not straightforward. It is therefore necessary to identify key features for the development of the extreme events that are possible to verify and to identify where also less extreme cases will be useful. In the presentation I will give examples of high-impact events to demonstrate the challenges in sub-seasonal, medium-range and short-range predictions and what type of signals are expected. I will give example of evaluation and diagnostics that can be undertaken to better understand the predictability and limitations of the capability.
Apr. 11Lunchtime Seminar - Tom KnutsonRecent Detection-Attribution Studies of global temperatures in 2016, and on Regional Precipitation Trends
Some Recent Detection/Attribution Studies: Record global temperatures and strong Arctic Winter Warmth in 2016, and Regional Precipitation Trends
Apr. 12Formal Seminar - Derek LemoineUniversity of ArizonaGeneral Bayesian Learning in Dynamic Stochastic Models: Estimating the Value of Science Policy
We integrate climate scientists into an economic model of climate change policy. First, we calibrate a statistical model for updating beliefs about the climate's sensitivity to greenhouse gas emissions to the actual history of scientific progress. Second, we extend recursive dynamic programming methods to allow for nonconjugate learning about an uncertain parameter. Improvements in scientific monitoring and modeling of the climate system are valuable because the policymaker can better adapt emission policy to the true state of the climate system. We find that such improvements can be worth up to $600 billion per year and can double the welfare gain from adopting optimal emission policy.
Apr. 25Lunchtime Seminar Series - Yi HuangMcGill University, Montreal, CAA more complete view of radiative forcing and feedback
Climate forcing and feedback are usually analyzed at the top of atmosphere or troposphere. In this talk I will discuss the radiative forcing and feedback also concerning the surface and atmospheric energy budgets. This analysis is enabled by a new set of surface and TOA radiation kernels that we developed. A few results will be discussed: 1)Changes in poleward energy transports in the atmosphere and ocean, which we find are both driven by the non-uniform distribution pattern of the CO2 radiative forcing and for which the TOA only perspective is misleading for some feedbacks; 2) ENSO, where we notice a positive feedback of cloud via atmospheric radiation that strongly influences the ENSO amplitude; and 3) Interannual variability of Arctic sea ice, the connection of which to surface radiative forcing and feedback is analyzed.
May. 2Lunchtime Seminar - Fuqing ZhangPenn StateESSPE: Ensemble-based Simultaneous State and Parameter Estimation for Earth System Data-Model Integration and Uncertainty Quantification
Building on advanced data assimilation techniques, we advocate to develop and apply a generalized data assimilation software framework on Ensemble-based Simultaneous State and Parameter Estimation (ESSPE) that will facilitate data-model integration and uncertainty quantification for the broad earth and environmental science communities. This include, but not limited to, atmospheric composition and chemistry, land surface, hydrology, and biogeochemistry, for which many of the physical and chemical processes in their respective dynamic system models rely heavily on parameterizations. Through augmenting uncertain model parameters as part of the state vector, the ESSPE framework will allow for simultaneous state and parameter estimation through assimilating in-situ measurements such as those from the CZO networks and/or remotely sensed observations such as those from radars and satellites. Beyond data model integration and uncertainty quantification, through systematically designed ensemble sensitivity analysis, examples will be given to the application of the ESSPE framework to: (1) identify key physical processes and their significance/impacts and to better represent and parameterize these processes in dynamical models of various earth systems; (2) design better observation strategies in locating the optimum sensitive regions, periods and variables to be measured, and the minimum accuracies and frequencies of these measurements that are required to quantify the physical processes of interest; explore the impacts of heterogeneity and equifinality; (3) understand predictability and nonlinearity of these processes, and parameter identifiability; and (4) facilitate upscale cascading of knowledge from smaller-scale process understanding to larger-scale simplified representation and parameterization.
May. 3Formal Seminar - Allison SteinerUniversity of MichiganAerosol-Cloud Interactions: A focus on aerosol composition
Depending on the particle size and composition, some aerosols can act as cloud condensation nuclei (CCN) and ice nucleating particles (INP) that influence cloud and precipitation processes. Prior studies have documented aerosol effects on cloud microphysics with observations and modeling across spatial scales, yet the uncertainty of the aerosol-cloud feedback remains large in global synthesis studies. Additionally, the contribution of aerosol composition to these processes is still not well understood. In this talk, I will focus on the role of chemical composition in simulations of the second aerosol indirect effect. This will include understanding the role of anthropogenic composition on aerosol-cloud interactions, as well as the role of biological particles such as pollen. For anthropogenic composition, we evaluate the impact of the magnitude of urban aerosol emissions and prescribed aerosol hygroscopicity on a squall line in the Central Great Plains. Results from WRF-Chem simulations suggest that urban emissions can play an important role in mesoscale weather systems and accounting for aerosol composition can improve simulations of high intensity events. In the second half, I will focus on the role of biological particles such as pollen on precipitation feedbacks over the continental US. Together, these studies show the role of composition and aerosol source as an important driver in aerosol-cloud interactions.
May. 8Modeling Sytems Group (Blanton Chris)CMIP6 Curator Training
CMIP6 training
May. 9Lunchtime Seminar - Elisa MantelliStanford UniversityModelling ice stream dynamics: fluid flow instabilities in large ice sheets
Ice flow within an ice sheet is far from uniform, with regions of slow flow alternating with narrow corridors of fast flowing ice. These ‘ice streams' dominate ice loss from Greenland and Antarctica, and their behavior is therefore key to predicting future sea level changes induced by ice sheets. Ice streams are also intriguing as a natural example of spontaneous pattern formation in a fluid flow. The regularity in the spacing of some ice streams and their ability to change location are suggestive of similar behaviour elsewhere in fluid dynamics, where it is often termed a 'fingering instability'. Even though the dynamics of many fingering instabilities are reasonably well-understood, the corresponding theory for ice streams is far more incomplete. Increased energy dissipation by faster flow can lead to a warming of the ice sheet base and the production of lubricating meltwater, and therefore to potentially even faster flow. This is readily identified as a basic positive feedback that could drive the instability. However, the way this positive feedback expresses itself through patterning or oscillatory changes in the flow of a three-dimensional ice sheet is poorly understood. In this talk, I address two outstanding aspects of this complex interaction. As far as time scales are concerned, observational evidence suggests that ice streams exhibit temporal dynamics over time-scales ranging from decades to millennia. I show that not only long-term variability is explained by the above-described thermal feedback, but also the short-term one, provided the interaction between noisy climatic forcing and the underlying dynamical system is taken into account. The second part of this talk concerns the spatial dynamics. Motivated by observational evidence that the bed between adjacent ice streams is frozen, whereas under ice stream is not, I investigate the alternative possibility that spatial structure may emerge as an instability of transitions from frozen to molten bed. This theoretical work suggests that patterns at the ice thickness scale or smaller may emerge before the bed is fully lubricated, through mechanisms that are currently not included in numerical ice sheet models. I conclude by discussing how information encoded in isochronous layers commonly present in ice sheets can contribute to place observational constraints on the onset of ice stream flow.
May. 10Formal Seminar - Ed RutherfordNOAA/GLERL - Ann Harbor, MIDeclining offshore productivity in the Great Lakes: the relative effects of nutrient loads, invasive species, and climate change
Declining offshore productivity in the Great Lakes: the relative effects of nutrient loads, invasive species, and climate change
May. 11Informal Seminar - Marion AlbertyObserving water mass transport and transformation
Situated in the western Pacific warm pool, the Solomon Sea is a marginal sea that contains the South Pacific low latitude Western boundary currents (LLWBCs). These LLWBCs chiefly exit the Solomon Sea through three channels (Vitiaz, St. Georges and Solomon Straits) and serve as the primary source water for the Equatorial Undercurrent (EUC). Modeling studies have shown that the water mass makeup of the EUC depends on Solomon Sea dynamics and nutrient concentrations are path dependent. As part of Southwest Pacific Ocean Circulation and Climate Experiment (SPICE), two hydrographic cruises were undertaken to deploy and recover an array of moorings in the three outflow channels of the Solomon Sea. Observations were made from July 2012 until March 2014 to resolve the velocity and density fields in each strait. Two facets of the SPICE observational program will be presented: (1) a survey of the spatial patterns of mixing within the Solomon Sea and (2) transport time series from the exit passages of the Solomon Sea. Data from the cruises and from Argo profiles are employed to indirectly infer mixing for the first time in the Solomon Sea. Dissipation is found to be maximum in the surface layers and decreases by 2-3 orders of magnitude by 2000 m depth. Within isopycnal layers dissipation varies by at least 2 orders of magnitude in the Solomon Sea. Moored velocity observations confirm that Vitiaz Strait is the primary pathway for transport to the Equatorial Pacific. Transport variability through Solomon Strait dominates total transport variability and seasonal exchange between Bismarck Sea and Solomon Sea is made through St. George's Channel. POC: Sonya Legg
May. 15Jane Baldwin FPOAtmospheric and Oceanic Sciences (AOS)Orographic Controls on Asian Hydroclimate, and an Examination of Heat Wave Temporal Compounding
Orographic Controls on Asian Hydroclimate, and an Examination of Heat Wave Temporal Compounding. Jane Baldwin Final Public Oral (FPO) Examination. POC: Ann Valerio
May. 17Formal Seminar - Jim KossinNOAA/NCEI - Madison WISocietally Relevant Trends in Tropical Cyclone Behaviors: Looking Beyond Frequency and Intensity Based Metrics
Detection and attribution of changes in tropical cyclone activity, which is generally described in terms of frequency, intensity, or a combination of the two, is substantially hampered by known heterogeneities in the historical tropical cyclone data. Longer-term trends (say, greater than 50 years) that show increases in frequency and intensity do exist in the data on both global and regional scales, and these trends can be large. But confidence in them is low because these measures depend strongly on the technology of the day, which has evolved substantially over time. Still, there are other measures of tropical cyclone behavior that are comparatively less sensitive to these data issues and allow for the analysis of longer time series, and these have only recently been exploited with the historical data. In this talk I'll discuss these metrics, which are highly relevant to society, and present trend analyses that span the last 70 years or so. Evidence for an anthropogenic fingerprint on observed changes in tropical cyclones continues to mount, which should facilitate formal detection and attribution studies.
May. 21Semiar - Alexis KaminskiThe efect of pre-existing turbulence on stratified shear instability
Ocean turbulence is an essential process governing, for example, heat uptake by the ocean. In the stably-stratified ocean interior, this turbulence occurs in discrete events driven by vertical variations of the horizontal velocity. Typically, these events have been modelled by assuming an initially laminar stratified shear flow which develops wavelike instabilities, becomes fully turbulent, and then relaminarizes into a stable state. However, in the real ocean there is always some level of turbulence left over from previous events, and it is not yet understood how this turbulence impacts the evolution of future mixing events. Here, we perform a series of direct numerical simulations of turbulent events developing in stratified shear layers, varying the amplitude of the initial perturbation to model flows are already at least weakly turbulent. We show that pre-existing turbulence has both qualitative and quantitative effects on both the development of the instability and the resulting turbulent mixing.
May. 23Lunchtime Seminar - Balaji VenkatramaniThe Global Data Infrastructure for CMIP6
We present recommendations for the global data infrastructure needed to support CMIP scientific design, and its future growth and evolution. We follow a dataset-centric design less prone to systemic failure. Scientific publication in the digital age is evolving to make data a primary scientific output, alongside the traditional peer-reviewed literature. We design toward that future scientific data ecosystem, informed by the need for reproducibility, provenance capture, future data technologies, and measures of costs and benefits.
May. 24Formal Seminar - Bruno TremblayMcGill University, Montreal, CAThe role of ocean heat transport on rapid sea ice declines in the Community Earth System Model Large Ensemble
Many Global Climate Models simulates rapid sea ice declines in the Arctic Ocean when the pack ice transitions from a perennial to a seasonal ice cover. Most of these events are linked with anomalous northward Ocean Heat Transport (OHT). Using the Community Earth System Model Large Ensemble (CESM-LE), we find that the pathway by which the ocean heat enters the Arctic (Barents Sea Opening (BSO), Fram Strait or Bering Strait) is key to this link with the rapid declines. The interaction between OHT and sea ice happens mainly over continental shelves where the BSO and Bering Strait OHT are strongly correlated with basal melt, ice-ocean heat flux, absorbed short wave radiation in the ocean and ice growth/melt. The Bering Strait OHT is linked with more rapid declines than the BSO OHT, presumably because of the broader Eurasian shelf. No clear link is found between rapid declines and the Fram Strait OHT: Atlantic water entering the Arctic through Fram Strait circulate around the Arctic Ocean at depth with little vertical heat transfer with the surface waters. In total, 64 of the 79 rapid simulated declines in CESM-LE are linked with anomalous OHT. When the September Sea Ice Extent (SIE) before the rapid decline is located only over deep basins in the central Arctic, we observe a decrease in basal melt during the decline. We hypothesize that this is due to an enhanced stratification that reduces heat transfer between the ocean and the ice. The ice-atmosphere heat flux anomalies are more strongly correlated with the sea ice concentration anomalies over the deep basins in the 21st century than the ice-ocean heat flux anomalies. Our results suggest that OHT are causing rapid sea ice declines mostly when the SIE is large enough to cover the continental shelves and that the atmosphere is the main driver when the initial SIE is located only over the deep basins."
May. 29Seminar - Danielle ToumaStanfordFrom ground measurements to global models: observed and future changes in frequency and spatial extent of drought and extreme precipitation
Anthropogenic global warming has altered the spatial and temporal characteristics of extreme climate events and modified the impact to human and natural systems. My research employs the multitude of observed and modeled climate datasets available to investigate the spatial and temporal characteristics of drought and extreme wet events regionally and globally under past and future anthropogenic warming. First, I present the expected changes of the frequency, duration, and spatial extent of drought over the globe in the 21st century under increased anthropogenic warming. By calculating four different drought indices which use precipitation, runoff, and moisture deficit projections from 15 global climate models (GCMs) in the CMIP5 database, we capture the magnitude and uncertainty of the expected changes in drought. We show a robust increase in the frequency and spatial extent of drought over the 21st century in the tropics and subtropics, especially when using deficit-based drought indices, which are highly influenced by significant increases in temperature. These findings suggest that there is an increasing risk in drought impacts in many regions given the current trajectory of greenhouse gas emissions and associated warming temperatures. Second, I present a geostatistical method we developed to assess the length scales of extreme precipitation in station data. A climatological assessment over the US from 1965-2014 reveals significant seasonal and regional variations in the length scales of extreme daily precipitation. The eastern half of the US has daily extreme precipitation length scales reaching 400km during the winter months, but the length scales are halved during the summer months. The Northwest region, on the other hand, has little seasonal variation, with short extreme precipitation length scales of approximately 150km year-round. Though the magnitude of extreme precipitation length scales can be sensitive to certain choices in our method, the seasonal and regional variations remain relatively intact and can plausibly be explained to well-known atmospheric phenomena. We explore the trends in the spatial extent of extreme precipitation in the recent past and possible links to changes in atmospheric phenomena. By quantifying the spatial characteristics of extreme precipitation as well as the factors that shape these characteristics, we can better understand possible future changes in extreme precipitation events. These investigations concerning the changes in extreme dry and wet events can inform adaptation and mitigation efforts to reduce future risks under anthropogenic warming.
May. 30Lunchtime Seminar - Qing LiBrown UniversityLangmuir Turbulence and Its Effects on Global Climate
Ocean surface gravity waves, especially the resulting Langmuir turbulence, affect the ocean surface vertical mixing, yet are missing in most of the global climate models (GCM). The lack of explicit representation of such effects in GCMs may contribute to persistent biases in the simulated ocean mixed layer depth (MLD), air-sea fluxes and temperature distribution and tracer concentrations in the upper ocean. To assess the effects of Langmuir turbulence on the simulation of global climate, parameterizations are developed based on large eddy simulations (LES) of the ocean surface boundary layer (OSBL). In particular, two effects of Langmuir turbulence are distinguished: enhanced vertical mixing within the OSBL, and enhanced entrainment at the base of the OSBL. The former is parameterized by a wave-related enhancement factor on the turbulent velocity scale in the K-Profile Parameterization (KPP) based on the scaling law of the root-mean-square vertical velocity from previous studies. The latter is parameterized by a wave-related unresolved shear term in KPP based on the scaling law of the entrainment buoyancy flux from a new set of LES experiments. The latter approach is supported by analyses of the structure and anisotropy of Langmuir turbulence in LES, which show no significant impact of Langmuir turbulence on the predominant processes that drive entrainment at the base of the OSBL except the extra energy through enhanced downward TKE transport. The modified KPP is then implemented and tested in the NCAR earth system model, CESM. A state-of-the-art ocean surface wave model, WAVEWATCH III, is incorporated into CESM to provide the necessary wave information. It is found that accounting for both effects of Langmuir turbulence in CESM significantly reduces the shallow MLD biases in the Southern Ocean, and improves the simulated intermediate water ventilation and ocean subsurface temperature. Point of Contact: Steve Griffies
May. 31Informal Seminar - Sage LiColumbia UniversityEffects of greenhouse gases and aerosols on the Asian summer monsoon
Visiting Science Candidate. Constraining the uncertainty of future climate projections remains a challenging task for state-of-the-art global climate models, particularly for regional hydroclimate such as the Asian monsoon region. Understanding the effects of anthropogenic climate change on monsoon rainfall is essential for improving the predictability and assessing the climate risks. As the two most important anthropogenic forcing agents, greenhouse gases (GHGs) and aerosols lead to distinct different responses in the hydrological cycle. In this talk, I will present our recent work on the Asian summer monsoon changes in the 20th and 21st century as well as the physical mechanisms using observations, Coupled Model Intercomparison Project - Phase 5 (CMIP5) models, and idealized atmospheric general circulation (AGCM) model experiments. CMIP5 models show a distinct drying of the Asian summer monsoon rainfall during the historical period but strong wetting for future projections. This contrasting change can be explained by the strong aerosol-induced dynamical weakening during the 20th century and the thermodynamic enhancement due to GHGs in the 21st century. Further analysis is performed using AGCM experiments to separate the total response into the fast response that is independent of changes in sea surface temperature (SST), and the slow response related to SST effects. Results show that the strongly weakened monsoon circulation over land due to aerosols is largely driven by the fast adjustments related to aerosol-radiation and aerosol-cloud interactions. For GHGs, however, the fast and slow responses show opposing effects and a large model spread, leading to an overall weak circulation change. I will also discuss future research directions on the changes of rainfall extreme events in response to GHGs and aerosols.
Jun. 5Informal Seminar w/ Gaurav Govardhan -Visiting Scientist Webinar Simulations of aerosol over the Indian region: Evaluation-Improvements and Climatic Implications
Aerosols affect climate by scattering and absorbing atmospheric radiation. In this study, upon evaluation of aerosol simulating chemistry transport models over Indian region, we find that the models underestimate mass concentration of Black Carbon (BC) aerosol by a large margin and the corresponding BC emissions appear to be the primary cause for it. The Aerosol Optical Depths (AOD) also appear to be unrealistic. The possible role of state of mixing of BC on such AOD simulations has been examined. It is found with the help of an offline model constrained by observations of aerosol particles that, the effects of realistic state of mixing of BC on AOD and related forcing are lesser than previously thought. Lastly, we examine the vertical profile of BC from model simulations and find that the model captures the observed sharp elevated layers of BC only after the prescription of BC emissions from aircraft. The analysis of model simulations and space-based LIDAR data shows that such BC layers can get vertically transported up into the stratosphere upon their interaction with the underlying strong monsoonal convection. Such lifted BC layers can potentially harm the stratospheric ozone layer. Speaker: Gaurav Govardhan, Centre for Atmospheric and oceanic Sciences, Indian Institute of Science, Bangalore, Karnataka, India
Jun. 6Lunchtime Seminar - Joseph Smagorinsky videoGFDLHistory of the GFDL-Princeton Connection
In November of 1989, Dr. Joseph Smagorinsky returned to GFDL to present a talk entitled "History of the GFDL-Princeton Connection." That talk was recorded and this is a re-airing of that talk in its entirety.
Jun. 13Lunchtime Seminar Series - Jessica LiptakQuick Fixes, Bug Buildup, and Sluggish Simulations: How technical debt slows down your science, and what you can do to manage it
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Jun. 20Ants Leetmaa SymposiumAnts Leetmaa Symposium
Ants Leetmaa Symposium will take place at Frick Auditorium in Taylor Hall. Registration Required at: https://www.gfdl.noaa.gov/leetmaa-symposium/
Jun. 21Formal Seminar - Mojib LatifUniversity of KielAlleviating climate model systematic error in the tropical Atlantic sector by enhancing atmospheric resolution: implications for seasonal to interannual variability and predictability
The influence of atmosphere model resolution on tropical Atlantic sector mean climate and seasonal to interannual variability is investigated in the Kiel Climate Model (KCM). Biases typical for state-of-the-art climate models such as large errors in the sea surface temperature (SST) over the eastern tropical Atlantic can be strongly reduced by employing high atmosphere model resolution, horizontal and vertical, while keeping the ocean model resolution relatively coarse. At high atmospheric resolution, simulation of the mean three-dimensional atmospheric circulation over the tropical Atlantic and the adjacent continents is much enhanced, which in turn improves simulation of the tropical Atlantic Ocean circulation. Companion uncoupled simulations performed with the atmospheric component of the KCM, in which observed SST is specified, reveal that the errors in the atmospheric circulation originate in the atmosphere model. The enhanced mean state and seasonal cycle greatly improves simulation of tropical Atlantic interannual SST variability, its amplitude and seasonal phase locking. Further, the representation of the West African Monsoon and its relationship to the cold tongue development in the tropical Atlantic is much enhanced. We conclude that sufficiently high atmosphere model resolution is a prerequisite to reduce climate model biases in the tropical Atlantic sector.
Jun. 27Lunchtime Seminar - Tom DelworthSPEAR - The Next Generation Seasonal to Decadal Prediction System at GFDL
Lunchtime Seminar - Tom Delworth
Jul. 11Lunchtime Seminar - Jan-Huey Chen & Lucas HarrisfvGFS: Next-generation weather prediction at GFDL
summarizing recent developments with FV3 and fvGFS
Jul. 16Dr. Corentin HerbertENS de Lyon, FranceRare events, bistability and equatorial superrotation
Even though they have a very low probability of occurrence, rare events play a crucial part in many systems because they can have a huge impact. In the climate system, examples range from heat waves and winter storms to the more dramatic possibility of a bifurcation of the general circulation. In all cases, a major obstacle to study the dynamics of such events is that they are difficult to sample, either from observations or from direct numerical simulations with GCMs. In the first part of the talk, I will show that numerical algorithms designed specifically to provide an efficient sampling of rare events alleviate this difficulty, and open the possibility to study atypical fluctuations and abrupt transitions in complex turbulent flows such as geophysical flows. In the second part, I will discuss a potential example of bistability in the atmosphere: equatorial superrotation. I will focus on the conditions for bistability and the nonlinear mechanisms leading to it: Rossby wave resonance and the Hadley cell.
Jul. 18SJ Lin - Lunchtime SeminarGFDLModeling the atmosphere in the Gray-zone, what's wrong with the current modeling framework, and how to fix it
Modeling the atmosphere in the Gray-zone, what's wrong with the current modeling framework, and how to fix it
Jul. 19Lunchtime Seminar - Tom KnutsonDetection and Attribution of Climate Change from a US Perspective
This is a OneNoaaSeminar
Jul. 24Laura QueenInternIntern PresentationsEffects of Anthropogenic Climate Change on the Extreme Flood Risk in the Columbia River Basin
People have congregated along river banks throughout history, from the earliest settlements to contemporary metropoles. Rivers are cultural, economic and ecological agents, providing transportation, food, power, recreation and habitats for diverse ecosystems. The close proximity of civilization and rivers, however, poses a serious threat when extreme flooding occurs. Understanding how climate change will affect the flow of rivers in the future is imperative for risk mitigation and infrastructural planning. GFDL's Seamless System for Prediction and Earth System Research (SPEAR) model employs the LM4.0 land model which contains a global river and lake network. We use the Columbia River as a case study in the identification and explanation of biases in the SPEAR model's river system. When comparing annual cycles for observational and model river discharge, we found that the model discharge peak occurred one month earlier and about two times greater in magnitude than the observational data. The magnitude bias is in part due to an excess in precipitation in the pacific northwest region, while snowmelt timing and water percolation affect the timing of the discharge peak. We suggest that a study of extreme precipitation under climate change within the Columbia River Basin with a discussion of runoff and caveats about overestimates of precipitation and seasonal lag would best inform stakeholders of the future conditions of the Columbia River flow.
Jul. 24Arianna KrinosInternUnderstanding spatial effects of climate change on Chesapeake Bay blue crab using statistical downscaling and agent-based modeling
Blue crab are an important economic resource in Chesapeake Bay, worth $78 million in 2009 (Chesapeake Bay Foundation). Blue crab are also an important link in the Bay ecosystem and a symbol of the Bay, particularly to local residents and fishermen. Climate change may impact the complex migration and reproduction strategies of blue crab, in particular their distribution and abundance. In this study, we develop a spatially-resolved, agent-based mechanistic blue crab population model. Using this approach, we can approximate observed fluctuations in the population on a monthly timestep, and simulate genetic variation and responses to environmental stimuli on short timescales. The effects of climate change on living resources is difficult to determine reliably via coarse global climate models. Statistical downscaling is increasingly used to apply model output to regional scales relevant to local biological processes. Here, we apply the Quantile Delta Mapping (QDM) bias correction method (Cannon et al. 2015) to Max Planck Institute Earth System Model (MPI-ESM) climate projections at low resolution. We use resulting historical and projected temperature and precipitation estimates as inputs to a Bay water balance model (Muhling et al. 2017). This model predicts surface temperature and salinity, estuarine habitat indicators which we use to drive our blue crab population model. We hope to use this model to show the possible trajectory of blue crab stock under the MPI-ESM-LR climate change scenario. Refining these estimates through updated models is key to informing the management of blue crab in the Chesapeake Bay
Jul. 26Science and Publishing in Science WebinarScience and Publishing in Science Webinar
Science was first published in 1880, and to this day continues to be the flagship journal of AAAS. In this presentation, Senior Editor Jesse Smith will discuss the essential elements of what is involved in publishing a manuscript in Science. About the Speaker: Dr. Smith is a stable isotope geochemist and climatologist with expertise in the areas of climate, paleoclimate, non-biological oceanography, atmospheric science and ice sheets. He earned his PhD from Scripps Institution of Oceanography, University of California, San Diego, and has been an Editor at Science since 1999.
Jul. 27Lily Wittle - InternMixing in the Orkney Passage Overflow
The Orkney Passage (OP), the deepest trench in the South Scotia Ridge, plays an important role in the flow of Antarctic Bottom Water from the Weddell Sea to the Scotia Sea. Observations from a recent field program suggest that intense mixing occurs in this region, but its extent and causes are unknown. I conducted numerical simulations to help identify mixing processes and their impact on water mass transformations. The first part of this project focused on bottom topography. To test the hypothesis that the roughness of the topography impacts mixing, I ran a simulation using "smoothed" topography that preserved general features but leveled out roughness. I calculated potential vorticity (PV), which indicates instability (gravitational, centrifugal, or symmetric) when it has opposite sign of planetary vorticity, to compare this simulation to an existing simulation with realistic topography. With rough topography, unstable areas extended kilometers from the bottom, especially around topographic peaks. With smoothed topography, unstable areas were smaller and closer to the boundary. The latter part of this project investigated how diffusivity affects transports throughout the OP region. I ran one simulation with variable diffusivity (higher near the bottom) and three with different values of constant diffusivity, then compared transports of neutral density classes at observational sections. Variable and high diffusivity values notably increased the peak transport of the neutral density = 28.34 kg/m^3 class through the OP. The similarities between variable and high diffusivity simulations near the OP and locations of PV reversal indicate that copious mixing takes place near bottom topography.
Jul. 27Montre Deshaun HudsonInternModeling Sea-Ice Rifting using Granular Material"
To Be Provided
Jul. 27Nicholas OrdonezInternImplementing Lagrangian Particle Tracking Capabilities in the Modular Ocean Model
Lagrangian particle tracking is a powerful analysis tool for understanding and quantifying ocean circulation in an Ocean General Circulation Model's (OGCM). Using stored ocean velocity data, a particle tracker traces the position of virtual particles over a given time period and stores particles' spatial information for a specified time step. As OGCMs are developed further and the volume of output rapidly increases, the demand for a more efficient Lagrangian particle tracking software grows. Our aim is to develop online particle tracking in the latest version of the Modular Ocean Model (MOM6). This addition to MOM6 is based on a similar program meant to track the movement of icebergs. If successful, MOM6's particle tracking will be able to advect millions of particles through a considerably large volume/area over the course of millenia.
Aug. 1Bobby Garza InternBit-for-Bit Reproductibility
Bit-for-Bit Reproducibility (BFBR) is getting the same answer on different machines, with the same data and code. However, this is easier said than done when working with climate models. Differing software and hardware can lead to vastly different answers from the chaotic tendencies of climate models. The truncation of floating point numbers on one machine and not the other can create entirely different climates even if the code and data is the same. This truncation can happen with different compilers, different optimizations, or different operating systems. An ensemble based climate model would help with BFBR by creating a statistical distribution that can be measured to determine if two instances of the same code with the same data statistically reproduce instead of checking that answers are the same bit-for-bit.
Aug. 7 Robin SehlerUncovering the connection between NOAA Forecasts and Financial Options Prices.
Covering the data acquisition and preparation; Intern Presentation; Point of Contact: Fabien Paulot
Aug. 9Ioana BociuCICS InternDECK Analysis of Ocean Carbon in GFDL's CM4 Contribution to CMIP6
The advent of the Industrial Era created large carbon cycle shifts in overall carbon balance. Understanding carbon cycle behaviour is crucial for climate change projections. While extensive observations have allowed for the understanding of changes to the carbon cycle, large gaps persist. Global modelling initiatives like CMIP can help bridge these gaps through the input of known mechanisms and patterns for improved description and understanding. One of GFDL's contributions to CMIP6 is CM4, which builds from previous GFDL models and seeks to provide increased robustness to the carbon cycle. CM4 includes a 1/4 degree MOM6 ocean with 75 hybrid layers and a second generation Biogeochemistry with Light, Iron, Nutrients, and Gas (BLINGv2) model. Tracers used in BLINGv2 are: DIC, Alk, PO4, DON, Fed, and O2. We present an overview of carbon cycle model component inventories, CM4 ocean anthropogenic carbon comparison with observations, as well as analysis of mechanisms enabling the vertical and horizontal transport of anthropogenic carbon throughout the ocean. Historically, the total modelled oceanic anthropogenic carbon is 109.5 PgC, with 91.5 percent in the upper 1500 m of the water column. The highest excess alkalinity values occur in the surface layers, where biology plays a large role in anthropogenic carbon uptake. Below the surface layer, downwelling associated with gyre circulation carries carbon further into the ocean basin, followed by mode and intermediate water formation (~850 m -1250 m). Below 1250 m, the Atlantic Meridional Overturning Circulation (AMOC) and deep convection carries the remaining anthropogenic carbon downward. Similar to observations, anthropogenic carbon penetration is deeper in the North Atlantic and the Southern Ocean; due to excess alkalinity and deeper mixed layers caused by mixing and deep water formation.
Aug. 13FPO - Zhaoyi ShenThe influence of aerosols on large-scale circulation and regional climate
The influence of aerosols on large-scale circulation and regional climate FPO - Zhaoyi Shen
Aug. 14David BonanIntern PresentationIs there a spring predictability barrier for Arctic sea ice?
The dramatic changes to sea ice in the Arctic have created significant interest surrounding its predictability on seasonal-to-interannual timescales. Of particular interest to many stakeholders is the prediction of the summer sea-ice extent (SIE) minimum. Recent studies suggest that forecasts of the summer SIE minimum are potentially skillful beyond 12 months in advance, while others have found a predictability barrier in the spring season. This barrier suggests that there may be a sharp limit on skillful predictions of the summer SIE minimum, as prediction skill for lead times beyond 3-5 months fall off dramatically. Here, we explore this emerging idea by examining an ensemble of general circulation models (GCMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Using the preindustrial control runs of 37 different GCMs, we show that this spring predictability barrier does indeed exist across the CMIP5 models and is most pronounced in the Kara, Laptev, East Siberian, Chukchi, and Beaufort Seas. In these regions, correlation values between sea ice volume and September sea ice area drop off significantly in the months preceding June and May. From these results, we discuss implications for operational predictions of the summer SIE minimum.
Aug. 15Eli TzipermanHarvardEnhanced frequency of Sudden Stratospheric Warming events due to a stronger equatorial Madden-Julian Oscillation, and suppression of Arctic air formation, in warm climates
First, it is proposed that in a warmer, higher CO2 world, the expected strengthening of the equatorial Madden-Julian Oscillation (MJO) can lead to more frequent sudden stratospheric warming (SSW) events. This may, in turn, affect tropospheric weather and extreme events. The proposed SSW enhancement mechanism involves an interaction of MJO-forced planetary waves with the mid-latitude tropospheric jet that amplifies its zonal asymmetry. This therefore amplifies the stationary waves generated at the mid-latitudes and propagating to the Arctic Stratosphere, triggering additional SSW events. Second, we consider the process of Arctic air formation currently occurring over northern North America during the winter season's polar night, and leading to extreme cold outbreaks further south. We propose that such Arctic air formation may be suppressed in a warmer climate by a low-cloud feedback. This may explain the existence of frost-intolerant animals and trees such as crocodiles and palm trees that thrived in northern North America 50 Million years ago (Eocene), where current temperatures could be as low as -40C. We further show that the proposed mechanism also explains recent climate observations and future climate projections, both showing an unexplained enhanced and surface-intensified warming over high-latitude continental areas.
Aug. 15AOS WorkshopAOS Workshop
AOS Workshop POC: Anna Valerio
Aug. 16Kalen FisherCICS InternPrediction of Extreme Precipitation Associated with Landfalling Tropical Cyclones using the Geophysical Fluid Dynamics Laboratory (GFDL) fvGFS Model
The 2017 Atlantic hurricane season was very active, producing three major hurricanes that made landfall in the US, with Hurricane Harvey causing the most damage and producing the largest rainfall amounts. The focus of this project is to assess the forecasting skill of extreme precipitation associated with Hurricane Harvey and other 2017 Atlantic tropical cyclones using quantitative verification methods. The NOAA Geophysical Fluid Dynamics Laboratory (GFDL) has developed a Finite Volume Global Forecast System (fvGFS), an improved version of the operational GFS with an upgraded dynamical core and microphysics, and this project verifies the fvGFS forecasts of precipitation against the National Center for Environmental Prediction (NCEP) Stage IV data. The National Center for Atmospheric Research (NCAR) Meteorological Evaluation Tools (MET) verification package is used to quantitatively assess the forecast skill. Using MET, the 13-km fvGFS forecast skill is compared against the skill of two operational models, the 13-km GFS and 3-km NAM. The skill metrics considered include the Equitable Threat Score and Multiplicative Bias, which are assessed for different accumulated precipitation thresholds.
Aug. 16Annika BarthInternSurvey and contextualization of various physiological effects of past, present and future pCO2 on fish
We reviewed over 40 studies to characterize the robustness of physiological responses to ocean acidification in marine organisms and explore appropriate methods for better representing fish physiological responses in ecosystem models. These responses included, but were not limited to increased otolith size, altered growth and survival, and impaired neurosensory function - the latter of which is attributed to acid base regulation and excitation of gamma-aminobutyric acid receptor. As most studies considered only a few levels of pCO2, we provide a more complete quantification of the anticipated emergence of these effects over past, present and projected future scenarios.
Aug. 16Pedro DiNezioUniversity of TexasBridging observations, theory and models of the El Nino/Southern Oscillation
New ideas on the dynamics and predictability of the ENSO phenomenon focusing on its oscillatory behavior and asymmetries between El Niño and La Niña.
Aug. 16Shang-Ping XieUniversity of California, San DiegoA spring view of El Nino Diversity
The eastern tropical Pacific features strong climatic asymmetry across the equator, with the intertropical convergence zone (ITCZ) displaced north of the equator most of time. In February-April (FMA), the seasonal warming in the Southern and cooling in the Northern Hemisphere weaken the climatic asymmetry, and a double ITCZ appears with a zonal rain band on either side of the equator. The relative strength between the northern and southern ITCZ varies from one year to another and this meridional seesaw results from ocean-atmosphere coupling. Surprisingly this meridional seesaw is triggered by El Niño-Southern Oscillation (ENSO) of moderate amplitudes. Although ENSO is originally symmetric about the equator, the asymmetry in the mean climate in the preceding season introduces asymmetric perturbations, which are then preferentially amplified by coupled ocean-atmosphere feedback in FMA when deep convection is sensitive to small changes in cross-equatorial gradient of sea surface temperature. Moderate ENSO follows a distinct decay trajectory in FMA than extreme El Niño. Moderate El Niño dissipates rapidly as southerly cross-equatorial wind anomalies intensify ocean upwelling south of the equator. In contrast, extreme El Niño remains strong through FMA as enhanced deep convection causes westerly wind anomalies to intrude and suppress ocean upwelling in the eastern equatorial Pacific.
Aug. 16AOS WorkshopAOS Workshop
AOS Workshop POC: Anna Valerio
Aug. 16Pedro DiNezio, Nat Johnson, George Philander, Eli Tziperman, Shang-Ping XieAOS Workshop Panel Discussion
1. What are the most important known unknowns about ENSO? 2. What lessons from our successes in learning about ENSO (especially in the last decade) can we apply to studying other modes of natural variability? 3. Is our ability to use paleorecords to study ENSO limited by data quality or by a gulf between paleoclimatologists and atmopsheric and oceanic scientists?
Sep. 6Intern Informal Seminar - Emily GeymanHollings InternCarbon Cycling on the Great Baham Bank
Much of our understanding of Earth history comes from shallow water carbonates because deep ocean archives tend to get metamorphosed or subducted at plate margins. However, little work has been done to calibrate how ocean chemistry is recorded in modern carbonates. As a result, interpretations of climate and environmental change from ancient stratigraphy have large and unquantified uncertainties. I integrate measurements of carbon and oxygen isotopes in the water column and modern carbonate sediments on the Great Bahama Bank with simple box model frameworks to understand how water and sediment chemistry evolve as water moves from the open ocean to the increasingly restricted shelfal waters. Ultimately, my study of the modern Bahamas serves as a calibration study to better assess whether the isotopic fluctuations in ancient stratigraphy represent global changes in ocean chemistry rather than natural intra-shelf variability.
Sep. 12Lunchtime Seminar - Brent LofgrenNOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MIAtmospheric and Water Dynamics Modeling and Other NOAA Activities in the Laurentian Great Lakes
The Laurentian Great Lakes - Superior, Michigan, Huron, Erie, and Ontario - contain 20% of the world's surface fresh water. They provide shipping, domestic and industrial water, recreation, and commercial fishing for over 30 million residents of the drainage basin. The NOAA/OAR's Great Lakes Environmental Research Laboratory provides science related to the dynamics of the lakes and regional atmosphere, hydrology of the watershed, ecosystem dynamics and environmental factors affecting native and invasive species, and develops and maintains instrumentation to monitor the lakes. Other NOAA offices also provide local weather services, satellite data analysis, habitat restoration, and National Marine Sanctuaries within the 7.5 Great Lakes states. This seminar will give an overview of these activities before moving to more specific topics. It will also include a brief summary of problems encountered in projecting lake levels under climate scenarios, in part due to lack of faith in results derived by GFDL and its peers. Some results from dynamical downscaling of GFDL CM3.0 using WRF will also be presented. Finally, I will present work that I did during my visit to GFDL in using the Finite Volume Community Ocean Model (FVCOM), driven by output from a historical time slice of GFDL CM 4.0, in terms of hurdles, technical requirements for input to FVCOM, lessons learned, and planned improvements and enhancements. POC: Dr. Brent M. Lofgren, ext. 452-6595.
Sep. 13Formal Seminar - Christian GramsInstitute for Meteorology and Climate Research, KIT, Karlsruhe, GermanyA new look at Atlantic-European weather regimes: physical processes governing their life cycles and applications
The large-scale midlatitude flow is dominated by Rossby wave activity along the upper-level midlatitude wave guide and jet stream. In the Atlantic-European region this activity occurs in preferred quasi-stationary, persistent, and recurrent states, so-called weather regimes. Weather regimes explain most of the atmospheric variability on sub-seasonal time scales. An extended definition of year-round Atlantic-European weather regimes based on 37 years of ERA-Interim reanalysis data helps to elucidate the physical processes governing their life cycles. A specific focus lays on the role of atmospheric blocking and of diabatic outflow driven by cloud-condensational processes at distinct weather regime life cycle stages. Weather regimes help to assess the potential for extreme weather as discussed exemplarily for atmospheric river occurrence in Europe. Also they help to understand multi-day volatility in continent-scale, near-surface wind speed with important implications for the planning of wind farm deployment across Europe. Finally, a recent forecast bust demonstrates the challenges in predictability imposed by the multi-scale interactions governing weather regime life cycles.
Sep. 17Lunchtime Seminar - Dr. Jessica LuoNational Center for Atmospheric ResearchZooplankton in marine ecosystems and biogeochemical cycles: a critical but under-represented link in global models
Marine ecosystems are increasingly stressed by anthropogenic activities that force broad-reaching changes to the biota and environment. Climate models project systematic declines in ocean oxygen, surface nutrients, primary productivity, and carbon export, which has direct impacts on atmospheric carbon feedbacks. However, models differ substantially in the spatial extent and mechanistic pathways that drive reductions in export flux, with marine zooplankton representing a large source of uncertainty in these processes. We developed a new size-structured and trait-based plankton ecosystem model for the Community Earth System Model (CESM), which reveals insights into the fundamental dynamics of energy transfer in the global oceans. Using the model to test basic ecological theories on biomass transfer, we show that there are two dominant marine trophic regimes. These regimes are driven by resource and grazing dynamics, and manifest in consumer-poor or consumer-rich ecosystems, which has strong implications for energy transfer to fisheries. Secondly, we use an offline modeling approach to evaluate the contribution of gelatinous zooplankton to global marine carbon cycle, a previously unconsidered flux. We estimate that fast-sinking particulate carbon mediated by gelatinous zooplankton could increase the carbon incident on the seafloor by up to three fold, which is globally significant and should be considered in future modeling efforts. Finally, I discuss perspectives and approaches for coastal biogeochemical modeling, including estuary models with biogeochemistry, the predictability of harmful algal blooms and other processes along the land-sea interface, regional ecosystem parameter optimization using machine learning, and submesoscale plankton behavioral modeling. POC: Charles Stock, ext. 452-5331.
Sep. 17Thomas C. SchulthessETH Zurich and Swiss National Super Computing CenterExascale computing at the dusk of Moore's Law: opportunities for weather and climate modelling?
Computational science has benefitted tremendously from Moore's Law, by which computer performance grew exponentially over nearly five decades at constant cost. This is especially true for weather and climate modelling, where very complex models could be implemented, maintained and systematically improved over decades. During the past 10 years, however, there has been a number of challenges, such as exploding parallelism, power consumption and hardware cost, and most recently the tapering of scalability of the underlying CMOS technology, that have raised severe concerns about established approaches to implement weather and climate models on modern supercomputers. At the same time, supercomputing initiatives in the USA, China, Japan and Europe seem to be determined to deliver exaflops supercomputing capabilities early next decade, at almost any cost. It is understood that such performance will require substantial investments in refactoring of software to exploit the performance of emerging exascale computing architectures. We will discuss the results of a collaboration between CSCS and MeteoSwiss that could serve as a template for such developments. In order to meet the performance needs of MeteoSwiss' new operational model within a constant budget envelop, it was necessary to substantially refactor the implementation of the COSMO code and build a system with GPU accelerators. The resulting software infrastructure is applicable to global models as well, and could serve as a basis for performance-portable implementations of weather and climate models that run on all emerging exascale computing architectures. Thomas Schulthess is Professor of Computational Physics at ETH Zurich and Director of the Swiss National Supercomputing Center (CSCS) since 2008. He studied physics at ETH Zurich and earned his doctorate in 1994 with a thesis on surface physics, in which he combined experiment and supercomputing-based simulations. He subsequently continued his research in the USA, working on the DARPA-funded spintronics project and spending more than 10 years at Oak Ridge National Laboratory (ORNL), from where he returned to Switzerland in 2008. Thomas led the teams that won the ACM Gordon Bell Prizes in 2008 and 2009 with the first production-level applications sustaining a petaflops on ORNL's first peta-scale supercomputers. In the past 10 years, as director of CSCS that hosts the operational weather forecasting systems of MeteoSwiss, Thomas took interest in developing software systems for weather and climate simulations, as wells a design of computing systems for numerical weather prediction. Under his leadership, CSCS was the first center in Europe that deployed a productive GPU-accelerated supercomputing system in 2013, and co-designed with Cray, NVIDIA and MeteoSwiss the first GPU-based weather forecasting system that has been deployed in 2015, and since spring 2016 is running MeteoSwiss' new COSMO-NEXT model at 1km horizontal resolution. For this work CSCS and MeteoSwiss received the 2016 Swiss ICT Award for Outstanding IT-Based Projects and Services.
Sep. 18Informal Intern Seminar- Curtis BechtelEngility InternAnalyzing climate data with parallelized empirical orthogonal functions
Empirical orthogonal function (EOF) analysis is a statistical method that can be used to find the underlying patterns and relationships among variables while filtering out unwanted noise. However, the calculation of EOFs can be difficult and computationally expensive, so we developed a C++ toolset that simplifies this process for the end-user and allows for easy analysis of large climate datasets. Chris Dupuis, ext. 5396
Sep. 18Informal Intern Seminar - Erixen CruzEngility InternUsing PCA and storm tracking to characterize AM4 ensembles
Differences between ensembles of year long AM4 model runs are explored with metrics from principal component analysis and a simple hurricane tracker. They are strapped into pyCECT to see how they can help differentiate ensembles with statistical significance. These new metrics will help in determining whether different runs produce different climates, disregarding bit-for-bit reproducibility. POC is Chris Dupuis, ext. 5396
Sep. 18Informal Seminar Series - Dr. Darren PilcherUW/JISAO Freshwater as a critical driver of coastal marine biogeochemistry
Freshwater river systems are the conduit connecting the land to the ocean. River runoff significantly impacts coastal biogeochemistry through buoyancy-driven circulation changes, inputs of nutrients and terrestrial carbon, and alkalinity dilution. Substantial spatial-temporal variability within coastal shelf systems makes it challenging to resolve the effect of these processes through traditional observationally-based programs. Here, I will discuss work using regional biogeochemical models to understand how freshwater runoff impacts coastal carbon cycling and projected ocean acidification in two adjacent high-latitude coastal shelf systems: The Gulf of Alaska and Bering Sea. In the Gulf of Alaska, freshwater runoff is delivered by a myriad of small rivers and streams, many of which also contain glacial meltwater. This glacial meltwater tends to suppress coastal carbon uptake and decrease carbonate saturation states due to alkalinity dilution. However, a projected change in the composition of this runoff, from tidewater to land-terminating glaciers, may reduce and even reverse this effect, thereby providing a temporary buffering effect against ocean acidification. In the Bering Sea, freshwater is delivered through several large rivers, namely the Yukon and Kuskokwim. This runoff is supersaturated with terrestrially-derived carbon, generating corrosive water conditions (i.e. carbonate saturation states less than one) throughout large portions of the inner Bering Sea shelf and Norton Sound. This process is likely to become stronger with climate change due to a projected increase in the magnitude of freshwater runoff and carbon export mobilized from melting permafrost. These results highlight the importance of resolving the present and projected future effects of freshwater runoff in marine coastal shelf systems in order to reduce uncertainty in longterm projections and build towards producing accurate seasonal forecasts for stakeholders. POC: Charlie Stock/Jonh Dunne
Sep. 19Lunchtime Seminar Series - Paul SpenceUniversity of New South Wales, Sydney AustraliaDoes the Southern Ocean have sleep apnea?
Satellite microwave observations of Antarctic sea ice started in 1973, just in time to capture a massive open water area enclosed in winter sea ice, known as a polynya, within the Weddell Sea. This polynya was roughly the size of the United Kingdom and it lasted thru the winters of 1974-1976 with mixed layer depths >3000m observed in its vicinity. A similar Weddell Sea polynya hasn't been seen since. However, September 2017 satellite observations indicate that a new Weddell Sea polynya may be starting to form. This first aim of this research is to determine the impact (magnitude and duration) of the 1970s polynya on ocean carbon, biology, temperature, and volume transports. Secondly, how will the formation of a new large polynya in 2018 impact 21st century climate projections? We address these questions with a coupled ocean (MOM5), sea-ice (SIS), biogeochemistry (WOMBAT) model at ¼° resolution with 50 vertical levels. In the model, we create a polynyas of similar size and duration as observed in the 1970s with a small wind perturbation localised over Maude Rise in 1973 and 2017. We find that most of the observed warming trend of AABW and the slowdown of the lower cell of the Southern Ocean overturning since the 1980s can be attributed to the multi-decadal recovery from the 1970s Weddell Sea polynya event. The polynya also increases oxygen concentrations by 50% and the ocean-to-atmosphere carbon flux by >200% in the Atlantic sector of the Southern Ocean. In essence, the Southern Ocean breathed deeply from 1974-1976, and has been holding its breath since. If the Southern Ocean starts breathing deeply again in the winter of 2018, the climate impacts will be pronounced and last for decades to come.
Sep. 19Informal Intern Seminar - Two SpeakersEngility (1) Gathering metrics on the computational cost of GFDL models (2) A GFDL I/T Intern Experience
Speaker 1: Curtis Bechtel - Abstract for Speaker #1: GFDL maintains several Earth climate models with multiple versions and thousands of archived model runs, but relatively little is known about the computational cost associated with different models, model components, and architectures. In order to gain better insight into these models and their efficiency, we developed a Python package that calculates various user-defined metrics when given the output directory of an experiment. We collected metrics from various international modeling centers in order to compare the efficiency among different models and configurations. The metrics used are defined in CPMIP, a standard set of metrics for comparing Earth climate models based on their computational performance. Speaker 2: Eva Toplistky; - Abstract to be determined. POC: Chris Dupuis Ext..5396
Sep. 20Lunchtime Seminar - Dr. Elizabeth DrenkardScripps Institution of Oceanography/UC San DiegoModeling Regional Marine Ecosystem Susceptibility to Climate Variability
Changing ocean conditions present pervasive marine conservation and management challenges. While global GCMs and historical satellite observations are essential tools in addressing these issues, they often inadequately resolve small-scale, costal processes that are relevant to valuable living marine resources. I will present my postdoctoral work using Regional Ocean Model System (ROMS) simulations to 1) diagnose physical ocean mechanisms that confer interannual environmental resilience to reef systems in the Coral Triangle and 2) project the impact of long-term anthropogenic climate change on California Current System (CCS) oceanography and fisheries, with the goal of informing implementation of future marine protected areas (MPAs) and fishery policy in these respective systems. Coral MPA Evaluation: Historically, global coral bleaching and mortality events have been caused by heat stress associated with extremes in the El Niño Southern Oscillation. Thus identifying reef systems that exhibit resilience to these events is a priority for targeted conservation efforts. Results from a 500m ROMS model of the Verde Island Passage (VIP, Philippines) suggest that the interaction between its strong currents and coastal geometry produces localized divergent circulation patterns that countered anomalously warm SSTs during the 1998 marine heat wave that devastated reefs throughout the Coral Triangle. CCS fisheries: The effects of global climate change on CCS oceanography may dramatically impact the lucrative US-west coast fishing industry. As part of a collaborative and interdisciplinary campaign, we are using output from a 4km ROMS model to predict changes in spawning habitat suitability and recruitment for key CCS market species. Simulations are forced climatologically by recent historical (1981-2010) or end-of-century (2081-2100) conditions, with future states (delta-additions) derived from end members of the NCAR Large Ensemble Community Project. ROMS output is then used in to inform general additive habitat models (e.g., sardine) and Lagrangian-particle tracking analyses (e.g., California spiny lobster) to assess spatial changes in egg-presence likelihood and potential connectivity due to long-term climate variability. POC: Charlie Stock/John Dunne
Sep. 27Formal Seminar - Patrick TaylorNASA LangleyThe Local and Remote Mechanisms of Arctic Amplification: Friend or Foe?
Over the last 30 years, rapid and, in many cases, unprecedented changes to Arctic temperatures, sea ice, snow cover, land ice, and permafrost have occurred. While the Arctic may seem far away, changes in the Arctic climate system have a global reach, affecting sea level, the carbon cycle, atmospheric winds, ocean currents, and potentially the frequency of extreme weather in northern mid-latitudes. State-of-the-art climate models are able to capture the rapid nature of recent Arctic climate change (a.k.a. Arctic Amplification), while also disagreeing more in the Arctic than anywhere else. In part, the large spread in climate projections of Arctic Amplification are due to our lack of understanding of the root cause(s) of rapid Arctic climate change, specifically the balance between the local and remote forcing mechanisms. The local mechanism represents the combined surface albedo (radiative) and ice-insulation (non-radiative) feedbacks whereby a warmer Arctic with less sea ice stores more energy in the ocean in summer via the surface albedo feedback supporting increased surface turbulent fluxes in fall/winter. Alternatively, the remote mechanism acts through changes in the non-polar (tropical and mid-latitude) circulation and increases atmospheric poleward heat transport into the Arctic and warms, moistens, and produces a cloudier Arctic atmosphere. Recent research points to a role for both the local and remote mechanisms and in fact the manner in which these mechanisms interact may be the most critical. Using a regional, process-oriented partitioning of the inter-model spread, we argue that differences in seasonal energy exchanges in sea ice retreat regions accomplished by increased absorption and storage of solar insolation in summer and increased surface turbulent fluxes in fall/winter are the leading cause of the inter-model spread. Moreover, models that more widely disperse the energy drawn from the surface in sea ice retreat regions Arctic-wide warm more, implying an important contribution of the local Arctic atmospheric circulation response to the inter-model spread. Our recent results point to two important findings: (1) the principle mechanisms driving the inter-model spread in AA operate on regional not Arctic-wide scales, and (2) reductions in the inter-model spread require an improved process representation of atmosphere-ocean-sea ice interactions in sea ice retreat regions.
Oct. 3Lunchtime Seminar Series - Rei ChemkeColumbia UniversityThe climate's response to anthropogenic emissions: the role of ocean circulation
The effects of ocean circulation on the climate's response to anthropogenic emissions at low and high latitudes are examined. At low latitudes, the Hadley cell plays an important role in setting the strength and position of the hydrological cycle. Climate projections show a weakening of the Hadley cell, together with widening of its vertical and meridional extents. These changes are projected to have profound global climatic impacts. Current theories for the Hadley cell response to increased greenhouse gases account only for atmospheric and oceanic thermodynamic changes, but not for oceanic circulation changes. Here, the effects of ocean circulation changes on the Hadley cell response to increased greenhouse gases are examined. First, using a hierarchy of ocean-model configurations under increased greenhouse gases or arctic sea-ice loss, we show that, by cooling the surface and atmosphere, ocean circulation contracts and strengthens the Hadley cell, and thus reduces its projected response. At high latitudes, we examine the effects of ocean circulation on the North Atlantic sea surface temperature, which has large climate impacts in the Northern Hemisphere. In recent years and in climate projections a cooling trend is found in the North Atlantic surface (the North Atlantic warming hole). Using observations and large ensemble of model simulations, we find that since the beginning of 21st century there has been a reduction in surface meridional heat advection, which cools the North Atlantic midlatitudes and is part of an emerged forced response to anthropogenic emissions and not part of internal climate variability, and thus projected to continue in coming decades.
Oct. 4Formal Seminar - Susanne BauerNASA/GISSAerosol Modeling, Climate Change and Air Pollution
Abstract: The presentation will give an introduction to the aerosol concept developed at NASA GISS including newest updates on simulating condensing and evaporating particles. The model will then be used to show two applications; Air Pollution and Climate Forcing. Air Pollution: The African continent continuously experiences extreme aerosol load conditions. Africa produces the world largest source of desert dust emissions, undergoes strong industrial growth, and produces approximately a third of the Earth's biomass burning aerosol particles. Sub-Saharan biomass burning is driven by agricultural practices, such as burning fields and bushes in the post-harvest season for fertilization, land management and pest control. Thus these emissions are predominantly anthropogenic. Here we use global atmospheric composition, climate, and health models to simulate the chemical composition of the atmosphere and calculate the mortality rates for Africa by distinguishing between purely natural, industrial/domestic and biomass burning emissions. Our results of ~780,000 premature deaths point to the extensive health impacts of natural emissions in Saharan and West Africa, high mortality rate caused by industrialization in Nigeria and South Africa, and to a smaller extent by fire emissions. Nevertheless, 43,000 premature deaths in Africa are linked to biomass burning mainly driven by agriculture. Air quality related deaths in Africa rank within the top leading causes of death in Africa, more deadly than HIV/AIDS. Subtracting natural causes of pollution, anthropogenic pollution has similar mortality rates as Malaria. Our results also show that natural sources, in particular windblown dust emissions, have large impacts on air quality and human health in Africa. Aerosol Forcing: The Earth's climate is changing. Over the past century, aerosols played an important role in counterbalancing some of the greenhouse gas (GHG)-caused global warming and thus preventing even higher surface temperatures to be reached by now. Recent trends in aerosol concentrations show that in many formerly polluted regions such as Europe or the US aerosol emissions have already decreased back to pre-1950 levels. How does this translate in climate forcing?
Oct. 10Lunchtime Seminar - John LanzanteGFDLAre Tropical Cyclones Really Slowing Down?
A recent study by James Kossin examined the speed of movement of tropical cyclones. He concluded that over about the past 70 years tropical cyclones have slowed their movement by about 10%. Hurricane Harvey, whose devastation was due in large part to its slow movement, provided timely motivation for this work. Also, prior studies suggest slower movement due to anthropogenic climate change. In this seminar I present a reexamination of the data and conclude that most if not all of the apparent slowdown is likely due to a combination of natural internal variability and observational artifacts. In particular, the limited observing capabilities during the pre-satellite era have probably biased the climate record, rendering a spurious decrease in estimated tropical cyclone translation speed.
Oct. 11Marjy FriedrichsVIMSRound table on Coastal Ocean Modeling Testbeds
Round table on Coastal Ocean Modeling Testbeds
Oct. 11Formal Seminar - Majorie FredrichsVirginia Institute of Marine SciencesChanging transport pathways of nitrogen and carbon in the Chesapeake Bay and mid- Atlantic Bight: results from a land-estuarine-ocean biogeochemical modeling system
The coastal boundary between land and ocean represents a small portion of the surface area of the earth, yet plays a major role in global carbon and nutrient cycling. The most productive marine ecosystems are located in coastal waters, which are, not coincidentally, adjacent to regions of highest human population density. As a result, these regions are particularly susceptible to anthropogenic impacts, such as those resulting from land cover and land use change. At the same time, changes in climate are posing significant stress on these regions, as witnessed by increasing temperatures, atmospheric CO 2 and sea levels. Until recently, however, biogeochemical fluxes across the land-ocean boundary have been largely overlooked in terms of study on continental and global scales, primarily because of the challenges associated with addressing the extreme heterogeneity between adjacent systems, and the difficulties associated with developing global scale models capable of resolving the strong variability of processes occurring on relatively small time and space scales along the land-ocean interface. Over the past decade, however, there has been considerable interdisciplinary research focused on studying the connections between these terrestrial and marine ecosystems, and the fluxes of carbon and nutrients from upstream landscapes to the coastal ocean. In this talk I will review our recent efforts to quantify the flux of inorganic/organic nitrogen and carbon from the Chesapeake Bay watershed to the coastal ocean through the use of a linked land-estuarine-ocean biogeochemical modeling system. Ultimately our goal is to better understand how these fluxes and transport pathways are being impacted by local anthropogenic changes and global climate change.Primary Host: John Dunne Secondary Host: Charlie Stock
Oct. 17Lunchtime Seminar - Daniel LecoanetPrinceton Center for Theoretical Science, Princeton UniversityTesting Parameterizations of Convective Overshoot
There are many natural systems with convectively unstable fluid adjacent to stably stratified fluid: the Earth's atmosphere and ocean, as well as most stars, and perhaps even the Earth's liquid core. The convective motions penetrating into the stable region can enhance mixing, leading to changes in transport within the stable region. In this talk, I will present convective overshoot simulations, in which I quantitatively measure the extra mixing due to overshooting motions. I parameterize the extra mixing as a spatially-dependent turbulent diffusivity. Finally, I will test the parameterization and interpret the results.
Oct. 25Formal Seminar - Suzana CamargoLamont-Doherty Earth Observatory Columbia UniversityTBD
In this talk, I'll discuss the characteristics of tropical cyclones in climate models, which are used in projections of TC activity under anthropogenic climate change. Some characteristics of TC climatology improve with model resolution, but not all do, and the improvement is not uniform across models. Using a large number of climate models, the relationship of standard TC diagnostics with the mean climate state is analyzed. Models with the same resolution can have a very different TC climatology, even if their large-scale environments are very similar. In order to understand these differences, two new diagnostics were developed that can give insight on how to improve models' TC climatology, as well as the reliability of their projections. In the second part of this talk the ability of the current generation of models in forecasting tropical cyclones (TCs) - hurricanes, typhoons - weeks in advance will be discussed. There is predictability in this time scales due to the well-known modulation of TC activity by the Madden-Julian Oscillation (MJO), with a higher level of TC activity when the MJO is in its active phase in a region. As the models' skill in forecasting the MJO has improved in the last few years, the possibility of forecasting TC formation weeks in advance can be examined. The questions we will discuss are: How well do models simulate the MJO-TC relationship? Do models have skill in forecasting the probability of TC formation weeks in advance? Is the model skill dependent on the amplitude of the MJO? Primary Host: Hiroyuki Murakami
Oct. 29Isaac Held SymposiumUnderstanding and Modeling the Earth's Climate: A symposium in honor of Isaac Held
This three-day symposium will foster scientific exchange at the interface of atmospheric and climate dynamics, celebrating Isaac Held's seminal contributions in advancing our understanding of the Earth's climate. A set of invited talks will provide the broad context for panel discussions and poster sessions that will address Isaac's core interests which include atmospheric general circulation, teleconnections, dynamical insights on climate change, geophysical turbulence, and tropical dynamics. Registration required. The symposium will be held in the Frick Chemistry Lab/Taylor Auditorium, Princeton, New Jersey. Program and additional information at splash.princeton.edu/heldfest
Oct. 30Isaac Held SymposiumUnderstanding and Modeling the Earth's Climate: A symposium in honor of Isaac Held
This three-day symposium will foster scientific exchange at the interface of atmospheric and climate dynamics, celebrating Isaac Held's seminal contributions in advancing our understanding of the Earth's climate. A set of invited talks will provide the broad context for panel discussions and poster sessions that will address Isaac's core interests which include atmospheric general circulation, teleconnections, dynamical insights on climate change, geophysical turbulence, and tropical dynamics. Registration required. The symposium will be held in the Frick Chemistry Lab/Taylor Auditorium, Princeton, New Jersey. Program and additional information at splash.princeton.edu/heldfest
Oct. 31Isaac Held SymposiumUnderstanding and Modeling the Earth's Climate: A symposium in honor of Isaac Held
This three-day symposium will foster scientific exchange at the interface of atmospheric and climate dynamics, celebrating Isaac Held's seminal contributions in advancing our understanding of the Earth's climate. A set of invited talks will provide the broad context for panel discussions and poster sessions that will address Isaac's core interests which include atmospheric general circulation, teleconnections, dynamical insights on climate change, geophysical turbulence, and tropical dynamics. Registration required. The symposium will be held in the Frick Chemistry Lab/Taylor Auditorium, Princeton, New Jersey. Program and additional information at splash.princeton.edu/heldfest
Nov. 2Informal Seminar - Zhihong TanUniversity of ChicagoHierarchical Modeling of Cloud-Radiation-Circulation Interaction
I introduce a model hierarchy spanning large-eddy simulation (LES), single-column model, and general circulation model (GCM) to investigate two key problems in the cloud-radiation-circulation interaction: (1) how do radiative differences impact the jet stream response, and (2) how do subtropical marine low clouds respond to warming. Using a GCM and a single-column radiative-convective equilibrium model, I show that gray radiation leads to a too shallow tropopause height and a split jet that shifts equatorward, whereas including four longwave bands and water vapor feedback is sufficient to recover the jet regime and poleward jet shift as comprehensive climate models. Using an LES coupled with a mixed-layer ocean, I show that the surface temperature feedback leads to a shallowing of the subtropical marine cumulus as the climate warms, which is verified by GCM but opposite to previous LES studies without surface temperature feedback.
Nov. 8Formal Seminar - John MarshallMassachusetts Institute of TechnologyThe Ice-Ocean governor: ice-ocean stress feedback limits Beaufort Gyre spin up
he Beaufort Gyre is a key circulation system of the Arctic Ocean and its main reservoir of freshwater. We describe a mechanism that is fundamental to its dynamics, namely the "ice-ocean stress governor". Wind blows over the ice and the ice drags the ocean. But as the gyre spins up, currents catch the ice up and turn off the surface stress. This governor sets the basic properties of the gyre, such as its depth, freshwater content, and strength. Analytical and numerical modeling is employed to contrast the equilibration processes in an ice-covered versus ice-free gyre. We argue that as the Arctic warms, reduced sea-ice extent and more mobile ice will result in a deeper and faster Beaufort gyre, accumulating more freshwater which will be released by Ekman upwelling or baroclinic instability. Finally, we describe how the Ice-Ocean governor might play an important role south of the Antarctic Divergence in the seasonal ice zone of the Southern Ocean. Primary Host: Liping Zhang
Nov. 8Erker BaysalLISA Conference Talks & Experiences
Share talks, and experiences from LISA'18
Nov. 14Lunchtime Seminar Series - Jian HeInvestigating Methane Trend and Variability using the GFDL-AM4
Changes in atmospheric methane abundance have implications for both chemistry and climate as methane is both a strong greenhouse gas and an important precursor for tropospheric ozone. A better understanding of the drivers of trends and variability in methane abundance over the recent past is therefore critical for building confidence in predictions of future methane levels. In this work, the representation of methane is improved in AM4 and the total methane emissions are optimized for the period of 1980-2014. The AM4 simulation with optimized methane emissions is able to reproduce the observed spatio-temporal variability in surface and column-averaged methane as well as vertical profiles. We also include methane source tagged tracers and a representation of methane isotope in the model to explore the role of individual sources and sinks in driving methane variability. The preliminary results indicate the methane stabilization during 1999-2006 is mainly due to the balance between increasing methane emissions and sinks while the renewed methane growth after 2006 is most likely due to the increased methane emissions (especially from energy sector) outweighing the methane sinks.
Nov. 15Formal Seminar - Timothy DelsoleGeorge Mason University How Do You Validate a Climate Model?
Climate models make millions of predictions over space and time about the state of the atmosphere and ocean. How should such predictions be validated against observations? A widely accepted paradigm for validating climate models is optimal fingerprinting. In this talk, I will review optimal fingerprinting and discuss reasons why it is not as stringent as it may seem. I will then discuss some new ways to validate climate models inspired by the question of whether the Atlantic Multidecadal Oscillation is primarily driven by human activities or a manifestation of natural variations. Primary Host: Nathaniel Johnson Secondary Host: Tom Delworth
Nov. 16Andy ChiodiUniversity of Washington/JISAO and NOAA PMELWind and Wind Uncertainty Impacts on Equatorial Pacific Air-sea Momentum and Carbon Exchange
Following frustrating attempts to ocean-model-hindcast the large 1982-83 El Niño event using the wind data sets available at the time, the tropical moored buoy array (a.k.a. TAO/Triton) was designed based on coherence length scale and spectral decomposition of variance analysis of wind records from western tropical Pacific islands. These studies provided information about the minimal buoy spacing needed to resolve the regional spatial variability in wind and also revealed a unique peak in zonal wind energy in the 3 to 60 day frequency band. Subsequent study of sub-seasonal timescale near surface equatorial Pacific wind variability has shown that westerly wind events, characteristic of the central and western tropical Pacific, play a fundamentally important role in the onset and development of El Niño events by both causing warming along the oceanic waveguide and becoming more frequent in response to that warming. More recently, we have found that there are easterly wind events that, although harder to find than the westerly events if looking just at winds, are associated with zonal wind stress anomalies over the oceanic waveguide that are comparable in magnitude to the westerly event wind stress anomalies, and can play a role in the development of La Niña akin to that of the role that the westerly events play in El Niño. A recurring aspect of these wind event studies has been the need to go directly to the moored buoy winds (rather than, say, use a reanalysis product such as ERA-Interim) for wind stress information in order to force accurate ocean model simulations of the observed central Pacific SSTA development - and thereby provide basis for understanding that development. This talk will highlight results that depended on having the tropical Pacific mooring winds available for understanding the observed oceanic behavior, as well as remaining questions about how to understand, and if possible predict, key characteristics of the observed annual wind event distributions. It will also describe methods for assessing equatorial Pacific zonal wind stress knowledge accuracy using forced ocean simulations of observed central Pacific SSTA and discuss the promise of using the right type of satellite winds to fill gaps in the mooring winds. I will also describe recent results based on using the tropical Pacific mooring winds to assess the accuracy of popular wind analysis products (NCEP1, NCEP2, and CCMP) in the context of estimating the mean, variability and 25-year trend in equatorial Pacific air-sea carbon flux. These carbon-flux results provide another cautionary reminder that trends in the analysis product winds are not to be trusted without careful validation by high-quality observations on relevant space and time scales. Speaker bio: A focus of Dr. Chiodi's research is air-sea interaction over the Tropical Pacific, with a particular focus on the roles that sub-seasonal near surface wind events play in the onset and development of El Nino and La Nina events, as well as the statistical linkages between various measures of the anomaly state of the Tropical Pacific (including outgoing-longwave-radiation observations for tracking changes in deep atmospheric convective activity) and the observed ENSO seasonal weather anomaly associations over land regions around the world. Dr. Chiodi's work has also examined broad scale variability of the global carbon cycle, including ENSO associations, as well as subtropical air-sea interaction. Dr. Chiodi is currently a member of the University of Washington's Joint Institute for the Study of the Atmosphere and Ocean (JISAO) and NOAA PMEL, in Seattle, WA.
Nov. 28Lunchtime Seminar Series - Xiao LiuCICS postdocTracing Nitrogen Across the River-Coast-Ocean Continuum
Marine environment is increasingly threatened in a high carbon dioxide, urbanized world. Coastal and oceanic stressors, such as occurrences of harmful algal blooms and oxygen deprivation, are forecast to intensify over the next century owing to combined effects of global warming and enhanced nutrient inputs. As a major terrestrial source of nutrients to the ocean, rivers play a critical yet poorly quantified role in driving both coastal biogeochemical processes and global carbon cycle. We investigate coastal retention time scales, transport pathway of river nitrogen, and its biogeochemical impact through application of high-resolution global ocean-ice-ecosystem models (MOM6-SIS2-COBALT) with time varying river inputs derived from an offline land model (LM3-TAN). Focused on ocean chlorophyll and oxygen, our century-long model simulations depict a global view of "river impacted zones"with boundaries extended up to thousands of kilometers from their discharge points. At regional scales, we show that intensity and distribution of coastal extremes (i.e. blooms and hypoxia) in some coastal systems are strongly influenced by temporal variability of river nitrogen, while these events are driven more by climate and oceanic dynamics in other systems. Our results emphasize that future prediction of marine ecosystem tipping points requires resolution of both oceanic and terrestrial (e.g. riverine) drivers of ocean change.
Nov. 29Formal Seminar - Charles KovenLawrence Berkeley LaboratoryTowards understanding the dynamics of permafrost carbon under climate change
Permafrost-affected soils make up the largest pool of organic carbon in the terrestrial system. Because the preservation of carbon in these soils is fundamentally tied to their thermal state, permafrost may be highly vulnerable to warming and act as a strong carbon-climate feedback. However permafrost has also been one of the last aspects of the terrestrial carbon cycle to be incorporated into ESMs. I'll discuss approaches to representing the physical and biogeochemical dynamics of permafrost in models, observational constraints on permafrost models, and how incorporating permafrost dynamics affects predictions of feedbacks in the Earth system. Primary Host: Elena Shevliakova Secondary Host: John Dunne
Dec. 4Informal Seminar -Dr. Navid ConstantinouAustralian National Univ. CanberraBaroclinic versus barotropic eddy saturation
Wind is an important driver of large-scale ocean currents, imparting momentum into the ocean at the sea surface. In particular, strong westerly winds help to drive the Antarctic Circumpolar Current, which of key importance for the global climate system. Over the past decades observations established that the strength of the westerlies over the Southern Ocean has increased as a result of climate change forcing. This increase is consistent with global climate model simulations. The future climate state depends strongly on how will the Antarctic Circumpolar Current respond to this strengthening. Eddy saturation is a theoretical regime where the transport of the current remains insensitive to the strengthening of the westerlies. Instead, the strengthening of the westerlies energizes transient eddies. Both satellite observations and numerical simulations suggest that the Antarctic Circumpolar Current is close to the eddy saturated limit. Traditionally eddy saturation has been attributed to baroclinic processes, but recent work suggests that barotropic processes that involve, e.g., standing meanders of the Antarctic Circumpolar Current, can also be responsible for producing eddy-saturated states. I will discus the different physical entities of the "usual" baroclinic eddy saturation as well as the recent notion of barotropic eddy saturation. I will assess the relative importance of barotropic and baroclinic processes in producing eddy-saturated states using numerical simulations of primitive equations in an idealized setup. Lastly, I'll discuss potential implications these processes have on global ocean modeling. POC: Stephen Griffies.
Dec. 6Formal Seminar - Paulo CeppiGrantham Institute, Imperial College of LondonThe role of tropospheric stability for the Earth's global energy balance
Previous work has demonstrated that climate feedbacks are not constant in time. Under CO2 forcing, they tend to become more positive in global climate models (GCMs), implying higher climate sensitivity. In the first part of this talk, I will show that the evolution of climate feedbacks in CMIP5 4xCO2 coupled GCMs is due to changes in the SST pattern causing a decrease in tropospheric stability (as measured by near-global-mean Estimated Inversion Strength over the oceans), resulting in more positive cloud and lapse-rate feedbacks. The modeled relationships between SST, stability and feedbacks are supported by observations, lending confidence in the GCM results. In the second part, I will seek to provide a quantitative understanding of the role of tropospheric stability for the radiative budget in two coupled slab ocean-atmosphere GCMs. The effect of stability is tested by abruptly forcing the GCMs with a variety of forcing agents (including CO2, solar irradiance, methane, aerosols, volcanic eruptions, and prescribed ocean heat uptake). In both models, we find a strong relationship between the stability response and the climate feedback parameter, in the sense that a greater increase in stability leads to smaller climate sensitivity. This suggests that differences in efficacy among forcing agents result from different SST patterns causing different stability responses. Based on these results, we propose a refined energy balance framework which assumes the radiative response to scale with both global-mean temperature and stability. I will discuss how this refined energy balance framework may be used to provide tighter observational constraints on climate feedbacks. Primary Host: Shiv Raghuraman Secondary Host: Leo Donner
Dec. 7Informal Seminar- Christopher J. SmithInstitute for Climate and Atmospheric Science, Univ of Leeds, U.K.Reduced-complexity earth system models for global temperature projections
General circulation and earth system models (ESMs) that are used to make global climate projections are computationally expensive to run. Furthermore, as full-complexity models take time to develop and test, and intercomparisons take several years to coordinate, simpler models have become an important tool in assessing climate responses to a broad pathway of emissions. A recent example is the IPCC Special Report on Global Warming of 1.5°C, where results needed to be produced quickly and timely engagement with stakeholders is critical. We have developed a simple open-source earth system model emulator, FaIR, which projects global mean temperature responses as a function of input emissions and radiative forcing. FaIR contains an interactive carbon cycle which replicates the behaviour of complex ESMs, and can be tuned to simulate a particular model, whereas emissions and forcing relationships are based on the IPCC Fifth Assessment Report and more recent peer-reviewed literature. The advantage of being a simple model is that large probabilistic ensembles can be run, where input parameters such as aerosol radiative forcing are varied within the assessed ranges of uncertainty, to produce a range of plausible temperature projections for a given emissions pathway. POC is: Dr.Ram & David Paynter.
Dec. 19Lunchtime Seminar Series - Bing PuGFDLRetrieving global distribution of threshold of wind erosion from satellite data and implementing it into GFDL AM4.0/LM4.0 model
Dust emission is initiated when surface wind velocities are greater than the threshold of wind erosion. Most dust models used constant threshold values globally. Here we use satellite products to constrain the frequency of dust events and surface characteristics. By matching this frequency derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products with surface winds, we are able to retrieve a climatological monthly global distribution of wind erosion threshold (Vthreshold) over dry and non-vegetated surface. This monthly two-dimensional threshold velocity is then implemented in the Geophysical Fluid Dynamics Laboratory coupled land-atmosphere model (AM4.0/LM4.0). It is found that the climatology of dust optical depth (DOD) and total aerosol optical depth, surface PM10 dust concentrations, and seasonal cycle of DOD are better captured over the "dust belt"(i.e. North Africa and the Middle East) by simulations with the new wind erosion threshold than those with the default globally constant threshold. The most significant improvement is achieved with the frequency of dust events, which is generally ignored in model evaluation. By using monthly rather than annual mean Vthreshold, all comparisons with observation are further improved. This monthly global threshold of wind erosion can be retrieved under different resolutions to match the resolution of dust models and may improve the climatology and seasonal cycle of dust simulation as well as dust forecasting.