GFDL Past Events & Seminars - 2010

Modeling Studies on Tropical Cyclones and Climate Change

ENSO and the North Pacific Gyre Oscillation: towards an integrated view of Pacific climate

Simulating the response of intense Atlantic hurricane activity to 21st century anthropogenic warming

Climate Change Detection and Attribution Methods

Climate impacts and ecosystem feedbacks: Building toward the next IPCC assessment

Aerosol-induced Changes in Boreal Winter Extratropical Circulation

Global Sea Level Rise: Closure of the budget over the GRACE era

Nutrient Constraints on the Land Carbon Cycle

Climate change and fishsticks: Dynamical projections of future walleye pollock populations in the Bering Sea

Spatiotemporal gradients in aerosol properties and radiative forcing over Bay of Bengal and Arabian Sea

The sensitivity of the coupled carbon cycle-climate system to natural variability and anthropogenic changes: Results from the NCAR CSM1.4-carbon model

Final Oral Exam Sayre Hall Seminar Room

Integrated Regional Earth System Modeling: Development and Application

Biosphere-Atmosphere Interactions: Controls on regional climate and atmospheric chemistry

Ice Sheets, Solid Earth and Sea Level: New Results

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John Waterbury: Water and Climate: Enduring Collective Action Challenges Bowen Hall Auditorium (next to E-Quad) on Princeton U. campus.

Discussion

Jerry Delli Priscoli: Water, Security and Global Policy Responses Bowen Hall Auditorium (next to E-Quad) on Princeton U. campus.

Modeling Carbon-Nitrogen Interactions in LM3V

Informal 0 Group seminar - The Force Balance of Wind-Driven Channel Models

Atmospheric circulation of giant planets inside and outside the Solar System

Charles Vorosmarty: Climate Uncertainty and Water Resources at the Global Scale Bowen Hall Auditorium (next to E-Quad) on Princeton U. campus.

Fires, farms, and trucks: perspectives from space on changes to atmospheric nitrogen

Decoupling of the temperature-nutrient relationship in the California Current Ecosystem with Global Warming

Droughts over the US Great Plains: A key role for Atlantic basin temperatures

NOAA Climate Services Line Office

The role of stratospheric dynamics in chemistry-climate coupling

Climate Response to Changing US Aerosol Sources

Ozone depletion, Montreal protocol, climate change and nitrous oxide: musings on science and policy

Why two-degrees?: policy origins, scientific rationale

The impact of global warming on marine boundary layer clouds over the eastern Pacific - A regional model study

Insights into the transport characteristics of the GEOS assimilated fields from analysis of satellite data for CO in the tropical upper troposphere

Hydrographic Preconditioning for Sea Ice in the Labrador Sea

Kathleen Miller: Science, Politics and Crystal Balls - Building Effective Approaches to Water Adaptation Planning Robertson Hall - Bowl l on Princeton U. campus.

The recalcitrant component of global warming

Fusion Energy: Accomplishments and Remaining Challenges

The mid-depth stratification of eddying ocean models

Aerosol impacts on clouds and storms

Non-equilibrium statistical mechanics of atmosphere and ocean flows

The effects of relative and absolute sea surface temperature on tropical cyclone potential intensity using a single column model

Convection-resolving deterministic and ensemble forecasts with radar data assimilation

Regional model downscaling of tropical cyclone activity in the Northwest Pacific basin

The Catastrophic Typhoon Morakot (2009) on Taiwan: Observational and Modeling Aspects

A Model Study of the Slope/Shelf Circulation and Cross-Slope/Shelf Transport in the Western Antarctic Peninsula and Marguerite Bay

Relationship Between Tropical Precipitation and Water Vapor in Current Climate and Under Warming

Using GCMs to predict coral bleaching

5 K Race

Differing Rates of Surface & Tropospheric Warming: Demystifying a Controversy

Towards IPCC AR5 - The Physical Science Basis: Science Gaps, Structure of the Report, and Schedule of Production

Examination of the influence of SST in the Gulf Stream region on individual midlatitude storms using synoptic models and data from a reanalysis product In Sayre Hall, Room 312

Chemistry of Hydrogen Oxide Radicals (HOx) in the Troposphere: From Arctic Spring to North America Summer

Long-lead seasonal hurricane forecasts

Status update on several GFDL facilities projects.

Japan Coastal Ocean Predictability Experiment: the Development of Parallel Ensemble Kalman Filter using the parallelized Princeton Ocean Model

Predicting Climate Change Effects on Marine Species: Integrating Physiology into Marine Ecosystem Models

absorbing aerosols: from radiative forcing to hydrological response

Spectral fingerprinting of climate forcing and feedback

Understanding the heterogeneity in aerosol characteristics over the Indo-Gangetic Basin - an observational portrayal

Verification of Temperature and Precipitation Trends in Climate Models

New developments in aerosol and cloud chemistry simulation in AM3: towards a chemistry-climate study on inter-continental transport of air pollution.

Some results on the nature and potential predictability of drought on monthly to decadal time scales

Loop Current and BP Oil Spill

Constraining Climate Feedbacks with Observations

Review AKF Schematic Design for GFDL Data Silo Area Construction Project

Pikas and dams and droughts: Creating regional-scale climate assessments for management & planning

Tendencies of shortwave radiation budget beyond 2000, global dimming and brightening and possible implications for climate

A Review of Cloud Microphysics Schemes used in Atmospheric Models

Discussion

Long term projections of stratospheric ozone

Simulation of mesoscale phenomena (including TC) using models with spectral bin microphysics (SBM)

The role of Atlantic multidecadal variability and the Gulf Stream in determining the spatial distribution of Northwest Atlantic fish stocks

Linking Marine Ecosystem and Climate Variability: Recent Results

Abstract: This talk will have two components, and there is something for everyone. We will begin with an analysis of the first consistent multi-year springtime measurements of peroxyacetyl nitrate (PAN) over the U.S. Pacific Northwest. PAN is an important constituent in the global atmosphere, responsible for redistributing reactive nitrogen. A limited number of case studies indicate that the NOx released from the thermal decomposition of imported PAN may represent a significant source of O3 to the eastern Pacific free troposphere. If changes in Asian NOx emissions are impacting O3 over North America, we expect a relatively larger parallel increase in PAN over the eastern Pacific. We will discuss factors driving the observed interannual variability in PAN at Mount Bachelor, including temperature and biomass burning. We will also explore whether consistent free tropospheric PAN observations could be the keystone to understanding increasing springtime O3 mixing ratios over western North America. The latter portion of this talk will present measurements of aerosol optical properties made at Mount Bachelor during spring 2008 and spring 2009. The overarching goal of this second project is to increase our understanding of how aging impacts the optical properties of Asian aerosols, particularly biomass burning smoke, industrial pollution and dust. We will explore two questions by examining 7 aerosol plumes of Asian origin observed at Mount Bachelor. 1) Are differences in the intensive optical properties of Asian aerosols observed over the western U.S. linked to variations in composition? 2) How do the aerosol optical properties observed in plumes of Asian origin over the western U.S. differ from those observed closer to the Asian source region?

Abstract Dynamical downscaling with a regional climate model (RCM) has been widely used for climate change assessment, seasonal predictions, understanding of climate processes and regional climate predictability (see the review by Wang et al. 2004). By this approach, a high-resolution limited area model is driven by relatively coarse resolution reanalysis or output of a coarse resolution global model to produce more detailed regional features. This has been approved to be particularly useful for the study of extreme climate events, including tropical cyclones. There have been several studies using RCMs to investigate the possible impact of global warming on the activity of tropical cyclones in different ocean basins. Knutson et al. (2007) demonstrated how well a nested regional atmospheric model driven by the reanalysis reproduced the recent multidecadal increase of Atlantic hurricane activity. However, the hurricane counts in the model were very sensitive to how strong the large-scale nudging in the interior of their model was. In this talk, following a brief review in the dynamical downscaling of tropical cyclone genesis, the performance of the regional atmospheric model (IRAM) developed at the International Pacific Research Center (IPRC) in reproducing the tropical cyclone genesis over the Northwest Pacific has been evaluated. The NCEP/NCAR reanalysis is used to provide both initial and lateral boundary conditions to the IRAM, which was run at a horizontal resolution of 0.3o lat/lon. The weekly mean Reynolds SST was used as the lower boundary conditions for the model over the ocean. Simulations for 17 years from 1990 to 2006 are analyzed in the study. The model was initialized at June 1 and integrated continuously through November 30 for each year without the use of any interior nudging. The model TCs are located and tracked using an objective algorithm previously developed by Stowasser et al. (2007) for the IRAM. The results show that the model reproduced not only the mean seasonal cycle but also the interannual variability of tropical cyclones in the Northwest Pacific realistically. The correlation coefficients between the modeled and observed annual tropical cyclone counts and the power dissipation index reach 0.82 and 0.74, respectively. The correlation coefficient between the modeled and observed seasonal cycle reaches 0.92. Further, the model also reproduced the spatial distributions of genesis locations and frequency occurrence reasonably well. Further experiments for the Northwest Pacific TC genesis in response to SST anomalies over the eastern Indian Ocean show that the model can reproduce the observed response quite well. Therefore, the results demonstrate that given accurate large-scale circulation from an ocean-atmospheric coupled global model, the IRAM can be used to provide skillful dynamical downscaling for seasonal prediction and climate change projection of tropical cyclone genesis over the Northwest Pacific.

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The Sahel, the semi-arid region of Africa just south of the Sahara desert, has experienced such a prolonged and devastating drought in recent decades as to be often cited in the non-scientific literature as an example of the perils of global warming. In this talk I will review current knowledge on the origin of drought in 20th Century Sahel and will present the projections for future changes in the seasonal evolution of Sahel rainfall in response to increasing greenhouse gases. Throughout the talk, I will emphasize the link of regional droughts and pluvials to global-scale climate anomalies and the consensus of the CMIP3 models. In this framework, we can interpret the projected delay and shortening of the rainy season in the Sahel as a regional manifestation of a global delay in the seasonal cycle of global precipitation and SST. While a phase delay in high latitude temperatures in response to CO2 had been simulated before, the delay of the global monsoon is a new result, one that might help increase our understanding and confidence in regional projections of tropical rainfall. Finally, I will describe two possible mechanisms for the global phase changes in surface temperature (a direct forcing by greenhouse gases and high latitude sea ice changes) and provide some preliminary analysis of their expected role.

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Most forests of the world are recovering from a past disturbance: 3% of the total forest area is disturbed each year by fire, pests, and weather. The net sequestration or loss of CO2 by forests after disturbance follows a predictable pattern determined by age, site, climate, and other factors. Forests of North America are currently a net carbon (C) sink due primarily to re-growth of previously harvested or abandoned forests. Projections of the future changes in C sources and sinks critically depend on understanding of the causes of past disturbances, the impacts of those disturbances, and scenarios of future disturbances. Observations indicate that tree mortality has increased significantly in North America over the last decade, the result of natural forest dynamics (aging) and increasing damage from climate and natural disturbance. Given the increasing significance of current and projected natural disturbances, what are the interactions with climate and the C cycle at regional and global scales?

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Atmosphere-ocean general circulation models (AOGCMs) predict a weakening of the Atlantic meridional overturning circulation (AMOC) in response to anthropogenic forcing of climate, but there is a large model uncertainty in the magnitude of the predicted change. The weakening of the AMOC is generally understood to be the result of increased buoyancy input to the north Atlantic in a warmer climate, leading to reduced convection and deep water formation. Consistent with this idea, model analyses have shown empirical relationships between the AMOC and the meridional density gradient, but this link is not direct because the large-scale ocean circulation is essentially geostrophic, making currents and pressure gradients orthogonal. Analysis of the budget of kinetic energy (KE) instead of momentum has the advantage of excluding the dominant geostrophic balance. Diagnosis of the KE balance of the HadCM3 AOGCM and its low-resolution version FAMOUS shows that KE is supplied to the ocean by the wind and dissipated by viscous forces in the global mean of the steady-state control climate, and the circulation does work against the pressure-gradient force, mainly in the Southern Ocean. In the Atlantic Ocean, however, the pressure-gradient force does work on the circulation, especially in the high-latitude regions of deep water formation. During CO2-forced climate change, we demonstrate a very good temporal correlation between the AMOC strength and the rate of KE generation by the pressure-gradient force in 50-70N of the Atlantic Ocean in each of nine contemporary AOGCMs, supporting a buoyancy-driven interpretation of AMOC changes. To account for this, we describe a conceptual model, which offers an explanation of why AOGCMs with stronger overturning in the control climate tend to have a larger weakening under CO2 increase.

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ORNL INCITE user meeting

Atmospheric convection is an enduring problem in climate service. With this talk, I address two questions of current interest: (1) What do observations tell us about the conditions that favor the transition from shallow to deep convection over land? and (2) What improvements in the simulation of tropical convection might be achieved by moderate increases in the horizontal resolution of climate models?

Superrotation in the Solar System

The notion that the West Antarctic Ice Sheet has a configuration that is unstable to small perturbations at its margins is an old one. Recent records showing that the Amundsen Sea sector of the ice sheet is retreating, coupled with the observation that a large scale retreat of the ice sheet will result in several meters of sea level rise, now make it important that the detailed mechanics of the instability mechanism are fully understood. This seminar will review the observational record from the 1990's that lead to the view that the ice sheet is retreating at an accelerating rate. It will consider whether the notion of instability is sufficient to explain the phenomenon, or whether it is more likely that external ocean 'forcing' better explains the observations. I will argue that the present configuration is not one of irreversible retreat, and that the important question to understand today is whether the recent increase in oceanographic heat flux to the base of the ice sheet at its grounding line is simply a decadal fluctuation, or a longer term, secular trend that will necessarily then result in irreversible retreat.

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Toward an integrated modelling of crop-climate interactions: including tropical croplands in a land surface model

During the past decades, heavy precipitation events have become more intense over a large part of the Northern Hemisphere land area. It has been suggested that human-induced increase in greenhouse gases may be partly responsible for the observed intensification of extreme precipitation in line with the increased water holding capacity of atmosphere with warming. However, because of the limited observational availability, most previous studies have examined only the potential detectability through model-model comparisons. Here we compare observed and multi-model simulated extreme precipitation changes using an optimal fingerprinting technique, and provide the first evidence that human influence has contributed to the observed intensification of heavy precipitation events during the latter half of the 20th century. Model projected changes and their impacts may nevertheless be underestimated because models tend to underestimate the observed increase in heavy precipitation with warming.

Emissions of a broad range of greenhouse gases of varying lifetimes contribute to global climate change. Carbon dioxide displays exceptional persistence that renders its warming nearly irreversible for more than a thousand years. This talk focusses on explaining the physical reasons for this behavior, and its consequences for global climate change. I will also show that the warming due to non-CO2 greenhouse gases, while not irreversible, persists notably longer than the anthropogenic changes in the greenhouse gas concentrations themselves. This occurs because the persistence of warming depends not just on the decay of a given greenhouse gas concentration but also on climate system behavior, particularly the time scales of heat transfer linked to the ocean. For carbon dioxide and methane, non-linear optical absorption effects also play a smaller but significant role in prolonging the warming. In effect, dampening factors that slow temperature increase during periods of increasing concentration also slow the loss of energy from the Earth's climate system if radiative forcing is reduced. Implications for future global climate change and human choices will be explored.

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