Abstracts for the
U.S. CLIVAR Climate Model Evaluation
Project (CMEP)
Awards were announced 1 October 2004
ABSTRACT
ATM-0444284
SGER: Simple Indices of Climate Variability and Change
David Karoly, U of Oklahoma
Five simple indices of large-scale surface temperature variations will be used to assess the performance of a number of climate models in simulating climate variability and change during the 20th century. These indices are based on the spatial fingerprint of greenhouse climate change and include the area-mean surface temperature, the land-ocean temperature contrast, the meridional temperature gradient in the Northern Hemisphere, the magnitude of the annual cycle in temperature over land, and the magnitude of the diurnal temperature range over land.
The indices will be calculated for the global domain and for the North American region from observational data for the period 1880-2003 and compared with data from model simulations for this period. The models to be analyzed include simulations from all three U.S. models (Community Climate System Model, at the National Center for Atmospheric Research at Boulder, Colorado; Geophysical Fluid Dynamics Laboratory model (GFDL) at Princeton; and Goddard Institute for Space Studies model (GISS) at New York City) being made available for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, together with several other international models. The variability and correlation structure of the indices will be compared between the observations and the models on three different timescales: interannual variability, decadal variability and trends on 50 year and century timescales.
This evaluation will provide greater confidence in using these models for climate change detection and attribution studies and for projection of future climate change.
This is a grant under the U.S. Climate Change Science ProgramÕs CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0444564
SGER: Sea Surface Temperature (SST) Influence on Surface Wind Stress in Climate Models
Chelton, Dudley and Eric Maloney, Oregon State University
Simulating the Earth's climate system is critically dependent on accurate representation of interactions at the air-sea interface where the effects of the ocean are communicated to the atmosphere. A robust manifestation of this ocean-atmosphere interaction is the relationship between sea surface temperature (SST) and surface wind stress. In regions where surface winds blow obliquely across SST fronts (e.g., over the cold tongue in the eastern tropical Pacific), the wind stress is modified by SST-induced changes in the structure and stability of the atmospheric boundary layer. This SST influence is most clearly evident in the wind stress divergence and curl (measures of two components of the total circulation), which have been shown to be linearly related to the downwind and crosswind components of the SST gradient, respectively.
The objective of this study is to investigate this coupling from analyses of the global surface wind stress and SST fields generated by the U.S. climate models that have been developed for the Intergovernmental Panel on Climate Change (IPCC) science assessment. The adequacies of the model representations of this ocean-atmosphere coupling will be assessed by comparing the relationships between the simulated SST and wind stress fields with the relationships deduced from 5 years of satellite measurements of SST and wind stress.
Broader Impacts: If successful, this research should provide better understanding of large-scale ocean-atmosphere interactions and improved estimates of uncertainty in prediction that result from improper representations of those interactions. These outcomes benefit environment managers and decision-makers, and thus, societal activities.
This is a grant under the U.S. Climate Change Science ProgramÕs CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0445134
SGER: Teleconnection Structure and Evolution in the Coupled Model Simulations
Nigam, Sumant and Joseph Renu, U of Maryland College Park
The recurrent patterns of interannual variability (teleconnections included) will be extracted from the Community Climate System Model (CCSM), the Geophysical Fluid Dynamics Laboratory (GFDL) model, and the Goddard Institute of Space Sciences (GISS), coupled simulations and closely compared with their observational counterparts, particularly, ENSO (the El-Nino-Southern Oscillation), PNA (Pacific/North American), NAO/AO (North Atlantic Oscillation/Annular Oscillation), and the Western Pacific (WP) patterns manifest during Northern winters of the present-day climate. The land/ocean surface temperature, ocean heat-content, 200 and 850 hPa geopotential, 200 hPa divergence, 1000 hPa (surface) winds, and the associated precipitation patterns will be the focus of intercomparison. The variables constitute a minimal set for monitoring the quality of simulated interannual variability; the variable choice will facilitate scrutiny of tropical-extratropical interactions, ocean-atmosphere interactions in the tropical and extratropical basins, hydroclimate variability, and of the global warming signal itself.
Intercomparison of the variability patterns' mature-phase structure will be followed by comparative analysis of the pattern evolution; this should provide a quick, albeit incomplete, check on the realism of the underlying variability mechanisms in the coupled simulations. The evolution analysis will be conducted at submonthly resolution; preferably, at pentad time scales.
An even more fundamental descriptor of the atmospheric general circulation is the zonally symmetric circulation, specially the zonal-mean zonal winds (U). Seemingly subtle differences in the (U) latitude-height structure can be consequential for climatological stationary waves and climate teleconnections, from modulation of wave propagation in/across the troposphere. The PIs will illustrate the dynamical significance of the inter-model variations of (U)-climatology by computing the orographic circulation response during winter, using a steady, linearized version of the atmospheric model's dynamical core (the diagnostic model). Additionally, since interannual variations of (U) in the middle-to-high latitude winters have figured prominently in recent discussions of troposphere-stratosphere interactions, specially, in context of the development of the NAO and global warming signals in the troposphere, a principal component analysis of (U) variability in the troposphere and stratosphere will be conducted. The significance of inter-model differences in the (U)-variability structures will again be illustrated through diagnostic modeling.
Broader Impacts:
This work will establish the baseline information for evaluating global and regional climate and water resource model projections for the 21st century. This is important information for environmental management and environmental policy decisions.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0445136
SGER: Diagnosis of North American Hydroclimate Variability in Coupled Model Simulations
Ruiz-Barradas, Alfredo and Sumant Nigam, U of Maryland College Park
This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called CMEP, for Climate Model Evaluation Project, with a special emphasis on water cycle, precipitation and land surface interaction.
The PIs will analyze the interannual variability of North American hydroclimate during summer and winter months in two coupled simulations of the 20th century climate. Current state-of-the-art atmospheric general circulation models have rather limited potential in simulating hydroclimate variability over North America, especially during summer when the climatological evaporation is large. The models exhibit intense local recycling of precipitation and weak convergent moisture fluxes, in contrast with warm-season observations. The PIs will first evaluate precipitation variability and the associated structure of the atmospheric water cycle during summer and winter in the Community Climate System Model (CCSM), Geophysical Fluid Dynamics Laboratory (GFDL) and Goddard Institute for Space Studies (GISS) coupled simulations.
The analysis will be carried out using monthly fields. However the issue of local recycling of precipitation (via surface-atmosphere feedback) versus remote water sources of precipitation (via convergent moisture fluxes) in the North American region will be given special consideration. The PIs will use both monthly and pentad anomalies to investigate the precipitation recycling issue in models and observations. Lead/lag analysis is expected to be particularly insightful here. They will also examine the linkages of the two adjoining ocean basins on North American summer hydroclimate. They will undertake principal component analysis of 700 hPa geopotential height and SST to identify the basin connections in the simulations; the corresponding observational analysis has been completed.
The PIs have a number of target data sets like the newly available European Center for Medium Range Weather Forecasting (ECMWF) reanalysis as well as other gridded observations for precipitation, evaporation, sea surface temperature, and satellite-based precipitation estimates that will be used to assess the simulations.
Broader Impacts: If successful, this research will result in the improvement of climate model projections of climate variability in a changing climate. This had great potential benefit to people and their environments.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0446780
SGER: Evaluation of Surface Solar Irradiance in Coupled Climate Models
Liepert, Beate and Anastasia Romanou, Columbia University
Observations from satellites and in situ measurements of surface downwelling irradiance will be analyzed and compared with global general circulation coupled model simulations of the late 19th century and 20th century runs to evaluate the model climatology, variability and cloud and aerosol effects. The incoming shortwave irradiance at the surface is one driving mechanism of the ocean/ice and land submodels and while it is directly affected by the physics in the atmosphere, such as clouds, aerosols, water vapor, ozone and other gases, it is only indirectly affected by the ocean/ice/land. Hence, aerosol and cloud variations have a strong direct signal on the downwelling shortwave surface irradiance, which can be easily interpreted. At the same time, surface solar irradiance and its link to clouds and aerosols represents one crucial part of the cloud feedback loop. Furthermore, there has been increased interest in the scientific community regarding the long-term variability of the surface incoming solar irradiance. Observations show that solar irradiance has recently been decreasing in stations worldwide by about 4% from 1961-1990, possibly due to changed aerosol concentrations and cloud variations. This has been described as a global dimming effect. Current research (from satellite observations) shows a reversal of this effect from the late 1980s and during the 1990s. The PIs will use two data sets, which represent two different classes of data retrieval methods, from satellites and in situ measurements. They will compare the observed climatology and variability of the surface downwelling shortwave flux to four coupled climate models, the Goddard Institute for Space Studies (GISS) model with two ocean submodels, the Geophysical Fluid Dynamics Laboratory (GFDL) model and the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM-3), on all resolved temporal and spatial scales. Since the models use different aerosol datasets and cloud parameterizations (some use indirect cloud-aerosol effects) the inter-model comparisons of the solar irradiance at the surface will be instructive of the quality of each models' representation of cloud and aerosol impacts. The PIs will a) assess the long-term variability and trend of the model downwelling shortwave flux at the surface and compare it to observations, b) assess the aerosol and cloud effects in the models and, c) examine the models' capability in simulating specific events (volcanic eruptions and El Nino conditions).
Broader Impacts: This research is important because it has the potential to improve the quality of climate prediction models, which would be a benefit to societal activities, such as, environmental management and decision-making.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0446791
SGER: Sensitivity of the West African Monsoon to Gulf of Guinea Sea Surface Temperatures (SSTs)
Cook, Kerry, Cornell University
Output from state-of-the art coupled atmosphere/ocean global models will be examined to evaluate the models' ability to capture a distinct mode of rainfall variability over West
Africa. When the eastern Atlantic (Gulf of Guinea) is warm, for example, summer monsoon precipitation is observed to be especially strong along the southern (Guinean) coast of Africa. At the same time, rainfall in the Sahel region to the north tends to be much lower than normal, bringing crop failure and severe hardship for the population.
Past studies of this mode of variability in models and observations have identified the physical processes that lead to this dipole precipitation response. Enhanced precipitation along the coast is due to increased evaporation to the south over the warm Gulf of Guinea, since the presence of an equatorial (east/west) Walker circulation with its sinking branch over the Gulf prevents locally-enhanced convection in association with the warmer sea surface. Reduced precipitation over the Sahel is a consequence of the enhanced sinking of warm, dry air flowing equatorward out of the Saharan high near 700 hPa, and the requirements of potential vorticity conservation for this flow.
Model output will be examined to understand the relationship between a model's ability to simulate the precipitation dipole and its resolution and physical treatments. Atmospheric moisture budget, vorticity, and moist static energy budget analyses will be used to evaluate the mechanisms of the simulated variability. The possibility that the dipole pattern will occur more frequently, or become permanently established, in the future as ocean temperatures rise will be investigated.
This study will contribute to our fundamental understanding of how drought occurs in the Sahel and lead to an improved ability to predict African drought on all time scales. It will also provide guidance to environmental managers and policy makers regarding the quality of climate projections for this part of the world.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0447034
SGER: Subantarctic Mode Water and Antarctic Intermediate Water: How Well Are They Represented in Climate Models?
Kamenkovich, Igor U of Washington
Processes in the Southern Ocean can influence global ocean circulation and density structure on the time scales relevant for global climate change. Evaluation of simulation of the Southern Ocean water masses in U.S. climate models will therefore assist in quantification and reduction of the uncertainty in predicting the response of the global thermohaline circulation to increasing concentration of greenhouse gases in the atmosphere. The goal of this study is to evaluate simulation of the Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) in three U.S. climate Models: the Community Climate System Model (CCSM), the Geophysical Fluid Dynamics Laboratory (GFDL) model, and the Goddard Institute of Space Sciences (GISS) model, using observational data.
The research has two main objectives:
(i) To evaluate simulation of the properties of SAMW and AAIW by ocean general circulation models (OGCMs) through comparison with the observational data from the World Ocean Atlas 2001. The analysis will focus on the volume, temperature and salinity of SAMW and AAIW and on the stratification along meridional sections at the southern boundary of the Pacific and Atlantic oceans.
(ii) To evaluate simulation of circulation and modification of the intermediate water using estimates of mass, heat and salt fluxes by a data-based inverse box model. The analysis will focus on the isopycnal fluxes into the Pacific and Atlantic basins, as well as on the diapycnal fluxes that modify properties of the intermediate water in the Southern Ocean.
The results of these analyses will help to identify sources of disagreement between the OGCM-simulated and observed properties of SAMW and AAIW.
The broader impacts of the work are that it will aid in assessing the uncertainty of the future climate change projections and will guide future model development. This is important for environmental management and decision-making activities.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0447804
SGER: Model Intercomparison: Thermohaline Circulation and Its Relation to Surface Fluxes
Sun, Shan, MIT
Three climate modeling centers in the U.S. (CCSM (NCAR), GFDL and GISS) will be releasing in September 2004, model simulations of the global climates of the late 19th and 20th centuries. These will be available as input to the next Intergovernmental Panel on Climate Change (IPCC) Assessment Report and also for general studies by climate scientists. The is a research project to use these model data sets, along with the best available observations of the past climate, to analyze the ability of global climate models to simulate the climate of the late 19th and 20th centuries.
The thermohaline circulation (THC) in the Atlantic plays an important role in regulating climate by accounting for nearly half of the poleward heat transport. However, there is a dearth of analytic tools for displaying quantitative details of the THC in a model. The PI will extract regional details of the 3-D circulation in potential density space (i.e., isopycnal as well as diapycnal mass flux components) from the archives of the models, using the method he has already developed. The PI has gained considerable experience in applying the same technique to output from z coordinate models. In other words, well-tested algorithms are available today for converting z coordinate model fields to isopycnal coordinates in a manner allowing isopycnal and diapycnal mass fluxes to be extracted. His study aims to shed light on the role of THC fluctuations in mediating atmosphere-ocean interactions on decadal time scales in the various coupled models. He will also investigate decadal variability linked to anthropogenic forcings in the past century, hoping to provide a stepping stone for follow-up studies of mechanisms which in the Third IPCC Assessment led to the large fluctuations in THC strength in greenhouse gas-forced simulations.
Broader Impacts: The Ocean's THC circulation strongly influences the climate of the North Atlantic and Western Europe. Its stability may be affected by global warming. This research has the potential to improve understanding of the physics that control the strength of the THC and thus, possible large-scale climate changes in the future. This would be important information for better-informed environmental policy decisions.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0447920
SGER: Evaluation of Midlatitude Storm Characteristics and Variability in Intergovernmental Panel on Climate Change (IPCC) Coupled Models
Tselioudis, George, Columbia University
The frequency and intensity of baroclinic storm systems determines to a large extent the energy and water cycles in the Northern and Southern midlatitudes. In light of potential systematic changes in midlatitude storm characteristics with climate change, it is crucial to test the ability of climate models to simulate correctly the characteristics and variability of midlatitude storm tracks. In this project, storm tracking techniques that have been applied to the National Centers for Environmental Prediction (NCEP) reanalysis data will be applied to the Intergovernmental Panel on Climate Change (IPCC) - Fourth Assessment Report (AR4) coupled model output to determine the spatial and temporal characteristics of midlatitude storm tracks in the 1960-2000 time period.
This study will evaluate the skill of coupled climate model historical runs to simulate the spatial characteristics of midlatitude storm tracks, the intensity distributions of midlatitude storms, and the temporal variability of storm tracks at time scales that range from the seasonal to the decadal. Preliminary analyses of the observed storm variability indicate potential trends in both storm frequency and intensity that are particularly evident in the Southern Hemisphere. The ability of climate model simulations to reproduce such trends will be evaluated along with the ability to reproduce Arctic Oscillation and El Nino related changes in storm track frequency and intensity. The results of the model evaluation will provide a first look at the effects of model resolution on storm track simulation, will test the ability of the models to simulate potential changes in extreme storm events with climate warming, and will help to attribute errors in model radiation and precipitation fields to model dynamical or microphysical schemes. The study will also provide leads to modelers that will help evaluate the use of damping mechanisms in model physics parameterizations.
Broader Impacts: To the extent that this study pinpoints and helps to improve deficiencies in the modeled representation of mid-latitude storm tracts in a changing climate environment, it will have a positive impact on the quality of future climate and water resources information provided to environmental managers and policy-makers.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0448921
SGER: Multivariate Climate Change Detection
Wehner, Michael, Lawrence Berkeley Lab
The PI will apply (previously developed) coupled climate model analysis methods to ensembles of historical period integrations of three new US models; the Community Climate System Model (CCSM), the Geophysical Fluid Dynamics Laboratory (GFDL) model, and the Goddard Institute of Space Sciences (GISS) models. The research is collaborative with DOE's Program for Climate Model Diagnosis and Intercomparison (PCMDI) scientists to perform climate change detection analysis on five model monthly output fields, Microwave Sounding Unit (MSU) Channel 2 temperature, MSU Channel 4 temperature, tropopause height, total columnar water vapor and surface wind stress. The statistical significance of late twentieth century trends in the model data will be judged against state of the art observational data or their proxies. An additional analysis of the daily output from the NCAR CCSM3 is planned to study the statistics of extreme events produced by the model. Return value fields will be calculated for annual maximum daily averaged surface air temperature and precipitation.
Broader Impacts:
This work will yield new information about whether and by how much our climate is changing. This is important information for environmental management and environmental policy decisions.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM-0451587
SGER: Evaluation of the Simulated Global Water in the NCAR, GFDL, and GISS Climate System Models
Dai, Aiguo, UCAR
The movement of water and associated energy within Earth's atmosphere, oceans and land, and the exchanges among these components are a major aspect of Earth's climate system. Accompanying the water cycle, there are large radiative and latent heat fluxes, and oceanic salt transports involved. Correct simulation of the global water cycle and the associated energy and other fluxes in global climate system models is an extremely challenging task, yet it is a prerequisite for these models to provide realistic simulations of current and future climates. The PI will analyze the global and large-scale water cycles in the Community Climate System Model (CCSM3), the Goddard Institute for Space Sciences (GISS) model and the Geophysical Fluid Dynamics Laboratory (GFDL) model, and compare them with available observations. He will examine the spatial and temporal (seasonal to interannual) variations in precipitation (amount, frequency, and intensity), cloudiness, oceanic evaporation, terrestrial evapotranspiration and runoff, streamflow, atmospheric and oceanic freshwater transports, tropics-extratropics water exchange, land-ocean water exchange, terrestrial water storage, as well as their variability associated with the El Nino-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO).
The broader impacts of the work are that it will aid in assessing the uncertainty of the future climate change projections and will guide future model development. This is important for environmental management and decision-making activities.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
ATM 0444682
Model Simulation of the Southern Hemisphere Atmospheric Circulation,
Antarctic Sea Ice, and their Interaction: An Evaluation
Marilyn N Raphael, UCLA and Marika Holland, NCAR
The proposed research is driven by the knowledge that there are important interactions between Antarctic sea-ice and the large-scale extratropical circulation that have to be properly represented in our climate models because these interactions have regional as well as global consequences. Within the twentieth century, large scale changes have been recorded in the atmospheric circulation of the Southern Hemisphere and in the Antarctic sea-ice. Therefore the major scientific goal of the proposed research is that of determining the accuracy of the models - CCSM3, GISS and GFDL - with respect to their representation of the Southern Hemisphere large scale circulation, the Antarctic sea-ice and their interaction.
To accomplish the stated goal, the study will compare satellite-observed sea-ice data and surface and mid-tropospheric observations with the equivalent data simulated by the three models. The study will focus on the models' ability to simulate the climatology and trends in the large-scale circulation and sea-ice distribution. It will also focus on the model's ability to simulate the observed relationships between sea-ice and the atmosphere. The atmospheric circulation features that will be investigated are the Southern Hemisphere Annular Mode, the Semi-annual oscillation, Zonal Wave 1 and Zonal Wave 3. Antarctic sea-ice concentration and extent as well as sea-ice motion will be examined. Ideally, the results of the proposed research should reveal how well the models simulate the climate. They should also give us more insight into the sea-ice/atmospheric circulation linkages.
The proposed work also has significant broader impacts. It will establish research collaboration between two women in science at two institutions - The National Center for Atmospheric Research (NCAR) and the University of California, Los Angeles (UCLA). Additionally, it will provide some support for a postgraduate This student will be guided in the research by Dr. Marilyn Raphael. The results of the research will be disseminated at conferences, workshops and in the scientific literature. The student will be encouraged to participate in this process.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
0449658
SGER: Hydrological Cycles in the Tropics
Robert Curran, U MD, Baltimore
William K Lau, GSFC, NASA
The PIs will analyze and compare with available observations, the late 19th - 20th century simulations carried out by the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM3), Goddard Institute for Space Studies (GISS) ModelE and the Geophysical Fluid Dynamics Laboratory (GFDL) coupled General Circulation Models (GCM)s. The goal is to document and understand the changes in the hydrological cycle of the atmosphere in the tropics simulated by the three coupled models.
The first aspect of the proposed work is on the trends and variability of precipitation and atmospheric temperature over the tropical land and oceans. In the second half of the 20th century, while the trends in surface-air temperature over the tropical land and oceans are all upward, the trend in precipitation over the land is opposite to that over the oceans. Precipitation over the tropical land has been decreasing in the past 50 years. Following their work, we will analyze the trends and variability of tropical precipitation, surface-air temperature, sea-surface temperature, soil moisture, 200-hPa geopotential height and large-scale overturning circulation simulated by the GCMs for the entire 140-year simulations. Observations in the past 50 years or so will be utilized to validate the GCM simulations. Discrepancies between GCM simulations and observations will be identified and the causes will be explored. The second aspect is on the warm rain processes over the tropical ocean. From analysis of satellite observations, Lau and Wu (2003) found that there is a substantial increase in precipitation efficiency (ratio of precipitation to cloud liquid water) of light warm rain as sea surface temperatures (SST)s increases, but precipitation efficiency of heavy rain associated with deep convection is not sensitive to SST changes. Following their work, we will analyze cloudiness, precipitation, and water vapor residence time (ratio of water vapor to precipitation) to document the recycling of water vapor, warm and cold rainfall efficiency, and their dependence on SSTs simulated by the three coupled models. Results from the 140-year simulations of the three models will be inter-compared to discern the commonality and discrepancy among the models. Recent observations, especially those from the satellite era will be used to validate and comprehend the GCM results.
Broader Impacts: If successful, this research will have a positive impact on the quality of future climate and water resources information provided to environmental managers, policy-makers and societal activities.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
South Asian Summer Monsoon Climatology and Variability in the
Control and 20th Century IPCC AR4 Simulations
K. Hamilton, PI, International Paci.c Research Center, University of Hawaii
kph@hawaii.edu, 808-956-8327
H. Annamalai, Co-PI (International Paci.c Research Center, University of Hawaii)
Ken Sperber (PCMDI) and Rupakumar (Indian Institute of Tropical Meteorology), collaborators
This research seeks to document, evaluate and understand the seasonal evolution of the mean South Asian summer monsoon precipitation and circulation in both the control and20th century integrations of the climate models from the US centers. A particular goal is to assess the relationship between ENSO and the monsoon at interannual and decadal timescales. The PIs will also examine the variability and possible trends in the statistical properties of aspects of sub-seasonal variability such as (a) monsoon lows and depressions, and (b) 30-50 day intraseasonal oscillations (ISOs) over the South Asian monsoon region. The model diagnostics will be compared with observations and reanalysis products to evaluate how well each model does in simulating present day monsoon climate, and whether any of the 20th century runs reproduce various apparent long term trends in observations. The results of this project will provide a valuable foundation for the next step, i.e. analysis of the IPCC AR4 projected 21st - 23rd century climate simulations. The PIs will analyze all the US coupled model simulations and they will also analyze a small number of the simulations obtained with the non-US models that have the best seasonal monsoon rainfall climatology (e.g., ECHO-G). Specific questions to be addressed include: Is the mean evolution of the monsoon precipitation and circulation realistic in the models? How is the ENSO monsoon relationship represented at both interannual and decadal timescales? Do the models capture the Òprolonged breakÓ monsoon conditions during severe drought years over India? Is the space-time evolution of ISOs, particularly associated with the 30-50 day mode, realistically represented in the models? Do the models simulate the decadal fluctuations in the number of monsoon depressions over Bay of Bengal, and in the frequency of monsoon break conditions over India? Do the models in the 20th century simulations show significant long-term variations in the frequency of monsoon depressions, and, in particular, do any of the models reproduce the dramatic drop in the number of monsoon depressions that was actually observed over the 20th century.
This is a grant under the U.S. Climate Change Science ProgramÕs CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
Interannual and Decadal Variability in the Tropical
Pacific Ocean: Description and Mechanisms
Antonietta Capotondi, NOAA/CIRES Climate Diagnostics Center
A realistic simulation of tropical climates is central to coupled models due to their local societal impacts as well as to their influence on global weather patterns through atmospheric teleconnections. In this study the PIs will examine the tropical climate of the Pacific sector in the 20th century integrations performed with the global coupled climate models developed at the National Center for Atmospheric Research (NCAR), Geophysical Fluid Dynamical Laboratory (GFDL), and Goddard Institute for Space Studies (GISS). They will first characterize the mean state in all three simulations using upper-ocean and atmospheric variables. The mean state, and its possible biases, can influence the characteristics of the variability. Both interannual and decadal timescales will be considered. At interannual timescales we will characterize the model El Nino Southern Oscillation (ENSO) phenomenon by examining amplitude and spatial structure, dominant timescales, phase relationship with the annual cycle, evolution of El Nino events in the upper-ocean. Key regions for decadal variations will be identified by computing standard deviations of low-passed filtered (timescales >~8years) fields, empirical orthogonal function analysis, and epoch differences. Results from these analyses will be compared with available observations. Understanding the dominant underlying dynamics of tropical variability is very important for a more insightful assessment of the robustness of the model results and of its predictive skills. The PIs will examine whether the characteristics of the variability in the models at both interannual and decadal timescales are consistent with some of the proposed dynamical paradigms. The proposed mechanisms invoke ocean processes (wave propagation and/or changes in equatorward mass transport) as the agents that can provide the negative feedbacks necessary for reversing the phase of the equatorial conditions. Both processes (waves and transports) and their relative influence upon tropical conditions will be examined. Dynamical similarities and differences between interannual and decadal timescales will be identified.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
Assessing Tropical Pacific Decadal Variability in Climate Models
Institutions:
Principal Investigators: Michael J. McPhaden, Dongxiao Zhang, PMEL
It is well documented that the decadal variability in the tropical Pacific has substantial effects on marine ecosystems, the carbon cycle, and climate variations world-wide (e.g. Mantua et al. 1997; Trenberth et al. 2002; Feely et al. 2002). The role of tropical Pacific in long-term climate change remains controversial, however. The sensitivity of tropical Pacific to the anthropogenic forcing varies significantly in climate models. While Òpermanent El NinoÓ conditions are simulated in many climate models, La Nina-like conditions are also seen in other simulations (IPCC 2001; Cane et al. 1997; Boer and Yu 2003). In addition, the amplitude of decadal variations is generally smaller than natural variability observed. All of these cast questions on the amplitude of global warming predicted by these climate models. The PIs will investigate the oceanic and atmospheric processes associated with the decadal variability in the tropical Pacific, and their atmospheric and oceanic tele-connections in all the climate models in this program, and compare them to the observation. The PIs focus will be on the upper tropical Pacific above thermocline or pycnocline and the global surface winds, sea level pressure (SLP), and surface temperature. The aim is to quantify trends and the amplitude of decadal and multi-decadal variations in the tropical Pacific in the various climate models and compare these model results with data for the last 50 years. Model-data comparison will be relied on the historical hydrographic data compiled from NODC World Ocean Dataset, newly available WOCE and PMEL hydrographic sections and ARGO float profiles, data from TAO/TRITON moored array, XBTs, and island and coastal tide gauges, as well as NCEP-NCAR reanalysis. Results of the proposed research will have applications to understanding the Pacific decadal variability, and potential links between natural variability to the anthropogenic-induced global warming, thus to improving future climate projection.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
Evaluation of the Coupled Climate Model Simulations over the Arctic
-- Contrasting the Warming in the 1990s versus 1930-50s
James E. Overland1 (PI) and Muyin Wang2
1 NOAA/Pacific Marine Environmental Laboratory,
2 Joint Institute for the Study of the Atmosphere and Ocean, University of Washington
Seattle, Washington
Although coupled Global Climate Models (GCM) predict the largest annual-mean zonal temperature change to be in the Arctic near the surface (1000-900 hPa), uncertainties are also large, which is shown by largest zonal mean temperature change range from the models (Fig. 9.8 of IPCC Report, Scientific Basis). The PIs will investigate whether coupled climate models which reproduce the late 20th century warm anomalies, also produce mid-century warm anomaly events in the Arctic. Their goal is to access the modelsÕ ability to produce Arctic climate and climate change during the 20th century, and to compare the physical mechanisms behind these warming events on a monthly/regional basis through a diagnostic study of the energy budget. This proposal supplements subprojects by G. Ostermeier (NAO/NAM related trends in coupled models) and by Kuzmina (Arctic climate, atmospheric circulation and ocean warming), because the PIs evaluate the modelsÕ performance to capture monthly/regional warm anomaly events (+ 4oC) in addition to large-scale circulation changes.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
Intraseasonal Variabilities: Structure and Feedback Analysis
Jialin Lin, Brian Mapes and Klaus Weickmann NOAA-CIRES Climate Diagnostics Center, Boulder
jialin.lin@noaa.gov
The PIs will undertake a comprehensive and constructive evaluation of the synoptic to intraseasonal variabilities (time-scale 1 day - 100 days) in all three U.S. coupled climate models: NCAR,G FDL and GISS. The emphasis will be on their Madden-Julian Oscillation simulations. The work consists of two parts: (1) evaluation of the general features (variance and propagation) of all equatorially trapped wave modes,and the detailed wave structure of the intraseasonal (30-95 day) mode; and (2) analysis of the feedback mechanisms at the intraseasonal time-scale which may o.er useful guidance on how to improve the model simulation.
This is a grant under the U.S. Climate Change Science ProgramÕs CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
Pacific Subtropical Cell Variability in Coupled Climate Model Simulations of the late 19th- 20th Century
Amy Solomon Principal Investigator NOAA-CIRES Climate Diagnostics Center University of Colorado
Amy.Solomon@noaa.gov
Mike Alexander Co-Principal Investigator NOAA-CIRES
Randall M. Dole, Climate Diagnostics
Observed sea surface temperatures averaged over the tropical Pacific Ocean show a warming trend since the 1970's (e.g. Levitus et al. 2000). Changes in sea surface temperatures (SSTs) in the tropical Pacific have a profound impact on the global climate (e.g. Trenberth et al. 1998). McPhaden and Zhang (2002) suggest that these changes are driven, in part, by transport variations in the Pacific Subtropical Cells (STCs), based on the observed correspondence between a decrease in transport convergence in the equatorial thermocline and an increase in tropical Pacific SSTs (their Figure 2). The STCs are shallow meridional circulation cells in which water flows out of the tropics within the surface layer, subducts in the subtropics, flows equatorward within the thermocline, and upwells in the eastern equatorial ocean (Bryan 1991, see his Figure 2; McCreary and Lu 1994; Liu et al. 1994; Blanke and Raynaud 1996; Rothstein et al. 1996; Lu et al. 1998). The STCs provide a pathway by which extratropical atmospheric variability can force tropical variability through the ocean by temperature anomalies, TÕ, that subduct in the extratropics and upwell at the equator (the VTÕ mechanism) (Gu and Philander 1997) or by transport anomalies, VÕ, that change the amount of water that upwells at the equator (the VÕT mechanism) (Kleeman et al. 1999). In this research the PIs will access how well coupled climate model simulations of the late 19th-20th centuries simulate the observed climate mean and variability of Pacific STCs, as well as, the relationship between tropical Pacific SST and STCs. The VÕT mechanism will be evaluated by comparing off-equatorial meridional transports on isopycnal (density) surfaces, from both the North and South Pacific, to observations. The VTÕ mechanism will be evaluated by comparing water mass properties of the equatorial thermocline to observations. The PIs will construct multi-model ensembles using all available model output in order to estimate confidence intervals of STC variability due to changes in external forcing. The observations used in this analysis will be the Simple Ocean Data Assimilation (Carton et al. 2000a,b). The PIs understand the concerns about using this dataset as observations given the errors based on comparisons with WOCE hydrographic sections (Carton et al. 2000b). However, they feel this dataset provides an adequate estimate of the state of the Pacific upper ocean by assimilating both temperature and salinity. The NCAR Oceanography Section and Dr. Tom Delworth at GFDL have agreed to act as unpaid consultants on this project.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
Diagnoses of Annular Mode Variability
in the IPCC Twentieth Century Simulations
Principal Investigator: Ron Miller, NASA Goddard Institute for Space Studies
rmiller@giss.nasa.gov
Annular modes make a significant contribution to extratropical climate variability at the surface. Forced changes to the annular modes in the coming century could have substantial regional impacts upon climate. The PIs will diagnose annular mode variations for the period 1880-2000 as simulated by 4 coupled general circulation models (CGCMs) whose forecast of 21st century climate will be included in the next assessment of the Intergovernmental Panel of Climate Change (IPCC). They will examine to what extent the simulated annular modes reproduce observed behavior, including spatial extent, decadal variability and trends, and linkage of surface and stratospheric variations. They will also examine the relation of the modes to forcing by volcanic aerosols and stratospheric ozone loss.
This is a grant under the U.S. Climate Change Science Program's CLImate VARiability and Predictability Program (CLIVAR).
ABSTRACT
SGER: Performance-based Probabilistic Multi-Model Climate Change
Scenarios
Lisa Goddard, Columbia University / IRI
This research is addressing the questions: How is anthropogenic forcing
likely to affect regional climate? With what certainty? To what degree?
The work consists of two main parts: (1) Verification of the performance
of 20th Century temporal characteristics, such as the trends in multi-decadal
means and the interannual variability about those means, from the
Atmosphere-Ocean Global Circulation Models (AOGCM)s used for 21st
Century climate change predictions; and, (2) Construction of probabilistic
multi-model scenarios for 21st Century climate and its variability,
using the results from (1) as an objective basis for assigning weights
to the model predictions.
For the verification analysis, a probabilistic skill metric will
be applied to the AOGCM ensembles relative to an ensemble of synthetic
observations, each of which possesses the same temporal characteristics
of the observed climate over the 20th Century. Similarly, sub-sets
of the observations will be used to construct the probability distributions
of the expected skill score. For regions where the probability distributions
of the Monte Carlo skill scores for the AOGCMs and observations are
significantly similar, the model performance for the 20th Century
will be deemed credible.
For the probabilistic multimodel change scenarios, a Bayesian approach
will be applied using the prior assumption that 21st Century variability
may be represented by the observed 20th Century variability. The
analyses will be performed spatially from the grid scale to the regional
scale for seasonal (i.e. 3-month mean) near-surface air temperature
and precipitation.
The results from this research are intended for inclusion in the
Fourth Assessment Report of the Intergovernmental Panel for Climate
Change (IPCC). The methods
employed in this research, applying techniques of multi-model ensembling that
are based on model performance, have not yet been applied in the context of climate
change predictions and can pilot further research for future IPCC reports. The
findings of this research also can be used to set the longer-range context for
seasonal-to-interannual climate variability and predictions. The suggestion here
is that proper synthesis of seasonal forecasts, and longer-term assessments,
taking into account the uncertainties of each, provides the best opportunity
to minimize losses, take advantage of opportunity, and work toward sustainable
practices.
Broader impacts include the training of a post-doc and the societal benefits
to be realized from credible estimates of the performance of climate prediction
models.
This is a grant under the U.S. Climate Change Science Program’s CLImate VARiability and Predictability Program (CLIVAR).