Abstract This paper presents the response to anthropogenic forcing in the GISS‐E2.1 climate models for the 21st century Shared Socioeconomic Pathways emission scenarios within the Coupled Model Intercomparison Project Phase 6 (CMIP6). The experiments were performed using an updated and improved version of the NASA Goddard Institute for Space Studies (GISS) coupled general circulation model that includes two different versions for atmospheric composition: A non‐interactive version (NINT) with prescribed composition and a tuned aerosol indirect effect and the One‐Moment Aerosol model (OMA) version with fully interactive aerosols which includes a parameterized first indirect aerosol effect on clouds. The effective climate sensitivities are 3.0°C and 2.9°C for the NINT and OMA models, respectively. Each atmospheric version is coupled to two different ocean general circulation models: The GISS ocean model (E2.1‐G) and HYCOM (E2.1‐H). We describe the global mean responses for all future scenarios and spatial patterns of change for surface air temperature and precipitation for four of the marker scenarios: SSP1‐2.6, SSP2‐4.5, SSP4‐6.0, and SSP5‐8.5. By 2100, global mean warming ranges from 1.5°C to 5.2°C relative to 1,850–1,880 mean temperature. Two high‐mitigation scenarios SSP1‐1.9 and SSP1‐2.6 limit the surface warming to below 2°C by the end of the 21st century, except for the NINT E2.1‐H model that simulates 2.2°C of surface warming. For the high emission scenario SSP5‐8.5, the range is 4.6–5.2°C at 2100. Due to about 15% larger effective climate sensitivity and stronger transient climate response in both NINT and OMA CMIP6 models compared to CMIP5 versions, there is a stronger warming by 2100 in the SSP emission scenarios than in the comparable Representative Concentration Pathway (RCP) scenarios in CMIP5. Changes in sea ice area are highly correlated to global mean surface air temperature anomalies and show steep declines in both hemispheres, with the largest sea ice area decreases occurring during September in the Northern Hemisphere in both E2.1‐G (−1.21 × 106 km2/°C) and E2.1‐H models (−0.94 × 106 km2/°C). Both coupled models project decreases in the Atlantic overturning stream function by 2100. The largest decrease of 56%–65% in the 21st century overturning stream function is produced in the warmest scenario SSP5‐8.5 in the E2.1‐G model, comparable to the reduction in the corresponding CMIP5 GISS‐E2 RCP8.5 simulation. Both low‐end scenarios SSP1‐1.9 and SSP1‐2.6 also simulate substantial reductions of the overturning (9%–37%) with slow recovery of about 10% by the end of the 21st century (relative to the maximum decrease at the middle of the 21st century).

AbstractSimulations of the CMIP6 historical period 1850–2014, characterized by the emergence of anthropogenic climate drivers like greenhouse gases, are presented for different configurations of the NASA Goddard Institute for Space Studies (GISS) Earth System ModelE2.1. The GISS‐E2.1 ensembles are more sensitive to greenhouse gas forcing than their CMIP5 predecessors (GISS‐E2) but warm less during recent decades due to a forcing reduction that is attributed to greater longwave opacity in the GISS‐E2.1 pre‐industrial simulations. This results in an atmosphere less sensitive to increases in opacity from rising greenhouse gas concentrations, demonstrating the importance of the base climatology to forcing and forced climate trends. Most model versions match observed temperature trends since 1979 from the ocean to the stratosphere. The choice of ocean model is important to the transient climate response, as found previously in CMIP5 GISS‐E2: the model that more efficiently exports heat to the deep ocean shows a smaller rise in tropospheric temperature. Model sea level rise over the historical period is traced to excessive drawdown of aquifers to meet irrigation demand with a smaller contribution from thermal expansion. This shows how fully coupled models can provide indirect observational constraints upon forcing, in this case, constraining irrigation rates with observed sea level changes. The overall agreement of GISS‐E2.1 with observed trends is familiar from evaluation of its predecessors, as is the conclusion that these trends are almost entirely anthropogenic in origin.

We introduce a new climate model (GISS E2.2) that has been specially optimized for the middle atmosphere and whose output is being contributed to the CMIP6 archive. The top of the model is at a geopotential altitude of 89 km, and parameterizations of moist convection and various forms of gravity wave drag based on tropospheric processes are chosen specifically for this optimization. We first evaluate the model in its configuration as a coupled atmosphere‐chemistry model with respect to its simulation of the mean state of the middle atmosphere, from the mesosphere down through the upper troposphere/lower stratosphere. Then we assess its use as a coupled atmosphere‐ocean climate model by exploring its mean ocean climatology. To evaluate its variability, we report on its simulation of the primary modes in the troposphere, stratosphere, and ocean. Two climate change simulations are presented, the responses to instantaneous increases of 2xCO2 and 4xCO2, run with two different ocean models. Sensitivity studies are performed to illustrate the effect of parameterizations on the model results. We compare these results to the lower vertical resolution/top GISS Model E2.1, whose output has also been submitted to CMIP6. The different choices made for these models are explored. It is shown that important improvements in the circulation above and below the tropopause can be obtained when attention is paid to representation of middle atmosphere processes in climate model development.

AbstractThis paper describes the GISS‐E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS‐E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden‐Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7–3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks.

This paper is dedicated to Wally Broecker, the "father of global warming", whose inquisitive mind has stimulated much of the world"s research aimed at understanding global climate.

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.

Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate 1 Modeling, and Modern Observations that 2°C Global Warming Could Be Dangerous 2 3 James Hansen 1 , Makiko Sato 1 , Paul Hearty 2 , Reto Ruedy 3,4 , Maxwell Kelley 3,4 , Valerie Masson-Delmotte 5 , Gary Russell 4 , 4 George Tselioudis 4 , Junji Cao 6 , Eric Rignot 7,8 , Isabella Velicogna 8,7 , Blair Tormey 9 , Bailey Donovan 10 , Evgeniya 5 Kandiano 11 , Karina von Schuckmann 12 , Pushker Kharecha 1,4 , Allegra N. Legrande 4 , Michael Bauer 13,4 , Kwok-Wai Lo 3,4 6 7 Abstract. We use numerical climate simulations, paleoclimate data, and modern observations to 8 study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize 9 the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and 10 ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in 11 the Southern Ocean and North Atlantic, thus increasing Earth’s energy imbalance and heat flux 12 into most of the global ocean’s surface. Southern Ocean surface cooling, while lower latitudes 13 are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, 14 slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice 15 sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that 16 ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better 17 approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 18 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling 19 times are near the lower end of the 10-40 year range, but the record is too short to confirm the 20 nature of the response. The feedbacks, including subsurface ocean warming, help explain 21 paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, 22 which in turn exercised tight control on global temperature and sea level. The millennial (50023 2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change and 24 thus the time scale for paleo global climate, ice sheet, and sea level changes, but this paleo 25 millennial time scale should not be misinterpreted as the time scale for ice sheet response to a 26 rapid large human-made climate forcing. These climate feedbacks aid interpretation of events 27 late in the prior interglacial, when sea level rose to +6-9 meters with evidence of extreme storms 28 while Earth was less than 1°C warmer than today. Ice melt cooling of the North Atlantic and 29 Southern Oceans, increases atmospheric temperature gradients, eddy kinetic energy and 30 baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and 31 ongoing observations together imply that 2°C global warming above the preindustrial level could 32 be dangerous. Continued high fossil fuel emissions this century are predicted to yield: (1) 33 cooling of the Southern Ocean, especially in the Western Hemisphere, (2) slowing of the 34 Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass 35 loss, (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of 36 the North Atlantic region, (4) increasingly powerful storms, and (5) nonlinearly growing sea 37

Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate 1 Modeling, and Modern Observations Implies that 2°C Global Warming Above the 2 Preindustrial Level Would Be Dangerous 3 4 James Hansen, Makiko Sato, Paul Hearty, Reto Ruedy, Maxwell Kelley, Valerie Masson-Delmotte, Gary Russell, 5 George Tselioudis, Junji Cao, Eric Rignot, Isabella Velicogna, Blair Tormey, Bailey Donovan, Evgeniya 6 Kandiano, Karina von Schuckmann, Pushker Kharecha, Allegra N. Legrande, Michael Bauer, Kwak-Wai Lo 7 8 Abstract. We use numerical climate simulations, paleoclimate data, and modern observations to 9 study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize 10 the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and 11 ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in 12 the Southern Ocean and North Atlantic, thus increasing Earth’s energy imbalance and heat flux 13 into most of the global ocean’s surface. Southern Ocean surface cooling, while lower latitudes 14 are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, 15 slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice 16 sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that 17 ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better 18 approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 19 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling 20 times are near the lower end of the 10-40 year range, but the record is too short to confirm the 21 nature of the response. The feedbacks, including subsurface ocean warming, help explain 22 paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, 23 which in turn exercised tight control on global temperature and sea level. The millennial (50024 2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change and 25 thus the time scale for paleo global climate, ice sheet, and sea level changes, but this paleo 26 millennial time scale should not be misinterpreted as the time scale for ice sheet response to a 27 rapid large human-made climate forcing. These climate feedbacks aid interpretation of events 28 late in the prior interglacial, when sea level rose to +6-9 meters with evidence of extreme storms 29 while Earth was less than 1°C warmer than today. Ice melt cooling of the North Atlantic and 30 Southern Oceans, increases atmospheric temperature gradients, eddy kinetic energy and 31 baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and 32 ongoing observations together imply that 2°C global warming above the preindustrial level 33 would be dangerous. Continued high fossil fuel emissions this century are predicted to yield: (1) 34 cooling of the Southern Ocean, especially in the Western Hemisphere, (2) slowing of the 35 Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass 36 loss, (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of 37

The NASA Modeling, Analysis, and Prediction (MAP) Climatology of Mid-Latitude Storm Area (MCMS) project is a set of tools for examining midlatitude cyclones in model-generated data. The MCMS software has two primary tasks. The first task identifies and tracks likely cyclones in sea level pressure fields. Special care is taken to minimize the known problems of this approach near steep or high topography. The second task finds the outermost closed pressure contour that uniquely surrounds each cyclone center, or collection of centers in the case of multicenter cyclones. This enclosed area is then used as a rough proxy for the domain over which a cyclone influences its immediate environment. Here the MCMS software is applied to several decades of re-analysis data. These results are shown to be consistent with the findings of a recent intercomparison of cyclone-finding methods. Besides providing details concerning cyclone storm area, the MCMS software departs from other cyclone-finding methods by providing a comprehensive record concerning every cyclone it processes. The MCMS software also provides extensive diagnostics about the actions of specific operations (filters) and adjustable parameters. The benefits of this accounting are demonstrated and discussed, as are those related to the use of cyclone storm area as a tool for climate research. MCMS datasets are available for several reanalysis products, as is the MCMS software itself, including the source code needed to generate new MCMS datasets and utilities for working with existing ones.

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth’s energy imbalance and heat flux into most of the global ocean’s surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40 year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (5002000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change and thus the time scale for paleo global climate, ice sheet, and sea level changes, but this paleo millennial time scale should not be misinterpreted as the time scale for ice sheet response to a rapid large human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 meters with evidence of extreme storms while Earth was less than 1°C warmer than today. Ice melt cooling of the North Atlantic and Southern Oceans, increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2°C global warming above the preindustrial level would be dangerous. Continued high fossil fuel emissions this century are predicted to yield: (1) cooling of the Southern Ocean, especially in the Western Hemisphere, (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss, (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region, (4) increasingly powerful storms, and (5) nonlinearly growing sea 1 Climate Science, Awareness and Solutions, Columbia University Earth Institute, New York, NY 10115, USA 2 Department of Environmental Studies, University of North Carolina at Wilmington, North Carolina 28403, USA 3 Trinnovium LLC, New York, NY 10025, USA 4 NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA 5 Institut Pierre Simon Laplace, Laboratoire des Sciences du Climat et de l’Environnement (CEA-CNRS-UVSQ), Gif-sur-Yvette, France 6 Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China 7 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 91109, USA 8 Department of Earth System Science, University of California, Irvine, California, 92697, USA 9 Program for the Study of Developed Shorelines, Western Carolina University, Cullowhee, NC 28723, USA 10 Department of Geological Sciences, East Carolina University, Greenville, NC 27858, USA 11 GEOMAR, Helmholtz Centre for Ocean Research, Wischhofstrasse 1-3, Kiel 24148, Germany 12 Mediterranean Institut of Oceanography, University of Toulon, La Garde, France 13 Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA 2 level rise, reaching several meters over a time scale of 50-150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.

Observations of climate change during the CMIP5 extended historical period (1850–2012) are compared to trends simulated by six versions of the NASA Goddard Institute for Space Studies ModelE2 Earth System Model. The six models are constructed from three versions of the ModelE2 atmospheric general circulation model, distinguished by their treatment of atmospheric composition and the aerosol indirect effect, combined with two ocean general circulation models, HYCOM and Russell. Forcings that perturb the model climate during the historical period are described. Five-member ensemble averages from each of the six versions of ModelE2 simulate trends of surface air temperature, atmospheric temperature, sea ice and ocean heat content that are in general agreement with observed trends, although simulated warming is slightly excessive within the past decade. Only simulations that include increasing concentrations of long-lived greenhouse gases match the warming observed during the twentieth century. Differences in twentieth-century warming among the six model versions can be attributed to differences in climate sensitivity, aerosol and ozone forcing, and heat uptake by the deep ocean. Coupled models with HYCOM export less heat to the deep ocean, associated with reduced surface warming in regions of deepwater formation, but greater warming elsewhere at high latitudes along with reduced sea ice. All ensembles show twentieth-century annular trends toward reduced surface pressure at southern high latitudes and a poleward shift of the midlatitude westerlies, consistent with observations.

We present a description of the ModelE2 version of the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) and the configurations used in the simulations performed for the Coupled Model Intercomparison Project Phase 5 (CMIP5). We use six variations related to the treatment of the atmospheric composition, the calculation of aerosol indirect effects, and ocean model component. Specifically, we test the difference between atmospheric models that have noninteractive composition, where radiatively important aerosols and ozone are prescribed from precomputed decadal averages, and interactive versions where atmospheric chemistry and aerosols are calculated given decadally varying emissions. The impact of the first aerosol indirect effect on clouds is either specified using a simple tuning, or parameterized using a cloud microphysics scheme. We also use two dynamic ocean components: the Russell and HYbrid Coordinate Ocean Model (HYCOM) which differ significantly in their basic formulations and grid. Results are presented for the climatological means over the satellite era (1980–2004) taken from transient simulations starting from the preindustrial (1850) driven by estimates of appropriate forcings over the 20th Century. Differences in base climate and variability related to the choice of ocean model are large, indicating an important structural uncertainty. The impact of interactive atmospheric composition on the climatology is relatively small except in regions such as the lower stratosphere, where ozone plays an important role, and the tropics, where aerosol changes affect the hydrological cycle and cloud cover. While key improvements over previous versions of the model are evident, these are not uniform across all metrics.

We present a description of the ModelE2 version of the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) and the configurations used in the simulations performed for the Coupled Model Intercomparison Project Phase 5 (CMIP5). We use six variations related to the treatment of the atmospheric composition, the calculation of aerosol indirect effects, and ocean model component. Specifically, we test the difference between atmospheric models that have noninteractive composition, where radiatively important aerosols and ozone are prescribed from precomputed decadal averages, and interactive versions where atmospheric chemistry and aerosols are calculated given decadally varying emissions. The impact of the first aerosol indirect effect on clouds is either specified using a simple tuning, or parameterized using a cloud microphysics scheme. We also use two dynamic ocean components: the Russell and HYbrid Coordinate Ocean Model (HYCOM) which differ significantly in their basic formulations and grid. Results are presented for the climatological means over the satellite era (1980–2004) taken from transient simulations starting from the preindustrial (1850) driven by estimates of appropriate forcings over the 20th Century. Differences in base climate and variability related to the choice of ocean model are large, indicating an important structural uncertainty. The impact of interactive atmospheric composition on the climatology is relatively small except in regions such as the lower stratosphere, where ozone plays an important role, and the tropics, where aerosol changes affect the hydrological cycle and cloud cover. While key improvements over previous versions of the model are evident, these are not uniform across all metrics.

Many of the aspects of the climate system that are of the greatest interest (e.g., the sensitivity of the system to external forcings) are emergent properties that arise via the complex interplay between disparate processes. This is also true for climate models most diagnostics are not a function of an isolated portion of source code, but rather are affected by multiple components and procedures. Thus any model-observation mismatch is hard to attribute to any specific piece of code or imperfection in a specific model assumption. An alternative approach is to identify diagnostics that are more closely tied to specific processes -- implying that if a mismatch is found, it should be much easier to identify and address specific algorithmic choices that will improve the simulation. However, this approach requires looking at model output and observational data in a more sophisticated way than the more traditional production of monthly or annual mean quantities. The data must instead be filtered in time and space for examples of the specific process being targeted.We are developing a data analysis environment called PROcess-Based Explorer (PROBE) that seeks to enable efficient and systematic computation of process-based diagnostics on very large sets of data. In this environment, investigators can define arbitrarily complex filters and then seamlessly perform computations in parallel on the filtered output from their model. The same analysis can be performed on additional related data sets (e.g., reanalyses) thereby enabling routine comparisons between model and observational data. PROBE also incorporates workflow technology to automatically update computed diagnostics for subsequent executions of a model. In this presentation, we will discuss the design and current status of PROBE as well as share results from some preliminary use cases.

We analyze daily wintertime cyclone variability in the central and eastern Mediterranean during 1958–2001 and identify four distinct “cyclone states,” corresponding to the presence or absence of cyclones in each basin. Each cyclone state is associated with wind flows that induce characteristic patterns of cooling via turbulent (sensible and latent) heat fluxes in the eastern Mediterranean basin and Aegean Sea. The relative frequency of occurrence of each state determines the heat loss from the Aegean Sea during that winter, with largest heat losses occurring when there is a storm in the eastern but not central Mediterranean (eNOTc) and the smallest occurring when there is a storm in the central but not eastern Mediterranean (cNOTe). Time series of daily cyclone states for each winter allow us to infer Aegean Sea cooling for winters prior to 1985, the earliest year for which we have daily heat flux observations. We show that cyclone states conducive to Aegean Sea convection occurred in 1991/1992 and 1992/1993, the winters during which deepwater formation was observed in the Aegean Sea, and also during the mid-1970s and the winters of 1963/1964 and 1968/1969. We find that the eNOTc cyclone state is anticorrelated with the North Atlantic Oscillation (NAO) prior to 1977/1978. After 1977/1978, the cNOTe state is anticorrelated with both the NAO and the North Caspian Pattern, showing that the area of influence of large-scale atmospheric teleconnections on regional cyclone activity shifted from the eastern to the central Mediterranean during the late 1970s. A trend toward more frequent occurrence of the positive phase of the NAO produced less frequent cNOTe states since the late 1970s, increasing the number of days with strong cooling of the Aegean Sea surface waters.

Hydrographic observations indicated a shift of the main deep water formation in the Mediterranean Sea from its usual location in the Adriatic Sea to the Aegean Sea during the late 1980s and early 1990s, during winters 1991/1992 and 1992/1993. This event is known as the Eastern Mediterranean Transient (EMT). We report here a connection between EMT and specific atmospheric conditions which created anomalously large buoyancy fluxes from the Aegean Sea during winters 1991/1992 and 1992/1993 (the “enhanced EMT winters”). We use newly available, state of the art datasets with high space and time resolution and show that atypical cyclonic activity in the central Mediterranean versus the eastern basin produced the enhanced atmospheric forcing which intensified the EMT. An abatement of the frequency of cyclones in the central Mediterranean during 1992/1993 drastically reduced the northward advection of warm air over the Aegean Sea compared to more typical years, while an increase in the frequency of cyclones in the eastern Mediterranean enhanced the southward advection of cold air over the Aegean Sea, especially during 1991/1992. These changes significantly increased buoyancy flux losses from the Aegean Sea during the enhanced EMT winters, intensifying deep water production.

Cloud vertical distributions across extratropical warm and cold fronts are obtained using two consecutive winters of CloudSat-Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations and National Centers for Environmental Prediction reanalysis atmospheric state parameters over the Northern and Southern Hemisphere oceans (30 degrees-70 degrees N/S) between November 2006 and September 2008. These distributions generally resemble those from the original model introduced by the Bergen School in the 1920s, with the following exceptions: 1) substantial low cloudiness, which is present behind and ahead of the warm and cold fronts; 2) ubiquitous high cloudiness, some of it very thin, throughout the warm-frontal region; and 3) upright convective cloudiness near and behind some warm fronts. One winter of GISS general circulation model simulations of Northern and Southern Hemisphere warm and cold fronts at 2 degrees X 2.5 degrees X 32 levels resolution gives similar cloud distributions but with much lower cloud fraction, a shallower depth of cloudiness, and a shorter extent of tilted warm-frontal cloud cover on the cold air side of the surface frontal position. A close examination of the relationship between the cloudiness and relative humidity fields indicates that water vapor is not lifted enough in modeled midlatitude cyclones and this is related to weak vertical velocities in the model. The model also produces too little cloudiness for a given value of vertical velocity or relative humidity. For global climate models run at scales coarser than tens of kilometers, the authors suggest that the current underestimate of modeled cloud cover in the storm track regions, and in particular the 50 degrees-60 degrees S band of the Southern Oceans, could be reduced with the implementation of a slantwise convection parameterization.