Quantitative Sensitivity Analysis of Physical Parameterizations for Cases of Deep Convection in the NASA GEOS-5

Abstract Parameterization of processes that occur on length scales too small to resolve on a computational grid is a major source of uncertainty in global climate models. This study investigates the relative importance of a number of parameters used in the Goddard Earth Observing System Model, version 5 (GEOS-5), atmospheric general circulation model, focusing on cloud, convection, and boundary layer parameterizations. Latin hypercube sampling is used to generate a few hundred sets of 19 candidate physics parameters, which are subsequently used to generate ensembles of single-column model realizations of cloud content, precipitation, and radiative fluxes for four different field campaigns. A Gaussian process model is then used to create a computationally inexpensive emulator for the simulation code that can be used to determine a measure of relative parameter sensitivity by sampling the response surface for a very large number of input parameter sets. Parameter sensitivities are computed for different geographic locations and seasons to determine whether the intrinsic sensitivity of the model parameterizations changes with season and location. The results indicate the same subset of parameters collectively control the model output across all experiments, independent of changes in the environment. These are the threshold relative humidity for cloud formation, the ice fall speeds, convective and large-scale autoconversion, deep convection relaxation time scale, maximum convective updraft diameter, and minimum ice effective radius. However, there are differences in the degree of parameter sensitivity between continental and tropical convective cases, as well as systematic changes in the degree of parameter influence and parameter–parameter interaction.

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The impact of precipitation evaporation on the atmospheric aerosol distribution in EC-Earth v3.2.0

Geoscientific Model Development ◽

10.5194/gmd-11-1443-2018 ◽

2018 ◽

Vol 11 (4) ◽

pp. 1443-1465 ◽

Cited By ~ 3

Author(s):

Marco de Bruine ◽

Maarten Krol ◽

Twan van Noije ◽

Philippe Le Sager ◽

Thomas Röckmann

Keyword(s):

General Circulation ◽

Large Scale ◽

Climate Models ◽

Circulation Model ◽

Global Climate Models ◽

Orthogonal Polarization ◽

Earth Model ◽

Climate Projections ◽

Aerosol Distribution ◽

The Impact

Abstract. The representation of aerosol–cloud interaction in global climate models (GCMs) remains a large source of uncertainty in climate projections. Due to its complexity, precipitation evaporation is either ignored or taken into account in a simplified manner in GCMs. This research explores various ways to treat aerosol resuspension and determines the possible impact of precipitation evaporation and subsequent aerosol resuspension on global aerosol burdens and distribution. The representation of aerosol wet deposition by large-scale precipitation in the EC-Earth model has been improved by utilising additional precipitation-related 3-D fields from the dynamical core, the Integrated Forecasting System (IFS) general circulation model, in the chemistry and aerosol module Tracer Model, version 5 (TM5). A simple approach of scaling aerosol release with evaporated precipitation fraction leads to an increase in the global aerosol burden (+7.8 to +15 % for different aerosol species). However, when taking into account the different sizes and evaporation rate of raindrops following Gong et al. (2006), the release of aerosols is strongly reduced, and the total aerosol burden decreases by −3.0 to −8.5 %. Moreover, inclusion of cloud processing based on observations by Mitra et al. (1992) transforms scavenged small aerosol to coarse particles, which enhances removal by sedimentation and hence leads to a −10 to −11 % lower aerosol burden. Finally, when these two effects are combined, the global aerosol burden decreases by −11 to −19 %. Compared to the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations, aerosol optical depth (AOD) is generally underestimated in most parts of the world in all configurations of the TM5 model and although the representation is now physically more realistic, global AOD shows no large improvements in spatial patterns. Similarly, the agreement of the vertical profile with Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite measurements does not improve significantly. We show, however, that aerosol resuspension has a considerable impact on the modelled aerosol distribution and needs to be taken into account.

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Improved simulation of clouds over the Southern Ocean in a General Circulation Model

10.5194/acp-2019-884 ◽

2019 ◽

Author(s):

Vidya Varma ◽

Olaf Morgenstern ◽

Paul Field ◽

Kalli Furtado ◽

Jonny Williams ◽

...

Keyword(s):

Southern Ocean ◽

General Circulation ◽

Climate Models ◽

Circulation Model ◽

Supercooled Liquid ◽

Short Wave ◽

Global Climate Models ◽

Ice Crystals ◽

Wave Radiation ◽

Short Wave Radiation

Abstract. The present generation of global climate models is characterized by insufficient reflection of short-wave radiation over the Southern Ocean due to a misrepresentation of clouds. This is a significant concern as it leads to excessive heating of the ocean surface, sea surface temperature biases, and subsequent problems with atmospheric dynamics. In this study we modify cloud micro-physics in a recent version of the Met Office's Unified Model and show that choosing a more realistic value for the shape parameter of atmospheric ice-crystals, in better agreement with theory and observations, benefits the simulation of short-wave radiation. In the model, for calculating the growth rate of ice crystals through deposition, the default assumption is that all ice particles are spherical in shape. We modify this assumption to effectively allow for oblique shapes or aggregates of ice crystals. Along with modified ice nucleation temperatures, we achieve a reduction in the annual-mean short-wave cloud radiative effect over the Southern Ocean by up to 4 W/m2, and seasonally much larger reductions. By slowing the growth of the ice phase, the model simulates substantially more supercooled liquid cloud. We hypothesize that such abundant supercooled liquid cloud is the result of a paucity of ice nucleating particles in this part of the atmosphere.

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Cloud Vertical Distribution across Warm and Cold Fronts in CloudSat–CALIPSO Data and a General Circulation Model

Journal of Climate ◽

10.1175/2010jcli3282.1 ◽

2010 ◽

Vol 23 (12) ◽

pp. 3397-3415 ◽

Cited By ~ 56

Author(s):

Catherine M. Naud ◽

Anthony D. Del Genio ◽

Mike Bauer ◽

William Kovari

Keyword(s):

Relative Humidity ◽

Southern Hemisphere ◽

General Circulation Model ◽

General Circulation ◽

Cloud Cover ◽

Climate Models ◽

Storm Track ◽

Circulation Model ◽

Global Climate Models ◽

Cold Fronts

Abstract 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°–70°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° × 2.5° × 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°–60°S band of the Southern Oceans, could be reduced with the implementation of a slantwise convection parameterization.

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Past and future trends in large-scale atmospheric circulations over Europe: Assessment of the Jenkinson-Collison classification with reanalyses and CMIP6.

10.5194/dkt-12-32 ◽

2020 ◽

Author(s):

Pedro Herrera-Lormendez ◽

Nikolaos Mastrantonas ◽

Jörg Matschullat ◽

Hervé Douville

Keyword(s):

General Circulation ◽

Large Scale ◽

Western Europe ◽

Climate Models ◽

Global Climate ◽

Coupled Model ◽

Global Climate Models ◽

Extreme Weather Events ◽

Dynamical Response ◽

Weather Patterns

Circulation classifications are a simple tool given their ability to portray aspects of day-to-day weather. As we start facing a dynamical response in general circulation patterns due to anthropogenic global warming, circulation changes can enhance or mitigate regional and local behaviour of extreme weather events. A weather type (WT) automatic classification, developed by Jenkinson-Collison (JC), is used to evaluate past and future changes in the seasonal frequencies of synoptic weather patterns over central and western Europe. A set of three reanalyses and four Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) are used, based on daily Sea Level Pressure (SLP) data. Discrepancies are found in the model outputs as they fall short of capturing interannual variabilities when compared to the reanalyses. Cyclonic and westerly circulations tend to be overestimated, whereas anticyclonics are underestimated. The projected frequencies, based on the Shared Socioeconomic Pathway 5 (SSP5) experiment, suggest significant increasing trends for unclassified WT (characterized by weak pressure gradients) during their summer half-year persistency for the coming 21st century. Winter trends indicate a surge in westerlies and a reduction in the events of cyclonic circulations and easterly flows. The results of this study support evidence of emergent changes in the occurrence of major synoptic configurations over Europe.

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Effects of Cloud Microphysics on Tropical Atmospheric Hydrologic Processes and Intraseasonal Variability

Journal of Climate ◽

10.1175/jcli3561.1 ◽

2005 ◽

Vol 18 (22) ◽

pp. 4731-4751 ◽

Cited By ~ 20

Author(s):

K. M. Lau ◽

H. T. Wu ◽

Y. C. Sud ◽

G. K. Walker

Keyword(s):

General Circulation ◽

Large Scale ◽

Water Cycle ◽

Deep Convection ◽

Intraseasonal Variability ◽

Lower Troposphere ◽

Circulation Model ◽

Cloud Microphysics ◽

Hydrologic Processes ◽

Warm Rain

Abstract The sensitivity of tropical atmospheric hydrologic processes to cloud microphysics is investigated using the NASA Goddard Earth Observing System (GEOS) general circulation model (GCM). Results show that a faster autoconversion rate leads to (a) enhanced deep convection in the climatological convective zones anchored to tropical land regions; (b) more warm rain, but less cloud over oceanic regions; and (c) an increased convective-to-stratiform rain ratio over the entire Tropics. Fewer clouds enhance longwave cooling and reduce shortwave heating in the upper troposphere, while more warm rain produces more condensation heating in the lower troposphere. This vertical differential heating destabilizes the tropical atmosphere, producing a positive feedback resulting in more rain and an enhanced atmospheric water cycle over the Tropics. The feedback is maintained via secondary circulations between convective tower and anvil regions (cold rain), and adjacent middle-to-low cloud (warm rain) regions. The lower cell is capped by horizontal divergence and maximum cloud detrainment near the freezing–melting (0°C) level, with rising motion (relative to the vertical mean) in the warm rain region connected to sinking motion in the cold rain region. The upper cell is found above the 0°C level, with induced subsidence in the warm rain and dry regions, coupled to forced ascent in the deep convection region. It is that warm rain plays an important role in regulating the time scales of convective cycles, and in altering the tropical large-scale circulation through radiative–dynamic interactions. Reduced cloud–radiation feedback due to a faster autoconversion rate results in intermittent but more energetic eastward propagating Madden–Julian oscillations (MJOs). Conversely, a slower autoconversion rate, with increased cloud radiation produces MJOs with more realistic westward-propagating transients embedded in eastward-propagating supercloud clusters. The implications of the present results on climate change and water cycle dynamics research are discussed.

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Hydroclimate variability in Scandinavia over the last millennium – insights from a climate model-proxy data comparison

10.5194/cp-2017-36 ◽

2017 ◽

Cited By ~ 1

Author(s):

Kristina Seftigen ◽

Hugues Goosse ◽

Francois Klein ◽

Deliang Chen

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Global Climate ◽

Model Performance ◽

Circulation Model ◽

Global Climate Models ◽

Last Millennium ◽

Atmospheric Variability ◽

Out Of Sample

Abstract. The integration of climate proxy information with General Circulation Model (GCM) results offers considerable potential for deriving greater understanding of the mechanisms underlying climate variability, as well as unique opportunities for out-of-sample evaluations of model performance. In this study, we combine insights from a new tree-ring hydroclimate reconstruction from Scandinavian with projections from a suite of forced transient simulations of the last millennium and historical intervals from the CMIP5 and PMIP3 archives. Model simulations and proxy reconstruction data are found to broadly agree on the modes of atmospheric variability that produces droughts/pluvials in the region. But despite these dynamical similarities, large differences between simulated and reconstructed hydroclimate time series remain. We find simulated interannual components of variability to be overestimated, while the multidecadal/longer timescale components generally are too weak. Specifically, summertime moisture variability and temperature are weakly negatively associated at inter-annual timescales but positively correlated at decadal timescales, revealed from observational and proxy evidences. On this background, the CMIP5/PMIP3 simulated timescale dependent relationship between regional precipitation and temperature is considerably biased, because the short-term negative association is overestimated, and the long-term relationship is significantly underestimated. The lack of adequate understanding for mechanisms linking temperature and moisture supply on longer timescales has important implication for future projections. Weak multidecadal variability in models also implies that inference about future persistent droughts and pluvials based on the latest generation global climate models will likely underestimate the true risk of these events.

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Constraints on Cumulus Parameterization from Simulations of Observed MJO Events

Journal of Climate ◽

10.1175/jcli-d-14-00832.1 ◽

2015 ◽

Vol 28 (16) ◽

pp. 6419-6442 ◽

Cited By ~ 46

Author(s):

Anthony D. Del Genio ◽

Jingbo Wu ◽

Audrey B. Wolf ◽

Yonghua Chen ◽

Mao-Sung Yao ◽

...

Keyword(s):

General Circulation ◽

Large Scale ◽

Deep Convection ◽

Circulation Model ◽

Longwave Radiation ◽

Tropical Rainfall Measuring Mission ◽

Cumulus Parameterization ◽

Cold Pools ◽

Atmospheric Radiation Measurement ◽

Goddard Institute

Abstract Two recent activities offer an opportunity to test general circulation model (GCM) convection and its interaction with large-scale dynamics for observed Madden–Julian oscillation (MJO) events. This study evaluates the sensitivity of the Goddard Institute for Space Studies (GISS) GCM to entrainment, rain evaporation, downdrafts, and cold pools. Single Column Model versions that restrict weakly entraining convection produce the most realistic dependence of convection depth on column water vapor (CWV) during the Atmospheric Radiation Measurement MJO Investigation Experiment at Gan Island. Differences among models are primarily at intermediate CWV where the transition from shallow to deeper convection occurs. GCM 20-day hindcasts during the Year of Tropical Convection that best capture the shallow–deep transition also produce strong MJOs, with significant predictability compared to Tropical Rainfall Measuring Mission data. The dry anomaly east of the disturbance on hindcast day 1 is a good predictor of MJO onset and evolution. Initial CWV there is near the shallow–deep transition point, implicating premature onset of deep convection as a predictor of a poor MJO simulation. Convection weakly moistens the dry region in good MJO simulations in the first week; weakening of large-scale subsidence over this time may also affect MJO onset. Longwave radiation anomalies are weakest in the worst model version, consistent with previous analyses of cloud/moisture greenhouse enhancement as the primary MJO energy source. The authors’ results suggest that both cloud-/moisture-radiative interactions and convection–moisture sensitivity are required to produce a successful MJO simulation.

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Improving the Southern Ocean cloud albedo biases in a general circulation model

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-7741-2020 ◽

2020 ◽

Vol 20 (13) ◽

pp. 7741-7751

Author(s):

Vidya Varma ◽

Olaf Morgenstern ◽

Paul Field ◽

Kalli Furtado ◽

Jonny Williams ◽

...

Keyword(s):

Southern Ocean ◽

General Circulation ◽

Climate Models ◽

Circulation Model ◽

Short Wave ◽

Cloud Microphysics ◽

Global Climate Models ◽

Ice Crystals ◽

Wave Radiation ◽

Short Wave Radiation

Abstract. The present generation of global climate models is characterised by insufficient reflection of short-wave radiation over the Southern Ocean due to a misrepresentation of clouds. This is a significant concern as it leads to excessive heating of the ocean surface, sea surface temperature biases and subsequent problems with atmospheric dynamics. In this study, we modify cloud microphysics in a recent version of the Met Office's Unified Model and show that choosing a more realistic value for the shape parameter of atmospheric ice crystals, in better agreement with theory and observations, benefits the simulation of short-wave radiation. In the model, for calculating the growth rate of ice crystals through deposition, the default assumption is that all ice particles are spherical in shape. We modify this assumption to effectively allow for oblique shapes or aggregates of ice crystals. Along with modified ice nucleation temperatures, we achieve a reduction in the annual-mean short-wave cloud radiative effect over the Southern Ocean by up to ∼4 W m−2 and seasonally much larger reductions compared to the control model. By slowing the growth of the ice phase, the model simulates substantially more supercooled liquid cloud.

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Assessing the performance of 33 CMIP6 models in simulating the large-scale environmental fields of tropical cyclones

10.21203/rs.3.rs-339002/v1 ◽

2021 ◽

Author(s):

Ying Han ◽

Mengzhuo Zhang ◽

Zhongfeng Xu ◽

Weidong Guo

Keyword(s):

Interannual Variability ◽

Tropical Cyclones ◽

General Circulation ◽

Large Scale ◽

Evaluation Method ◽

Climate Models ◽

Circulation Model ◽

Horizontal Resolution ◽

Vertical Shear ◽

Multiple Variables

Abstract General circulation model (GCM) biases are one of the important sources of biases and uncertainty in dynamic downscaling–based simulations. The ability of regional climate models to simulate tropical cyclones (TCs) is strongly affected by the ability of GCMs to simulate the large-scale environmental field. Thus, in this work, we employ a recently developed multivariable integrated evaluation method to assess the performance of 33 CMIP6 (phase 6 of the Coupled Model Intercomparison Project) models in simulating multiple fields. The CMIP6 models are quantitatively evaluated against two reanalysis datasets over five ocean areas. The results show that most of the CMIP6 models overestimate the mid-level humidity in almost all tropical oceans. The multi-model ensemble mean overestimates the vertical shear of the horizontal winds in the Northeast Pacific and North Atlantic. An increase in model horizontal resolution appears to be helpful in improving the model simulations. For example, there are 6–8 models with higher resolution among the top 10 models in terms of overall model performance in simulating the climatology and interannual variability of multiple variables. Similarly, there are 7–8 models with lower resolution among the bottom 10 patterns. The model skill varies depending on the region and variable being evaluated. Although no model performs best in all regions and for all variables, some models do show relatively good capability in simulating the large-scale environmental field of TCs. For example, the MPI-ESM1-2-LR, MPI-ESM1-2-HR, and FIO-ESM-2-0 models show relatively good skill in simulating the climatology and interannual variability of the large-scale environmental field in the Northern and Southern Hemispheres.

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Past and future trends in large-scale atmospheric circulations over Europe: Assessment of the Jenkinson-Collison classification with reanalyses and CMIP6

10.5194/egusphere-egu21-3150 ◽

2021 ◽

Author(s):

Pedro Herrera-Lormendez ◽

Jörg Matschullat ◽

Hervé Douville

Keyword(s):

General Circulation ◽

Large Scale ◽

Western Europe ◽

Climate Models ◽

Global Climate ◽

Coupled Model ◽

Global Climate Models ◽

Extreme Weather Events ◽

Dynamical Response ◽

Weather Patterns

Circulation classifications are a simple tool given their ability to portray aspects of day-to-day weather. As we start facing a dynamical response in general circulation patterns due to anthropogenic global warming, circulation changes can enhance or mitigate regional and local behaviour of extreme weather events.An automatic weather type (WT) classification, developed by Jenkinson-Collison, is used to evaluate past and future changes in seasonal frequencies of synoptic weather patterns over central and western Europe. A set of three reanalyses and eight Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) are used, based on daily Sea Level Pressure (SLP) data.Discrepancies are found in some of the model outputs as some fall short of capturing interannual variabilities when compared to reanalyses. Cyclonic and westerly circulations tend to be overestimated, whereas anticyclonic are underestimated.Based on the historical data and Shared Socioeconomic Pathway 5 (SSP5-8.5) scenario, the evaluated trends suggest more robust signals during the summer half-years given their lesser synoptic-scale variability. During this season, increasing frequencies are found for the WT characterized by weak pressure gradients, mostly at the expense of decreasing frequencies of the westerlies. Our findings indicate that the time of emergence of these signals only occurs towards the end of the 21st century, even in such a high-emission scenario.

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