Convergence of aqua-planet simulations with increasing resolution in the Community Atmospheric Model, Version 3

2008 ◽  
Author(s):  
David L. Williamson
Keyword(s):  
Atmospheric Model ◽  
Model Version

Mechanisms of Low Cloud–Climate Feedback in Idealized Single-Column Simulations with the Community Atmospheric Model, Version 3 (CAM3)

2008 ◽  
Vol 21 (18) ◽  
pp. 4859-4878 ◽  
Author(s):  
Minghua Zhang ◽  
Christopher Bretherton
Keyword(s):  
Dynamic Effect ◽  
Atmospheric Model ◽  
Cloud Feedback ◽  
Climate Feedback ◽  
Stratus Clouds ◽  
Model Version ◽  
Boundary Layer Turbulence ◽  
Thermodynamic Effect ◽  
Single Column ◽  
Low Cloud

Abstract This study investigates the physical mechanism of low cloud feedback in the Community Atmospheric Model, version 3 (CAM3) through idealized single-column model (SCM) experiments over the subtropical eastern oceans. Negative cloud feedback is simulated from stratus and stratocumulus that is consistent with previous diagnostics of cloud feedbacks in CAM3 and its predecessor versions. The feedback occurs through the interaction of a suite of parameterized processes rather than from any single process. It is caused by the larger amount of in-cloud liquid water in stratus clouds from convective sources, and longer lifetimes of these clouds in a warmer climate through their interaction with boundary layer turbulence. Thermodynamic effects are found to dominate the negative cloud feedback in the model. The dynamic effect of weaker subsidence in a warmer climate also contributes to the negative cloud feedback, but with about one-quarter of the magnitude of the thermodynamic effect, owing to increased low-level convection in a warmer climate.

SL-AV atmospheric model version using σ-p hybrid vertical coordinates

2017 ◽  
Vol 42 (9) ◽  
pp. 554-563 ◽  
Author(s):  
V. V. Shashkin ◽  
M. A. Tolstykh ◽  
A. R. Ivanova ◽  
E. N. Skriptunova
Keyword(s):  
Atmospheric Model ◽  
Model Version

Comparison of three ice cloud optical schemes in climate simulations with community atmospheric model version 5

2018 ◽  
Vol 204 ◽  
pp. 37-53 ◽  
Author(s):  
Wenjie Zhao ◽  
Yiran Peng ◽  
Bin Wang ◽  
Bingqi Yi ◽  
Yanluan Lin ◽  
...  
Keyword(s):  
Atmospheric Model ◽  
Ice Cloud ◽  
Model Version ◽  
Climate Simulations

scholarly journals Convectively Coupled Equatorial Waves in High-Resolution Hadley Centre Climate Models

2009 ◽  
Vol 22 (8) ◽  
pp. 1897-1919 ◽  
Author(s):  
Gui-Ying Yang ◽  
Julia Slingo ◽  
Brian Hoskins
Keyword(s):  
High Resolution ◽  
Energy Conversion ◽  
Phase Speed ◽  
Atmospheric Model ◽  
Equatorial Waves ◽  
Kelvin Wave ◽  
Near Surface ◽  
Model Version ◽  
Convectively Coupled Equatorial Waves ◽  
Hadley Centre

Abstract A methodology for diagnosing convectively coupled equatorial waves is applied to output from two high-resolution versions of atmospheric models, the Hadley Centre Atmospheric Model, version 3 (HadAM3), and the new Hadley Centre Global Atmospheric Model, version 1 (HadGAM1), which have fundamental differences in dynamical formulation. Variability, horizontal and vertical structures, and propagation characteristics of tropical convection and equatorial waves, along with their coupled behavior in the models, are examined and evaluated against a previous comprehensive study of observed convectively coupled equatorial waves using the 15-yr ECMWF Re-Analysis (ERA-15) and satellite observed data. The extent to which the models are able to represent the coupled waves found in real atmospheric observations is investigated. It is shown that, in general, the models perform well for equatorial waves coupled with off-equatorial convection. However, they perform poorly for waves coupled with equatorial convection. Convection in both models contains much-reduced variance in equatorial regions, but reasonable off-equatorial variance. The models fail to simulate coupling of the waves with equatorial convection and the tendency for equatorial convection to appear in the region of wave-enhanced near-surface westerlies. In addition, the simulated Kelvin wave and its associated convection generally tend to have lower frequency and slower phase speed than that observed. The models are also not able to capture the observed vertical tilt structure and signatures of energy conversion in the Kelvin wave, particularly in HadAM3. On the other hand, models perform better in simulating westward-moving waves coupled with off-equatorial convection, in terms of horizontal and vertical structures, zonal propagation, and energy conversion signals. In most cases both models fail to simulate well a key picture emerging from the observations, that some wave modes in the lower troposphere can act as a forcing agent for equatorial convection, and that the upper-tropospheric waves generally appear to be forced by the convection both on and off the equator.

scholarly journals Convection Parameterization, Tropical Pacific Double ITCZ, and Upper-Ocean Biases in the NCAR CCSM3. Part I: Climatology and Atmospheric Feedback

2009 ◽  
Vol 22 (16) ◽  
pp. 4299-4315 ◽  
Author(s):  
Xiaoliang Song ◽  
Guang Jun Zhang
Keyword(s):  
Critical Role ◽  
Atmospheric Model ◽  
Upper Ocean ◽  
Climate System Model ◽  
Physical Mechanisms ◽  
Model Version ◽  
Double Itcz ◽  
Convection Schemes ◽  
Convection Parameterization

Abstract The role of convection parameterization in the formation of double ITCZ and associated upper-ocean biases in the NCAR Community Climate System Model, version 3 (CCSM3) is investigated by comparing the simulations using the original and revised Zhang–McFarlane (ZM) convection schemes. Ten-year model climatologies show that the simulation with the original ZM scheme produces a typical double ITCZ bias, whereas all biases related to the spurious double ITCZ and overly strong cold tongue in precipitation, sea surface temperature (SST), wind stress, ocean thermocline, upper-ocean currents, temperature, and salinity are dramatically reduced when the revised ZM scheme is used. These results demonstrate that convection parameterization plays a critical role in the formation of double ITCZ bias in the CCSM3. To understand the physical mechanisms through which the modifications of the convection scheme in the atmospheric model alleviate the double ITCZ bias in the CCSM3, the authors investigate the impacts of convection schemes on the atmospheric forcing and feedback in the uncoupled Community Atmospheric Model, version 3 (CAM3). It is shown that the CAM3 simulation with the original ZM scheme also produces a signature of double ITCZ bias in precipitation, whereas the simulation with the revised ZM scheme does not. Diagnostic analyses have identified three factors on the atmospheric side (i.e., the sensitivity of convection to SST, the convection–shortwave flux–SST feedback, and the convection–wind–evaporation–SST feedback) that may contribute to the differences in the coupled simulations.

Climate Model Forecast Experiments for TOGA COARE

2008 ◽  
Vol 136 (3) ◽  
pp. 808-832 ◽  
Author(s):  
J. Boyle ◽  
S. Klein ◽  
G. Zhang ◽  
S. Xie ◽  
X. Wei
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Atmospheric Model ◽  
Static Stability ◽  
Geophysical Fluid Dynamics Laboratory ◽  
State Variables ◽  
Tropical Ocean ◽  
Model Version ◽  
Toga Coare

Abstract Short-term (1–10 day) forecasts are made with climate models to assess the parameterizations of the physical processes. The time period for the integrations is that of the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The models used are the National Center for Atmospheric Research (NCAR) Community Climate Model, version 3.1 (CAM3.1); CAM3.1 with a modified deep convection parameterization; and the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model, version 2 (AM2). The models were initialized using the state variables from the 40-yr ECMWF Re-Analysis (ERA-40). The CAM deep convective parameterization fails to demonstrate the sensitivity to the imposed forcing to simulate precipitation patterns associated with the Madden–Julian oscillations (MJOs) present during the period. AM2 and modified CAM3.1 exhibit greater correspondence to the observations at the TOGA COARE site, suggesting that convective parameterizations that have some type of limiter (as do AM2 and the modified CAM3.1) simulate the MJO rainfall with more fidelity than those without. None of the models are able to fully capture the correct phasing of westerly wind bursts with respect to precipitation in the eastward-moving MJO disturbance. Better representation of the diabatic heating and effective static stability profiles is associated with a better MJO simulation. Because the models’ errors in the forecast mode bear a resemblance to the errors in the climate mode in simulating the MJO, the forecasts may allow for a better way to dissect the reasons for model error.

scholarly journals Evaluation of climate simulations produced with the Brazilian global atmospheric model version 1.2

2020 ◽  
Author(s):  
Caio A. S. Coelho ◽  
Dayana C. de Souza ◽  
Paulo Y. Kubota ◽  
Simone M. S. Costa ◽  
Layrson Menezes ◽  
...  
Keyword(s):  
Atmospheric Model ◽  
Model Version ◽  
Global Atmospheric Model ◽  
Climate Simulations

Radiative and Dynamical Feedbacks over the Equatorial Cold Tongue: Results from Nine Atmospheric GCMs

2006 ◽  
Vol 19 (16) ◽  
pp. 4059-4074 ◽  
Author(s):  
D.-Z. Sun ◽  
T. Zhang ◽  
C. Covey ◽  
S. A. Klein ◽  
W. D. Collins ◽  
...  
Keyword(s):  
Climate Model ◽  
Atmospheric Model ◽  
Equatorial Pacific ◽  
Cold Tongue ◽  
Regulatory Effect ◽  
Community Climate Model ◽  
Model Version ◽  
Negative Feedbacks ◽  
Community Climate Model Version ◽  
Community Climate

Abstract The equatorial Pacific is a region with strong negative feedbacks. Yet coupled general circulation models (GCMs) have exhibited a propensity to develop a significant SST bias in that region, suggesting an unrealistic sensitivity in the coupled models to small energy flux errors that inevitably occur in the individual model components. Could this “hypersensitivity” exhibited in a coupled model be due to an underestimate of the strength of the negative feedbacks in this region? With this suspicion, the feedbacks in the equatorial Pacific in nine atmospheric GCMs (AGCMs) have been quantified using the interannual variations in that region and compared with the corresponding calculations from the observations. The nine AGCMs are the NCAR Community Climate Model version 1 (CAM1), the NCAR Community Climate Model version 2 (CAM2), the NCAR Community Climate Model version 3 (CAM3), the NCAR CAM3 at T85 resolution, the NASA Seasonal-to-Interannual Prediction Project (NSIPP) Atmospheric Model, the Hadley Centre Atmospheric Model (HadAM3), the Institut Pierre Simon Laplace (IPSL) model (LMDZ4), the Geophysical Fluid Dynamics Laboratory (GFDL) AM2p10, and the GFDL AM2p12. All the corresponding coupled runs of these nine AGCMs have an excessive cold tongue in the equatorial Pacific. The net atmospheric feedback over the equatorial Pacific in the two GFDL models is found to be comparable to the observed value. All other models are found to have a weaker negative net feedback from the atmosphere—a weaker regulating effect on the underlying SST than the real atmosphere. Except for the French (IPSL) model, a weaker negative feedback from the cloud albedo and a weaker negative feedback from the atmospheric transport are the two leading contributors to the weaker regulating effect from the atmosphere. The underestimate of the strength of the negative feedbacks by the models is apparently linked to an underestimate of the equatorial precipitation response. All models have a stronger water vapor feedback than that indicated in Earth Radiation Budget Experiment (ERBE) observations. These results confirm the suspicion that an underestimate of the regulatory effect from the atmosphere over the equatorial Pacific region is a prevalent problem. The results also suggest, however, that a weaker regulatory effect from the atmosphere is unlikely solely responsible for the hypersensitivity in all models. The need to validate the feedbacks from the ocean transport is therefore highlighted.

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