scholarly journals Understanding biases in shortwave cloud radiative forcing in the National Center for Atmospheric Research Community Atmosphere Model (CAM3) during El Niño

2008 ◽  
Vol 113 (D2) ◽  
Author(s):  
Gang Li ◽  
Guang Jun Zhang
Keyword(s):  
El Niño ◽  
Radiative Forcing ◽  
El Nino ◽  
Research Community ◽  
Cloud Radiative Forcing ◽  
Atmospheric Research ◽  
Community Atmosphere Model ◽  
Atmosphere Model

scholarly journals The Role of Nonconvective Condensation Processes in Response of Surface Shortwave Cloud Radiative Forcing to El Niño Warming

2014 ◽  
Vol 27 (17) ◽  
pp. 6721-6736 ◽  
Author(s):  
Lijuan Li ◽  
Bin Wang ◽  
Guang J. Zhang
Keyword(s):  
Liquid Water ◽  
El Niño ◽  
Radiative Forcing ◽  
El Nino ◽  
Atmospheric Stability ◽  
Cloud Amount ◽  
Liquid Water Path ◽  
Cloud Radiative Forcing ◽  
Water Path ◽  
Low Cloud

Abstract The weak response of surface shortwave cloud radiative forcing (SWCF) to El Niño over the equatorial Pacific remains a common problem in many contemporary climate models. This study shows that two versions of the Grid-Point Atmospheric Model of the Institute of Atmospheric Physics (IAP)/State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) (GAMIL) produce distinctly different surface SWCF response to El Niño. The earlier version, GAMIL1, underestimates this response, whereas the latest version, GAMIL2, simulates it well. To understand the causes for the different SWCF responses between the two simulations, the authors analyze the underlying physical mechanisms. Results indicate the enhanced stratiform condensation and evaporation in GAMIL2 play a key role in improving the simulations of multiyear annual mean water vapor (or relative humidity), cloud fraction, and in-cloud liquid water path (ICLWP) and hence in reducing the biases of SWCF and rainfall responses to El Niño due to all of the improved dynamical (vertical velocity at 500 hPa), cloud amount, and liquid water path (LWP) responses. The largest contribution to the SWCF response improvement in GAMIL2 is from LWP in the Niño-4 region and from low-cloud cover and LWP in the Niño-3 region. Furthermore, as a crucial factor in the low-cloud response, the atmospheric stability change in the lower layers is significantly influenced by the nonconvective heating variation during La Niña.

scholarly journals The Influence of the 1998 El Niño upon Cloud-Radiative Forcing over the Pacific Warm Pool

2001 ◽  
Vol 14 (9) ◽  
pp. 2129-2137 ◽  
Author(s):  
Robert D. Cess ◽  
Minghua Zhang ◽  
Bruce A. Wielicki ◽  
David F. Young ◽  
Xue-Long Zhou ◽  
...  
Keyword(s):  
El Niño ◽  
Radiative Forcing ◽  
El Nino ◽  
Warm Pool ◽  
Cloud Radiative Forcing ◽  
The Pacific ◽  
Pacific Warm Pool

Influence of Dynamics on the Changes in Tropical Cloud Radiative Forcing during the 1998 El Niño

2002 ◽  
Vol 15 (14) ◽  
pp. 1979-1986 ◽  
Author(s):  
Richard P. Allan ◽  
A. Slingo ◽  
M. A. Ringer
Keyword(s):  
El Niño ◽  
Radiative Forcing ◽  
El Nino ◽  
Cloud Radiative Forcing

scholarly journals Impact of Parameterized Physical Processes on Simulated Tropical Cyclone Characteristics in the Community Atmosphere Model

2015 ◽  
Vol 28 (24) ◽  
pp. 9857-9872 ◽  
Author(s):  
Fei He ◽  
Derek J. Posselt
Keyword(s):  
Radiative Forcing ◽  
Deep Convection ◽  
Physical Parameters ◽  
Entrainment Rate ◽  
Physical Processes ◽  
Cloud Radiative Forcing ◽  
Water Path ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
The Impact

Abstract This study advances the understanding of how parameterized physical processes affect the development of tropical cyclones (TCs) in the Community Atmosphere Model (CAM) using the Reed–Jablonowski TC test case. It examines the impact of changes in 24 parameters across multiple physical parameterization schemes that represent convection, turbulence, precipitation, and cloud processes. The one-at-a-time (OAT) sensitivity analysis method quantifies the relative influence of each parameter on TC simulations and identifies which parameters affect six different TC characteristics: intensity, precipitation, longwave cloud radiative forcing (LWCF), shortwave cloud radiative forcing (SWCF), cloud liquid water path (LWP), and ice water path (IWP). It is shown that TC intensity is mainly sensitive to the parcel fractional mass entrainment rate (dmpdz) in deep convection. A decrease in this parameter can lead to a change in simulated intensity from a tropical depression to a category-4 storm. Precipitation and SWCF are strongly affected by three parameters in deep convection: tau (time scale for consumption rate of convective available potential energy), dmpdz, and C0_ocn (precipitation coefficient). Changes in physical parameters generally do not affect LWCF much. In contrast, LWP and IWP are very sensitive to changes in C0_ocn. The changes can be as large as 10 (5) times the control mean value for LWP (IWP). Further examination of the response functions for the subset of most sensitive parameters reveals nonlinear relationships between parameters and most output variables, suggesting that linear perturbation analysis may produce misleading results when applied to strongly nonlinear systems.

scholarly journals A robust equatorial Pacific westerly response to tropical volcanism in multiple models

2020 ◽  
Vol 55 (11-12) ◽  
pp. 3413-3429
Author(s):  
Jing Chai ◽  
Fei Liu ◽  
Chen Xing ◽  
Bin Wang ◽  
Chaochao Gao ◽  
...  
Keyword(s):  
El Niño ◽  
Land Surface ◽  
Radiative Forcing ◽  
El Nino ◽  
West African Monsoon ◽  
Equatorial Pacific ◽  
West African ◽  
Surface Cooling ◽  
Easterly Wind ◽  
African Monsoon

Abstract After each of the 1963 Agung, 1982 El Chichón, and 1991 Pinatubo eruptions, an El Niño was observed. The increased likelihood of an El Niño after a tropical eruption has also been found in long-term reconstructed proxy data. Through examining simulations over the last millennium by 11 different models, we show that a tropical volcano eruption can robustly excite a western-to-central equatorial Pacific (WCEP) westerly anomaly at 850 hPa in eight out of the 11 models; such a westerly anomaly is favorable for El Niño development. Under the volcanic forcing, there are significant extratropical continent surface cooling and tropical drying with negative precipitation anomalies over the South–South East Asia (SSEA), West African monsoon, and Intertropical Convergence Zone (ITCZ) regions. This common precipitation suppression response occurs in most of the models. Sensitivity experiments show that a WCEP westerly anomaly can be excited by the tropical land cooling, especially the SSEA cooling induced precipitation suppression rather than by the extratropical land surface cooling. Theoretical results show that a WCEP westerly anomaly is excited due to a Gill response to reduced precipitation over the SSEA and West African monsoon regions; and the SSEA contributes more than the West African monsoon does. The ITCZ weakening, however, excites an easterly wind anomaly. The models with more sensitive convective feedback tend to simulate an El Niño more easily, while a failed simulation of an El Niño after a robust westerly anomaly in some models calls for further studies on these models’ delayed responses to radiative forcing induced by volcano eruptions.

Exposing Global Cloud Biases in the Community Atmosphere Model (CAM) Using Satellite Observations and Their Corresponding Instrument Simulators

2012 ◽  
Vol 25 (15) ◽  
pp. 5190-5207 ◽  
Author(s):  
J. E. Kay ◽  
B. R. Hillman ◽  
S. A. Klein ◽  
Y. Zhang ◽  
B. Medeiros ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Climate Model ◽  
Substantial Improvement ◽  
Satellite Observations ◽  
Cloud Properties ◽  
Community Atmosphere Model ◽  
Realistic Representation ◽  
Model Cloud ◽  
Atmosphere Model

Abstract Satellite observations and their corresponding instrument simulators are used to document global cloud biases in the Community Atmosphere Model (CAM) versions 4 and 5. The model–observation comparisons show that, despite having nearly identical cloud radiative forcing, CAM5 has a much more realistic representation of cloud properties than CAM4. In particular, CAM5 exhibits substantial improvement in three long-standing climate model cloud biases: 1) the underestimation of total cloud, 2) the overestimation of optically thick cloud, and 3) the underestimation of midlevel cloud. While the increased total cloud and decreased optically thick cloud in CAM5 result from improved physical process representation, the increased midlevel cloud in CAM5 results from the addition of radiatively active snow. Despite these improvements, both CAM versions have cloud deficiencies. Of particular concern, both models exhibit large but differing biases in the subtropical marine boundary layer cloud regimes that are known to explain intermodel differences in cloud feedbacks and climate sensitivity. More generally, this study demonstrates that simulator-facilitated evaluation of cloud properties, such as amount by vertical level and optical depth, can robustly expose large and at times radiatively compensating climate model cloud biases.

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