TY - JOUR
T1 - Improved tropical modes of variability in the NCEP Climate Forecast System (Version 2) via a stochastic multicloud model
AU - Goswami, B. B.
AU - Khouider, B.
AU - Phani, R.
AU - Mukhopadhyay, P.
AU - Majda, A. J.
N1 - Funding Information:
Acknowledgments. The research of BK is partially funded by a grant from the government of India through the National Monsoon Mission (NMM) and Discovery Grant RGPIN/4288-2015 from the Canadian Natural Sciences and Engineering Research Council. BBG is a postdoctoral fellow through BK’s NMM grant.
Publisher Copyright:
© 2017AmericanMeteorological Society.
PY - 2017/10/1
Y1 - 2017/10/1
N2 - A stochastic multicloud model (SMCM) convective parameterization, which mimics the interactions at subgrid scales of multiple cloud types, is incorporated into the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), model (CFSsmcm) in lieu of the preexisting simplified Arakawa-Schubert (SAS) cumulus scheme. A detailed analysis of the tropical intraseasonal variability (TISV) and convectively coupled equatorial waves (CCEW) in comparison with the original (control) model and with observations is presented here. The last 10 years of a 15-yr-long climate simulation are analyzed. Significant improvements are seen in the simulation of the Madden-Julian oscillation (MJO) and most of the CCEWs as well as the Indian summer monsoon (ISM) intraseasonal oscillation (MISO). These improvements appear in the form of improved morphology and physical features of these waves. This can be regarded as a validation of the central idea behind the SMCM according to which organized tropical convection is based on three cloud types, namely, the congestus, deep, and stratiform cloud decks, that interact with each other and form a building block for multiscale convective systems. An adequate accounting of the dynamical interactions of this cloud hierarchy thus constitutes an important requirement for cumulus parameterizations to succeed in representing atmospheric tropical variability. SAS fails to fulfill this requirement, which is evident in the unrealistic physical structures of the major intraseasonal modes simulated by CFSv2 as documented here.
AB - A stochastic multicloud model (SMCM) convective parameterization, which mimics the interactions at subgrid scales of multiple cloud types, is incorporated into the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), model (CFSsmcm) in lieu of the preexisting simplified Arakawa-Schubert (SAS) cumulus scheme. A detailed analysis of the tropical intraseasonal variability (TISV) and convectively coupled equatorial waves (CCEW) in comparison with the original (control) model and with observations is presented here. The last 10 years of a 15-yr-long climate simulation are analyzed. Significant improvements are seen in the simulation of the Madden-Julian oscillation (MJO) and most of the CCEWs as well as the Indian summer monsoon (ISM) intraseasonal oscillation (MISO). These improvements appear in the form of improved morphology and physical features of these waves. This can be regarded as a validation of the central idea behind the SMCM according to which organized tropical convection is based on three cloud types, namely, the congestus, deep, and stratiform cloud decks, that interact with each other and form a building block for multiscale convective systems. An adequate accounting of the dynamical interactions of this cloud hierarchy thus constitutes an important requirement for cumulus parameterizations to succeed in representing atmospheric tropical variability. SAS fails to fulfill this requirement, which is evident in the unrealistic physical structures of the major intraseasonal modes simulated by CFSv2 as documented here.
KW - Atmospheric
KW - Climate models
KW - Intraseasonal variability
KW - Madden-Julian oscillation
KW - Model evaluation/performance
KW - Tropical variability
KW - Waves
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U2 - 10.1175/JAS-D-17-0113.1
DO - 10.1175/JAS-D-17-0113.1
M3 - Article
AN - SCOPUS:85031101399
SN - 0022-4928
VL - 74
SP - 3339
EP - 3366
JO - Journal of the Atmospheric Sciences
JF - Journal of the Atmospheric Sciences
IS - 10
ER -