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ESRL/PSD Seminar Series

Equatorial Rossby and Mixed Rossby-gravity Waves in the Simulated Asian Monsoon

Charlotte DeMott
Atmospheric Sciences, Colorado State University


Simulations of the Asian monsoon by three general circulation models (GCMs) using various combinations of 1) a coupled versus prescribed oceans and 2) conventional versus super-parameterized (SP) convection are studied, where super-parameterization refers to an embedded cloud resolving model used to estimate convective tendencies. CCSM is a coupled model with conventionally parameterized convection, SP-CAM is an uncoupled model with super-parameterized convection, and SP-CCSM is a coupled model with super-parameterized convection. SP-CCSM is the only model of the three to reasonably simulate the magnitude and spatial distribution of the eastward-, westward-, and northward-propagating components of the Asian monsoon. SP-CCSM produces a rich variety of tropical waves whose spectral characteristics exhibit unusually close agreement with observations. The simulation of equatorial Rossby (ER) and mixed Rossby-gravity (MRG) waves in the three models leads to a different simulation of the NPISO in each model. All three models exhibit at least some northward propagation for ER waves, but only SP-CCSM produces northward-propagating MRG waves, as is seen in observations. The combination of northwestward- versus southwestward- or westward-propagating ER and MRG waves over the Indian Ocean influences the spatio-temporal structure of the NPISO, and contributes to the differences seen in each model. Influences of the models' different basic state environment, air-sea coupling, and convective treatment and their impact on the simulated will also be considered.

Wednesday, February 9

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