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Monsoon intraseasonal oscillations as simulated by the superparameterized Community Atmosphere Model

Goswami, BB and Mani, NJ and Mukhopadhyay, P and Waliser, DE and Benedict, JJ and Maloney, ED and Khairoutdinov, M and Goswami, BN (2011) Monsoon intraseasonal oscillations as simulated by the superparameterized Community Atmosphere Model. Journal of Geophysical Research D: Atmospheres, 116 (22).

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The relative success of the Community Atmosphere Model with superparameterized convection (SP-CAM) in simulating the space-time characteristics of the Madden Julian Oscillation encourages us to examine its simulation of the Indian summer monsoon and monsoon intraseasonal oscillations (MISOs). While the model simulates the onset and withdrawal of the Indian monsoon realistically, it has a significant wet bias in boreal summer precipitation over the Asian monsoon region. The space-time characteristics of the MISOs simulated by the SP-CAM are examined in detail and compared with those of the observed MISO to gain insight into the model's bias in simulating the seasonal mean. During northern summer, the model simulates a 20 day mode and a 60 day mode in place of the observed 15 and 45 day modes, respectively. The simulated 20 day mode appears to have no observed analog with a baroclinic vertical structure and strong northward propagation over Indian longitudes. The simulated 60 day mode seems to be a lower-frequency version of the observed 45 day mode with relatively slower northward propagation. The model's underestimation of light rain events and overestimation of heavy rain events are shown to be responsible for the wet bias of the model. More frequent occurrence of heavy rain events in the model is, in turn, related to the vertical structure of the higher-frequency modes. Northward propagation of the simulated 20 day mode is associated with a strong cyclonic vorticity at low levels north of the heating maximum associated with a smaller meridional scale of the simulated mode. The simulated vertical structure of heating indicates a strong maximum in the upper troposphere between 200 and 300 hPa. Such a heating profile seems to generate a higher-order baroclinic mode response with smaller meridional structure, stronger low-level cyclonic vorticity, enhanced low-level moisture convergence, and higher precipitation. Therefore, the vertical structure of heating simulated by the cloud-resolving model within SP-CAM may hold the key for improving the precipitation bias in the model.

Item Type: Article
Additional Information: Copyright of this article belongs to American Geophysical Union.
Uncontrolled Keywords: Asian monsoon; Baroclinic; Baroclinic mode; Cloud resolving model; Community atmosphere model; Cyclonic vorticity; Gain insight; Heavy rain event; Higher order; Indian monsoon; Indian summer monsoon; Intraseasonal oscillations; Low level; Madden-Julian oscillation; Moisture convergence; Rain events; Seasonal mean; Summer precipitation; Upper troposphere; Vertical structures, Atmospheric thermodynamics; Cams; Heating; Rain; Tropical engineering; Vorticity, Computer simulation, air-sea interaction; atmospheric modeling; baroclinic mode; heating; Madden-Julian oscillation; meridional circulation; monsoon; parameterization; seasonal variation; spatiotemporal analysis; vorticity, Asia
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 25 Jul 2014 06:43
Last Modified: 25 Jul 2014 06:43

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