Simulation of monsoon intraseasonal oscillations in a coarse resolution aquaplanet GCM

Thursday, 18 December 2014
Ajaya Mohan Ravindran, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates, Boualem Khouider, University of Victoria, Victoria, BC, Canada and Andrew Majda, Courant Institute-NYU, NEW YORK, NY, United States
The skill of the global climate models (GCMs) to realistically simulate theMonsoon Intraseasonal Oscillations (MISOs) is related to the sensitivity of their convective parameterization schemes. Here, we show that by coupling a simple multicloud parameterization to a coarse resolution aquaplanet GCM,realistic MISOs can be simulated. We conduct three di fferent simulations with a fi xed non-homogeneous Sea-Surface Temperature (SST) mimicking the Indian Ocean/Western Paci c warm pool centered at the three latitudes 5°N,10°N and 15°N, respectively, to replicate the seasonal migration of the Tropical Convergence Zone (TCZ). This results in the generation of mean circulation resembling the monsoonal flow pattern in boreal summer. Successionof eastward propagating Madden-Julian Oscillation (MJO) disturbances with phase speed, amplitude and structure similar to summer MJOs are simulated when the WP is at 5°N. When the WP is located over 10°N, northward and eastward propagating MISOs are simulated. This case captures the meridional seesaw of convection between continental and oceanic TCZ observed during boreal summer over south Asia. Westward propagating Rossby-wave like disturbances are simulated when the WP is over 15°N congruous with the synoptic disturbances seen over the monsoon trough. The initiation of intraseasonal oscillations in the model can occur internally through organization of convective events above the WP associated with internal dynamics.