REPRESENTATION OF MONSOON INTRASEASONAL OSCILLATIONS IN REGIONAL CLIMATE MODEL: SENSITIVITY TO CONVECTIVE PHYSICS

Abstract:

We use latest version of International Center for Theoretical Physics (ICTP) regional climate model RegCM4.4 for the study of seasonal mean and monsoon intraseasonal oscillations (MISOs) during Indian summer monsoon season over south Asian CORDEX domain. First time we have done detailed analysis to evaluate RegCM4.4 for space-time evolution characteristics of MISOs. The model is initialized at 1st January, 2000 for a 13-year continuous simulation at a spatial resolution of 50km. The sensitivity of the model performance to cumulus physics in simulating MISOs has been evaluated by considering three different combinations of Grell (G) and Emanuel (E) cumulus schemes. The models reasonably simulate the seasonal mean precipitation and 850-hPa wind with a notable bias in precipitation over Indian subcontinent and Equatorial Indian Ocean (EIO). The models exhibit higher skill in simulating seasonal mean wind than moisture and precipitation. On seasonal scale, the performance of RegCM-EG is more close to observation. However, on intraseasonal time scales, RegCM-EG fails to capture 25-90 day filtered precipitation variance over EIO which reflects in improper representation of features of MISOs. The space-time characteristics of MISOs are well captured by RegCM-EE over RegCM-GE, however it fails to show the eastward propagation of the convection across the Maritime Continent. Except RegCM-EE all other models completely underestimated the moisture advection from EIO onto Indian land region throughout the life-cycle of MISOs. It is found that the improvement in the representation of moist processes in RegCM-EE makes it useful for the study of characteristics of MISOs at regional scales.

Figure below is lag composite of vertically integrated 25-90 day filtered horizontal moisture advection (shaded) and precipitation (black contour).