The influence of the tropical circulation on Indian summer monsoon during ENSO

The influence of the El Nino Southern Oscillation (ENSO) on the Indian Summer Monsoon circulation is studied; focus is on the mechanism involving the change in the tropical circulation, particularly in the western Pacific. The Community Atmosphere Model (CAM) is used for mechanistic studies on how the tropical circulation changes (especially movement of regions of ascent and descent) during ENSO influence the Indian Summer Monsoon. For this purpose, additional idealized heating is inserted into the full CAM in the context of summer simulations with climatological SST in order to induce rising motion anomalies that represent the modification of the Walker circulation under different summer time ENSO SST conditions. In this manner, the inadequacies of the parameterization of deep convection in responding to ENSO SST anomalies are avoided. The sensitivity of response of the idealized heating is also tested with different magnitudes and locations of the heating. The coefficients of 2K/day and 1K/day are used for the different magnitudes of the heating. The different locations of heating are inserted from the tropical Indian Ocean to the tropical central Pacific. The inserted heating in each tropical region simulated Gill type responses, although the strength and propagation of the responses are different with the different locations of the heating. Despite of the different locations of the heating, strong remote responses over the Indian region are consistently simulated in CAM while the heating moves from the Indian Ocean to the central Pacific. This is a sort of geophysical fluid dynamics approach, but in the context of a realistic model. My metrics for judging changes in Indian Monsoon circulation will emphasize the Monsoon 3-d circulation.