Monsoon low-frequency intraseasonal oscillation and ocean-atmosphere coupling over the Indian Ocean

The impact of coupled interaction over Indian Ocean on the monsoon low-frequency intraseasonal oscillation is investigated by analysing the simulations of MRI coupled general circulation model (CGCM) and its stand alone atmospheric version (AGCM). Composites of northward propagations constructed based on objective criteria show that the characteristics of CGCM simulated low-frequency intraseasonal oscillation are close to observation. In CGCM, the atmosphere impacts SST through wind, evaporation, and radiation anomalies and the ocean modulates atmospheric convection through intraseasonal SST fluctuations. But, in AGCM, SST acts only as a boundary forcing without any significant contribution from atmosphere in modulating SST. As a result, the simulated low frequency oscillation lacks many of the important features associated with its amplitude, phase and life-cycle. These results warrant the use of coupled GCMs for simulating and studying monsoon low-frequency oscillation.