Role of Air–Sea Interactions in the Intensifying and Decaying of an MJO Event over the North Indian Ocean

Madden-Julian oscillation (MJO) is the leading mode of tropical intraseasonal variability. Air-sea interactions play a major role in maintaining such oscillations. This study focuses on role of Sea surface temperature (SST) and surface heat fluxes like latent heat flux (LHF) and sensible heat flux (SHF) in modulating the intensity of MJO over the north Indian Ocean. Space time filtering technique is used to isolate the MJO signals from interpolated daily outgoing longwave radiation from the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites from 1979 to 2013. NOAA SST dataset is used from 1982 to 2013 and surface fluxes are taken from ERA-Interim and is presented from 1979 to 2013 in the study. Composites of MJO cycle are divided into 8 phases and used to study the relation with SST and surface heat fluxes anomalies over Arabian Sea (AS) and Bay of Bengal (BoB) during intensifying and decaying periods of the event. Intensifying and decaying phases are identified based on the increasing or decreasing trends of running variance over the Indian region. It is observed that the maximum SST is one phase ahead of peak precipitation and LHF peaks two phases ahead of wet phase and SHF maximum is observed four phases ahead of the wet phase on average. The time difference between two consecutive phases is approximately equal to 5 days. When the cycle is divided into intensifying or decaying periods, the major changes observed are both in the magnitude and the phase relationship with precipitation peak. During intensifying period, SST modulation is higher over BoB and the maximum LHF is three phases ahead while during the decaying phase both maximum of LHF and SST are two phases ahead of the wet phase. The SHF is almost same over BoB during both intensifying and decaying periods but over the Arabian Sea, changes in the magnitude of SHF is significant.