Indian Ocean intraseasonal sea surface temperature variability during boreal summer: Madden-Julian Oscillation versus submonthly forcing and processes

Intraseasonal sea surface temperature (SST) variability in the Indian Ocean during boreal summer is investigated with a series of experiments using the Hybrid Coordinate Ocean Model (HYCOM). QuickSCAT winds and satellite-observed outgoing longwave radiation (OLR) are used to identify the wind and convection patterns associated with atmospheric intraseasonal oscillations (ISOs). Effects of the Madden-Julian Oscillation (MJO; 30-90 days) and submonthly ISOs are separately examined. Similar to winter, MJO forcing dominates summertime SST variability, even though submonthly forcing is stronger. Wind plays a much larger role in altering SSTs than either shortwave fluxes or precipitation. Different from winter cases, the maximum summertime SST variability shifts to the Arabian Sea ( AS) and the Bay of Bengal ( BOB), when ISOs also shift to the Northern Hemisphere. In the BOB, surface heat fluxes due to changes in wind speed have a stronger influence on SST than upwelling and advection induced by wind stress, whereas in winter, the effects of surface heat fluxes and oceanic upwelling and advection are comparable. This difference arises from the barrier layer and thin surface mixed layer in the BOB, which reduce the effects of upwelling and amplify the effects of surface heat fluxes. In the AS, surface heat fluxes and entrainment cooling due to changes in wind speed have a larger effect on MJO-scale SST than upwelling induced by wind stress, while the two have comparable effects on submonthly SST. In the equatorial region, wind speed and stress are equally important.