Role of Air Sea Interactions On Convectively Coupled Equatorial Waves and Intraseasonal Oscillations

Abstract

The tropical intraseasonal oscillations play a vital role in maintaining the weather across newlinethe tropics as well as extratropics. These oscillations are known to modulate many of the tropical newlineatmospheric and oceanic phenomena like monsoons, El-Nino, tropical cyclones, extreme weather newlineevents etc. The frequency of extreme events like extreme precipitation and heat waves are newlineinfluenced by the phases of MJO and other convectively coupled waves in the tropics. A thorough newlineunderstanding of the dynamics and prediction of these waves is thus valuable in intraseasonal newlineprediction of various tropical phenomena. newlineThese oscillations mainly consist of equatorial Kelvin, Rossby, MRG (Mixed-Rossby newlinegravity), TD (tropical depressions) and MJO (Madden Julian Oscillation). All these oscillations newlinehave characteristic spatio-temporal structures with definitive range of wave numbers and newlinefrequencies. Among these, MJO is the leading mode of tropical intraseasonal oscillation which is newlinea large scale coupling between atmospheric circulation and tropical deep convection. MJO is much newlinemore explored than the other equatorial waves but the dynamics behind the MJO is still not newlinecompletely understood. These waves can be extracted from the OLR (outgoing longwave newlineradiation) data by using space-time filtering for their respective wavenumber and period. Intensity newlineof the wave is represented by running variances of OLR for different window lengths. newlineThese waves highly depend on the SST (sea surface temperature) as warm Ocean basins newlineare favourable for the generation and intensification of the waves. Global mean intensity of waves newlineis observed to be more related to the dominant oceanic phenomena over tropics like El Nino and newlineIOD (Indian Ocean Dipole). However, locally, it is shown that the effect of increased SST is to newlineincrease the wave intensity, in particular over the regions (central and east Pacific) and during the newlineseasons with relatively low climatological wave activity