Role of sea surface temperature on the equatorial waves and intraseasonal oscillations

Abstract

Ocean interactions are known to play a major role in the modulation of intraseasonal variability. The role of sea surface temperature (SST) and major oceanic processes like ENSO (El Nino-Southern Oscillation) and IOD (Indian Ocean Dipole) on intraseasonal oscillations like Madden-Julian Oscillation (MJO) and convectively coupled equatorial waves (Kelvin wave, equatorial Rossby (ER), mixed-Rossby gravity and tropical depressions (together MT)) is explored using 32 years of satellite observations and reanalysis data. It is shown that the relationship between wave activity and SST is highly seasonal and region dependent. The study also shows that the global wave activity is more related to major oceanic phenomena like ENSO and IOD, while regionally, local intensification of the waves is observed to be directly associated with corresponding regional SST. But this relation is mostly limited to the western hemisphere. Globally, while Kelvin and Rossby waves intensify during El Nino, MT waves are shown to intensify during La Nina. MJO and ER are suppressed and MT is intensified during positive IOD. It is shown that the zonal and meridional distribution of moist static energy (MSE) during different phases of ENSO and IOD is the major factor in modulating the observed changes in the intensity of waves along with the distribution of vertical shear. Seasonal variations in these relationships are also explored.