Tropical Indian Ocean Mediates ENSO Influence Over Central Southwest Asia During the Wet Season

Abstract

El Niño-Southern Oscillation (ENSO) modulates wet season (November-April) precipitation over Central Southwest Asia (CSWA), however, intraseasonal characteristics of its influence are largely unknown, which can be important for its subseasonal to seasonal hydroclimate predictability. Here we show that the ENSO-CSWA teleconnection varies intraseasonally and is a combination of direct and indirect positive influences. The direct influence is through a Rossby wave-like pattern in the tail months. The indirect influence is through an atmospheric dipole of diabatic heating anomalies in the tropical Indian Ocean (TIO) as a result of ENSO-forced response, which also generates a Rossby wave-like forcing and persists throughout the wet season. ENSO exerts its strongest influence when both direct and indirect modes are in phase, while the relationship breaks down when the two modes are out of phase. The atmospheric teleconnection through the atmospheric diabatic heating anomalies in the TIO is reproducible in numerical simulations. Plain Language Summary El Niño-Southern Oscillation (ENSO) exerts a strong positive influence on the precipitation variability over Central Southwest Asian (CSWA) region during the wet season that spans from November to April. We note that the ENSO influence varies intraseasonally and has two components, one directly through the equatorial Pacific region and one indirectly through the tropical Indian Ocean. In both cases, ENSO exerts its influence through Rossby wave-like atmospheric anomalies. When the two components are in phase, ENSO has the strongest influence while it is weakest when they are out of phase. These findings suggest that improvements in subseasonal to seasonal scale predictability requires the better representation of intraseasonal variability of ENSO teleconnection, as well as the role of interbasin interactions in its propagation.

The Role of the Indian Ocean Basin-Wide and El Niño–Southern Oscillation Modes in Interannual Rainfall Variability over South America during Austral Summer

“…In fact, a weak low-level cyclone south of the equator in the western Indian Ocean forms a pair with the cyclone over the North Arabian Sea, Pakistan, and northwestern India (Figure 9d). Since the circulation associated with the IOBW shows a barotropic structure in southwest Asia (Figure 9c,d), our results are consistent with previous findings on the Rossby wave generated by the tropical Indian Ocean warming with an upper-level trough over southwest Asia [57,58]. Our results are also consistent with Liao and Wang [59], who documented a connection between the warming in the tropical Indian Ocean and a warming in the equatorial Atlantic during the austral summer.…”

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