Impact of air-sea interaction during two contrasting monsoon seasons

Abstract

The air-sea interaction processes and their relation to Indian summer monsoon rainfall via dynamic and thermodynamic components are vital. The present study examined the two contrasting monsoon years 2016 (normal) and 2017 (below normal) and highlighted the significance of air-sea interaction in the understanding the rainfall over central India. We investigate the difference in the sea surface height anomaly and propagation of oceanic Kelvin and Rossby wave over the tropical Indian Ocean and other atmospheric parameters during the contrasting monsoon years. The study gives information on how equatorial and coastal Kelvin/Rossby waves cause upwelling/downwelling and modulate convection and influence rainfall during 2016 and 2017. The high (low) sea surface height anomaly, sea surface temperature, and upper ocean heat content during 2016 (2017) lead to enhanced (subdued) convection in the Bay of Bengal and thereby contributing more rainfall to central India. During 2016 (2017), high (low) tropospheric temperature draws more (less) moisture through mid-tropospheric heat flux, and net convergence (divergence) is dominated over the central India that results in enhanced (diminish) convection. Also, the velocity potential determines the strengthening (weakening) of Walker circulation through associated atmospheric circulation and upper-level divergence (convergence) that become favorable for rainfall in the year 2016 (2017). This study will help in understanding the variations in the air-sea interaction processes over the tropical Indian Ocean and the Indian subcontinent, the results of which may improve the predictability of the rainfall.