Joint Seminar: Association of the tropical climatic events to the Indian summer monsoon using moisture budget theory

The Indian summer monsoon (ISM) is the coupled ocean-atmosphere system, largely governed by the local and remote responses of the sea surface temperature variability of the various ocean basins such as El Nino Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and ATLantic tropical variability (ATL). These tropical climatic patterns modulate the large-scale circulation and impact moist convection over India either through the tropics or mid-latitude. We propose a unified theory for tropical teleconnections to the ISM through the net moisture convergence driven by the surface pressure (Ps) gradients surrounding the Indian region. The positive and negative phases of the tropical variability modulate the pressure gradients asymmetrically in the zonal or meridional directions leading to an asymmetric change in moisture convergence and thus rainfall.For instance, asymmetric change in precipitation during El Nino and La Nina is associated with a strong decrease in incoming moisture flux at 70E for El Nino as compared to its corresponding increase during La Nina. Moreover, a similar relationship between precipitation and moisture convergence holds good for ATL and preceding winter ENSO but insignificant for IOD. We use the same approach to understand why only 41% of the ENSO extremes (El Nino and La Nina) can lead to ISM rainfall extremes (drought and flood) in the Climate Forecast System version 2 (CFSv2) model albeit of strong ENSO-ISM relationship in comparison to observation. We observe that ENSO extremes which strongly modulate the meridional Ps gradient over the Arabian Sea and Bay of Bengal can lead to ISM extremes by significantly changing the net moisture convergence over India. This relationship is strongly (weakly) captured over the Bay of Bengal (Arabian Sea) by the model, resulting in making the outgoing eastward moisture flux an important factor controlling ENSO related ISM extremes and non-extremes in the model.




13:30–14:30 Uhr


Virtual Seminar


Priyanshi Singhai


Chetankumar Jalihal

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