On El Niño’s impact upon the climate characteristics of the Indian monsoon

Abstract

The statistical analysis of the secular hydrometeorological data sets revealed a particular El Nino impact on the climatic system of the Indian Ocean domain. The spatial distribution of the sequent anomalies showed prominent local effects depending on the climatic season as well. The El Nino signal turned out to be better visible within the considered fields during the transitional phases of the Indian monsoon, when its activity is rather weak, unstable, or even almost absent. The hints of certain phase shifts found to appear in the monsoon cycle coincided timely with the El Nino event. First of all, this concerns the hamper effect, which being applied to the wind stress field in the spring season leads to the later onset of the wet southwest monsoon, which is accompanied by a precipitation shortage over huge inhabited territories. During the northeast monsoon, the equatorial-tropic part of the domain is affected by El Nino in such a way that the eastern near surface air transport arises and after this the Winter Monsoon Equatorial Current notably increases its speed. Quantitative estimations showed that the El Nino signal’s relative energy in the Indian Ocean area is nearly an order of magnitude lower when compared to the total monsoon energy. This implies that the total impact of El Nino upon the Indian Ocean domain’s climate system could not lead to a fundamental change of its regime, as, for example, a reversal of the monsoon circulation.