Lack of influence of cross-equatorial ocean heat transport on the interannual variability of the indian summer monsoon

The Indian Summer Monsoon (ISM) has long been considered a self-regulated coupled ocean-atmosphere system. This framework implies that a drought monsoon year is often followed by a flood monsoon year, or the reverse, due to ocean-atmosphere coupling. To support this argument, observations showed that it is rare for more than two consecutive ISM floods or droughts to occur, where a flood/drought is ±10% deviation from the climatological rainfall. During boreal summer, ISM winds drive a southward cross-equatorial OHT of roughly 2 PW, frequently cited as a central element of this feedback. Yet its capacity to warm the ocean surface and sustain year-to-year rainfall reversals has received little scrutiny. Here, we present a critical examination of the role of OHT in the regulation of the interannual variability of ISM. Our analyses suggest that the effect of cross-equatorial OHT does not last beyond one season. While the difference in the ISM rainfall between flood and drought years can exceed 20%, the difference in OHT is only about 2%. The response of local Hadley Cell to OHT variability is also negligible. These results suggest that cross-equatorial OHT plays a minor role in governing interannual ISM variability.