Role of the North Atlantic in Indian Monsoon Droughts

TL;DR

This paper reveals that nearly half of Indian monsoon droughts are sub-seasonal and linked to North Atlantic cold anomalies, providing new insights for improving drought prediction models.

Contribution

It identifies a novel North Atlantic teleconnection as a driver of sub-seasonal monsoon droughts, expanding understanding beyond Pacific influences.

Findings

Nearly 50% of droughts are sub-seasonal with late-season rainfall decline.

North Atlantic cold anomalies influence monsoon droughts via atmospheric wavetrains.

The teleconnection offers potential for better drought predictability.

Abstract

The forecast of Indian monsoon droughts has been predicated on the notion of a season-long rainfall deficit linked to warm anomalies in the equatorial Pacific. Here, we show that in fact nearly half of all droughts over the past century were sub-seasonal, and characterized by an abrupt decline in late-season rainfall. Furthermore, the potential driver of this class of droughts is a coherent cold anomaly in the North Atlantic Ocean. The vorticity forcing associated with this oceanic marker extends through the depth of the troposphere, and results in a wavetrain which curves towards the equator and extends to East-Asia. This upper-level response triggers an anomalous low-level anticyclonic circulation late in the season over India. This teleconnection from the midlatitudes offers an avenue for improved predictability of monsoon droughts.