Indian monsoon derailed by a North Atlantic wavetrain
La mousson indienne perturbée par un train d'ondes de l'Atlantique Nord
Goswami, B. N. ; Borah, P. J. ; Venugopal, V. ; Sukhatme, J. ; Muddebihal, P.
The forecast of Indian monsoon droughts has been predicated on the notion of a season-long rainfall deficit linked to a warm equatorial Pacific. Here we show that nearly half of all droughts over the past century differ from this paradigm in that they occur when Pacific temperatures are near-neutral and are subseasonal phenomena, characterized by an abrupt decline in late-season rainfall. This severe subseasonal rainfall deficit can be associated with a Rossby wave from mid-latitudes. Specifically, we find that the interaction of upper-level winds with an episodic North Atlantic vorticity anomaly results in a wavetrain that curves toward East Asia, disrupting the monsoon. This atmospheric teleconnection offers an avenue for improved predictability of droughts, especially in the absence of telltale signatures in the Pacific. </p>
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