2019/11/22 by Borah, Pritam, Venugopal, V., Sukhatme, Jai +2
#Atmospheric and Oceanic Physics (physics.ao-ph) #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn)
paper · doi:10.48550/arxiv.1911.10013
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.