Internal Feedbacks from Monsoon–Midlatitude Interactions during Droughts in the Indian Summer Monsoon

• DOI: 10.1175/2008jas2723.1
• Publication Date: 2008-09-19T21:10:50Z
• Authors: R. Krishnan; Vinay Kumar; M. Sugi; J. Yoshimura
• Keywords: Extratropical cyclone; Anomaly (physics); Middle latitudes; Anticyclone; Westerlies; Hadley cell; East Asian Monsoon

Abstract Results from a 20-yr simulation of high-resolution AGCM forced with climatological SST, along simplified model experiments and supplementary data diagnostics, are used to investigate internal feedbacks arising monsoon–midlatitude interactions during droughts in the Indian summer monsoon. The not only shows fairly realistic mean monsoon rainfall distribution large-scale circulation features but also exhibits remarkable interannual variations precipitation over subcontinent, run showing incidence four “monsoon droughts.” present findings indicate that internally emanate largely prolonged breaks” occur on subseasonal time scales involve dynamical between convection extratropical anomalies. In this feedback, suppressed is shown induce Rossby wave dispersion summertime subtropical westerlies set up an anomalous quasi-stationary pattern extending across continental Eurasia middle upper troposphere. This composed cyclonic anomaly west central Asia Indo-Pakistan region, meridionally deep anticyclonic East (∼100°E), Far East. results suggest anchoring by stagnant ridge located downstream induces cooling troposphere through cold-air advection, which reduces meridional thermal contrast subcontinent. Additionally, intrusion dry winds into northwest India can decrease convective instability, so turn weaken flow. sustenance breaks such generate droughtlike conditions India.