5.4
Mechanisms of increasing North Indian Ocean and the Indian subcontinent precipitation after major El Nino events
Hyo Seok Park, Univ. of California, Berkeley, CA; and J. C. H. Chiang, B. R. Lintner, and G. J. Zhang
Major winter El Niņo events produce warmer sea surface temperatures (SSTs) and intensify deep convection over the South Indian Ocean during the subsequent early boreal spring. The above normal column-integrated water vapor associated with these conditions propagates northward into the North Indian Ocean (NIO) by the start of the South Asian summer monsoon season.
The propagation occurs as the weakening of monsoonal winds warms the NIO via reduced surface evaporation during the early monsoon season (Jun-Jul). Idealized atmospheric general circulation model (AGCM) experiments demonstrate that the contemporaneous, residual warming in the Eastern Equatorial Pacific following winter El Niņo conditions can greatly enhance the NIO warming by weakening the monsoonal winds.
During the early monsoon season (Jun-Jul) following El Niņo, a warmer NIO increases column-integrated water vapor and northward moisture transport, but the Indian subcontinent does not experience stronger monsoon rainfall due to reduced dry static energy advection. The early season NIO warming is accompanied by substantial rebounds of the surface latent heat flux and low-level winds during the late season (Aug-Sep). The rebound of low-level winds initiated by the disappearance of the remote subsidence signal substantially contributes to the surface latent heat flux increase in the Arabian Sea, which may further strengthen monsoon circulation.
Session 5, Monsoons - II
Tuesday, 13 January 2009, 11:00 AM-12:00 PM, Room 129A
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