HR: 14:20h
AN: A53E-05    [Abstracts]
TI: Mechanism of Increasing Indian Monsoon Rainfall Following a Winter El Nino
AU: * Park, H
EM: hspark@berkeley.edu
AF: University of California Berkeley, 531 McCone, Berkeley, CA 94720, United States
AU: Chiang, J C
EM: jchiang@atmos.berkeley.edu
AF: University of California Berkeley, 531 McCone, Berkeley, CA 94720, United States
AU: Lintner, B R
AF: UCLA University of California Los Angeles, 7234 Mathematical Sciences Bldg, Los Angeles, CA 90095, United States
AB: The mechanism of increasing Indian monsoon rainfall following major El Nino – Southern Oscillation (ENSO) events has been investigated using an atmospheric general circulation model (AGCM) coupled to a thermodynamic mixed layer. In our simulations, El Nino produces a warming of the troposphere and intensification of convection over the equatorial south Indian Ocean during the early spring. The anomalous convection progresses northwards up to the subcontinent of India during the early monsoon season (Jun-Jul). This progression occurs via anomalous moisture transport by the mean cross-equatorial flow, even though the intensity of the monsoon circulation decreases. Our simulations also suggest an intraseasonal evolution of the mechanisms associated with anomalous summer monsoon rainfall conditions over the north Indian Ocean and Indian subcontinent following a winter El Nino. During the early period of the monsoon (Jun-Jul), moisture transport by the mean cross-equatorial flow is the main source for increasing monsoon rainfall. As the moisture perturbation homogenizes during the late period (Aug-Sep), large-scale moisture transport weakens. Instead, anomalous surface latent heat fluxes associated with north Indian Ocean warming increase boundary layer moist static energy and support above normal rainfall. Additional idealized experiments demonstrate that the winter- early spring El Nino-induced Indian Ocean warming and subsequent local boundary layer moist processes are mostly responsible for increasing the monsoon rainfall. However, the strength of the monsoonal cross-equatorial flow is strongly modulated by the contemporaneous remote forcing from the eastern equatorial Pacific (Nino3 area), where El Nino's residual (decaying) signal remains. We discuss competing effects of the north Indian Ocean warming versus the anomalous subsidence on the Indian monsoon rainfall.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0429 Climate dynamics (1620)
DE: 1620 Climate dynamics (0429, 3309)
DE: 4522 ENSO (4922)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting