12th Conference on Interactions of the Sea and Atmosphere


Atmosphere-ocean variations in the Indo-Pacific sector during ENSO episodes

Ngar-Cheung Lau, NOAA/GFDL, Princeton, NJ

The influences of El Nino-Southern Oscillation (ENSO) events on air-sea interaction in the Indian-Western Pacific Oceans have been investigated using various model tools. The numerical experiments analyzed in this study include a 16-member ensemble of 50-year integrations with an atmospheric general circulation model (GCM) which incorporates observed monthly-varying sea surface temperature forcing in the tropical central and eastern Pacific, as well as coupling with an oceanic mixed layer model outside of that forcing region. The output from a 900-year run with a global, fully coupled atmosphere-ocean GCM has also been examined. The model results have been compared with available observations.

In the East Asian Monsoon region, warm ENSO events are seen to be accompanied by an anomalous surface anticyclone over the South China Sea and subtropical western Pacific during the winter season. The circulation changes associated with this feature oppose the winter monsoon over the East Asian coast, thus resulting in warm SST anomalies in that region and above-normal precipitation over southern China. The anticyclone maintains its identity through much of the following spring and summer, during which it migrates steadily eastward. The springtime SST anomalies in the subtropical western Pacific could feedback on the atmospheric circulation, and thereby affect the rainfall anomalies along the Meiyu-Baiu front.

The ENSO forcing also exerts considerable impacts on the atmospheric circulation and precipitation patterns in the Indian Ocean basin through displacements of the near-equatorial Walker Circulation and generation of Rossby-wave modes in the subtropics. Such atmospheric responses modulate the surface fluxes as well as the oceanic circulation in the Indian Ocean, thus leading to prominent SST signals in that region in various phases of the ENSO cycle. Diagnosis of a suite of auxiliary experiments also reveals interesting feedbacks between SST changes in the Indian Ocean sector and the overlying atmospheric circulation.

Session 6, Monsoon-ocean interaction
Tuesday, 11 February 2003, 3:30 PM-5:30 PM

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