HR: 1340h
AN: A43A-0038    [Abstracts]
TI: Impact of Indian Ocean sea surface temperature on developing El Ni¤o
AU: * Annamalai, H
EM: hanna@hawaii.edu
AF: IPRC< University of Hawaii, 1680 East West Road, Honolulu, HI 96822 United States
AU: Xie, S
EM: xie@hawaii.edu
AF: IPRC< University of Hawaii, 1680 East West Road, Honolulu, HI 96822 United States
AU: McCreary, J
EM: jay@hawaii.edu
AF: IPRC< University of Hawaii, 1680 East West Road, Honolulu, HI 96822 United States
AB: Prior to the 1976-77 climate shift (1950-76), sea surface temperature (SST) anomalies in the tropical Indian Ocean consisted of a basin-wide warming during boreal fall of the developing phase of most El Ni¤os whereas after the shift (1977-99) they had an east-west asymmetry, a consequence of El Ni¤o being associated with the Indian Ocean Dipole/Zonal Mode. In this study, we investigate the possible impact of these contrasting SST patterns on the on-going El Ni¤o, using atmospheric reanalysis products and solutions to both an atmospheric general circulation model (AGCM) and a simple atmospheric model (LBM), the latter used to identify basic processes. Specifically, analyses of reanalysis products during the El Ni¤o onset indicate that after the climate shift a low-level anticyclone over the South China Sea was shifted into the Bay of Bengal and that equatorial westerly anomalies in the Pacific Ocean were considerably stronger. Our study focuses on determining influence of Indian Ocean SST on these changes. A suite of AGCM experiments, each consisting of a 10-member ensemble, is carried out to assess the relative importance of remote (Pacific) versus local (Indian Ocean) SST anomalies in determining precipitation anomalies over the equatorial Indian Ocean. Solutions indicate that both local and remote SST anomalies are necessary for realistic simulations, with convection in the tropical West Pacific and the subsequent development of the South China Sea anticyclone being particularly sensitive to Indian Ocean SST anomalies. Prior to the climate shift, the basin-wide Indian-Ocean SST anomalies generate an atmospheric Kelvin wave associated with easterly flow over the equatorial western-central Pacific, thereby weakening the westerly anomalies associated with the developing El Ni¤o. In contrast, after the shift the east-west contrast in Indian-Ocean SST anomalies does not generate a significant Kelvin-wave response, and there is little effect on the El Ni¤o-induced westerlies. The LBM solutions confirm the AGCM's results.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting