2000), A possible triggering process of eastwest asymmetric anomalies over the Indian Ocean

Anomalous east-west asymmetric anomalies were seen in sea surface temperature (SST), and convective activity over the equatorial Indian Ocean during October-December 1997. Using NCEP/NCAR reanalysis and sea surface height data obtained from TOPEX/POSEIDON satellite altimeter, its triggering process and strengthening mechanism are identified. The climatological wind over the equatorial Indian Ocean exhibits different seasonal cycle between its western and eastern region. During the summer monsoon season, westerly wind prevails over the western Indian Ocean, on the other hand, easterly wind is dominant over the eastern Indian Ocean at almost the same time. During the 1997 summer, divergent easterly wind anomalies were obvious over the equatorial Indian Ocean due to a warm episode of the El Nino, which weakened (accelerated) the climatological westerly (easterly) wind over the western (eastern) Indian Ocean. As a result, the east-west SST contrast was produced in the succeeding autumn through changing evaporative cooling and upwelling. Corresponding to these SST changes, the convective activities were enhanced (suppressed) over the western (eastern) Indian Ocean and actual wind became easterly in place of climatological westerly wind during October-December 1997