Characteristics of the double intertropical convergence zone over the tropical Indian Ocean

摘要

Investigations on the double intertropical convergence zone (DITCZ) over the Indian Ocean using the monthly mean surface wind divergence data obtained from scatterometers on board the ERS-1/2 and QuikSCAT satellites (1991–2005) and the monthly mean cloud amount obtained from the International Satellite Cloud Climatology Project (1988–1989, 1998–2005) and the Advanced Very High Resolution Radiometer (AVHRR) data (1996–2003) reveal that its frequency of occurrence is considerably larger than that reported earlier, though the DITCZ feature in this region is rather diffused compared to Pacific. The 14-year analysis of monthly mean surface wind divergence shows that DITCZ structure is clearly discernible in April (frequency of occurrence, f = 64%), November (f = 73%) and December (f = 60%) in the 50–85°E longitude band over the tropical Indian Ocean. Though less frequent, DITCZ occur during other months also, except the Asian summer monsoon season. Most preferred latitudes of the north and south bands of DITCZ are ～6°N and ～7°S, respectively, during November and December. The DITCZ structure is well manifested in the cloud amount also during November and December, while it is less prominent in April. A weak but clearly identifiable hemispherical asymmetry is observed in latitude of occurrence and amplitude of the DITCZ bands. Since the sea surface temperature (SST) at the equatorial region over the Indian Ocean is nearly uniform, the DITCZ appears to be generated mainly by the atmospheric dynamics. This provides a unique opportunity to investigate the structure of ITCZ created by the atmospheric dynamics alone, which is one of the important problems in ITCZ dynamics.