Temperature Changes in Equatorial Indian Ocean in Association with El Nino

Abstract:

Monthly mean vertical profile of temperature of the top 100m of the equatorial Indian Ocean between latitudes 5ºS and 5ºN has been studied using the Hadley Center reanalysis (EN4 data set from http://www.metoffice.gov.uk/hadobs/en4) which has used all available data sets including Argo floats of recent years. Data in respect of eight strong El-Nino zero years (1965, 1972, 1982, 1987, 1994, 1997, 2004 and 2009) have been composited for the September – November seasons and their previous years (El-Nino -1 years namely 1964, 1971, 1981, 1986, 1993, 1996, 2003 and 2008) for the same season. During the September – November season of the El-Nino previous years, the warmest equatorial area of Indian Ocean is its eastern part between longitudes 90ºE and 100ºE in the top 50m of the ocean. During September – November of the El-Nino zero years, the warmest area has shifted westward and the western Indian Ocean has warmed through more than 1ºC in a deep layer. In contrast, the eastern Indian Ocean has cooled slightly. Thus the effect of an El-Nino is to induce a positive IOD signal in temperature in the Indian Ocean. The atmospheric surface wind field changes during this period have been analyzed to understand the dynamics of ocean-atmosphere coupling that has resulted in these temperature changes in the Indian Ocean.