Is there an Indian Ocean dipole and is it independent of the El Niño-Southern Oscillation?

Abstract

The papers by Saji et al (1999) and Webster et al (1999) describe an equatorial Indian Ocean sea surface temperature (SST) dipole pattern (IOD) which they claim modulates rainfall in East Africa and Indonesia, and operates independently of the global-scale El Nino-Southern Oscillation (ENSO). The concept of possible independence of Indian Ocean SST variability form ENSO has been shaped by research focusing on climate events during the 1990s (eg Behera et al, 1999; Murtugudde et al., 2000). However, in an earlier paper Nicholls (1989) describes a different IOD pattern of variability related to Australian winter rainfall, and argues that this pattern operates largely independently of ENSO. In this paper we demonstrate clearly that with consideration of the evolution of ENSO events, the varying lag correlations between IOD end ENSO indices, and using seasonally stratified data, the apparent ENSO independence disappears form both IODs.