Indo‐Pacific relationships in terms of sea‐surface temperature variations

Abstract

AbstractIn the last decade, a great deal of attention has been paid to the irregular interannual oscillation, known to the acronym writers as ENSO, or El Niño–Southern Oscillation. Algorithms have been developed which model the interaction between the ocean and the atmosphere, and because of the dependency of such modelling on the state of the oceans, various attempts have been made to predict the sea‐surface temperature (SST) anomalies and, further, to understand the relationship between the oceans and their role in the global propagation of the ENSO signal. To this end, a statistical study, using singular value decomposition (SVD), has been made of the relationship between the SSTs of the Pacific and Indian Oceans in the last 4 decades and, in particular, the changes which have taken place, especially in the Indian Ocean. The point of using SVD is that it enables the user to compare the Pacific and Indian Oceans as two separate entities with different dimensions, not one as an adjunct of the other. For the purpose of this analysis, it is assumed that the two oceans are distinct and have separate characteristics. A simple EOF analysis treating the two oceans as one tropical system, for example, would not accomplish this objective. While SVD analyses in meteorology and climatology have mainly been applied to two different meteorological parameters, for example SST and sea level pressure, in the same area, there is no valid reason why SVD should not be applied to the same (or different) parameter(s) in different regions. Although the Indian and Pacific Oceans are of different dimensions, SVD does not weight the result in favour of either the smaller or the larger of the two. SVD is a statistical tool which gives results comparable with canonical correlation analysis, though several authors warn against its indiscriminate use. It is found that the Indian Ocean SSTs have a strong association with Pacific Ocean SSTs, particularly when the Indian Ocean lags the Pacific Ocean by one season in mid‐summer. It is also found that there is a distinct change in the SST patterns in the equatorial Indian Ocean in the second half (1977–1996) of the period under study. Copyright © 2001 Royal Meteorological Society