EOFs of Pseudo-Stress over the Indian Ocean (1977–85)

Abstract

The method of empirical orthogonal function (EOF) analysis is applied to pseudo-stress vectors over the Indian Ocean from 1977 to 1984. The EOF method is first reviewed, as it provides an easy method for comprehensive study of the climatology and variance of the pseudo-stress dataset. The results confirm that the monsoon flow is the dominant feature in the Indian Ocean, with strong southeasterly trades near the equator in summer and strong southwesterlies in the Arabian Sea, Bay of Bengal, and South China Sea. During the Northern Hemisphere winter, the pattern is weaker, with the wind switching to northeasterlies in these areas. Strong summer monsoons occurred in 1980, 1982, and 1984. Strong winter monsoons occurred in 1980, 1983, and 1984. An interesting pattern contributing to the decay and reversal of the monsoon flow is examined here. During the 1977?83 period, most of the interannual variability occurred in the Southern Hemisphere in the southeast trades. Strong southeast trades occurred in 1981 and 1982. Weaker periods of southeast trades were present from 1977 to 1979, with more northerly southeast trades in 1978 and 1979. Weak southeast trades occurred in 1983 but slowly changed to strong southeast trades by 1985.