INTERNATIONAL SYMPOSIUM ON INFORMATION TECHNOLOGY IN OCEANOGRAPHY (ITO-98) GOA, INDIA 12-16 OCTOBER 1998

Climatological and interannual variability aspects of monthly mean pseudo-stress curl over the Indian Ocean for the period 1970-1995 are explored. A harmonic analysis of the curl fields finds most of the variance of the northern basins dominated by semi-annual variability. In particular the coastal areas of Somalia and south/southwestern India have large contributions from this harmonic. In the southern basin, interannual harmonics are the primary harmonics of curl variance. Biennial oscillatory behavior is only sporadically evident in various harmonics between 20 and 30 months, and is absent north of 10B S. An EOF analysis confirms the summer monsoon is the dominant feature compared to the winter monsoon. The strong positive curl in the summer monsoon along the coastal areas of the Indian peninsula, Somalia, northeast of Madagascar, and South China Sea indicate upwelling favourable regions. The winter monsoon pattern highlights the relatively southward location of the southern trades, and the negative curl in the northern half of the Arabian Sea. The transition of the monsoons, fall and late winter are reflected in a separate EOF and elucidates curl variance in the region to the east of Madagascar and in the eastern Arabian Sea. In contrast to recent findings, we note the mean positive curl in the eastern Arabian Sea indicating positive Ekman velocities (upwards) enhancing coastal upwelling in this region. Notable (25-33%) increases in curl magnitude are noted during the period prior to 1988/89. These are most detectable in the NE and SW monsoon. During February, the increase is noted to peak earlier (1980-1986) for the curl associated with seasonal westerlies between 0B and 10B S. More exceptional and not previously noted is an opposite and somewhat dramatic reduction of curl magnitude since 1988/89. The rate of decline is much larger than the (positive) trend in the early 1980's and is most notable in the early part of the summer monsoon. Additional evidence supports this change in variability patterns.

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Copyright© National Institute Of Oceanography, Goa,India,1998
updated on 7th July'98