Trends, spectral characteristics, and rainfall relationships of low-latitude sea surface temperatures at different longitudes

The sea surface temperature (SST) data for low latitudes in the Pacific, At lantic, and Indian Oceans for 1950-1996 (47 years) showed different seasona l variation patterns at different longitudes. When the seasonal patterns we re subtracted from the monthly values, the deseasoned residuals showed cons iderable anomalies (interannual variability). In the Pacific the main featu res were the Fl Nino events. In the Atlantic, North and South Atlantic SST showed dissimilar anomalies, and these did not have any fixed lag or lead r elationships with the Pacific events. The same was true for the low-latitud e Indian Ocean SST. The correlation of Pacific SST with Atlantic or Indian Oceans' SST was less than similar to 0.65, yielding a common variance (squa re of the correlation) of less than similar to 40%. Thus, whereas SST anoma lies might have some common origin, the manifestation of SST anomalies at d ifferent longitudes was erratic, with no preference for any longitude to st art with, nor any definite sequence of occurrence in the Pacific relative t o the Atlantic or Indian Oceans. A spectral analysis showed that all region s had quasi-biennial, quasi-triennial, and higher periodicities, but the ex act values of these periodicities differed significantly at different longi tudes. All parameters had long-term trends. These were mostly nonuniform, a lmost negligible in the first half (1950-1973) and mostly upward in the sec ond half (1973-1996), indicating warming in recent decades, which is also r eflected in decreases in snow cover area in the Northern Hemisphere. Rainfa lls in various regions are considerably influenced by local SST regimes. Fo r northeast Brazil, Atlantic SST influence is overpowering and often operat es independently of the Pacific SST (El Ninos). Hence the emphasis given in mass media (press, radio, and television) to the role of Fl Nino events on ly in influencing the rainfalls may turn out to be misleading, as seems to have happened for the 1997 Fl Nino. This El Niiio started in early 1997 but did not have any significant influence on rainfall in northeast Brazil and India. It continued strongly in 1998, causing a severe drought in northeas t Brazil but no drought in India.