OBSERVED SEASONAL VARIABILITY OF HEAT-CONTENT IN THE UPPER LAYERS OF THE TROPICAL INDIAN-OCEAN FROM A NEW GLOBAL OCEAN TEMPERATURE CLIMATOLOGY

A subset of the recently published temperature climatology for the glo bal oceans is utilized to characterize the observed seasonal variabili ty in the heat content (HC) of the upper layers, estimated from surfac e to fixed depths (50, 100, 200 and 300 m), and with respect to fixed isotherm (27, 26, 25 and 20 degrees C) depths, for the entire tropical Indian Ocean (TIO). The most prominent features of the observed annua l cycle of the HC are described in terms of amplitude and phase of the annual and semi-annual frequencies employing Fourier analysis. The re lationship between the SST and the upper layer HC over an annual cycle is explored through correlation analysis. The distributions of the HC of the uppermost SO m and with respect to 27 degrees C depth show sim ilar seasonal variability with peak values during May, registering a d ramatic drop during the summer monsoon in the Arabian Sea and the Bay of Bengal. The distributions of HC show the most prominent annual mode in the uppermost 50 m in the southern TIO and in the 50-300 m off Ara bia and southwest and southeast India. The annual mode of HC is weak i n the equatorial band. On the other hand, both the western and eastern equatorial regions show the most pronounced semi-annual mode in the 5 0-300 m layer. This mode is also strong in the uppermost 100 m over th e northwestern Arabian Sea. The dominant annual mode in the HC with re spect to isotherms is most prominent in the southeastern Arabian Sea. The semi-annual mode of HC with respect to 20 degrees C is most promin ent in the northwestern Arabian Sea and the western and the eastern eq uatorial regions. The correlation between the SST and the HC of 50 m i s high over the entire basin. In the southern and western TIG, the reg ions of strong surface wind field with deep and diffuse thermocline, t he correlation between the SST and the HC is high and penetrates deepe r. The correlation degrades with depth, in particular in the warm pool region where the surface wind held is weak and the thermocline is sha llow and sharp. The correlation between the SST and the HC with respec t to isotherm depths also shows a similar degradation with depth in th e warm pool rep ion with the exception of a pocket in the southeastern TIG. where the thermocline topography is determined by propagating Ro ssby waves. (C) 1998 Elsevier Science Ltd. All rights reserved.