Sections in the western Indian ocean—variability in the temperature structure

Abstract

The seasonal cycle of the temperature structure in the western Indian Ocean is presented along two sections monitored with XBT's. Both sections cut the Great Whirl near 8°N, where variations of isotherm depths are concentrated between June and November. Between 5°N and 8°S the variability is predominantly semi-annual, whereas further south it is annual. The seasonal cycle of vertical displacements of isotherms for temperatures colder than 15°C is similar to the cycle obtained in the core of the thermocline, with a slight lag. Variability in other parameters, such as SST, heat content or mixed layer depth, has little in common with vertical isotherm displacements. The deviations from the mean seasonal cycle are generally coherent over 5° of latitude. They are smaller near the equator and are not well correlated vertically, nor on long time scales. However, north of the equator anomalies may be related to variations in the strength of the southwest monsoon. In September and in November 1982, a year with a weak southwest monsoon, the intensity of the Great Whirl was weaker than normal. In 1983, the reverse occurred.