Mean state of the troposphere over south-east Asia and the East Indies, December 1978

Abstract

The mean state of the troposphere over south-east Asia from 8–30 December 1978 is described. In the lower troposphere, a jet was observed over the South China Sea extending south-westward from the Philippines. Evidence suggests that this north-easterly jet was supported by downstream blocking induced by the Borneo land mass. At the equator, the jet had the appearance of being channelled between the highlands of Borneo and Sumatra. On its left flank, near the west coast of Borneo, was a semi-permanent and quasi-stationary vortex. Being warm core, this vortex was probably maintained, in part, by latent heat release in cumulus convection. By partitioning the data into means at 00 and 12 GMT, the intensity of the rising branch of the Hadley circulation over Borneo was shown to increase by a factor of two, from −100 × 10−5 to −200 × 10−5mb s−1, from 00 to 12 GMT.