OSCILLATIONS OF A MONSOON SYSTEM - 1. OBSERVATIONAL ASPECTS.

Abstract

The elements of a monsoon system are defined, and its oscillations are determined from spectral analysis of long observational records. The elements of the monsoon system include pressure of the monsoon trough, pressure of the mascarene high, cross-equatorial low-level jet, Tibetan high, tropical early jet, monsoon cloud cover, monsoon rainfall, dry static stability of the lower troposphere, and moist static stability of the lower troposphere. The summer monsoon months over India during normal monsoon rainfall years are considered as guidelines in the selection of data for the period of this study. The salient result is that there seems to exist a quasi-biweekly oscillation in almost all of the elements of the monsoon system. Soon after the maximum dry and moist static instabilities are realized in the stabilizing phase, there occur in sequence an intensification of the monsoon trough, satellite brightness, Mascarene high, Tibetian high and the tropical easterly jet. Soon after that the rainfall maximum over central India, arising primarily from monsoon depressions, is found to be a maximum. Some plausible mechanisms are offered for these quasi-biweekly oscillations.