A Pronounced Continental-Scale Diurnal Mode of the Asian Summer Monsoon

Abstract

A pronounced continental-scale diurnal mode of the Asian summer monsoon is mapped using data from recent satellites Meteosat-5 and TRMM. These datasets were available at high temporal resolutions. A result that stands out is the diurnal divergent circulation that in the afternoon hours has an ascending lobe over north-central India and has a descending lobe that reaches out radially toward central China, the southern part of China, the equatorial Indian Ocean, and the western Arabian Sea. The reverse circulation is clearly seen during the early morning hours. This diurnal pulsation of continental-scale divergent circulation appears to be an integral part of the monsoon. Another finding relates to the diurnal slowing down and speeding up of the Tibetan high circulations, especially in the southern flanks where the tropical easterly jet resides and exhibits a pulsation of intensity. The amplitude of pulsation was found to reach up to 7 m s?1. Thus this continental-scale change appears to be a pronounced feature. The phase and amplitude of various satellite datasets derived from the 90-min datasets are also displayed to confirm this major mode, that is, the diurnal oscillation of monsoon.