Abstract
Some of the characteristic features of the Asiatic summer monsoon were investigated using outgoing longwave radiation data obtained from NOAA polar orbiting satellites during the summer mouths in 1974–77. Monthly mean outgoing longwave radiation patterns clearly reflect pronounced monsoon activity over the India-Southeast Asian and Philippines-western North Pacific regions. Between these two regions, values of outgoing longwave radiation are relatively high and indicate less pronounced monsoon activity over the South China Sea along about 110°E.
Empirical orthogonal function analysis was applied to identify the major modes of intraseasonal oscillations present in outgoing longwave radiation data during the summer. Spectral analyses of the amplitude functions for the four largest eigenvectors exhibit marked peaks in a period range of about 20–30 days. The first four eigenvector patterns were examined to investigate the zonal and meridional phase propagation of 20–30 day perturbations. Zonal phase propagation is westward (eastward) at about 10–20°N (equator). It appears that rainfall fluctuations between “active” and “break” monsoon periods over the Indian region are strongly associated with these zonally propagating, 20–30 day perturbations in outgoing longwave radiation fields. Distinct northward phase propagation was found over the South China Sea along about 110°E. Therefore, this region is characterized by eastward propagating modes near the equator, westward moving perturbations around 10–20°N and northward penetration into China.
