Some Effects of the Intraseasonal Oscillation on the Equatorial Waves over the Western Tropical Pacific–South China Sea Region during the Northern Summer

Abstract

Previous studies have shown that the life cycle of the Asian summer monsoon is modulated by the 30?60-day oscillation; the arrival of the 30?60-day monsoon trough (ridge) at 15°?20°N intensifies (weakens) the monsoon flow over the South China Sea?western tropical Pacific region and, in turn, extends eastward (west-ward) the monsoon westerlies (trade easterlies) over this region. Since equatorial waves are important synoptic disturbances to the weather of this region, an effort was made in this study to explore the possible impact of the 30?60-day mode an the occurrence frequency and westward propagation of these waves. The major findings of this study are as follows: 1) the westward intrusion of trade easterlies during the break monsoon facilitates the occurrence and westward propagation of equatorial waves along trade easterlies in the southern flank of the North Pacific anticyclone, and 2) the eastward expansion of monsoon westerlies during the active monsoon varies relative to the activity of equatorial waves in a way opposite to the break monsoon condition. Since this is a pilot study, some future efforts are suggested.