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 summermonsoon is modulated by the 30-60-day oscillation; the arrival ofthe 30-60-day monsoon trough (ridge) at 15 degrees-20 degrees N intensifies(weakens) the monsoon flow over the South China Sea-western tropicalPacific region and, in rum, extends eastward (westward) the monsoonwesterlies(trade easterlies) over this region. Since equatorial wavesare important synoptic disturbances to the weather of this region,an effort was made in this study to explore the possible impact ofthe 30-60-day mode on the occurrence frequency and westward propagationof these waves. The major findings of this study are as follows:1) the westward intrusion of trade easterlies during the break monsoonfacilitates the occurrence and westward propagation of equatorialwaves along trade easterlies in the southern Rank of the North Pacificanticyclone, and 2) the eastward expansion of monsoon westerliesduring the active monsoon varies relative to the activity of equatorialwaves in a way opposite to the break monsoon condition. Since thisis a pilot study, some future efforts are suggested.