The recent strengthening of walker circulation

Abstract

This study calculated the Walker circulation index and then discovered strengthening of the circulation in recent years. Thus, this study analyzed a difference of averages between 1999-2013 and 1984-1998 periods to determine the cause of the strengthening of the Walker circulation in recent years. With regard to 850 hPa stream flows, analysis on difference between two periods showed that anomalous easterlies (anomalous trade wind) were dominant due to strengthening of anomalous anticyclonic circulations at the subtropical Pacific of both hemispheres. In order to determine whether upward flows are strengthened at the tropical western Pacific and downward flows are strengthened at the tropical central and eastern Pacific in recent years, a difference in zonal atmospheric circulation averaged over 5°S-5°N between two periods was analyzed. The Walker circulation, in which air ascended at the equatorial western Pacific was descended at the equatorial central and eastern Pacific, was strengthened more in recent years.