The 30–60-Day Convection Seesaw between the Tropical Indian and Western Pacific Oceans

Baozhen Zhu Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii

Search for other papers by Baozhen Zhu in
Current site
Google Scholar
PubMed
Close
and
Bin Wang Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii

Search for other papers by Bin Wang in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The tropical Indian and western Pacific oceans are two prominent action centers for tropical 30–60-day convective variability. When convection is enhanced over the equatorial Indian Ocean, the tropical western Pacific often experiences an abnormal dry condition (phase I), whereas the development of the convection over the tropical western Pacific tends to be accompanied by suppressed convection in the equatorial Indian Ocean (phase II). This convection seesaw is a fundamental characteristic of the tropical 30–60-day oscillation.

The seesaw is intimately associated with the activity of propagating low-frequency convective systems (LFCSs). Its formation process is season dependent. Typical boreal summer seesaw results from a time-lagged development of two systems: a western system that originates in the equatorial Indian Ocean and moves eastward and/or northward and an eastern system that develops in the western Pacific monsoon region and moves westward and/or northward. The boreal winter seesaw, on the other hand, is caused by the longitudinal dependence of the evolution of eastward-moving LFCSs that strongly amplify in the equatorial Indian Ocean, weaken and/or split when rapidly passing over the maritime continent, and reintensify in the South Pacific convergence zone (SPCZ).

There are two phases of the seesaw. During the first phase, the LFCSs interact with the Indian monsoon in boreal summer and Indonesian–Australian monsoon in boreal winter. Likewise, during the second phase, the LFCSs interplay with monsoon circulations over the western Pacific monsoon trough in boreal summer and over the SPCZ in boreal winter. The convection seesaw activity is closely tied to the corresponding active-break monsoon cycles over the two polar regions of the seesaw.

Abstract

The tropical Indian and western Pacific oceans are two prominent action centers for tropical 30–60-day convective variability. When convection is enhanced over the equatorial Indian Ocean, the tropical western Pacific often experiences an abnormal dry condition (phase I), whereas the development of the convection over the tropical western Pacific tends to be accompanied by suppressed convection in the equatorial Indian Ocean (phase II). This convection seesaw is a fundamental characteristic of the tropical 30–60-day oscillation.

The seesaw is intimately associated with the activity of propagating low-frequency convective systems (LFCSs). Its formation process is season dependent. Typical boreal summer seesaw results from a time-lagged development of two systems: a western system that originates in the equatorial Indian Ocean and moves eastward and/or northward and an eastern system that develops in the western Pacific monsoon region and moves westward and/or northward. The boreal winter seesaw, on the other hand, is caused by the longitudinal dependence of the evolution of eastward-moving LFCSs that strongly amplify in the equatorial Indian Ocean, weaken and/or split when rapidly passing over the maritime continent, and reintensify in the South Pacific convergence zone (SPCZ).

There are two phases of the seesaw. During the first phase, the LFCSs interact with the Indian monsoon in boreal summer and Indonesian–Australian monsoon in boreal winter. Likewise, during the second phase, the LFCSs interplay with monsoon circulations over the western Pacific monsoon trough in boreal summer and over the SPCZ in boreal winter. The convection seesaw activity is closely tied to the corresponding active-break monsoon cycles over the two polar regions of the seesaw.

Save