Synoptic climatology of transient tropical intraseasonal convection anomalies: 1975–1985

Summary

Pentad mean anomaly maps were used to study the climatology of tropical intraseasonal convection anomaly (TICA) as a dynamic system. One hundred and twenty-two events were identified and classified into three categories: eastward (77), independent northward (27), and westward (18) propagation. The eastward propagation is more active in boreal winter than in summer, while the independent northward propagation, which is not associated with equatorial eastward propagation, occurs in boreal summer from May to October.

The eastward moving TICA exhibits three major paths: 1) eastward along the equator from Africa to the mid-Pacific, 2) first eastward along the equator, then either turning north-east to the northwest Pacific or turning southeast to the southwest Pacific at the maritime continent, and 3) the main anomaly moves eastward along the equator with split center(s) moving northward over the Indian and/or western Pacific Oceans. The equatorial Indian Ocean and the western Pacific intertropical convergence zone are preferred geographic locations for their development, while the maritime continent and central Pacific are regions of dissipation.

Independent northward propagation is confined to the Indian and western Pacific monsoon regions. Its existence suggests that the mechanism responsible for meridional propagation may differ from that for eastward propagation.

The dynamic effect of the equator and the thermodynamic effect of the underlying warm ocean water are basic factors in trapping TICA in the deep tropics, while the annual march of maximum SST (thermal equator) and the monsoon circulation have profound influences on the annual variation and meridional movement of TICA.