An Eastern Pacific Tropical Plume

Abstract

Synoptic-scale cloud systems, called tropical plumes, develop from disturbances in the eastern Pacific ITCZ and in conjunction with amplifying troughs to the north; a common spatial pattern and temporal evolution accompany most events. A blend of disparate data and analyses yields a three-dimensional description of a case study during the FGGE January 1979 special observing period. That this tropical plume is typical is corroborated with a climatology of 41 systems and a less detailed climatology encompassing over 200 plumes. Tropical plumes are accompanied by intense drying and subsidence within the trough to the northwest and a strong subtropical jet within the plume. Wind observations for the case study show that the jet originates near the equator. A disturbance in the low-level easterly trades exists independently from the upper trough when the plume initiates; such anticyclonic curving wind patterns are common at initiation. The plume developed simultaneously out of several disturbances along its axis. A frontal pattern of intensifying moisture gradient, developing thermal gradient and inversion, strengthening jet level winds, solenoidal overturning, and deepening of the tradewind inversion appears along the northwest flank and downstream of the plume. Plumes cease normally when their tropical and nontropical aspects become separated.