A case study on the use of digitized cloud brightness to represent large-scale convection in the tropics

Abstract

Digitized cloud brightness data for July 1969 are examined to determine the degree of relationship between organized brightness patterns and the large-scale convection field in the tropical western North Pacific. Correlation coefficients between kinematically computed vertical motion fields and cloud brightness are generally low, except for a few notable days. This may be due to the quality of the available data, particularly the vertical motion field. Nevertheless, indications of better correspondence between the two fields are noted late in the month for the western portion of the region, for the latitude band between 10˚N and 20˚N. Examination of time-longitude sections reveals a close association between propagating brightness patterns and vertical motion fields, indicating that the former are reflections of synoptic wave passages, rather than simply inactive clouds advected by zonal flow. In view of the potential usefulness of such satellite data, a technique is proposed that uses satellite cloud data to objectively determine the large-scale tropical flow.