Equatorial Response to Northeasterly Cold Surges as Inferred from Satellite Cloud Imagery

Abstract

Day-today convective activity in the equatorial regions (10°N?10°S and 90?180°E) during December 1974 and January 1975 was estimated from NOAA satellite visible imageries using simple visual techniques. The daily convective estimates were composited with respect to the phase of individual cold surge episodes occurring during the two-month period. By decomposing the data into symmetric and anti-symmetric components with respect to the equator, it was shown that eastward and westward propagating cloud clusters had phase speeds ?10 m s?1 and ?5 m s?1, respectively, and were generated near southwestern Borneo following a cold surge onset. The strong equatorially trapped character of the eastward moving components suggested the possibility of Kelvin wave responses. The eastward moving convective clusters interacted strongly with westward moving disturbances which may be identified with low-order symmetric Rossby waves originating from the western Pacific. The predominantly larger response amplitude of the symmetric compared with that of the antisymmetric component, especially near the equator, suggested that the most strongly trapped of these waves were likely generated from heat sources concentrated near the equator.