A study of the variation of convective activity associated with easterly waves in the tropical Pacific using satellite radiation data.

Abstract

A composite study is carried out to deduce the structure of convective activity associated with easterly waves at five tropical Pacific radiosonde stations, Majuro, Ponape , Truk , Yap, and Koror, for the latter halves of 1974, 1975 and 1976. The data used include digitized satellite infrared radiation and albedo. The resultant structure, in general, shows maximum convective activity in or near the wave troughs. The distribution is similar to that of the humidity field composited previously by Bepristis (1977). In order to examine the possible effects of sea-surface temperature on tropical convection, the wave-organized convection and the seasonal-mean convective fields as indicated by the satellite data are compared to the seasonal mean seasurface temperature. It is found that west of Majuro the interannual and spatial variation of the 10-degree upstream sea-surface temperature have a much better positive correlation with those of the wave-organized convective field than those of the seasonal mean. This result is consistent with that for the latter halves of 1972 and 1973 obtained by Delaney (1977) using subjectively-digitized satellite cloud data, and Bepristis' (1977) result of a positive correlation between the waves' upper-tropospheric thermal structure and the 10-degree upstream sea-surface temperature. It suggests that the sea-surface temperature in the immediate upstream vicinity may exert a positive influence on the convective activity modulated by an easterly wave. However, no similar influence of the local sea-surface temperature can be found for the total convection.