| This study is concerned with climatic variability in three important regions of the tropics, namely Australasia and western Pacific, the equatorial Pacific, and the tropical Americas. (i) For Australasia and the western Pacific composite analyses show for the low/warm as compared to the high/cold phase of the Southern Oscillation, increased convective activity over the equatorial Pacific, a statistically significant northeastward shift of the South Pacific Convergence Zone, enhanced lower-tropospheric convergence, upward motion, and upper-tropospheric divergence. The divergent component of the wind at 200 mb is directed primarily northward into a broad band of upper-tropospheric convergence, which feeds subsidence, lower-tropospheric divergence, and clear skies, and contributes to positive surface pressure departures in the western North Pacific. (ii) For the equatorial Pacific trends of circulation and climate during 1948-92 were analyzed from observations of sea surface temperature (T), cloudiness (C), sea level pressure (P), specific humidity (Q), and zonal wind component. From indices compiled for the cold tongue in the East, the central equatorial Pacific, the warm pool in the West, and the eastern equatorial Indian Ocean, interannual relationships were compared with long-term trends. On the interannual time scale the significant negative T-P correlations in the eastern Pacific indicate a hydrostatic forcing of T on P, and the negative P-C correlations in the western Pacific and eastern Indian Oceans are consistent with anomalously high P through subsidence favoring clear sky. The tropical Pacific is warming and most markedly in the East; there is a weakening of the westward pressure gradient; slackening of the easterlies in the central equatorial Pacific; and increasing Q and C in the East. In context these evolutions reflect a tendency towards patterns characteristic of the low/warm phase of the Southern Oscillation. (iii) Regarding the tropical Americas during April the South Atlantic has warmed more than the North Atlantic, strengthening the interhemispheric temperature gradient, and contributing towards an enhanced interhemispheric pressure gradient, southward displacement of the ITCZ, and accelerated Northeast trades. Over the Amazon basin, increasing mid-tropospheric ascending motion and upper-tropospheric divergence accompany trends of increasing convective activity and river discharge. |
