2 - Climate and Rainfall Variability in the Humid Tropics

Summary

ABSTRACT

Although the absolute variability of weather features in the tropics is less than that at higher latitudes, tropical weather and climate are rich in variation on time scales from the diurnal to decadal. Moreover, the climate of the tropics is closely linked to the behaviour of the upper oceans, which provide inertia to the climate system and which act as a moisture source for convective heating of the atmosphere. Latent heating from convection is a common factor in all aspects of variability in the tropical climate. The links between the major causes of variability are reviewed in the present work.

INTRODUCTION

Weather at the mid-latitudes is clearly associated with baroclinic fronts and other synoptic features that are controlled by the earth's rotation. It is, therefore, natural to assume that the tropics, where these Coriolis effects are small, should have weather with a distinctive lack of structure. Charney & Shukla (1981) quantify this effect by showing that the temperature variance increases away from the equator. This apparent lack of structure is supported by the observation that persistence is a useful weather forecast in the tropics. Indeed, operational short-range weather forecasting is generally no more accurate than persistence (Holland et al., 1987). But this result suggests that the basically quiescent weather is punctuated by intermittent and unpredictable events. In this paper, these events, their interconnections and progress on improving our understanding of them are reviewed.

One manifestation of the apparent lack of features in tropical weather is the observation that the temperature generally does not vary greatly, even following the passage of a weather system.