Shallow cumulus and cumulonimbus clouds are nearly ubiquitous throughout the tropics. They are the basic building blocks from which larger cloud features develop. Tropical cyclones, for example, develop out of the growth of many clouds that were at one point relatively isolated and shallow. Mesoscale systems in the intertropical convergence zone or the Madden-Julian Oscillation are preceded by shallow convection, and shallow convection may, in some instance, precede monsoon onset. An inability to represent such small clouds in models of the atmosphere contributes to difficulty in explaining much larger events that directly impact human civiliation. However, little is known about the detailed structure of small convective clouds in the tropics.
Few past field experiments involved directly gathering information about cumulus cloud structure. Many things need to be directly observed: temperature and humidity inside clouds and in their immediate environments, the 3-dimensional motions in and near clouds, and drop size distributions inside clouds are a few examples. Some limited information might be gained using Doppler radar. While dual-Doppler radar can provide some estimate of horizontal wind motions, single Doppler radar might provide rough estimates of the same for a composite shallow, isolated tropical cumulonimbus cloud. Using dual-polarimetric radar, my current work looks at the size of cloud updraft cores relative to the width of surrounding cloud area, the aspect ratio of drops inside the cloud, and in a composite form, vertical profiles of divergence within the cloud.
In the future, in situ measurements of cumulus and shallow cumulonimbus clouds must be gathered with greater frequency. This will become more important as global models of the atmosphere increase in horizontal resolution as computing power presumably increases. In future field experiments down the road, we hope to equip unmanned aerial vehicles, or simple drones, with GPS tracking and meteorlogical instrumentation that can sample small tropical clouds that are simultaneously viewed by radar.