Three-dimensional wind structure around convective elements over a tropical island

Abstract

During the summer of 1973 a pilot balloon experiment was undertaken on the island of Barbados. One of the objectives was to obtain measurements of the flow fields around cumulus clouds during undisturbed conditions. The main results were: less than 1% of the balloons entered the base of clouds; no balloon was observed to enter the sides of the clouds; the clouds moved on the average of 2 m s−1 slower than the surrounding air when positive vertical shear existed; balloons accelerated over the clouds on the cloud's upwind side instead of entering or circumscribing them; when in close proximity of the clouds balloons on either side of the clouds moved laterally, not into them, but into the overriding current on the upwind side; up‐ and downdrafts associated with the clouds were of the order of 1–3 m s−1; and circulation around a horizontal axis through the cloud and perpendicular to the general flow may support the existence of a cumulus cloud street parallel to the flow for hours.