INTERACTIONS BETWEEN THE VELOCITY FIELDS OF SUCCESSIVE THERMALS

Abstract

Solitary thermals and continuous plume thermals both occur in nature, and the intermediate case of interacting successive thermals in a series may also be an important part of atmospheric convection. This analysis shows that residual updraft and vorticity concentration in the wake of a preceding thermal can have important effects on its successor. A fluid mechanics model of buoyant clouds rising through a rotating medium is constructed for the purpose of predicting some of the sequential thermal effects that can be measured quantitatively for thermals simulated in the laboratory. The agreement with theory is satisfactory for the parameters that are subject to measurement, but some relevant constants can only be determined experimentally. For a situation in which a first thermal reacts strongly with the rotation field, it is shown that a succeeding thermal may receive a sizable enhancement of its vertical momentum even though its predecessor was suppressed by the interaction. These findings may be relevant to the generation and maintenance of small-scale atmospheric vortexes such as tornadoes, waterspouts, and dust devils.