What do thermals look like?
Copyright 1995 by Wayne M. Angevine May be freely redistributed on Internet as long as this message is included. Model sailplane and free flight fliers are interested in the structure of thermals, which provide the energy for their flying. Here is my attempt to describe thermals. I’m an atmospheric physicist working in the boundary layer. This is not a scientific article, but my views based on extensive reading and observations. The short answer to the question is that thermals are columns of rising air. A longer answer requires what may seem like a digression into boundary layer physics. The boundary layer is the layer of air near the earth’s surface that is affected by the surface on scales of an hour or so. The sort of boundary layers we’re interested in are *convective* boundary layers, which occur in the daytime over land in weak to moderate wind conditions. There are other sorts, but they don’t produce thermals as such. I’ll also assume relatively flat and uniform terrain, and at
