The influence of thermal effects can be classified into three categories: stable,unstable and neutral stratification. Unstable stratification occurs when there is a lotof surface heating, causing warm air near the surface to rise. As it rises, it expandsdue to reduced pressure and therefore cools adiabatically. If the cooling is notsufficient to bring the air into thermal equilibrium with the surrounding air then itwill continue to rise, giving rise to large convection cells. The result is a thickboundary layer with large-scale turbulent eddies. There is a lot of vertical mixingand transfer of momentum, resulting in a relatively small change of mean windspeed with height.
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