Heat Convection from the Earth's Surface

Abstract

EVIDENCE has been presented1 which suggests quite strongly that a regime of effectively free convection of heat begins to operate in the surface layers of the atmosphere at a negative Richardson number as low as 0.02 or 0.03. It is improbable that this can take the form of regular cellular convection of the type studied by Rayleigh and recently elaborated by Malkus2, for this would require in a layer of depth h that the symbols having their usual significance. If we replace x and v by their turbulent counterparts and average through the depth of the layer, then where α is less than but comparable with unity. This transforms the Rayleigh criterion into a Richardson criterion When there is some wind and wind shear, therefore, cellular convection should not set in until −Ri exceeds a value of order 1–10, whereas the free-convection regime in fact effectively sets in at a very much smaller value.