Instability of Viscous Fluid Motion

Abstract

THE experiments of Bénard, and the theoretical discussion by the late Lord Rayleigh, referred to by Major Low, deserve careful consideration from the point of view of their application in meteorology. Rayleigh showed that a layer of fluid can remain stable, even with the denser fluid above, in virtue of its conduction and viscosity. In the atmosphere it is customary to regard stability as associated with a fall of temperature with height limited by the adiabatic lapse-rate, 1° C. per 100 metres for dry air, a greater lapse-rate, or fall of temperature with height, denoting instability. It is, however, an accepted fact that lapse-rates greatly in excess of this value are of frequent occurrence, especially in the lowest 10 or 20 metres, at which height they can be observed at some time of day on almost any day of the year.