On an instability mechanism in a stably stratified atmospheric layer over a moistened surface

Abstract

In air stratified by a specific humidity gradient, the vertical motions result in variations in specific humidity (mixing ratio) near the underlying surface. This, in turn, causes a variation of evaporation from the surface, resulting in horizontal thermal inhomogeneities on the surface, which under certain conditions can strengthen the initial vertical motions. The linear problem of the stability of the system under consideration is solved in this paper, boundaries of the unstable region are defined, and specific values of growth rates of disturbances are investigated. The estimates show that even in a density-stratified atmospheric layer over a moist surface, rapid development of disturbances with horizontal scales of several hundred metres is possible. The horizontal sizes of the most rapidly growing modes, as a rule, are an order of magnitude larger than the vertical sizes. The possibility of observing this instability under natural conditions is discussed.