An instability mechanism in the atmosphere over a water body

Abstract

¶The previously unexplored mechanism of the hydrodynamic instability of the atmospheric boundary layer over a water body is theoretically investigated. In air, stratified with respect to moisture, vertical motions produce variations in specific humidity (mixing ratio) near the interface surface. This, in turn, causes variation in evaporation from the water surface and horizontal thermal inhomogeneities result on the surface which, under certain conditions, can strengthen the initial vertical motions. In this paper the linear problem of the stability of the system under consideration is solved. Boundaries of the unstable region in the space of physical parameters are defined, and specific values of growth rates of disturbances are investigated. The results show the possibility of the development of disturbances with horizontal scales of several hundred metres for a period of about one hour even for the stable stratified atmospheric layer over a water surface and in the absence of destabilizing shears of velocity. The horizontal sizes of the most rapidly growing modes, as a rule, are an order of magnitude larger than the vertical ones.