Gravity Waves Generated during Frontogenesis

Abstract

Gravity waves forced by nonhydrostatic and nongeostrophic processes within a frontal zone are discussed. In particular, stationary waves immediately above and below the surface front are considered. The waves that appear above the front are horizontally stationary with respect to the front, but are vertically propagating. The vertical wavelength here is given by 2π?/N, since the waves are nearly hydrostatic. The horizontal wavelength of the waves above the front is determined by standing waves that set up below the Front. These waves corrugate the frontal surface, and these corrugations, in turn, determine the horizontal scale of the waves above the front. The waves under the front are standing and are trapped between the earth's surface and the frontal zone which, due to its conditions of flow reversal and small Ri, is assumed to be a reflector of gravity waves. The horizontal scale of the standing waves is determined by their vertical wavelength and the slope of the frontal surface. These waves are shown to break, and additional stationary waves appear above each of the breaking zones. We suggest that the waves described here might account for some of the banding seen in satellite images of frontal zones.