FRONTOGENESIS AND FRONTOLYSIS AS A THREE-DIMENSIONAL PROCESS

Abstract

A detailed analysis is presented to show the atmospheric structure during the earlier formative stages of a deep, upper trough. Over the western United States, a well-marked west-east frontal layer extends through the whole troposphere; in upper levels, this disappears within a short distance eastward. Individual changes in vorticity, vertical shear, horizontal temperature gradient, and vertical stability are discussed for air particles streaming eastward, out of the frontal layer. Factors in individual frontolysis vary in relative importance at different levels. In particular, variations of the vertical and horizontal components of vorticity and potential temperature gradient are chiefly effected, in the middle troposphere, by horizontal gradients of vertical motion and vertical gradients of the non-geostrophic wind component normal to the frontal layer. Near the maximum-wind level and near the earth's surface, divergence processes and deformation fields in the horizontal flow are of predominant importance. A general scheme is suggested for the vertical and transverse motions during frontolysis (or frontogenesis), in which the varying processes leading to changes in wind and temperature fields at different levels are interrelated in a three-dimensionally consistent manner.