On the Influences of Fields of Motion, Baroclinicity and Latent Heat Source on Frontogenesis

Abstract

This study clarifies the dependence of frontogenesis on vertical and horizontal motion, baroclinicity and the liberated latent heat of vaporization. In a typical case, the relative contributions of the horizontal and vertical deformation fields were examined at the 800- and 600-mb levels. A comparison of the vertical deformation field under the dry adiabatic and pseudo-adiabatic assumptions was made to estimate the importance of the released latent heat. The vertical circulation associated with low-level convergence along a cold front was studied also. The following results emerged: 1) Low-level convergence is of primary importance in maintaining frontogenesis in the lowest layers. This convergence is chiefly responsible for drawing moist warm air and cold air into closer contact. This resulted in a solenoidally direct circulation. 2) The effect of this circulation is to cause frontolysis at higher levels. However, when the release of latent heat is taken into account frontogenesis may result, depending upon the amount and the distribution of the heat released. 3) Meteorological quantities, such as temperature, wind, etc., are normally not uniform (horizontally) along the front and the variations, although not conspicuous, are often quite important in determining the distribution of vertical motion.