A case study of coupling between low- and upper-level jet-front systems: investigation of dynamical and diabatic processes

Abstract

An example of coupling between an upper-level and a low-level jet-front system is analyzed using the mesoscale hydrostatic model SALSA. In both simulations it is shown that the low-level branch of the indirect and tranverse ageostrophic circulation, associated with the exit region of the upper-level jet streak, is the origin of the cold-front undulation beneath the upper-level jet axis. Other effects of the coupling processes are diagnosed in the full-physics simulation: the intensification of the low-level jet, the formation of the frontal band ahead of the cold front on the left side of the low-level jet, the intensification of the convective system close to the ascending branch of the transverse indirect circulation, and the kinetic energy generation in the exit region of the upper level jet streak. An examination of the isentropic components of the ageostrophic wind shows that the upper-level branch of the indirect circulation is the inertial advective component of the ageostrophic wind, whereas the low-level branch is mainly isallobaric. -from Authors