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. The case study chosen is the cold front sampled during the intensive observation period 2 of the Mesoscale Frontal Dynamic Project FRONTS 87 experiment (11 November 1987). Two prominent features of the cold front are a well-developed undulation and a frontal band ahead of the undulation. Dynamic and diabatic processes of the coupling are investigated through the results of two numerical simulations: full physics and adiabatic. In particular, the roles of ageostrophic circulations are investigated through the decomposition of the ageostrophic wind into its isentropic components: the advective inertial and the diabatic inertial components, and the isallobaric component. In both simulations it is shown that the low-level branch of the indirect and transverse ageostrophic circulation, associated with the exit region of the upper-level jet streak, is the origin of the...