Baroclinic Instability in a Two-Layer Model with Parameterized Slantwise Convection

Abstract

A two-layer primitive equation model with a parameterization for slantwise convection is used to study explosive cyclones. The parameterization includes a simple representation of the planetary boundary layer, as well as deep and shallow cloud types. The major results are 1) the two-layer model produces a realistic explosive cyclone, 2) the explosive deepening coincides with the formation of the ?bent-back warm front,? 3) fronto-genetic calculations reveal an indirect circulation due to ?tilting? in the intense warm front, and 4) the quasi-Lagrangian heat and vorticity budgets indicate strong interaction of the lower- and upper-level flow during the rapid spinup stage. These results suggest a sequence of events involved in some explosive cyclogenesis: Convection leads to rapid frontogenesis and the formation of a bent-back warm front. The sudden surge of cold advection in the regions of the bent-back warm front then forces the upper-level heights over the cyclone center to fall in a rather dramatic way. Increased upper-level vorticity advection interacts with the low-level system, leading to explosive cyclogenesis.