BAROCLINIC INSTABILITY IN A 2-LAYER MODEL WITH PARAMETERIZED SLANTWISE CONVECTION

A two-layer primitive equation model with a parameterization for slant wise convection is used to study explosive cyclones. The parameterizat ion 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 explosi ve deepening coincides with the formation of the ''bent-back warm fron t,'' 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 sugg est a sequence of events involved in some explosive cyclogenesis: Conv ection leads to rapid frontogenesis and the formation of a bent-back w arm front. The sudden surge of cold advection in the regions of the be nt-back warm front then forces the upper-level heights over the cyclon e center to fall in a rather dramatic way. Increased upper-level vorti city advection interacts with the low-level system, leading to explosi ve cyclogenesis.