A diabatic generalization of the quasigeostrophic frontogenesis function

Abstract

A generalized frontogenesis function is defined in terms of the ice-liquid water potential temperature, which is a thermodynamic variable conservative under all water phase changes. The generalized frontogenesis function is the projection of a new vector, Q*, on the quasihorizontal ice-liquid water potential temperature gradient. Q* can be seen as the diabatic version of the quasigeostrophic Q-vector. In regions of large latent heat release due to phase change, the generalized frontogenesis function, F*, is a more complete and precise tool for delimiting upward air flow in frontal zones than the classical quasigeostrophic frontogenesis function. The proposed quasigeostrophic frontogenesis function is tested on a real meteorological situation characterized by the genesis and development of a warm front over northern Iberian Peninsula. The new quasigeostrophic frontogenesis function is compared with the classical Pettersen's function obtaining an improvement not only in the diagnosis of frontal development but also in the location of frontal zones.