A diabatic generalization of the quasigeostrophic frontogenesis function

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 t he projection of a new vector, Q*, on the quasihorizontal ice-liquid water potential temperature gradient. Q* can be seen as the diabatic version of t he quasigeostrophic Q-vector. In regions of large latent heat release due t o phase change, the generalized frontogenesis function, F*, is a more compl ete and precise tool for delimiting upward air flow in frontal zones than t he classical quasigeostrophic frontogenesis function. The proposed quasigeo strophic frontogenesis function is tested on a real meteorological situatio n characterized by the genesis and development of a warm front over norther n Iberian Peninsula. The new quasigeostrophic frontogenesis function is com pared with the classical Pettersen's function obtaining an improvement not only in the diagnosis of frontal development but also in the location of fr ontal zones.