Generation of Moist Potential Vorticity in Extratropical Cyclones. Part II: Sensitivity to Moisture Distribution

Abstract

The effects of different moisture distributions on the generation of moist potential vorticity (MPV) in extratropical cyclones are examined by numerical simulations. These sensitivity experiments show that low-level negative MPV generation depends on the initial distribution of potential temperature and moisture gradients. The generation of negative MPV depends on the baroclinic and moisture gradient vectors. It can also depend on the locations of condensation. Although condensation has no direct effect on MPV production, MPV can be generated in the neighborhood of condensation where the gradients of potential temperature and moisture have significantly changed. It is found in the sensitivity experiments that the bent-back warm front is the most favored regions for negative MPV generation because strong deformation of moisture and potential temperature fields occur. After the cyclones mature, negative MPV moves into the warm core. It can be transported upward through the enhanced vertical motion induced by latent heat release.