GENERATION OF MOIST POTENTIAL VORTICITY IN EXTRATROPICAL CYCLONES - PART II - SENSITIVITY TO MOISTURE DISTRIBUTION

The effects of different moisture distributions on the generation of m oist potential vorticity (MPV) in extra tropical 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 negati ve MPV depends on the baroclinic and moisture gradient vectors. It can also depend on the locations of condensation. Although condensation h as no direct effect on MPV production, MPV can be generated in the nei ghborhood of condensation where the gradients of potential temperature and moisture have significantly changed. It is found in the sensitivi ty experiments that the bent-back warm front is the most favored regio ns for negative MPV generation because strong deformation of moisture and potential temperature fields occur. After the cyclones mature, neg ative MPV moves into the warm core. It can be transported upward throu gh the enhanced vertical motion induced by latent heat release.