Diagnosis on the Characteristics of the Mesoscale Potential Vorticity in Intensity-Maintaining Tropical Cyclone

The distribution of Potential Vorticity (PV) in the intensity-maintaining of Tropical Cyclone (TC) Fitow (2013) at different stages are investigated by using the high-resolution data. Results show that the high value PV band and its change in the inner core are associated with the intensity change of TC. The high value PV area is not only corresponded with the convective bursts in the inner core, but also well consistent with the maintaing intensity period. Moreover, the highest radial PV gradient occurs in the eyewall. The changes of the mesoscale high value PV are analyzed both in time and in space. It is found that the vertical cross-section of high value PV transfers from a monopole (in the development period of TC) to a hollow pole pattern (in the intensity-maintaining phase), while the monopole structure with a smaller PV value is re-formed in the rapid decay period of TC. The horizontal distribution of PV presents an annular ring of high vlaue PV during the intensification of TC Fitow. The PV budget is diagnosed and the results show that the horizontal and vertical advection of PV, as well as the initial enhancement of condensation heating in the inner core play an important role in the mesoscale high PV distribution. In addition, it is indicated that the condenstion heating has an important effect on developing the hollow structure of PV at the intensity-maintaing stage, while the horizontal advection has a positive contribution on PV tower in the upper-middle level and the vertical advection plays an intermediary role in the redistribution of high value PV.

Keywords: Tropical Cyclone(TC) ; Meso-scale PV; Hollow PV and Monopole PV; PV budget.

ACKNOWLEDGMENTS

This work was supported by the National Natural Science Foundation of China(40775055,41675058,41175054,41275002,41230421) .