Numerical Study on the Rapid Decaying and Re-intensification of a Mid-latitude Typhoon

摘要

A numerical simulation and piecewise potential vorticity (PV) inversion diagnosis are conducted on the rapid decaying and re-intensification of Typhoon Bart (1999) over the western North Pacific Ocean. The simulated typhoon during the decaying stage was weakened by a negative PV anomaly associated with an outflowing cloud shield in strong vertical shear environment. The negative PV anomaly formed at the upper side of the latent heat release maximum in cumulus convections. In its re-intensification stage, a positive PV anomaly associated with an upper-level trough vertically coupled with the low-level typhoon remnant, resulting in its unexpected re-intensification. The negative PV anomaly, which has caused the rapid cyclolysis, played an important role in developing a jet streak at the upper troposphere and forcing a vertical ascent in the typhoon remnant. We suggest that the processes of extratropical transition of a mid-latitude typhoon are very much dependent on negative PV anomalies due to diabatic heating processes.