The characteristics of landfalling tropical cyclones are quite different. Some of them will quickly dissipate (6-12 hours, refer to STC) right after they touch the ground surface while others will be sustainable over land for a long period (3-5 days, refer to LTC) after they made landfall. Statistical analyses demonstrated that the severe calamities were closely related to those typhoons who were sustained over land for longer time period. Therefore, it is necessary to study the sustaining mechanism of TC over land.

In this study,diagnostic analyses were employed with composite data of 7 cases of LTC and 7 cases of STC which made landfall on Chinese coastal area. Then using PSU/NCAR MM5v3 model,five sets of numerical experiments were performed on a LTC with different vapor transportations and contrasted with the control experiment.

Composite analysis results indicate that the vapor transportations of LTC and STC have different characteristics. LTC connects with the lower layer southwesterly moisture channel after its landfall while the STC disconnects with such moisture transportation. Simulation results show that the intensity of the LTC would decrease obviously if without the vapor transportation from all lateral boundaries, its circulation would dissipate after 42h. The vapor transportation from the south boundary plays an important role for the sustaining of the tropical cyclone over land.