Preliminary Study Of Tropical Cyclone Intensity Change In Western North Pacific

Intensity rapid change of tropical cyclones(TC) have considerable effect on TC impacts. It is a great problem for forecasting, and also a frontier topic in TC research. In this thesis, characteristics of the intensity change of TC in western north Pacific Ocean from the year of 1984 to 2013 is analyzed. Its relationship with environmental factors, such as vertical wind shear(VWS), sea surface temperature(SST), and inner core structure, such as radius of maximum wind(RMW), is also analyzed. A group of rapid intensifying(RI) TC and a group of rapid weakening(RW) TC are composited, and characteristics of each group are compared. Finally, the rapid intensification of super typhoon Muifa is diagnosed, and effects of factors above on RI are analyzed.Statistical analysis indicates that,(1) There are 20983 samples in total, only 12.0% in which are with rapid changing phenomenon, while about 92.7% of RI samples occur are stronger than typhoon(TY) level.(2) TCs with VWS over 12 m/s have difficulty in intensifying or RI, except for the strong ones. TCs with strong VWS in low level are more hardly formed and intensified.(3) The intensifying and RI of TC mainly occur in a sea region with 28.5-30°C SST, the intensity level of TC which can appear RI in relatively low SST tends higher.(4) 76.3%(23.7%) of 24-hour variation of radius of maximum winds for the intensifying tropical cyclone is reduced(dilated), and 68.2%(31.8%) of 24-hour variation of radius of maximum winds for the weakening tropical cyclone is dilated(reduced).Composite analysis shows that,(1) VWS of RI TC is under 3m/s, which is smaller than VWS of RW TC – 8m/s. VWS of RW TC decreases rapidly during the RW process.(2) The RI TC occur in a sea region with SST higher than 29°C. To the northeast of RI TC, there is an area with SST higher than 30°C. The RW TC occur in a sea region with SST lower than 29°C. To the north of RW TC, there is an area with SST lower than 26°C.(3) RMW of RI TC decreases rapidly. RMW of RW TC decreases slowly before RW, but decreases rapidly after RW.Diagnosed analysis of super typhoon Muifa(1109) verifies results above. The rapid intensification of Muifa lasts for 24 hours. Results show that, during Muifa rapid intensification, its environmental VWS decreases rapidly, the SST is higher than 28°C, and the RMW decreases rapidly. The kinetic energy budgets of Muifa shows that the generation term of kinetic energy is the main source of kinetic energy, while the vertical flux divergence term is very small, and the fraction term and horizontal flux divergence term is the sink.