Tropical cyclones(TCs) have a significant impact on China's Mainland.The purpose of this study is to develop an impact index which correlates with both the strong wind and heavy rainfall/flood damage caused by TCs in China's Mainland.By considering the radius of TCs,we first define the total destructiveness index(TDI) and total column water vapor index(TVI).Economic loss is used to represent the impact of landfalling TCs.The analysis is based on 30 landfalling TCs between 2001 and 2007,and identified significant correlations between the impact of landfalling TCs and the TVI(TDI).The correlations between the impact of landfalling TCs and TVI,TDI and maximum wind speed of TCs before landfall are 0.751,0.59 and 0.345,respectively.This study also shows that landfalling TCs with a higher TVI usually bring heavier rainfall,and result in more economic losses in China.A TC impact index is defined as a function of TVI and TDI.The correlation between TC impact index and economic loss was found to be significant(r=0.769).Tropical storm Bilis in 2006 is classified as the landfalling TC with the highest impact index between 2001 and 2007 and Matsa,in 2005,as the second highest impact index in this same interval.Using a system cluster analysis method,30 landfalling TCs in this study were graded into five categories according to their impact indices.Category 5,which is the highest level,included only one TC,which constituted 4% of the total TCs studied.Category 4 included three TCs(10%).Categories 3 and 2 included seven TCs each(23%) and Category 1 included 12 TCs(40%).
ZHANG QingHong1,WEI Qing2 & CHEN LianShou3 1 Department of Atmospheric and Oceanic Science,School of Physics,Peking University,Beijing 100871,China
The effects of different planetary boundary layer （PBL） processes on the secondary eyewall formation （SEF） and eyewall replacement cycle （ERC） in Typhoon Sinlaku （2008） are investigated by using the Weather Research and Forecasting （WRF） model with six different PBL schemes. The SEF and ERC have been successfully simulated with all the six PBL schemes and the mechanism for the SEF and ERC proposed in our previous study has been reconfirmed. It is demonstrated that both the intensification of the storm and the inward-moving outer spiral rainband contribute to the SEF. After the SEF, the associated diabatic heating enhances the secondary eyewall further, and the transfer of moist air from outer region to the primary eyewall is cut off by the secondary eyewall. In such a way, the primary eyewall dies and an ERC completes. It is found that some simulated features of the SEF and ERC, such as the time and location of the SEF and duration of the ERC, do vary from one simulation to another. In order to describe the features of the SEF and ERC quantitatively, a concentric eyewall index （CEI） is defined and a threshold of the CEI is suggested to determine the onset of the secondary eyewall. The differences in the simulated SEF and ERC are discussed and some possible causes are suggested. In addition, based on the CEI threshold and the conservation law of angular momentum, a formula to predict the location of SEF is also proposed and applied to all the six simulations. The success and failure of the formula are then discussed.
Diurnal variation of tropical cyclone (TC) rainfall in the western North Pacific (WNP) is investigated using the high-resolution Climate Prediction Center's morphing technique (CMORPH) products obtained from the National Oceanic and Atmospheric Administration (NOAA). From January 2008 to October 2010, 72 TCs and 389 TC rainfall days were reported by the Joint Typhoon Warning Center's (JTWC) best-track record. The TC rain rate was partitioned using the Objective Synoptic Analysis Technique (OSAT) and interpolated into Local Standard Time (LST). Harmonic analysis was applied to analyze the diurnal variation of the precipitation. Obvious diurnal cycles were seen in approximately 70% of the TC rainfall days. The harmonic amplitude and phase of the mean TC rainfall rate vary with TC intensity, life stage, season, and spatial distribution. On the basis of intensity, tropical depressions (TDs) exhibit the highest precipitation variation amplitude (PVA), at approximately 30%, while super typhoons (STs) contain the lowest PVA, at less than 22%. On the basis of lifetime stage, the PVA in the decaying stage (more than 37%) is stronger than that in the developing (less than 20%) and sustaining (28%) stages. On the basis of location, the PVA of more than 35% (less than 18%) is the highest (lowest) over the high-latitude oceanic areas (the eastern ocean of the Philippine Islands). In addition, a sub-diurnal cycle of TC rainfall occurs over the high-latitude oceans. On the basis of season, the diurnal variation is more pronounced during summer and winter, at approximately 30% and 32%, respectively, and is weaker in spring and autumn, at approximately 22% and 24%, respectively.
