： Using the National Center for Environmental Prediction reanalysis data on 1.0°×l.0° grids and data from theTropical Cyclone yearbook （2000）, a diagnostic analysis and numerical simulation were performed to investigate the characteristics and mechanism underlying the rapid weakening of typhoon Xangsane. The results show that a sharp decline in the intensity of typhoon Xangsane resulted from its movement into the cool sea surface temperature area in the East China Sea, the intrusion of cold air from the mainland into the typhoon, and a rapid increase of the vertical wind shear in the surrounding environment. An important factor that led to the demise of the typhoon was a significant decrease in the moisture transport into the typhoon. Furthermore, the results of the numerical simulation and sensitivity experiments indicate that sea surface temperature largely modulated the rapid weakening of typhoon Xangsane.
The cause of the rapid weakening of Typhoon“Bebinca”was analyzed in this paper,by using the NCEP FNL(Final)Operational Global Analysis data on 1°×1°grids and the Tropical Cyclone(TC)Annual Report.The result shows that during the middle to late stage of its life cycle,the meteorological environments did not sustain“Bebinca”to maintain its intensity:the water vapor transport at low level decreased significantly;cold air intruded from north at low to middle level;both the divergence at high level and the convergence at low level reduced at the same time in the late stage.All these above factors restrained the development of“Bebinca”.In particular,the rapid reduction of sea surface temperature(SST)was the main factor that induced the rapid weakening of the Typhoon,which occurred about 6 hour ahead of its weakening.Compared to the 500-850 hPa vertical wind shear,which shows a relatively high correlation with the weakening,the impact of the 200-850 hPa vertical wind shear on the intensity change was not significant.Therefore,the Typhoons in the South China Sea would possibly weaken and disappear rapidly in fall and winter.So we have to pay more attention to the time effectiveness of the forecasting and correct the results in time.
Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article,the Weather Research and Forecast(WRF) model was used to study the rapid intensification of Typhoon Haikui(1211)off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity.
To investigate the impacts of the diurnal cycle on tropical cyclones （TCs）,a set of idealized simulations were conducted by specifying different radiation （i.e.,nighttime-only,daytime-only,full diurnal cycle）.It was found that,for an initially weak storm,it developed faster during nighttime than daytime.The impacts of radiation were not only on TC intensification,but also on TC structure and size.The nighttime storm tended to have a larger size than its daytime counterparts.During nighttime,the radiative cooling steepened the lapse rate and thus reduced the static stability in cloudy regions,enhancing convection.Diabatic heating associated with outer convection induced boundary layer inflows,which led to outward expansion of tangential winds and thus increased the storm size.
利用中尺度模式HWRF(Hurricane Weather Research and Forecast System)模拟双热带气旋"狮子山"(2010)与"南川"(2010)涡旋合并过程,并通过强度敏感性试验揭示两涡旋强度对合并过程的影响。分析表明:在两者的合并过程中,"狮子山"涡旋强度明显大于"南川";"狮子山"涡旋对"南川"涡旋具有更大的"吸引"效应,两者西侧呈相对强的能量、水汽"连体"通道。HWRF能够较好的模拟出双热带气旋"狮子山"与"南川"的强度、移动路径,尤其是两涡旋的合并过程。进一步分析控制试验双热带气旋水平与垂直结构揭示出两涡旋"互旋"过程中,"弱涡旋"并入"强涡旋"相互影响特征。有关"狮子山"与"南川"强度的敏感试验亦表明,两者各自涡旋强度"合并方向"具有关键影响。在敏感性试验中,改变涡旋强度后两者路径亦存在"互旋"现象,但与控制试验两涡旋"合并方向"相反,即敏感性试验热带气旋"狮子山"涡旋削弱,而"南川"涡旋强度相对增强,导致原涡旋西侧水汽、能量输送连体通道明显削弱,同时由于"南川"涡旋的强度强于"狮子山",两者东侧水汽、能量输送通道亦加强,导致"南川"涡旋对"狮子山"的涡旋存在"吸引"效应。"狮子山"涡旋残留云带一部分合并入"南川",一部分则随西南气流进入台风"圆规"。
