By statistical research on the occurrence pattern of severe convective weather in Jiangsu province under the influence of tropical cyclones within a 10-year period(from 2001 to 2010),this paper discovers that among different severe convective weather,the occurrence frequency of short-range heavy precipitation is the highest,thunderstorms and gales come in second,and general thunderstorms rarely happen,while hailstorms and tornadoes never occur.The statistical results also showed that within the research period there are 21 tropical cyclones(TCs) affecting the Jiangsu area and most of them are in the stage of weakening to tropical depressions.Moreover,through studying indices for relevant cases of severe convection,it is discovered that their thresholds are lower than that of previous research,which indicated that convective instability and energy accumulation can easily lead to severe convective weather eventually due to the influence of TCs.
The mean kinematic and thermodynamic structures of tropical cyclones （TCs） making landfall in main-land China are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanied with a decrease in low-level wind speed, an expansion of the radius of strong wind, weakening of the upper-level warm core, and drying of the mid-tropospheric air. On average, the warm core of the TCs dissipates 24 h after landfall. The height of the maximum low-level wind and the base of the stable layer both increase with the increased distance to the TC center;however, the former is always higher than the latter. In particular, an asymmetric structure of the TC after landfall is found. The kinematic and thermodynamic structures across various areas of TC circulation diff er, especially over the left-front and right-rear quadrants （relative to the direction of TC motion）. In the left-front quadrant, strong winds locate at a smaller radius, the upper-level temperature is warmer with the warm core extending into a deep layer, while the wet air occupies a shallow layer. In the right-rear quadrant, strong wind and wet air dwell in an area that is broader and deeper, and the warmest air is situated farther away from the TC center.
The changes of tropical cyclone （TC） activities in response to influencing environmental conditions have been paid more and more attention to in recent years, The potential contributions of single and multivariate environmental variables to annual TC frequency and intensity from 1970 to 2009 are investigated in this study. Instead of using correlation coefficient that assumes a set of samples satisfying the normal distribution, a quantitative measurement is formulated based on the information theory. The results show that dynamic environmental variables play an important role in variations of TC activities over the western North Pacific, North Atlantic, and eastern Pacific. These dynamic factors include wind shear between 850 and 200 hPa and 850-hPa relative vorticity. However, the effects of thermal factors on TC activities are distinct over different basins. The thermal environmental variables only have significant contributions to TC frequency and intensity over the eastern Pacific as well as to TC frequency over the North Atlantic. It is found that the primary factors influencing TC activities are indeed not the same over different basins because of the differences in atmospheric conditions and their changes across different areas. The effects of dynamic variables should be considered more in the regions such as the western North Pacific where the thermal conditions are always satisfied.
In daily typhoon operation, identifying the intensity of typhoons is always a contentious problem, which can be attributed to the absence of direct observational data when typhoons are present on the ocean. When typhoons move to the offshore region, where many automatic weather stations(AWSs) are present, utilizing automatic observations in non-standard conditions is a good way of identifying the intensity or wind of a typhoon. Before identification, AWS data should be conversed or revised based on statistical experiences from a multilayer wind tower. In this study, the intensity of Haikui(1211) at the landing stage(from 08071200 UTC to 08071920 UTC) is revised carefully. Calculating the wind conversion coefficient between different heights from a 300 m multilayer tower observation, the wind data caught by two offshore AWSs were converted to the standard wind of 10 meters and used to identify the intensity of the landing Haikui. The maximum surface wind of Haikui in the landing period was about 45 m/s to 48 m/s and then reduced to 40 m/s to 42 m/s approximately just before landing.On the basis of the discussion in this study, the AWS data in a non-standard environment can be utilized to determine the surface wind at 10 m height by arithmetic conversion. This implies that we should pay more attention and patient to the wind data observed in offshore island AWSs during typhoon identification.
This work studies the impact of the vertical shear of gradient wind （VSGW） in the free atmosphere on the tropical cyclone boundary layer （TCBL）. A new TCBL model is established, which relies on five- force balance including the pressure gradient force, Coriolis force, centrifugal force, turbulent friction, and inertial deviation force. This model is then employed to idealize tropical cyclones （TCs） produced by DeMaria＇s model, under different VSGW conditions （non-VSGW, positive VSGW, negative VSGW, and VSGW increase/decrease along the radial direction）. The results show that the free-atmosphere VSGW is particularly important to the intensity of TC. For negative VSGW, the total horizontal velocity in the TCBL is somewhat suppressed. However, with the maximum radial inflow displaced upward and outward, the radial velocity notably intensifies. Consequently, the convergence is enhanced throughout the TCBL, giving rise to a stronger vertical pumping at the TCBL top. In contrast, for positive VSGW, the radial inflow is significantly suppressed, even with divergent outflow in the middle-upper TCBL. For varying VSGW along the radial direction, the results indicate that the sign and value of VSGW is more important than its radial distribution, and the negative VSGW induces stronger convergence and Ekman pumping in the TCBL. which favors the formation and intensification of TC.
