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《Chinese Journal of Atmospheric Sciences》 2017-01
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Variations of ITCZ in the South China Sea and Their Possible Influences on the South China Sea–Generated Tropical Cyclone(SCS-G TC) Activities

HUANG Xiaoyan;GUAN Zhaoyong;HE Jielin;HE Li;Key Laboratory of Ministry of Education for Meteorological Disaster,Nanjing University of Information Science & Technology;State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences;Guangxi Research Institute of Meteorological Disasters Mitigation;Guangxi Climate Center;  
Using the Outgoing Long-wave Radiation(OLR) from NOAA, the NCEP/NCAR reanalysis data and the tropical cyclone(TC) best track dataset over the western North Pacific(WNP) provided by Shanghai Institute of Typhoon Of CMA, an intensity index of Intertropical Convergence Zone(ITCZ) over the region of(5°N–20°N, 105°E–120°E) in the South China Sea(SCS) was defined. Impacts of ITCZ variations on the South China Sea-generated tropical cyclone(SCS-G TC) have been studied in the present paper. Results show that there is a significant negative correlation between the intensity index of the ITCZ and the occurrence frequency of SCS-G TC on the interannual and interdecadal time scale. However, long-term trends are different between the two time scales. These results indicate that the intensity of the ITCZ may strongly affect the occurrence of SCS-G TC. However, the ITCZ intensity does not significantly affect the location of the TC genesis,life time,moving path and intensity of SCS-G TC. Furthermore, large differences in the dynamic and environmental conditions were found between the strong and weak ITCZ years. The anomalous conditions in the strong ITCZ years are conducive to the development of SCS-G TC; the cyclonic circulation in the lower troposphere cooperates with the anticyclonic circulation in the upper troposphere as usual, and the location of the monsoon trough is located more southern in the SCS. These match with the deep convection zone as shown by OLR. The warmer SST(Sea Surface Temperature) and stronger positive vorticity along with stronger convergence in the lower troposphere and stronger divergence in the upper troposphere all facilitate stronger vertical movement. In weak ITCZ years, the situations are opposite. Moreover, the SSTA in strong ITCZ years is usually characterized by a La Ni?a pattern with more vigorous SCS convection. On the contrary, if the El Ni?o events occur, the ITCZ in SCS will become weaker. All these results are important for us to better understand the formation mechanism for the SCS-G TC and are beneficial for predicting the occurrence of the locally generated TC in SCS.
【Fund】: 国家自然科学基金项目41465003、41575051;; 公益性行业(气象)科研专项GYHY201406024;; 灾害天气国家重点实验室课题2015LASW-A03;; 2014气象关键技术集成与应用项目CMAGJ2014M41~~
【CateGory Index】: P732
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