利用美国NOAA提供的向外长波辐射(OLR)资料、NCEP/NCAR再分析资料以及上海台风所提供的热带气旋(TC)资料等,通过定义一个描写南海范围内(5°N～20°N,105°E～120°E)的热带辐合带(Intertropical Convergence Zone,简称ITCZ)强度指数,研究了南海ITCZ年际和年代际异常变化特征及其对非移入性南海TC[South China Sea-generated tropical cyclone (SCS-G TC)]活动的可能影响,并从异常强、弱南海ITCZ年份的大气环流背景和海表温度等变化特征来尝试揭示南海TC的活动规律.结果表明:在年际和年代际时间尺度上,南海ITCZ强度指数与南海TC的生成频数存在显著的负相关关系,长期趋势变化间的关系存在不同.南海ITCZ的强、弱显著地影响到南海TC的生成频数.强南海ITCZ年,南海TC频数偏多;弱南海ITCZ年,南海ITCZ频数偏少.强、弱南海ITCZ年对于南海TC的生成源地、TC的维持时间以及路径和强度的影响不显著.进一步分析表明,动力和环境条件方面,强、弱南海ITCZ年可能差异较大.异常偏强年,对流层低层出现气旋性环流,上层出现反气旋性环流;季风槽在南海区域偏强、位置偏南.与OLR表示的深对流区相配合,存在暖的海表温度和低层强烈的正涡度和强辐合,在高层存在相应的强的气流辐散,形成了极有利于南海TC发生发展的条件.弱南海ITCZ年则相反.另外,ITCZ强年,太平洋异常SST (Sea Surface Temperature)出现为La Ni(n)a特征,南海ITCZ区对流活跃,强度偏强.反之,ITCZ弱年则表现为E1 Ni(n)o特征,南海ITCZ关键区的对流强度偏弱.这些结果可为深刻认识南海TC的生成规律以及对南海TC的预报提供线索.%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(n)a pattern with more vigorous SCS convection.On the contrary,if the E1 Ni(n)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.
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