热带季节内振荡与南海热带气旋活动的关系

RELATIONSHIP BETWEEN TROPICAL CYCLONE ACTIVITY OVER THE SOUTH CHINA SEA AND TROPICAL ISO PROPAGATION

利用1949-2009年台风年鉴和NCEP/NCAR再分析资料分析了热带季节内振荡（Iso）与南海热带气旋活动的关系.主要结论包括：（1）针对南海地区定义了纬向风指数,经验证该指数能较好描述南海大气ISO的具体特征；（2）CPC120指数反映的对流空间尺度相对于南海小尺度海域太大,且不能很好判明南海地区气旋活动归属于活跃与否两类,这从反面证明了纬向风指数对南海地区热带ISO活动的适用性；（3）利用纬向风指数把热带ISO活动划分了8个位相,发现其位相变化与南海热带气旋活动有较好的对应关系：不活跃期（第4～6位相）时,气旋在南海生成和登陆均明显减少,而在活跃期（第7～3位相）时情况相反；（4）合成分析表明,热带ISO东传时,伴随对流中心位置的东移,南海气旋活动表现也不同,其活跃期以第2位相特征最明显,此时南海地区对应强对流和气旋式切变,同时副高强度较弱位置偏东,这些均有利于南海气旋的生成和发展；不活跃期则情况相反,以第6位相特征最明显；（5）迸一步从能源供应角度来探讨发现,南海地区的水汽凝结加热中心、强对流中心及水汽通量散度均配合一致.此外,活跃位相时整层热源垂直剖面均反映南海上空为强上升运动和中层加热；不活跃位相则情况相反.因此,热带ISO东传也会影响南海上空加热配置,从而影响热带气旋活动.

The relationship between the tropical intraseasonal oscillation （ISO） and cyclones over the South China Sea （SCS） was studied by using the tropical cyclones data from 1949 to 2009 and NCEP/NCAR reanalysis data.The main conclusions are as follows：（1） A new index named zonal wind index was defined,which has been proved to be effective to describe the ISO activity over the SCS; （2） The spatial scale of convection reflected by the CPC120 index was too large for the SCS region and also found to be incapable of grouping the TC activity over the SCS into two classes （active and inactive periods）.Thus,the zonal wind index turns out to be more suitable for the SCS area; （3） The tropical ISO propagation was divided into eight phases using the zonal wind index,the phase variation of which was found in accordance with the tropical cyclone （TC） activity over the SCS that less TC formation and landfall were found during the inactive period （phase 4 ～ 6） while the situation was contrary during the active period （phase 7～ 3）; （4） The composite analysis indicated strong convection,cyclonic shear and weak subtropical high during the active ISO period （phase 2）,which created a favorable environment for TC generation and grow-up,while the situation during the inactive period （phase 6） was the contrary; （5） Modulation of TC activity by ISO can be also revealed from the energy aspect.The convective heating centers,strong convective centers and water flux divergence centers were found to correspond well with each other.In addition,the vertical integral of Q 1 showed strong ascending motion and mid-layer heating over the SCS area during the active phase,and vice versa.Thus,the eastward propagation of tropical ISO can influence the tropical cyclones by affecting the heating configuration over the SCS area.