影响2018年盛夏热带气旋群发的多尺度环流特征

以2018年盛夏一次典型的热带气旋群发(Multiple Tropical Cyclogenesis,MTC)事件为例,分析了多尺度环流(包括大尺度环流、季节内振荡及热带波动等)对MTC的影响,并探讨了MTC群发期和间歇期整层大气垂直扰动场的差异。结果表明:1)2018年盛夏西北太平洋经历了一次持续时间长达16 d有8个TC相继生成的MTC群发期和紧接着长达19 d仅1个TC生成的MTC间歇期;2)MTC群发期越赤道气流增强,季风槽加强东伸,南海和西北太平洋上空低层辐合高层辐散的环流配置有利于TC生成;3)夏季东亚-西北太平洋季节内振荡北传对MTC次季节变化具有显著的调制作用,MTC群发期(间歇期)南海和西北太平洋正好处于一次较强的季节内振荡(Intraeasonal Oscillation,ISO)北传湿(干)位相上;4)群发期内8个TC的生成皆与热带波动有关,其中5个同时受两种热带波动的影响,热带波动通过改变局地热动力状况为TC生成提供触发条件;5)多尺度环流的共同影响最终导致MTC群发期和间歇期在温压扰动场配置、垂直运动扰动和比湿扰动的垂直结构特征上表现出显著的差异,扰动分析法的应用为MTC生成的延伸期预报提供了一个新的思路。

Multiscale circulation characteristics affecting the multiple tropical cyclogenesis in midsummer of 2018

Taking a typical MTC (multiple tropical cyclogenesis) event in midsummer of 2018 as an example,this paper investigates the effects of multi-scale circulations (including large-scale circulation,intra-seasonal oscillation (ISO) and tropical waves) on MTC,and discusses the deviation of vertical disturbance field of the whole atmosphere in MTC active and inactive phases.The results are as follows.(1)The western North Pacific (WNP) undergoes a 16 d MTC active phase with eight tropical cyclones (TCs) generated in sequence and a 19 d MTC inactive phase with only one TC generated in midsummer of 2018.(2)During the MTC active phase,the cross-equatorial airflow strengthens,and the monsoon trough strengthens and extends eastward.The atmospheric circulation configuration of low-level convergence and upper-level divergence over South China Sea (SCS) and WNP is conducive to TC formation.(3)The northward propagation of ISO (intraseasonal oscillation) in East Asia and WNP in summer has a significant modulation effect on the sub-seasonal variation of MTC.The SCS and WNP are just in a northward wet (dry) phase of a strong ISO during the MTC active (inactive) phase.(4)The formation of eight TCs in the MTC active phase is all related to tropical waves,of which five are affected by two kinds of tropical waves simultaneously.Tropical waves provide triggering conditions for TC formation by changing the local thermal and dynamic conditions.(5)The combined effects of multi-scale circulation eventually leads to significant differences in the vertical structure characteristics of temperature-pressure disturbance field configuration,vertical motion disturbance and specific humidity disturbance in the MTC active and inactive phases.The application of the disturbance analysis method provides a new idea for MTC extended range forecast.