Impact of Intraseasonal Oscillations on the Activity of Tropical Cyclones in Summer Over the South China Sea: Nonlocal Tropical Cyclones
Impact of Intraseasonal Oscillations on the Activity of Tropical Cyclones in Summer Over the South China Sea: Nonlocal Tropical Cyclones
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DOI：
10.3389/feart.2020.609776
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发表时间：
2016-01
期刊：
影响因子：
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通讯作者：
Zheng Ling;Yuqing Wang;Guihua Wang;Hailun He
中科院分区：
文献类型：
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作者：
Zheng Ling;Yuqing Wang;Guihua Wang;Hailun He
除在南海中国海局部形成的热带气旋外，还有一些热带气旋最初形成在西北太平洋并向西移动进入南海(通常称为非本地热带气旋)。目前还不清楚这些非本地的TC是如何受到季节内气候变化的影响的。本文利用1979-2018年全球再分析资料和最佳路径热带气旋资料，分析了夏季(5-9月)南海非局地形成的季节内振荡(MJO)和准双周振荡(QBWO)对南海热带气旋的影响。结果表明，在MJO和QBWO对流位相中，西太平洋副热带高压东移，进入南海的热带气旋较多。这主要是因为在季内振荡的对流位相中，NWP中形成的热带气旋较多，其生成位置向西移动，更靠近南海。除TC计数外，季节内振荡还影响非局地TCS进入南海的强度，其中QBWO的影响比MJO更显著。在QBWO的对流活动期(2~5期)，34个非局地热带气旋达到台风强度，而在对流非活动期(1、6、7、8级)，只有2个非局地热带气旋达到台风强度。进一步的分析表明，非局地热带气旋常常随着准白云对流信号的西北传播而移动，导致气旋在准白云对流位相进入南海的次数更多、强度更强。随着季节内振荡的北传，非局地热带气旋进入南海的平均位置也向北移动。
In addition to tropical cyclones (TCs) locally formed in the South China Sea (SCS), there are also TCs that initially form over the Northwest Pacific (NWP) and move westward to enter the SCS (often called nonlocal TCs). It is unclear how those nonlocal TCs are modulated by the intraseasonal climate variability. In this study, the impacts of two types of intraseasonal oscillations, namely the Madden–Julian Oscillation (MJO) and the quasi-biweekly oscillation (QBWO), on nonlocally formed TCs over the SCS in summer (May–September) are analyzed based on best-track TC data and global reanalysis during 1979–2018. Results show that in the convective phases of both MJO and QBWO, the western Pacific subtropical high shifted more eastward, and more TCs entered the SCS. This is mainly because more TCs formed in the NWP in the convective phases of intraseasonal oscillations and the genesis locations of the NWP TCs shifted westward and closer to the SCS. In addition to TC count, intraseasonal oscillations also affected the intensity of nonlocal TCs entered the SCS, with the influence of QBWO being more significant than MJO. In the convectively active phases of QBWO (phases 2–5), 34 nonlocal TCs reached typhoon intensity, while only two nonlocal TCs reached typhoon intensity in the convectively inactive phases (phases 1, 6, 7, 8). Further analysis indicates that nonlocal TCs often moved with the northwestward propagating convective signals of QBWO, resulting in more and stronger TCs that entered the SCS in the convective phases of QBWO. The mean location that the nonlocal TC entered the SCS also shifted northward with the northward propagation of intraseasonal oscillations.