Downward propagation of the weak stratospheric polar vortex events: the role of the surface arctic oscillation and the quasi-biennial oscillation
Downward propagation of the weak stratospheric polar vortex events: the role of the surface arctic oscillation and the quasi-biennial oscillation
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DOI：
10.1007/s00382-024-07121-5
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发表时间：
2024-01
期刊：
影响因子：
4.6
通讯作者：
Ji Ma;Wen Chen;Ruowen Yang;Tianjiao Ma;Xiaocen Shen
中科院分区：
文献类型：
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作者：
Ji Ma;Wen Chen;Ruowen Yang;Tianjiao Ma;Xiaocen Shen
基于JRA-55再分析资料，分析了弱平流层极涡（WPV）事件的持续下行影响。选取具有持续对流层影响的副热带气旋事件，根据事件发生日前后是否存在北极表面涛动（AO）的相位转换，将其分为两类。结果表明，在对流层中存在负AO异常的情况下（即- AO- wpv前事件），对流层影响的持续时间比表面AO由正向负转换的情况下（即+AO- wpv前事件）长1个月。发现地面AO前兆异常与后续向下传播的联系与两类事件的不同背景状态密切相关。在−ao - wpv前事件期间，观测到30 hPa强烈的东部准两年生振荡（QBO）信号，引起行星波向极地的异常传播和平流层下层波通量的辐合异常。这种缓慢变化的QBO信号在−ao - wpv前事件期间在平流层下层极区施加连续波强迫，延迟极地涡旋的恢复，导致对流层影响持续时间较长。此外，在去除每个独立情况的背景状态后，−AO- wpv前事件的负表面AO也消失了。然而，在+ ao - wpv前事件期间的向下传播没有受到事件背景去除的影响，可能是因为QBO信号非常弱。研究结果揭示了前期地面AO和背景QBO对副热带气旋事件向下传播的可能作用，为副热带气旋的亚季节预报提供了有用的信息。
Based on the JRA-55 reanalysis data, the persistent downward impacts of the weak stratospheric polar vortex (WPV) events are examined. The WPV events with persistent tropospheric impacts are selected and classified into two groups according to whether there is a phase switch of the surface Arctic Oscillation (AO) around the onset day of the cases. The results suggested a one-month longer duration of the tropospheric impacts for the cases with preexisting negative AO anomalies in the troposphere (i.e., the −AO-pre-WPV events), than the cases with a phase switch of the surface AO from positive to negative (i.e., the +AO-pre-WPV events). The connections between the precursory surface AO anomalies and the following downward propagation are found to be closely related to the different events background state of the two types of events. A strong signal of the east quasi-biennial oscillation (QBO) at 30 hPa is observed during the −AO-pre-WPV events, which induces an anomalous poleward propagation of the planetary waves and convergence anomalies of the wave flux in the lower stratosphere. This slow-changing QBO signal exerts continuous wave forcing in the polar region of the lower stratosphere during the −AO-pre-WPV events and delays the recovery of the polar vortex, leading to the long-persistent tropospheric impacts. Moreover, after the background state of each independent case is removed, the preexisting negative surface AO for the −AO-pre-WPV events also disappears. However, the downward propagation during the +AO-pre-WPV events has not been affected with the events background removed, probably because the QBO signal is quite weak. The results reveal the possible role of the precursory surface AO and the background QBO on the downward propagation of the WPV events, which may offer useful information for the subseasonal prediction.