Subtropical Westerly Jet Influence on Occurrence of Western Disturbances and Tibetan Plateau Vortices
Subtropical Westerly Jet Influence on Occurrence of Western Disturbances and Tibetan Plateau Vortices
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DOI：
10.1029/2018gl077734
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发表时间：
2018-08-28
影响因子：
5.2
通讯作者：
Schiemann, R.
中科院分区：
文献类型：
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作者：
Hunt, K. M. R.;Curio, J.;Schiemann, R.
西部扰动(WD)是中上层对流层中尺度涡旋，通常沿着副热带西风急流传播，在北方冬季给巴基斯坦和印度北部带来强降雨。它们在动力学上与青藏高原低涡相似，青藏高原低涡在春夏两季影响中国的西南部，并从青藏高原发出。在这里，我们认为它们的相似性意味着存在一组更一般的上对流层涡旋，其特征是与兴都库什-喜马拉雅-青藏高原地区的地形相互作用。利用ERA中期再分析得到的WDS和TPV的现有轨迹数据库，我们发现它们各自的出现频率在季节周期中彼此高度反相关，但两者都与急流纬度有很强的相关性。我们的研究结果表明，热带气旋和热带气旋灾害的发生率在年内和年际尺度上存在相关性，特别是通过高层斜压性。简而言之，印度北部和中国南部(包括西藏)分别经历了季节性的中层气旋系统，称为西部扰动(WDS)和青藏高原涡旋(TPV)。这些系统可能对与它们相关的地区的强降雨，甚至是灾难性的降雨负责，因此，改善预测和风险关联至关重要。在本研究中，我们发现：第一，以前的文献暗示这两类系统具有相似的结构；第二，两者的年平均周期都受到副热带西风急流的强烈影响；第三，它们的年际种群是相关的；第四，这种关系可以通过考虑急流的强度和位置等特征来解释。因此，我们得出结论，WDS和TPVs很可能是一类更一般的天气尺度涡旋的具体例子。
Western disturbances (WDs) are midtropospheric to upper-tropospheric mesoscale vortices, which typically propagate along the subtropical westerly jet stream and bring heavy rainfall to Pakistan and northern India during boreal winter. They are dynamically similar to Tibetan Plateau vortices (TPVs), which affect southwest China during spring and summer and emanate from the Tibetan Plateau. Here we propose that their similarity implies the existence of a more general group of upper-tropospheric vortices featuring interactions with the orography of the Hindu Kush-Himalaya-Tibetan Plateau region. Using existing track databases for WDs and TPVs derived from ERA-Interim reanalysis, we show that their respective occurrence frequencies are highly anticorrelated with each other through the seasonal cycle, yet both are strongly correlated with jet latitude. Our findings imply that the incidence of hazards due to WDs and TPVs is correlated on intra-annual and interannual time scales, particularly through upper-level baroclinicity.Plain Language Summary North India and south China (including Tibet) experience seasonal midlevel cyclonic systems, referred to as western disturbances (WDs) and Tibetan Plateau vortices (TPVs), respectively. These systems can be responsible for heavy, even catastrophic, rainfall in the areas associated with them, and thus improving prediction and risk correlation is vital. In this study, we show that: first, previous literature alludes to the two types of system bearing similar structures; second, the mean annual cycles of both are strongly affected by the subtropical westerly jet; third, the interannual populations of each are related; and fourth, this relationship can be explained by considering features of the jet, such as strength and position. We thus conclude that it is likely that WDs and TPVs are specific examples of a more general class of synoptic-scale vortex.