基于K-means聚类分析识别的北半球春季平流层极涡型态及其对对流层的影响

The Polar Vortex Patterns in the Boreal Spring Stratosphere Identified by the K-means Clustering Analysis and Their Impacts on the Troposphere

  • 摘要: 利用K-means聚类分析方法识别出6类主要的北半球春季平流层极涡空间型态。第1类分型平流层极涡中心偏向欧亚大陆,亚洲中低纬度地区对流层中层被高压控制。第2类分型极涡强度强于第1类分型,极涡中心偏向北美大陆,北美南部对流层呈高压异常。第3类分型发生的频次在所有分型中最高,占比33%,该分型平流层异常信号的强度及对对流层的影响最弱。第4类分型平流层和对流层极涡强度偏弱。第5类分型极涡强度较第4类分型更弱,呈更典型的环状模结构。第6类分型平流层行星波1波活动异常增强,同时对流层波动活跃。在各类分型中,当对流层中层为异常高(低)压时,低层气温升高(降低),地表降水减少(增多),但各类分型对低层气温的影响比对降水的影响更显著。此外,在平流层最后增温事件(Stratospheric Final Warming,SFW,即极涡崩溃)爆发前,以第1类分型发生频次最多;在SFW爆发偏晚时,第1类分型占比最高,达80%;SFW爆发后,主要表现为第3类和第4类分型,其中,第4类分型更多地出现在SFW偏早事件爆发后,而第3类分型更多地出现在SFW偏晚事件爆发后。

     

    Abstract: This study utilizes the K-means clustering method to identify six primary spatial patterns of the spring stratospheric polar vortex in the northern Hemisphere. In the first cluster, the center of the stratospheric polar vortex is skewed towards the Eurasian continent, resulting in an anomalous high pressure in the mid-troposphere over mid- to low-latitude regions of Asia. The second cluster exhibits a stronger intensity of the polar vortex compared to the first type, with its center biased towards North America. This configuration induces anomalous high-pressure conditions that dominate southern North America. Among all clusters, the third cluster occurs most frequently, accounting for 33% of the total cases. In this cluster, both stratospheric anomalous signals and their impacts on the troposphere are the weakest. The fourth cluster reveals a generally weaker polar vortex in both stratosphere and troposphere. In the fifth cluster, polar vortex intensity further weakens compared to that in the fourth cluster while exhibiting a more typical annular mode structure. The sixth cluster indicates enhanced activity of planetary wave 1 in the stratosphere alongside active wave dynamics in the troposphere. When associated with anomalous high (low) pressure in the mid-troposphere, temperatures in the lower troposphere tend to rise (drop), while precipitation decreases (increases). However, it is noteworthy that these clusters have a more pronounced impact on temperature than on precipitation. In addition, this study also explores connections between these clusters and spring stratospheric final warming (SFW) events. Prior to SFW onset, the occurrence frequency of the first cluster is the highest among all clusters. During late SFW events, the prevalence of the first cluster can reach up to 80%. Following the onset of SFW, occurrences predominantly shift towards the third and fourth clusters, with an increased frequency of the fourth cluster after early SFW events. Conversely, occurrences of the third cluster become increasingly prevalent following the onset of late SFW events.

     

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