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.