55 / 2021-07-13 15:18:28

Influence of Siberia blocking on long-lived cold surges over the South China Sea

blocking high,cold surge,South China Sea

Cold surges occur frequently over the South China Sea (SCS) in winter, and most of them last only a few days. However, some cold surge events can persist longer, for instance, more than 5 days. This study focuses on these long-lived cold surge events and investigates the associated extratropical circulation anomalies. The results indicate that long-lived cold surges, characterized as strong northerlies over the SCS, can be triggered by a successive high anomaly center over East Asia. Accompanied is an anomalously extensive and quasi-stationary anticyclone over Siberia in the mid-to-upper troposphere, hinting a more frequent occurrence of Siberia blocking. Further analyses reveal that the blocking frequency is indeed significantly high over 90–150°E from day −4 to day +2 relative to the onset of long-lived cold surge events. Furthermore, there exist significant correlations between the leading occurrence of Siberia blocking and the sea-level pressure (SLP) anomalies over East Asia, which are directly related to long-lived cold surges. The intensification of the high SLP anomaly over East Asia is found to mainly result from cold advections induced by the anomalous northerly winds along the southeastern edge of the Siberia blocking.