Evolving Vertical Structure of the Winter Siberian High

The Siberian High (SH) significantly influences East Asian winter climate by modulating the East Asian Winter Monsoon. Although previous studies largely attribute the SH variability to surface warming, comprehensive analyses including upper-level atmospheric dynamics remain limited. To bridge this gap, we investigate the vertical thermal structure of the SH during boreal winter season (DJF). First, consistent with previous findings, we confirm the documented recovery and intensification of SH intensity since the early 2000s, particularly in December with increased variability. However, surface air temperature anomalies over the SH region have shown relatively modest warming trends compared to global and northern hemispheric averages, and concurrent increases in sea-level pressure suggest that lower-tropospheric processes alone cannot fully explain recent SH variability. Therefore, we analyzed atmospheric column thickness anomalies (1000-100hPa), which have decreased as 0.9hPa in 2000-2022 compared to 2.2hPa of 1980-1999. This reduction in thickness implies upper-level cooling or reduced near-surface warming efficacy, altering atmospheric stability and radiative balance. Further, DJF 200hPa eddy geopotential height reveals a systematic weakening of planetary-scale wave amplitudes in the recent period. Vertical temperature anomaly profile exhibits significant warming of approximately 0.7°C in the upper troposphere (225hPa). Correspondingly, the anomaly temperature lapse rate between 1000-200hPa has flattened from -0.41 K/km (1980-1999) to -0.07 K/km (2000-2022), indicating that SH-centered temperature anomalies have become vertically less stratified. In summary, these findings point to a potential influence of upper-tropospheric thermal dynamics on recent SH variability. These vertical changes likely alter planetary wave activity and potentially interact with ozone-related warming in the upper troposphere-lower stratosphere.