Energetics of Boreal Wintertime Blocking Highs around the Ural Mountains

Based on the daily Japanese 55-yr reanalysis data, this study analyzes the maintenance mechanism for 53 boreal winter blocking highs around the Ural Mountains (UBHs) during 1958–2018 based on the atmospheric energy budget equations. After decomposing the circulation into background flow, low-frequency anomalies, and high-frequency eddies, it was found that the interaction between the background flow and low-frequency anomalies is conducive to the maintenance of the UBHs. Due to the southwestward gradient in the climatological mean air temperature over the Eurasian continent, it is easy for the air temperature anomalies as well as the wind velocity anomalies in the middle and lower troposphere induced by the UBHs to facilitate the positive conversion of baroclinic energy associated with the background flow into the UBHs. Likewise, the conversion of barotropic energy associated with the background flow is also evident in the upper troposphere, in which the climatological mean westerlies have evident southward gradient to the northwest of Lake Baikal and southwestward gradient over Barents Sea. Note that the conversion of baroclinic energy associated with the background flow is dominant throughout the lifecycle of UBHs, acting as the major contributor to the maintenance of the UBHs. Although transient eddies facilitate maintenance of the UBHs via positive conversion of barotropic energy in the middle and upper troposphere, they hinder the maintenance of UBHs via negative conversion of baroclinic energy in the lower troposphere. The diabatic heating anomalies tend to counteract the local air temperature anomalies in the middle and lower troposphere, which damps the available potential energy of UBHs and acts as a negative contributor to the UBHs.