Abstract:
In winter, the long-duration blocking highs often cause the accumulation of cold air with greater intensity, which lead to the occurrence of widespread severe cold waves, and the study of the establishment and long-term maintenance mechanism of blocking highs has great scientific significance. By used the ERA5 daily reanalysis data provided by the European Centre for Medium Range Weather Forecasts (ECMWF) from 1979/1980 to 2019/2020, 6 long-duration blocking high events (the lifetime is equal or greater than 10 days) were selected from 114 Ural blockings (UB) during the last 41a winter. The similarities and differences between the long-duration blockings and other blockings were compared, focusing on the thermal and momentum transport characteristics at different subseasonal scales during the development and maintenance of long-duration blocking highs. The results show that: (1) The geopotential height in Ural Mountains exhibits significant intra-seasonal oscillations, and the establishment and maintenance of long-duration blockings mainly depends on intra-seasonal scale component (20~80 days) of the geopotential height anomaly, while the establishment and maintenance of other blockings depends on the quasi-biweekly scale component (10~20 days) and intra-seasonal scale component, respectively. (2) During the development stage of long-duration blockings, both the quasi-biweekly and intra-seasonal scale components of stationary thermal flux gradient are beneficial to the increase of geopotential height, and the quasi-biweekly scale heat transport contributes more, while the intra-seasonal heat transport is the largest contributor in the maintenance stage. In comparison, only intra-seasonal heat transport is beneficial to the establishment of other blockings, with decreasing in values that is not favourable for its maintenance. (3) The influence of momentum transport on blocking high events cannot be ignored. The development of blockings is the result of quasi-biweekly and intra-seasonal scale momentum transport. However, the quasi-biweekly scale momentum transport is concentrated in the early part of development stage, while the intra-seasonal scale momentum transport occurs throughout the development stage in the long-duration blockings. In other blockings, the momentum transport is relatively small. During the maintenance stage, the long-duration blockings is dominated by intra-seasonal scale component of stationary momentum flux, and the other blockings is dominated by quasi-biweekly scale component.