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不同次季节尺度热量和动量输送对冬季乌拉尔山超长阻塞高压事件的影响

The Influence of Thermal and Momentum Transport at Different Subseasonal Scales on long-duration Ural Blockings in Winter

  • 摘要: 冬季,长持续时间的阻塞高压往往造成更大强度的冷空气堆积,从而导致大范围强寒潮事件的发生,研究阻塞高压的建立和长时间维持机理具有重要的科学意义。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)提供的1979/1980-2019/2020年ERA5逐日再分析数据,从近41年冬季114次乌拉尔山阻塞高压(以下简称乌山阻高)事件中筛选出6次超长阻高事件(生命期≥10天),对比超长阻高事件与其他阻高事件的异同点,着重探究超长阻高事件发展和维持过程中不同次季节尺度的热、动量输送特征。结果表明:(1)乌山地区位势高度具有显著季节内振荡特征,超长阻高事件的建立和维持均以位势高度异常的季节内尺度分量(20~80天)为主,其他阻高事件的建立和维持则分别取决于位势高度异常的准双周尺度分量(10~20天)和季节内尺度分量。(2)在超长阻高事件发展阶段,定常热量通量梯度的准双周尺度分量和季节内尺度分量均有利于位势高度增加,并且准双周尺度热量输送贡献更大,而在阻高维持阶段贡献最大的是季节内尺度热量输送。相较而言,其他阻高事件中仅季节内尺度分量的热量输送有利于其建立,数值逐渐减小,不利于其维持。(3)动量输送对阻高事件的影响同样不可忽视。阻高事件的发展是准双周尺度和季节内尺度动量输送共同作用的结果,不同的是超长阻高事件中准双周尺度动量输送集中在发展阶段前期,季节内尺度动量输送贯穿整个发展阶段,而其他阻高事件中动量输送相对较小。维持阶段超长阻高事件以定常动量通量的季节内尺度分量为主,其他阻高事件则以定常动量通量的准双周尺度分量为主。

     

    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.

     

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