Dynamical Differences Between Short and Long Blocks in the Northern Hemisphere
Dynamical Differences Between Short and Long Blocks in the Northern Hemisphere
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北半球短块体和长块体之间的动力学差异
DOI：
10.1029/2020jd034082
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Drouard M
中科院分区：
文献类型：
--
作者：
Drouard M
阻塞事件是持续的天气系统，强烈影响日常天气，更重要的是我们的社会。其强大影响背后的一个原因是其潜在的长期持续时间，因为阻塞事件可以持续5天到四五周。然而，解释这种持续时间差异的机制尚未得到适当的研究。在这里，我们研究了短块（持续5天）和长块（持续至少10天）之间的差异。我们对这一问题采取了一个广泛的半球和年度办法，同时认识到其他具体因素可能在特定地区和季节发挥作用。我们发现，长块往往涉及气旋Rossby波破碎，而短块同样与气旋和反气旋波破碎。这一主要结果在一个耦合的气候模式集合中得到了再现。长的反气旋性阻塞的数量较少可能是由于三个主要原因：一是反气旋性阻塞时下游一侧的反气旋得到加强，不利于持续;两个/正的天气涡旋反馈往往迫使平均纬向风向更北的位置在反气旋块，而它迫使平均纬向风向南部的块在气旋块，这在以前已经被证明与更持久的天气模式有关;需要三个/特别是持续的涡流反馈来维持长的反气旋块。
Blocking events are persistent weather systems that strongly impact daily weather and more importantly our societies. One reason behind their strong impact is their potential long duration, as blocking events can last from 5 days up to four‐five weeks. However, the mechanisms explaining this difference of duration have not been properly studied yet. Here, we investigate the differences between short blocks, which last 5 days, and long blocks, which last at least 10 days. We take a broad hemispheric and annual approach to this question, while recognizing that other specific factors may play a role in particular region and seasons. We show that long blocks often involve cyclonic Rossby wave breaking, while short blocks are equally associated with cyclonic and anticyclonic wave breaking. This main result is reproduced in a coupled climate model ensemble. The lower number of long anticyclonic blocks might be due to three main reasons: One/the anticyclone is reinforced on the downstream side during anticyclonic blocks which is less conducive to persistence; two/positive synoptic eddy feedback tends to force the mean zonal wind toward a more northward position during anticyclonic blocks, whereas it forces the mean zonal wind to the south of the block during cyclonic blocks, which has been previously shown to be associated with more persistent weather patterns; three/particularly sustained eddy feedback is needed to maintain long anticyclonic blocks.
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