The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength
The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength
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DOI：
10.5194/acp-5-239-2005
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发表时间：
2004-10
影响因子：
6.3
通讯作者：
K. Walter;H. Graf
中科院分区：
文献类型：
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作者：
K. Walter;H. Graf
抽象的。由于冬季北方涡旋的状态对对流层变率有很大的影响，我们分别定义了冬季50 hPa和65° N纬向风高于或低于纬向行星波1垂直传播临界速度时北大西洋的遥相关型。我们认为，遥相关结构在对流层中上部的极涡的两个制度之间有很大的不同，而在海平面上的情况并非如此。当极涡强时，对流层中上层存在一个纬向偶极子结构，位于北大西洋中部。如果极涡弱，则存在两个这样的偶极子，一个在北大西洋西部，一个在北大西洋东部。对流层中上部的条件决定了风暴路径（以及与之相关的降水），我们发现平流层制度之间这些参数的显着差异。对于强极涡制度，在负的上层对流层“NAO”指数的情况下，我们发现东北大西洋的阻塞高度的情况下，最强的风暴轴。它正在向北延伸到北冰洋，并在丹麦海峡上空形成第二个最大值。这样的风暴轨迹是没有发现在复合材料的基础上，一个经典的NAO定义的冰岛低和亚速尔群岛高之间的表面压力差。我们的研究结果表明，重要的是要包括极涡强度的状态在北大西洋的变化的任何研究。
Abstract. Motivated by the strong evidence that the state of the northern hemisphere vortex in boreal winter influences tropospheric variability, teleconnection patterns over the North Atlantic are defined separately for winter episodes where the zonal wind at 50hPa and 65° N is above or below the critical velocity for vertical propagation of zonal planetary wave 1. We argue that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the polar vortex is strong, there exists one meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the polar vortex is weak, there exist two such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results suggest that it is important to include the state of the polar vortex strength in any study of the variability over the North Atlantic.