Geophysical Research Letters

Extra-tropical synoptic cyclones and downward propagating anomalies in the Northern Annular Mode

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Abstract

[1] During most winters, anomalies in the Northern Annular Mode (NAM) propagate downward from the stratosphere to the troposphere. In this paper, the relationship between extra-tropical synoptic-scale cyclones and downward propagating positive (NAM+) and negative (NAM−) anomalies is investigated. Both Pacific and Atlantic storm tracks are significantly influenced by the downward propagating NAM+ anomalies, while only the Atlantic storm tracks are significantly influenced by the downward propagating NAM− anomalies. The number of cyclones changes by up to 30 % during both NAM+ and NAM− within certain regions. Also, fluctuations in the NAM follow corresponding fluctuations in the storm activity with a lag of three days during NAM+ and NAM−.

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