ISSN 1006-9895

CN 11-1768/O4

The Effect of the Variation of the North Atlantic Oscillation on Winter Blocking Activities in the Northern Hemisphere
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    Abstract:

    The linear regression analysis shows that there is a significant correlation between the North Atlantic Oscillation (NAO) and the variation of blocking frequency and intensity in the Atlantic Ocean, Europe, and the Ural Mountains. During the negative NAO phase, the blocking activities are more frequent and stronger in the Atlantic region. In the positive NAO phase, the blocking activities in the Atlantic region and their frequency diminish, which enhance in Continental Europe, and at the same time the blocking activities reduce markedly in the Ural Mountains. The increase and decrease of positive NAO index correspond to different variations of the blocking activities in the Atlantic Ocean and Europe. The local distribution of blocking activities frequency demonstrates that during the increasing phase of the positive NAO index the blocking activities in the Atlantic Ocean are significantly restrained, which enhance evidently in Continental Europe, and their center shifts to the Continent. But in the weakening stage of the positive NAO index, the center of blocking activities shifts westward to the Atlantic Ocean. The annual changes in the regional blocking events show that the blocking situations in the Atlantic and the Urals region have a downward trend during the enhancing phase of the NAO index, which increase in Europe; in the weakening phase of the NAO index, the Atlantic blocking cases present a weak uptrend, which trend downwards in Europe and the Ural region.  The strength and position of mid\|latitude eddy play an important role in the NAO phase variations. The eastward strengthening of the Atlantic storm track is beneficial to NAO tending to positive phase, corresponding to increasing in blocking frequency in Continental Europe, but further strengthening can increase blocking activities in the Atlantic Ocean.

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  • Received:
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  • Online: December 06,2011
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