Feature analysis and preliminary causes study of the frequent cooling winter in northern Eurasia since 2004
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Abstract
By using the monthly NCEP/NCAR reanalysis datasets of 1961-2013, anomalous features and potential causes of the frequent cooling winter in northern Eurasia (40°-65°N, 50°-120°E) since 2004 are analyzed in this paper. The results show that: Cooling winters took place frequently in northern Eurasia since 2004, but there is a notable difference in the distribution of temperature anomalies, especially the cold center position. It shows that 2005, 2009, 2010 and 2012 appear as whole-region-colder years, while 2004, 2007 and 2011 as south-region-colder years. The whole-region-colder years are mainly caused by the significant negative phase of the Arctic Oscillation (AO), and the corresponding SST features are zonally distributed with a Northeast-Southwest "positive-negative-positive" pattern from high latitudes, middle latitudes to low latitudes in the North Atlantic, which is beneficial to continuous negative phase of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). While south-region-colder ones were caused by the enhanced Ural-Baikal (UB) blocking with the AO/NAO generally in the weak positive phase, which mainly corresponds to the warm SST in the middle latitudes of the North Atlantic, and secondly to "similar La Niña events" under the Pacific Decadal Oscillation (PDO) negative phase.Both of the SST anomalies above can accelerate the Rossby waves which is similar to the Eurasian Teleconnections pattern and is helpful to enhanced UB blocking and trough activities in central Aisa. Either in the circulation or SST anomalies, the two types of cooling winters in northern Eurasia since 2004 are similar to the corresponding typical years in history.
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