Study On The Characteristics Of Frequent Cold Winter In The North Of Europe And Asia In The Early 21st Century And Its Relationship With The High Temperature In The Middle And Lower Reaches Of The Middle

By using the monthly reanalysis datasets of 1961-2013 NCEP/NCAR, anomalous features and causes about frequent cooling winter in Northern Eurasia (40-65°N,50-120°N) since 2004 are analyzed in this paper. The result shows 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, were displayed the whole-region-colder years, while 2004,2007 and 2011 were displayed south-region-colder years. The main cause of the whole-region-colder years is the significant negative phase of AO, corresponding SST features are zonally distributed with a Northeast-Southwest(NW-SE) "positive-negative-positive" pattern from high latitudes, middle latitudes to low latitudes in North Atlantic, which is beneficial to continuous negative phase of AO/NAO. While south-region-colder were caused by enhanced Ural-Baikal (UB) blocking, AO/NAO is generally weak positive phase, which mainly corresponds to the warm SST in middle latitudes of the North Atlantic, secondly is "similar LaNina events" under PDO negative phase, the SST anomalies above can accelerate the Rossby waves which is similar to Eurasian (EU) teleconnections pattern and is helpful to enhanced UB blocking and trough activities in central Aisa. Both in circulation and SST anomalies, two types cooling winters in Northern Eurasia since 2004 are similar to corresponding typical years in history. Under global warming, cold winters over Northern Asia are highly correlated with hot days (HDs) over middle and lower reaches of the Yangtze River valley (MLYRV) during the subsequent summers. This high correlation may result from the oceanic’s bridge in the Western Pacific. The mechanism may be described as follows:the atmospheric circulation anomalies of cold winters corresponds with a simultaneous warmer Western Pacific warm pool (WPWP) by decreasing surface latent heat fluxes. The warmer SST can persist and move eastward gradually in the subsequent summer through the oceanic processes, and thus in turn affect the HDs over MLYRV. Furthermore, the atmospheric circulations in year 2005/2006,2008/2009,2009/2010 are similar to 2012/2013 from winter to the subsequent summer. The similarity in 500hPa geopotential height anomalies are "positive-negative-positive" pattern from high latitudes, middle latitudes to low latitudes in first phase, and "positive-negative-positive" from west to the east in the second phase, and significant positive anomalies over subtropics which includes MLYRV in the third phase. The consistent warm SST in the WPWP is very important to the circulation evolution between contiguous phases, especially in years when SST positive anomaly is increasing from the first phase to the second phase. The mechanism may be described as follows:the increase of SST from the first phase to the second phase means energy accumulation, while relative high SST from the second phase to the third phase in the WPWP means energy release. So the atmospheric anomalies evolution from the first phase to the second phase are opposite to those from the second phase to the third phase.