Climatic Characteristics Of The North Hemisphere Blockings In Wintertime And The Relationship With North Atlantic Oscillation (NAO)

This paper mainly introduce two parts of researches: the first part is investigating the decadal variability of the wintertime (DJFM) blockings in the North Atlantic and North Pacific oceans in the years 1955-2004 and the reasons; the second part is investigating the relationship between the wintertime (DJFM) blockings and North Atlantic Oscillation (NAO) in three regions (ATL, EUR and PAC) in the years 1955-2001.The blocking is an important component of the low-frequency anomalies in the atmospheric circulation in mid-latitude. Meteorologists have regarded it as an important problem since long ago. From observations, it has been indicated that the wintertime blockings appear most frequently in three regions: the Atlantic Ocean, Europe, the Pacific Ocean in the North hemisphere. Therefore in this paper, we focus the spatial area of the blocking in the three regions. And because we investigate it from climatologic viewpoint, so the temporal scale is the 50 winters (DJFM) from 1955 to 2004.In the first part of this paper, we analyze the baroclinicity and blockings in the North Pacific and North Atlantic based on daily mean NCEP-NCAR reanalysis, and found that the decadal variability of baroclinicity is very important to the decadal variability of blockings in the North Pacific and North Atlantic. As a result of the large atmosphere-ocean coupling in the mid-latitudes, the baroclinicity exhibits a decadal variability, then the blockings exhibits a decadal variability likewise. It is found that the blocking activity can exhibits a remarkable linear downward trend w h e n t h e b a r o c l i n i c i t y u p s t r e a m e x h i b i t s a l i n e a r u p w a r d t r e n d .At present, North Atlantic Oscillation (NAO) has become a very important...