Zonally Symmetric Mode Of Northern Hemisphere General Circulation Of Atmosphere And Its Relationship With Anomalous Climate In China Wintertime

The zonally symmetric modes of general circulation of atmosphere in theNorthern Hemispheric extra-tropics wintertime are extracted by using NCEP/NCARreanalysis data and method of empirical orthogonal function (EOF). The leadingmode which is called Arctic Oscillation (AO), is characterized by anomalouswesterly in high-middle latitudes and anomalous easterly in mid-latitudes below thelower stratosphere during its high phase showing quasi-barotropic structure vertically.The second mode loaded on the sub-tropics emerges as anomalous westerly inmid-latitude regions and anomalous easterly in mid-low latitude regions in the wholetroposphere during its high phase. The first two modes can account for 34%and 20%of the total variance respectively. The spatial structure of the second mode is studied.The results indicates that it shows prominent zonal symmetric structure horizontallyand quasi-barotropic structure vertically. The sea level pressure (geo-potential height)of the high-middle latitude regions are anti-related with that of sub-tropics fromsurface to tropopause. So we define the second mode as Sub-Tropical Oscillation(STO). A further study shows that STO can also be found during the cold time of ayear, but not the warm time of a year.The article also provides primary explanation for physical mechanism of themaintenance of the zonally symmetric modes. It argues that the meridional transportof eddy momentum corresponded with the zonally symmetric modes plays importantroles in the maintenance process.We found that there is better correlation between STO and China wintertimetemperature in the inter-annual variability. The Siberia High,Aleutian Low and EastAsian trough are all weaken during STO' high phase year. So East Asian WinterMonsoon is weaken, China wintertime temperature is higher. When STO shows itslow phase during a year, East Asian Winter Monsoon is strengthened, China wintertime temperature is lower. It also shows that there is closely correlationbetween them in the inter-decadal variability. Before the middle of 1980s, STO wasin its low phase, at the same time, the Siberia High was strengthened. The northwestflow in front of Siberia High was colder and stronger, which leaded cold air intoChinese mainland. At the high altitude of Eurasian, the EU teleconnection was in itshigh phase, so that, stationary troughs and ridges were both strengthened. Thegeneral circulation of atmosphere developed meridionally. Chinese mainland'stemperature declined. Cold winter feature was prominent. But after the middle of1980s, when STO shows its high phase, the circulation is entirely converse. Warmwinter occurs frequently in China.