Approaches To Several Problems About The Abnormal Features Of The Global Wind Fields Climatic Change

Based on the NCEP/NCAR reanalyzed monthly mean wind data from 1948 to 2004, this paper investigates some problems of the climatic change of the global wind fields. The main contents and results are as follows.Firstly, based on the study of the temporal-spatial features of zonal and meridional wind at 200hPa,500hPa,850hPa level during 1948-2004, evidence suggests that global zonal wind shows positive tendency with the negative of meridional wind at 500hPa in the mid-seventies. These features are consistent with the increase of global temperature from 1970s.Positive trend of zonal wind at 850hPa in the mid-equatorial Pacific Ocean indicates the augment of west wind and the weakening of Walker circulation.The trend of wind fields in every 10° latitudinal zone suggests that equatorial convergence of the meridional wind at low level is fortified.Secondly,by analysing the EOF main models of the wind field at 500hPa,temperature field and rainfall field in the midsummer during 1951-2004,it is found that the first EOF main model of wind field has close relation to that of the temperature field and rainfall field at the same time. The abnormal characters of large scale wind field at 500hPa cause the exceptional distribution of temperature and rainfall fields.hi the end, by using the meridional wind data at grid point of 10 levels during 1948-2004,the strength of Global Cross-equatorial flow are calculated. The Spatial-temporal variation of Global Cross-equatorial flow at 850hPa level are shown and discussed. The results show the strength of Global Cross-equatorial flow at 850hPa represents obviously secular change and decadal change during the period. Evidence suggests that the Cross-equatorial flow of the passages of 45°-50°E, 105°E-1150E,1300E-140°E intensified in the recent 57 years with a increase of 0.25m/s/10a for summer Somali Jet and 0.32m/s/10a for Cross-equatorial flow of 130°E-140°E,May to September. The results of Singular Spectrums analysis for the time series of Cross-equatorial flow indicated that the decadal and secular trend change of Cross-equatorial flow at 850hPa are evidenced with 35%-45% rate of variance contribution of the Cross-equatorial flow average and rate of variance contribution for interannual variation of the Cross-equatorial flow average no more than 30%.The results also revel that the interannual variation of intensity of Cross-equatorial flow in summer in Pacific has significantly correlated with Southern Oscillation. While weak Southern Oscillation occur, strong Cross-equatorial flow in Pacific will happens. But summer Somali Jet only has little positively correlated with NAO.