论文部分内容阅读
Years and regions that regime shift of winter temperature occurred in late 1980s are detected.NCEP/NCAR reanalysis winter mean temperature is used for the detection.Differences of five/ten year mean winter temperature between two periods,before and after a given year are calculated.Values of Lepage test are also calculated for the same periods.Years and regions in which regime shift occurred are specified by using these values.As a result,regions where regime shift of winter temperature occurred are detected in 1987,1988,and 1989.In 1989 of these three years,regime shift appeared simultaneously in East Asia mainly above 40 degrees north (East Asia North) and in North Europe where the north coast of Scandinavian Peninsula is the center (North Euro East).On the other hand,regime shift in 1987 is detected in East Asia mainly below 40 degrees north (East Asia South),and that in 1988 is recognized in North Europe where the tip of Scandinavian Peninsula is the center (North Euro West).In each of four regions,decadal mean winter temperatures after regime shift are relatively higher than that before regime shift.Difference of decadal mean winter temperature between before and after regime shift is 1.09 degrees C in East Asia North,1.37 degrees C in East Asia South,2.07 degrees C in North Europe East,and 2.14 degrees C in North Europe West.Secondly,relations between these regime shifts and changes of atmospheric circulation patterns are discussed.Arctic oscillation (AO),one of atmospheric circulation patterns,has changed in 1989 from a state which negative phase is dominant to a state positive phase is dominant.Two regions where regime shift is detected in 1989 are involved in major fluctuant area of AO.In addition,correlation coefficient between AO index and winter temperature of these two regions is significant (r=0.44 in East Asia North,r=0.68 in North Europe East).Furthermore,five-day mean AO index corresponds to five-day mean temperature of these two regions.Thus,it seems clear that regime shift occurred in East Asia North and North Europe East in 1989 is well associated with AO which changed significantly in 1989.Meanwhile,1989’s regime shift occurred in East Asia South is related to West Pacific (WP) pattern.WP pattern is one of the atmospheric circulation patterns which consist of a north-south dipole of barometric anomalies,with one center located part of East Asia and another center of opposite anomaly located over the Kamchatka Peninsula.WP index has a high correlation with winter temperature in East Asia South (r=0.66).Although this region is quite close to East Asia North where regime shift occurred in 1989,1987’s regime shift should be considered different from 1989’s because winter temperature fluctuation of these two regions is different (r=0.21) and temperature in East Asia North has opposite relation to WP index (r=-0.26).However,it is possible that 1987’s change left some signals which affect subsequent atmospheric condition.1988’s regime shift occurred in North Europe West seems to be partly affected by North Atlantic Oscillation (NAO) which changed its dominant phase in 1988.In fact,five-day mean winter temperature in this region corresponds to five-day mean NAO index in 1988.However,whether 1988’s regime shift is different from 1989’s regime shift is not clear,because winter temperature in former region corresponds to winter temperature in latter region and relationship of winter temperature to atmospheric circulations in both regions is quite similar.