Variations Of Seasonal Transition Time Of Zonal Thermal Difference In East Asian And Its Impact On China Climate

Based on NCEP/NCAR reanalysis datasets and CMAP precipitation data,the linear trend analysis,Mann-Kendall test and Morlet wavelet analysis methods are applied to analyze the time of zonal thermal difference seasonal transition.Then,we discuss when the time of zonal thermal difference reverse early or late what features of atmospheric circulation situation and how to influence on climate in China.?1?There are significant seasonal reversal characteristics of the zonal thermal contrasts in East Asian-Northwest Pacific.Corresponding to the thermal field,the sea level pressure has similar characteristics of the seasonal transition,both of them are consistent with the seasonal transition time.?2?In climatological mean situation,from winter status to summer status takes place at about the 18^th pentad,and the transition time from summer status to winter status occurs at about the 54^th pentad.The transition time of zonal thermal difference from winter?summer?status to summer?winter?status has significant interannual and interdecadal variabilities,all of them inclinating slightly ahead with a changing rate of about-0.37 pentad/10a and 0.25 pentad/10a in recent 60 years.But there are not significant correlation relationship between the two.The result of Mann-Kendall test indicates that the UF value of the seasonal transition time from winter status to summer status constantly increases more than the 0.05 significance level?�1.96?since the mid-1950s to early 1980s,showing it obviously delay.The UF curve of the transition time from summer status to winter status decreases in 1956-1970,then around 1971-2015 rises.According to UF and UB curve intersection on the confidence intervals and cumulative anomaly,it may experience an abrupt change in year 1971 and 2000.Fainally,the transition time from winter status to summer status has a significant 26a,12a,7a periodic oscillation,however the first principal period is not yet pass 95%significance level.The transition time from summer status to winter status fluctuates primarily with an 9a,17a cycle,wherein 9a is a first primary cycle by 95%significance test.?3?When the zonal thermal difference from winter status to summer status earlier rervses,the position of Western Pacific Subtropical High is eastward and the position of the South Asian High is westward in the summer.While the transition time is quite late,the line 5860gpm of West Pacific Subtropical High is westward and the South Asia High is westward,weaker.Lower?850hPa?southerly wind spreading to north or south,upper?200hPa?meridional wind shift and vertical shear of meridional wind are expressed as the early years of zonal thermal transition time will shift earlier than the late years.When the transition time from summer status to winter status changing in advance,the center strength of Mongolia High slightly is weaker than late years,but the Aleutian Low is stronger than late years.Next,when years of zonal thermal difference from summer status early changing to winter status,the East Asian trough I_EAT strength index is 5.17,while 4.5 of the late years.On the51^st pentad,the lower?850hPa?meridional wind of each latitudes almost reverse simultaneously to northerly wind,while late years northerly wind has established periodicity,first in the 20�-30�N latitudes belt reversal,then 30�-40�N latitudes,untill 63^th pentad complete onsets.?4?Analyzing anomalies early/late years influences on the begining time of East Asian subtropical monsoon rainfall,we can discover that in earlier years,at the 10^thh pentad?6mm/d precipiation stably exist in southern region of China,marking into the East Asian subtropical monsoon rainfall.while in later years,untill the 15^thh pentad precipitation more than 6mm/d.Discussing anomalies years impact of the temperature at late autumn and winter in China,we conclud that:Overall,early years lead to low temperature and earlier to set in winter.