Extreme Climate Change And Its Relationship With Atmospheric Circulation And Sea Surface Temperature In The Arid Area Of Northwest China

This article takes advantage of the meteorological data of daily maximum temperature,daily manimum temperature and daily precipitation of 72 ground stations from 1960 to 2013 in the arid area of Northwest China,six extreme temperature indices about cool nights(TN10p),cool days(TX10p),frost days(FD),warm nights(TN90p),summer days(SU),warm days(TX90p)and six extreme precipitation indices about max 1-day precipitation amount(RX1day),Simple daily intensity index(SDII),number of heavy precipitation days(R10),max 5-day precipitation amount(RX5day),very wet days(R95p),consecutive dry days(CDD),were selected from the “Climate Change Monitoring Indicators System”developed and recommended by the World Meteorological Organization's Climate Research Council,applying climate tendency rate,morlet continuous complex wavelet analysis,empirical orthogonal function,Mann-Kendall trend test and mutation test and synthetic analysis method to preliminary study the temporal and spatial variation characteristics,Periodicity and mutation law of extreme temperature and precipitation events in the arid area of Northwest China;Using the data of geopotential height field,cloud cover,water vapor flux,sea surface temperature to make synthetic analysis with representative extreme temperature,precipitation index in order to Preliminary discuss the possible relationship between the extreme temperature,precipitation events and the cloud cover,sea temperature,atmospheric circulation and water vapor flux in the arid area of northwest china,Revealing the possible effects of atmospheric circulation and sea surface temperature(SST)on extreme weather events.The preliminary results are as follows:(1)The EOF first spatial pattern of extreme temperature index in the arid area of Northwest China during1960-2013 shows that the spatial variation characteristics of the six extreme temperature indices have good consistency,that is,the extreme temperature index is more or less uniform;The first modal Standardized time coefficient clearly shows that the extreme temperature indexes indicating the warmth changed from decreasing to increasing,while the extreme temperature indexes indicating the cold shifted from increasing to decreasing in the late 1980 s and early 1990 s.The EOF second spatial pattern generally shows the spatial characteristic of extreme temperature index in the arid area of Northwest China have an opposite distribution between the north and south.(2)From the temporal and spatial variation characteristics of extreme temperature index,There are significant differences in the decrease or increase trend of cold and warm index.the extreme temperature indexes indicated the warmth have significant upward trend,while the extreme temperature indexes indicated the cold have an obvious downward trend.To a certain extent,it indicates that the temperature in the arid area of Northwest China is developing to the warm trend,which is consistent with the global warming background.(3)The EOF first and second spatial pattern of extreme precipitation index in the arid area of Northwest China shows that the spatial variation characteristics of each extreme precipitation index are different.From the temporal and spatial variation characteristics of extreme precipitation index,There are significant differences in the decrease or increase trend of each index;The fluctuations in extreme precipitation indexes Characterizing wetting show a significant upward trend,while the fluctuations in extreme precipitation indexes Characterizing drought have a obvious downward trend.To some extent,it indicates that the climate of arid region in Northwest China is developing towards the trend of wetting,which may be associated with global warming.(4)The extreme temperature index Characterizing cold in the arid area of Northwest China is significantly reduced since the mutation years,while the extreme temperature index Characterizing warmth showed a remarkable increasing trend after the year of mutation.To some extent,it is indicated that the temperature increase trend in the northwest arid area is obvious after the year of mutation.the extreme precipitation index Characterizing wetting in the arid area of Northwest China is significantly increased since the mutation years,while the extreme precipitation index Characterizing drought showed a remarkable decreasing trend after the year of mutation.To some extent,it is indicated that the humidification increase trend in the northwest arid area is significant after the year of mutation.(5)Each extreme precipitation index has a strong or weak Periodic change signal in 1980 s,indicating that the extreme precipitation change is more active in 1980s;the cycle characteristics of extreme temperature index Characterizing cold and warmth are differernt,which indicate that the change of extreme temperature cycle characteristics is more complicated in the arid area of Northwest China.(6)In the arid area of Northwest China,The high and low temperatures corresponding to positive and negative anomalies of 500 hPa geopotential height respectively;The cloud cover has a significant effect on the day-night temperature in study area;The northwest arid area is mainly affected by the westerly circulation,the warm and humid airflow of the North Atlantic cannot be effectively transported to the arid area of Northwest China,resulting in extremely dry climate;After the mutation years,water vapor flux divergence field of extreme precipitation index shows that the extreme precipitation indexes have a general trend of increase.The divergence value of water vapor flux in northern Xinjiang,central and western regions of Hexi Corridor and eastern part of southern Xinjiang is negative,it is easy to form effective precipitation,and the climate has the tendency of becoming moist.(7)In the arid region of Northwest China,when the extreme temperature anomaly high years,the sea surface temperature in most of the world's sea areas is abnormally warm,while the cold years take on the opposite situation.The western North Atlantic,the Okhotsk Sea and the Mediterranean Sea may have a close relationship with the extreme temperatures in the arid regions of northwest China,the extreme high temperature years correspond to the sea surface temperature abnormally warm,while extreme low temperature years have the opposite situation.(8)In the arid region of Northwest China,the sea surface temperature in most of the sea area is positive anomaly,the partial sea area is negative anomaly,and the dry year is the opposite.When the North Atlantic,India ocean,Okhotsk sea,Mediterranean sea surface temperature is positive anomaly and the Pacific(29 ~ 45N°,148 ~ 176° W)sea area for the sea surface temperature shows negative anomaly distribution,the extreme precipitation in the arid area of Northwest China is prone to abnormally increase,while abnormally decrease on the contrary.The results show that the extreme precipitation anomalies in the arid area of Northwest China are closely related to the sea area above mentioned.