Atmosphere Anomaly Of The Hot And Cool Summer Over The Yangtze River Basin In China In Resent Years

While high temperature events occur frequently in the global warming climate,low temperature events also appear from time to time.This text makes a comparative analysis of low temperature years and high temperature years in recent 30 years.In particular,the persistent low temperature in summer 2014 and the persistent high temperature in summer 2013 are studied as typical cases in recent years.Observations show that the low temperature abnormality in 2014 can extend to the ocean,in a pattern of a large-scale belt.Such abnormality belt appears not only in the near surface,but also in all the atmospheric levels(925hPa-500hPa),which is different from other low temperature years that the negative anomalies of temperature are large range.Therefore,the mechanism of the emergence and maintenance of this belt is discussed.Analysis shows,(1)The summer temperature changes in the Yangtze River Basin in China during 30 years from 1986 to 2015 show a warming trend.The summer temperature in the Yangtze River Basin during the period from the mid-1980s to the early-1990s is relatively cold,and then increases.The temperature in the 21st century is relatively warm.(2)Intensity and location of the Western Pacific Subtropical High,the strength of East Asian monsoon system,and the anomalies of SST can cause abnormally warm or abnormally cold in summer in southern China through the atmospheric circulation.There are obvious differences between atmospheric circulation of typical high and low temperature years.In low temperature years,the intensity of the Western Pacific Subtropical High is generally weak,and moves southwards or eastwards,while East Asian monsoon system weakens.In high temperature years,the intensity of the Western Pacific Subtropical High is strong,and extends westwards,while East Asian monsoon system strengthens.Thus,the temperature in the Yangtze River Basin increases.(3)The same as other low temperature years,in 2014,the Yangtze River Basin in China is under the control of a cyclone-type anomalous wind field,and East Asian monsoon system is weak.During the periods of low temperature,the northerly air flow brings cold air from the North to the South,causing the temperature in the Yangtze River Basin to drop.The difference is that in the geopotential height anomaly field,in 2014,each layer has the pattern of positive anomalies of geopotential height-low temperature belt-negative anomalies of geopotential height.This type tilts from South to North.In other low temperature years,there is no such pattern.(4)The low temperature in the atmosphere in 2014 is mainly caused by the anomalous systems in the high latitudes.In the geopotential height field,the belt-like positive anomalies at 60°N may lead to the intrusions of the colder-than-normal air from the north or the northeast,and thus the formation of the low temperature belt in its southern region.The positive anomalies of the geopotential height are shown in all levels.Correspondingly,there are negative anomalies of geopotential height at low latitudes(40°N).The low temperature region is between them.This distribution pattern exists in all levels.From the near surface to the upper levels,these systems display an overall tilt from the south to the north,thus the vertical cross-section is in a large-scale front-like structure.This is understood with a simple conceptual model.The vertical structure may be maintained by the interaction of the dynamical and therm-dynamical anomalies in the atmosphere.