Decadal Difference Of Spring Extreme Low Temperature In North China Associated With Sea Temperature Anomalies In The North Atlantic

Based on daily temperature data from 501 stations in northern China,the reanalyze data from European Centre for Medium-Range Weather Forecasts(ECMWF)and the sea temperature data from Hadley Center(Hadley),this paper investigated the temporal and spatial characteristics of extreme low temperature in spring in North China and compared the characteristics of atmospheric abnormal circulation between the two types of decadal extreme low temperature in the around 1980 s and the 21 st century.And using wave action flux method to explore the difference of energy dispersion characteristics of extreme low temperature Rossby wave in North China before and after 1997 and its possible causes.Then this paper analyzes the source of energy in the key areas east of Greenland and its kinetic energy budget after 1997 by using the multiscale energy and vorticity analysis(MS-EVA).The relationship between extreme low temperature in North China and Eurasian wave trains and sea surface temperature in North Atlantic and its possible mechanism is studied.Finally,it is verified by CAM5.1 numerical mode.The results are as follows:(1)The three interdecadal time periods of extreme low temperature cold deviation in North China(II)are in the 1960 s,around 1980 s and early 21 st century.There are obvious meridional and zonal anomalies in the circulation situation of extreme low temperature events in North China around the 1980 s and in the 21 st century.The extreme low temperature circulation in 21 st century presents a "quasi-2-wave" structure from the North Atlanticto Eurasia,with longer wavelength,better stability,longer duration at low temperature,and obvious wave trains structure at mid-high latitudes;However,the extreme low temperature circulation in the around 1980 s presents a "3-wave" structure,with shorter wavelength,poorer stability,shorter duration at low temperature and less obvious wave trains structure at mid-high latitudes.(2)There are significant differences between the key forcing sources of the interdecadal extreme low temperature circulation anomalies around the 1980 s and the 21 st century.Before 1997,the energy of the North Atlantic near the south of Greenland and the Northern Europe was propagated Eastwards,and the Eurasian wave train(EU)was excited through the key Eurasia.The cyclonic abnormal circulation was enhanced,which was conductive to the maintenance and development of low temperature.However,after 1997,the ocean surface east of Greenland became the key forcing source.The energy propagated to the east was in favor of EU strengthening.The trough in southwestern part of the Lake Baikal was strengthened to form a cyclonic abnormal center,which was conductive to the maintenance of low temperature.(3)The North Atlantic "Horse Hoof" sea surface temperature mode has a significant correlation with the Eurasian Wave Train(EU)affecting North China.At the same time,the North Atlantic "Horse Hoof" sea surface temperature mode has a significant correlation with the vertical wave energy(TNZ2)in the key areas of the North Atlantic after 1997.After 1997,the surface 2 metre temperature on the eastern side of Greenland showed an increasing trend in positive region with anomalies thermal forcing.At the same time,the westerly jet stream increased,which could stimulate the Eurasian Wave Train and formed warm ridges on the downstream Eurasian continent.Due to the abnormal thermal focing and pressure gradient force of the surfacee temperature of the key area on the eastern side of Greenland do positive work in the whole troposphere,leading to the increase of high-level kinetic energy and divergence to the outside,making the Northern Europe ridge strengthen to the north.Through Eurasian Wave Train(EU),the cyclonic anomaly in the downstream North China was strengthened,and the Asian polar vortex was strengthened and maintained.The temperature in the North China decreases sharply and the extreme low temperature events increase.(4)The CAM5.1 model simulation further proves that the North Atlantic "Horse Hoof" sea surface temperature mode can affect the atmospheric circulation anomalies in the Eurasia by stimulating the Eurasian Wave Train,which is conductive to the transport of cold advection to North China and the increase of extrem low temperature events in the North China.The above results reflect the interdecadal characteristics of extreme low temperature in the North China and some of its causes,providing a basis for monitoring and forecasting extreme weather and climate disasters.