The Relationship Between The Horseshoe-shaped Sea Surface Temperature Mode In The North Atlantic In Autumn And The Temperature Anomaly In Early Winter In My Countr

Based on the monthly reanalysis data of NCEP/NCAR,sea surface temperature(SST)data of Hadley Center,ERA5 reanalysis data of ECMWF,the temperature data of 160 stations in China,the interannual variability of North Atlantic SST anomaly(SSTA)in autumn and its association with local atmosphere–ocean system and early winter temperature in China are studied by using a variety of statistical methods such as Empirical Orthogonal Function(EOF)and correlation analysis to obtain the following main conclusions:(1)The first mode of North Atlantic SST anomaly EOF in autumn is North Atlantic Horseshoe Pattern(NAH)with negative(positive)SST anomalies in southeastern Newfoundland,and positive(negative)SST anomalies in the subpolar,subtropical and eastern North Atlantic,which revealed 20.5% variance;the second mode of EOF mainly reflects the characteristics of SSTA in northwestern North Atlantic,with a variance contribution rate of15.1%.(2)There is a significant negative relationship between the NAO and NAH in autumn.Autumn positive(negative)phase NAO is conducive to the formation of negative(positive)phase NAH SSTA in autumn.In addition,the NAH SSTA in autumn can produce an anomaly response similar to that of the NAO type atmospheric circulation,which has a feedback effect on the local atmospheric circulation in the North Atlantic.The positive(negative)phase of the NAH SSTA in autumn weakens(strengthens)the baroclinicity of the North Atlantic atmosphere at 45°～60°N,abnormally increases(decreases)the geopotential height on the north side and decreases(increases)the geopotential height on the south side,and thus forms an NAO type atmospheric circulation anomaly with a relatively positive pressure structure in the vertical direction.(3)The NAH SSTA in autumn has a significant positive correlation with the air temperature in most parts of China in early winter,but the NAH SSTA in autumn has a weak relationship with the interannual variation of the air temperature in January and February,which may be related to the change of the abnormal structure of the North Atlantic SST.Further analysis shows that the NAH SSTA in autumn may affect the NAO anomaly in early winter,and the latter forces the NAH SSTA in early winter,making the autumn NAH SSTA maintain until early winter.In the late winter,the abnormal center of sea level pressure field associated with autumn NAH SSTA changes significantly compared with the early winter,thus leading to obvious changes in the abnormal structure of sea level temperature in late winter,making the autumn NAH SSTA cannot be maintained until the late winter.(4)The NAH SSTA can last from autumn to early winter,and stimulate the Rossby wave spreading downstream over the North Atlantic Ocean,affecting the East Asian atmospheric circulation anomaly,and affecting the temperature anomaly in China through the effect of diabatic heating.When the NAH SST is in a positive(negative)phase in autumn,the heating(cooling)of NAH SSTA over the subpolar and subtropical in early winter can cause divergence(convergence)in the upper troposphere,two Rossby wave trains are stimulated in the north and south branch.The north branch of the wave train propagates northeastward from the North Atlantic subpolar to the vicinity of the Barents Sea,and then propagates southeast along Siberia to the China.The south branch of wave train propagates eastward from the subtropical North Atlantic to China.Under the influence of the south and north branch of wave trains,convergence(divergence)occurs in the upper troposphere over China.Through the sinking(rising)movement,the total cloud cover in the above area is reduced(increased),the shortwave radiation reaching the surface has increased(reduced),and the longwave radiation transmitted from the surface to the lower atmosphere has increased(reduced).Under the action of diabatic heating,the temperature in most areas of China is abnormally high(low).NCAR CAM5.3 was used to simulate the effects of the NAH SSTA on atmospheric circulation,radiative forcing and air temperature in early winter.The simulation results were basically consistent with the statistical analysis results of the observational data.This further confirms that the SST mode can affect the atmospheric circulation anomalies in East Asia by stimulating the teleconnected wave train,thereby affect the interannual variation of air temperature anomalies in China through the effect of diabatic heating.