Subseasonal Variability Of Two Asian Upper-level Jets In Winter And Their Climatic Effects

This paper uses the reanalysis data of ERA5 and NCEP / NCAR,as well as the return data of subseason to season plan(S2S).Based on the investigation and collation of the previous work,seventeen jet indices,including eleven subtropical jet indices and six polar front jet indices,are calculated,which respectively represent the area,intensity and location of the jet and represent different aspects of jet change.On this foundation,the subseasonal variation characteristics of all aspects of the jet stream are analyzed,the influence of subseasonal variation of jet stream on the winter temperature in China is investigated,and the bridge function of the jet stream in the atmosphere of the northern hemisphere is preliminarily discussed.On the subseasonal scale,the correlation between the indices representing the same characteristics of the jet is significant,while the correlation between the indices representing different characteristics is generally not significant,and the wind field distribution modes corresponding to different jet indices have certain differences.The results of spectral analysis show that all jet indices have significant subseasonal periodic variation characteristics,especially on the scale of 10-30 days;Wavelet analysis further shows that there are some interannual differences in the subseasonal variation characteristics of the jet stream.After 10-90 days band-pass filtering of jet indices and 2m temperature,it is found that the area index and location index(intensity index)of subtropical jet are significantly positively(negatively)correlated with the winter temperature in China.In addition,there is a significant negative(positive)correlation between the intensity(location)of the polar front jet and the winter temperature in China.Through the synthetic analysis of 500 h Pa geopotential height field,850 h Pa temperature advection and E-P flux,it is found that when the subtropical jet is relatively strong,the E-P flux converges between 30°N and 50°N,and the atmospheric fluctuation energy increases,which is conducive to the development of the weather system in this region.At 500 h Pa,there is a positive anomaly of geopotential height and the development of the continental high pressure system,which enhances the cold air activity in China and leads to the anomaly of cold advection over China,It makes the intensity of the jet and the temperature in China appear negative anomalies.When the area of subtropical jet is too large,the E-P flux between 50°N and 60°N diverges and the atmospheric fluctuation energy weakens,which is not conducive to the development of the weather system in this region.The negative anomaly of potential height at 500 h Pa is not conducive to the development of the continental high pressure system and weakens the cold air activity in China.There is a warm advection anomaly over China,resulting in a positive anomaly between the area of subtropical jet and the temperature in China.In addition,the wave current interaction can also explain the positive abnormal relationship between the north-south(east-west)position of the subtropical jet and the temperature in China.When the intensity of the polar front jet is strong(located to the South),the E-P flux is divergent between 30°N and 50°N,and the atmospheric fluctuation energy is weakened,which is not conducive to the development of the weather system in this region.The negative anomaly of the potential height at 500 h Pa is not conducive to the development of the continental high pressure system,weakening the cold air activity in China,resulting in the warm advection anomaly over China,resulting in the positive(negative)anomaly between the intensity(location)of the polar front jet and the temperature in China.Finally,on the subseasonal scale,the bridge role of jet in the tropical middle and high latitude atmospheric interaction is discussed.Firstly,using the S2 S return data,it is found that when the AO is in the positive phase,in most S2 S modes,the prediction skill of AO is higher when the MJO activity is active,and the role of jet in it is preliminarily investigated.It is found that when MJO activity is active,there is a negative anomaly of zonal wind in the latitude belt between 40 ° N and 60 ° N,a positive anomaly of zonal wind in the latitude belt between 60°N and 80°N,and the ring mode in the northern hemisphere is enhanced,resulting in the increase of the intensity of the positive phase of AO.In short,the jet has significant subseasonal periodic changes,and has a significant impact on winter temperature in China,which plays an important role in the subseasonal changes of the atmosphere in the northern hemisphere.