Responses Of The Middle And Upper Atmosphere Wind To Geomagnetic Activity

During geomagnetic storms,the middle and upper atmosphere has enhanced energy sources in the high latitude,such as Joule heating and particle heating,which are transmitted and coupled in the atmosphere.The deposition and propagation of these energies can cause various changes in the temperature,wind,electron density,etc.The study of the responses of the middle and upper atmosphere wind to geomagnetic activities is helpful to understand the energy coupling,and the dynamic in this region,so we can availably explain many phenomena in the middle and upper atmosphere.In the present study,the wind data observed by meteor radars at Mohe(53.5°N,122.3°E),Beijing(40.3°N,116.2°E)and Wuhan(29.6°N,113.5°E)and the geomagnetic activity Kp index were used to investigate the responses of the middle and upper atmosphere wind to geomagnetic activities.We adopted two methods for data analysis.Research 1 is to make a comparison with international peers: we used the diurnally averaged wind data,and then conducted statistical study.In research 2,the diurnally averaged wind data was used and we filtered the fluctuations with a period of5-20 days by digital filter and then conducted statistical study.The main analysis results are shown as follows:1.Research 1(tides removed): The influence of geomagnetic activity on zonal wind is about 5 m/s to 10 m/s,with seasonal differences and different performance in different latitudes.In spring,the three stations have similar tendencies,wind are more westerly in the mesosphere and more easterly in the lower thermosphere during disturbed conditions.The situation is similar in summer and winter.At Mohe station(higher latitude),more westerly wind was found in the mesosphere,while more easterly wind in the lower thermosphere.At Beijing and Wuhan stations(lower latitude),more easterly wind was found,and the influence at Beijing is stronger than that at Wuhan.As for autumn,easterly wind intensified at Mohe and Beijing stations during geomagnetic disturbances,while the anomalies at Wuhan station are thought to be related to the fluctuations from the lower atmosphere.In autumn,Mohe station in higher latitude is more affected than Beijing and Wuhan at lower latitude.The influence of geomagnetic activities on meridional wind is also different in different seasons: stronger in spring and winter than in summer and autumn.In winter,the influence of geomagnetic activities on meridional wind is stronger at Beijing and Wuhan than that at Mohe,and the order is about 3 m/s to 5 m/s.2.Research 2(tides,and fluctuations with a period of 5-20 days removed): The effects of geomagnetic activities on zonal wind vary from season to season.Generally speaking,the effects of geomagnetic activities range from 5 m/s to 10 m/s,and vary in different latitudes.In summer,the geomagnetic activities have weak effect,and only in higher latitudes,more westerly wind was found in the middle and upper atmosphere.In spring,wind was more westerly in the mesosphere and more easterly in the lower thermosphere.In autumn,it is the opposite,more easterly wind was found in the mesosphere and more westerly wind in the lower thermosphere.The influence of geomagnetic activities on meridional wind is small(about 3m/s to 5m/s),and weak in summer and winter.In spring,more southerly wind was found in the mesosphere and more northerly wind in the lower thermosphere.In autumn,wind was more northerly during disturbed condition in this region.3.Comparison between the research 1 and research 2: In general speaking,after removing 5-20 days fluctuations,the differences between disturbed and quiet conditions in each season become small.In autumn,before filtering fluctuations,the influence of geomagnetic activity on Wuhan at lower latitude is different from that of Mohe and Beijing station at higher latitude,but after filtering fluctuations,the performance of the three stations is consistent.In winter,before filtering fluctuations,the differences of zonal wind between disturbed and quiet conditions at Beijing and Wuhan stations are quite different from that without filtering fluctuations.Therefore,it is considered that the fluctuations of the middle and upper atmosphere is stronger in autumn and winter.