The Study On Wind Fields In The Mesosphere Observed By MST Radars

MST(Mesosphere-Stratosphere-Troposphere)radar is a large Doppler phased array radar operating in the Very High Frequency(VHF)band.It can perform longterm unattended detection of the atmosphere in the mesosphere,low stratosphere and troposphere.The MST radar is mainly based on the echo mechanism of Bragg scattering and Fresnel reflection/scattering to obtain atmospheric echoes,and deduce the information of the three-dimensional wind field.Since the advent of MST radar,the observations and researches of the mesosphere have always been the most worthy of attention in the area of MST radar research.Using MST radar to observe the threedimensional wind field in the mesosphere will help us have a deeper understanding of the atmospheric state,dynamic process,and atmospheric propagation and coupling process in the mesosphere.Based on the Wuhan MST radar(29.51°N,114.13°E)and Beijing MST radar(39.75°N,116.96°E)constructed in the first phase of the China Meridian Project,we focused on the statistical study of the mesospheric vertical winds and the case study of the exceptionally zonal wind reversal in the mesosphere of Wuhan in January 2016.The main research contents and results are as follows:1.Using the observation results of the Wuhan MST radar during 2012-2017 and Beijing MST radar during 2012-2014,the statistical characteristics of the vertical winds in the mesosphere were studied.The mesospheric echoes of MST radar are mainly concentrated in the altitude range of 65-85 km and the time range of 6:00-18:00 local time,but the data acquisition rates over Wuhan and Beijing are different in seasons.We give the statistical characteristics of the sub-daily,seasonal and annual variations of the mesospheric vertical winds observed by the Wuhan and Beijing MST radars.The statistical results show that the mesospheric vertical winds over Wuhan and Beijing MST radars have no obvious sub-daily and seasonal variations and the annual variations of the mean vertical winds are downward in most of time.The mean vertical winds at Wuhan become smaller in summer and turn to upward at some heights,while those of Beijing only become smaller in summer.The analyses show that the difference of vertical winds between the two places in summer is related to the gravity wave activities.The Wuhan MST radar is located to the east side of the Qinghai-Tibet Plateau and also in the East Asian monsoon region.Mesospheric gravity wave activities in summer over Wuhan are more abundant,thus the vertical winds over Wuhan MST radar are may experience more influence of gravity wave compared with those over Beijing.We also discussed and analyzed the possible bias sources in the vertical wind measurement of the two MST radars and the presented wind velocities are proved to be credible.The measured average velocity magnitude is similar to other VHF radar observations,but much larger than that of model simulation.We tried to discuss the underlying causes of this discrepancy.2.Using Wuhan MST radar observation data,MERRA-2 reanalysis data,and HWM-14 model data,the exceptionally zonal wind reversal lasting for 10 days in the mesosphere in January 2016 observed by Wuhan MST radar was studied.The climatological characteristics of the zonal and meridional winds in the mesosphere over Wuhan MST radar are presented using the 6-year observation results of Wuhan MST radar and the model data of HWM-14.The horizontal wind fields show obvious seasonal variations.Using the Wuhan MST radar and MERRA-2 reanalysis data,the exceptionally zonal wind reversal in the mesosphere over Wuhan in January 2016 is showed,which is similar to the structure of the zonal winds in the mesosphere in summer.According to the analysis,we think that the extremely strong polar vortex in the winter of 2015/16 caused the stationary planetary waves with wave number 1 and wave number 2(SWP1,SPW2)to propagate to the mid-latitude mesospheric regions,which leads to the exceptionally zonal wind reversal in the mesosphere over the Wuhan MST radar in January 2016.Meanwhile,the SPW2,which extended to the mid-latitude mesospheric regions,reversed the meridional temperature difference of the lower mesosphere above Wuhan.According to the thermogenic wind balance and geostrophic wind balance,the zonal wind will also reverse.More eastward propagating gravity waves uploaded to the mesosphere heights and produced energy and momentum deposition.It makes the zonal wind reversed to the eastward wind at the higher height of the mesosphere and finally presented a zonal wind structure similar to summer.