Research On The Aspect Sensitivity Of MST Radar In The Lower Atmosphere

Wuhan(Mesosphere-Stratosphere-Troposphere)MST radar is one of the most important facilities in the Meridian Project—a National Major Science and Technology Infrastructure Project.Based on the clear-air echo principle,it is able to detect the troposphere,lower stratosphere and part of the mesosphere.Among the first batch of MST radars built in China,Wuhan MST radar is widely used in 3D wind profile detection,air wave observation,midlatitude tropopause study,aspect sensitivity research and electron draft observation.To make further use of the product data,it is also feasible to derive the air temperature profile from vertical wind velocity and make statistical research about momentum flux.In order to improve the detection performance of the MST radar and take advantage of long time uninterrupted detection features in special events,experiments are conducted during normal days and cold front weather respectively to determine a best zenith angle in mid mod detection and explain the detailed coupling mechanism between troposphere and lower stratosphere during a cold front.The main works include:1.The correction for zenith detecting angle in mid mode.According to the theory of aspect sensitivity,the SNR(Signal-Noise-Ratio)of radar in VHF(Very-High-Frequency)band trends to decrease rapidly especially near the tropopause,where the fluctuation of the refraction index is relatively rough.This phenomenon may further result the loss of echoes,for the echoes from large zenith angles are too weak to detect.However,if the zenith angle is too small,the resolution of horizontal wind will be rather low and the error in wind measurement will be rather large affected by the stronger echoes scatter from smaller angles.To better improve the data quality of Wuhan MST radar,analyses focus on four aspects—the SNR affect by aspect sensitivity,the error of wind measurement affect by aspect sensitivity,the resolution of horizontal wind and the uniformity of the horizontal wind—respectively.2.The Analysis and explanation to the abnormal phenomena in the stratosphere due to the effect of frontal system.During a cold front passage,a long time multi-angle detection is made to observe the variation of echo patterns.Because the features of aspect sensitivity will disappear where the flow is convective instable,it is available to learn the condition of atmosphere by comparing echoes in different angles.The result of the experiment shows a strong echo band at 16-17km.Data from radiosonde is used to extract the inertia gravity wave and calculate the key parameters of the wave.In further study,the source of the gravity wave,the wave-shear interactions and the relationship between breaking wave and turbulence generation are discussed.It is concluded that the strong turbulence layer is caused by gravity waves.The gravity wave generated from frontal surface propagates upward and breaks up at 16-17km,which decelerates the background wind and induces a large wind shear.