Research On The Scattering Characteristics Of Dusty Plasmas In The Mesopause Region

PMSE are extremely strong radar echoes scattering from the polar mesosphere(80-90km)during the summer.Since it was first observed by Ecklund and Balsley,scientists have carried out a lot of experimental and theoretical work.In general,the atmosphere echoing mechanisms are two ways: turbulent scatter and Fresnel(partial)reflection.The theory of turbulence scattering is mainly based on neutral atmospheric turbulence,and analyzing the electromagnetic scattering from the small-scale(Bragg scale)structure.Fresnel reflection theory shows that the gradients in the refractive index can reflect the energy based on the horizontally stratified structure in the polar mesosphere.Both of these physical mechanisms can generate strong enough under certain conditions.However,the existing theoretical model can not well explain the PMSE phenomenon,and the experiment results show that PMSE may not be caused by only single mechanism.It is of great significance for enriching the theory of radio wave propagation in the atmosphere that understanding the physical mechanism caused PMSE.Electromagnetic scattering from PMSE region is studied in this paper based on the current problem.Firstly,the structure of the mesosphere and PMSE are briefly introduced.According to the previous experimental observation results of PMSE,it can be found that PMSE has large variation with time and space.In addition,the observed ice particle can absorb free electrons makes the structure of mesopause more complicated.For studying the relationship between ice particle and free electron,we calculated the correlation between electron density disturbance and dust density disturbance in the electron “bitouts” region.The result shows a large negative correlation,it means that electron density decrease in this region is likely caused by ice particles.And then,the perturbation power spectrums of dust density and electron density at different altitudes in the summer polar mesopause are calculated based on the data of ECT-02 experiment.Fourier analysis method is applied and numerical results shows that the perturbation power spectrum index is not-5/3 in all altitudes,it is proved that the irregular plasma structure at mesopause region is not always generated by neutral atmospheric turbulence.Then the intensity of turbulent scattering echoes in the mesopause region is calculated based on the perturbation power spectrum of electron density and compared with the experimental data.The results show that the theoretical results are larger than the experimental results in some areas,which indicates that the turbulent scattering theory can not explain the anomalous echo phenomena in the whole mesopause region.Based on the result,we build an electromagnetic scattering model which include refraction from horizontally stratified structure and bragg scattering from small-scale structure.Radar echo signal-to-noise ratio profile with altitude is calculated based on electronic density data measured by rocket compare the result with the radar data measured in the experiment.The comparison results that the calculated SNR is in the same order of magnitude as the experimental results which shows the model is reasonable.The results obtained in this paper are of great significance for understanding the physical mechanism of polar mesosphere summer echoes.