极区中层夏季回波与频率关系的初步分析

研究不同频率的雷达体在不同时间和地点测量的极区中层夏季回波(Polar Mesosphere Summer Echoes,PMSE)体反射率,发现雷达体反射率与工作频率的4次方成反比,即产生PMSE回波的散射体的雷达散射截面与频率的4次方成反比,这种频率依赖关系不同于传统湍流理论.最后提出了PMSE实验和理论研究的新方法. 

Preliminary Analysis on the Relationship between Polar Mesosphere Summer Echoes and Frequency

Polar Mesosphere Summer Echoes(PMSE)are very strong radar echoes primarily stud- ied in the VHF and UHF wavelength band from altitudes near the polar summer mesopause.PMSE have also been detected in the MF and HF wavelength band.In the paper,by analyzing the volume reflectivities of PMSE at different time,stations and frequencies in related references,the volume reflectivities can be found a tremendous decrease with frequencies increasing(or wavenumbers de- creasing).This frequency dependence plays an important part in any physical explanation of PMSE. By studying experimental results in some references,the relationship between volume reflectivity and working frequency is obtained.One finds that the volume reflectivity is inverse proportional to the fourth power of the working frequency,namely the backscattering cross section per unit volume is inverse proportional to the fourth power of the frequency,and the relationship is different from that of the traditional turbulence theory.On the basis of the neutral air turbulence in combination with a large Schmidt number of the electrons,the volume reflectivity is reproduced with the data in the published papers.The result computed by M.Rapp is in an agreement with that mentioned above.Because of the presence of heavy charged ice aerosol particles,electron diffusivity significantly reduces and the irregularity of electron density occurs.The irregularity is the main factor leading to abnormally strong radar echoes.Finally some new problems about PMSE experiments and theories are put forward,the generation mechanism of PMSE may be explained with the theory of dusty plasma.