Experimental study of stimulated electromagnetic emissions in polar region
Stimulated electromagnetic emissions(SEE)with complex spectral features provide a powerful research tool are an effective tool to study the physical mechanism in ionospheric heating.In this paper,we investigate the effects of the polarization,frequency,power,and beam direction of the heating electromagnetic waves on the SEE spectral features during the ionospheric heating experiments conducted by our researchers using the EISCAT heating facilities in 2017 and 2022.The results show that:(1)A variety of SEE structures,including an upshifted maximum(UM),a thermal narrow continuum(NCth)and a downshifted maximum(DM),are more likely to be detected using heating wave with ordinary-mode polarization than with extraordinary-mode polarization.(2)The downshifted peak(DP)frequency offset exhibits a linear correlation with the heating frequency from 4.07 MHz to 4.10 MHz.When the heating frequency reaches the electron gyro-harmonic frequency,the DP and DM spectra disappear,and the process of the generation of the upper hybrid wave is suppressed.Therefore,the electron gyro-harmonic frequency can be rapidly estimated in real time by combining the DP and DM spectral features during the ionospheric heating process.(3)The intermediate downshifted maximum(IDM),a new type of downshifted spectral feature,appears between the DM and the heating wave frequency when heating power increases from 24 MW to 192 MW.It is observed that the dynamic behavior of UM mirrors IDM with respect to heating frequency.(4)In conjunction with the ultrahigh frequency incoherent scattering radar detection,it is found that the heating wave beam direction at an anticlockwise angle of 6° from vertical is more likely to excite the density pure-growing mode of the oscillating two-stream instability,which excites more artificial field-aligned irregularity structures and results in higher DM spectral intensity.
万方数据
维普
