资源环境科技发展态势分析平台

Many phenomena in the high-frequency pumped ionosphere exhibit dependence on the pump beam incident angle a. This motivates a systematic study of the a dependence of the stimulated electromagnetic emission (SEE), particularly near electron gyroharmonics. We report the first observations of stationary SEE spectra for a ranging from -28 degrees (north) to 28 degrees (south) at three receiving sites, for the pump frequency (f(0)) sweeping near the fourth gyroharmonic (4f(c)). The following is established: (i) For pumping near the magnetic zenith (alpha = 7 degrees, 14 degrees, 21 degrees), when existent dynamic broad upshifted maximum in the SEE spectrum indicates that artificial ionization layers are excited, suppression of the downshifted maximum at f(0) approximate to 4f(c) is weakest, and 4f(c) increases. (ii) Weaker similar effects occur for alpha = -14 degrees (a condition called "mirror magnetic zenith"). (iii) For northern pump beam inclinations, the SEE intensity decreases (in comparison with southern inclinations and vertical), most strongly at the southernmost receiving site.