The distinctive features of the ion gyro-harmonic discrete structures in the narrowband stimulated electromagnetic emission (NSEE) spectra (within ±1 kHz of the heater frequency), excited by an extraordinary (X-mode) polarized high frequency (HF) pump wave in the F-region of the high latitude ionosphere, are reported. Results were obtained from three sets of experiments at the EISCAT (European incoherent Scatter) HF Heating facility at pump frequencies of 5.423, 6.77 and 7.953 MHz, which are below the fourth, fifth, and sixth electron gyro-harmonics. High power HF radio waves were radiated in the magnetic field-aligned direction with an effective radiated power of 238–740 MW. Discrete spectral features, ordered by the ion gyro frequency (for O⁺ ions), were recorded at a large distance (1,200 km) away from the Heating facility. Up to 10 downshifted discrete ion gyro-harmonic structures paired with the upshifted spectral components (Stokes and anti-Stokes modes) in the NSEE spectra have been excited in the course of these experiments. It was found that preconditioning effects have a significant impact on the temporal evolution of the discrete spectral structures. The ion gyro-harmonic structures coexisted with field-aligned artificial irregularities (FAIs). Comparing the NSEE and EISCAT incoherent scatter radar observational results, it was concluded that the electron accelerations along and across the geomagnetic field coexist during X-mode heating. The magnetized stimulated Brillouin scatter and stimulated ion Bernstein scatter are discussed as relevant processes for the observed multiple down- and upshifted ion gyro-harmonic structures in the NSEE spectra.

中文翻译：

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EISCAT 中 X 模式高功率 HF 无线电波激发的受激发射中的离子陀螺谐波结构

窄带受激电磁发射 (NSEE) 光谱（加热器频率的 ±1 kHz 内）中的离子陀螺谐波离散结构的独特特征，由异常（X 模式）极化高频 (HF) 泵浦波激发报告了高纬度电离层的F 区域。结果是从 EISCAT（欧洲非相干散射）HF 加热设施在 5.423、6.77 和 7.953 MHz 泵浦频率下的三组实验中获得的，这些实验低于第四、第五和第六电子陀螺谐波。高功率 HF 无线电波沿磁场对齐方向辐射，有效辐射功率为 238-740 MW。离散光谱特征，按离子陀螺频率排序（对于 O ⁺离子），是在距离加热设施很远（1,200 公里）处记录的。在这些实验过程中，已激发多达 10 个下移离散离子陀螺谐波结构与 NSEE 光谱中上移的光谱分量（斯托克斯和反斯托克斯模式）配对。发现预处理效应对离散光谱结构的时间演化有显着影响。离子陀螺谐波结构与场对齐的人工不规则（FAI）共存。比较 NSEE 和 EISCAT 非相干散射雷达观测结果，得出的结论是，在 X 模式加热过程中，沿地磁场和穿过地磁场的电子加速度并存。