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Jutao YANG 《等离子体科学和技术》2019,21(7):75301
It is now well known that amplitude modulated (AM) high frequency (HF) radio wave transmissions into the ionosphere can be used to generate very/extremely low frequency (VLF/ ELF) radio waves using the so-called ‘electrojet antenna’. Duty cycle and heating frequency are analyzed and discussed with the lower-ionosphere modulated heating model, so as to improve the radiation efficiency of VLF/ELF waves in AM ionospheric heating experiments. Based on numerical simulation, the ranges of parametric selectivity in optimal duty cycle and heating frequency ( fHF) are derived. The International Reference Ionosphere 2015 (IRI-2015) model and two-parameter model are used to predict background electron density profiles, and optimized ranges of duty cycle for different density profiles are analyzed and compared. The influences of wave polarizations on optimal duty cycle are also discussed. It is shown that intensity of the VLF/ELF equivalent radiation source (M) firstly rises and then falls with the increase of duty cycle. When using the IRI model, M peaks at a duty cycle of 50%, optimally ranging from 40% −70%. For the two-parameter model case, an optimal duty cycle is 40% and the optimized ranges vary from 30%−60%. Heating with an X-mode polarization is more efficient than with the O-mode case in VLF/ELF wave generation. Nevertheless, an optimal duty cycle is almost independent of HF wave polarizations. To obtain better VLF/ELF generation, optional fHF may be 0.8−0.9 times of foE for the O-mode heating and 0.75−0.85 times for the X-mode polarization case. Finally, the variations of these two parameters in different latitudes are discussed. 相似文献
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研究了电离层加热激发受激布里渊散射效应.利用受激布里渊散射匹配条件, 结合国际地磁场参考模型, 模拟计算了离子声波(Ion Acoustic, IA)与静电离子回旋波(Electrostatic Ion Cyclotron, EIC)频率随地理纬度、加热频率、波束指向、电子温度等参数变化特性, 并以我国海南与美国高频主动极光研究项目(High Frequency Active Auroral Research Program, HAARP)为例, 研究IA与EIC频率随纬度的变化.模拟结果表明:随着纬度的增加, IA与EIC频率增大; 与IA频率相比, EIC频率随加热频率、波束指向及电子温度的变化相对较小; 随加热频率的增加高纬地区IA频率增大, 而低纬地区基本不变; 随加热波束指向从南到北变化, 海南IA频率单调下降, HAARP则为先上升后下降的形态, EIC具有相反的变化; 电子温度越高, IA与EIC频率越大.本文模拟结果可为我国将来开展同类实验提供参考. 相似文献
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电离层背景状态对大功率短波加热电离层效应的影响 总被引:3,自引:0,他引:3
从电离层加热实验出发,模拟研究了低纬地区(Arecibo)和高纬地区(Troms?)加热效应.首先验证了该文计算的正确性,在此基础上研究了背景电离层电子密度梯度和泵波频率 HFf 与临界频率0F2f 比值对电离层加热效应的影响,结果表明:电子密度梯度越小,加热效果越强;过密加热时,加热效果随泵波频率与临界频率的比值增大而增强,但同时受电波反射高度影响,该比值较低时可能也会存在一个使加热效果增强的取值范围.最后分析了在不利的电离层背景状态下如何有效选择加热参数,以获得较为理想的加热效果. 相似文献
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从基本的电离层能量方程和连续性方程出发,构造了预加热模式下低电离层幅度调制加热理论模型,详细研究了预加热模式对电离层幅度调制加热产生极低频/甚低频(Extremely Low Frequency/Very Low Frequency,ELF/VLF)强度的影响.以HAARP加热站点为例,对比分析了正常幅度调制模式和预加热幅度调制模式两种模式下产生的ELF/VLF偶极矩的大小.分析结果表明,当加热系统有效辐射功率较大、调制频率较小时,预加热幅度调制模式更有效;在一定加热条件下,相对正常幅度调制模式,预加热幅度调制模式辐射ELF/VLF强度可提高约5.3 dB. 相似文献
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