Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications
Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications
复制标题
150 公里回波的共体积双频雷达观测及其意义
DOI：
10.1029/2019ja027317
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
P. Kamaraj
中科院分区：
文献类型：
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作者：
A. Patra;P. Chaitanya;M. D. Rao;P. Kamaraj
本文介绍并讨论了采用相同的发射机功率和天线波束宽度，从Gadanki在30和53 MHz频率下对150公里回波进行的常见双频雷达观测。这些受控实验表明，150公里的回波在30 MHz时比在53 MHz时更强，频谱宽度更宽，出现频率更高。发现30和53 MHz的回波强度与150公里区域米尺度不规则波数谱的火箭载观测结果一致。频谱宽度的频率依赖性虽然与电喷1型回波相似，但与电喷2型回波和垂直于磁场方向的非相干散射相反。两个雷达观测到的回波频谱宽度与信噪比无关。将这些观测结果与之前的观测结果进行详细比较表明，仪器功能在显示150公里回波的信噪比依赖/独立谱宽特性方面起着重要作用。回波强度和谱宽的窄谱特性和频率依赖性清楚地表明，造成雷达后向散射的不规则性与弱等离子体湍流有关，造成雷达回波的米尺度不规则性应该随着在米尺度上直接注入能量以克服阻尼而增加。我们推测了光电子和大气重力波在等离子体不稳定过程中的潜在作用。
We present and discuss common‐volume dual‐frequency radar observations of 150‐km echoes made at 30 and 53 MHz from Gadanki by employing identical transmitter power and antenna beam width. These controlled experiments reveal that 150‐km echoes are stronger, broader in spectral width, and more frequent in their occurrence at 30 MHz than at 53 MHz. Echo intensities at 30 and 53 MHz are found to be consistent with the rocket‐borne observations of wave number spectrum of meter‐scale irregularities in the 150‐km region. The frequency dependence of spectral widths of the echoes while is found to be somewhat similar to that of electrojet type‐1 echoes it is opposite to that of electrojet type‐2 echoes and also to that of incoherent scattering in direction perpendicular to magnetic field. Spectral widths of the echoes observed by both radars are found to be independent of SNR. A detailed comparison of these observations with those made earlier suggests that instrument functions play an important role in manifesting SNR‐dependent/independent spectral width property of the 150‐km echoes. The narrow spectral properties and frequency dependence of echo intensity and spectral width clearly suggest that the irregularities responsible for the radar backscatter are linked with weak plasma turbulence and the meter‐scale irregularities responsible for radar echoes ought to be growing with direct injection of energy at the meter scale itself to overcome damping. We surmise the potential role of photoelectrons and atmospheric gravity waves in the underline plasma instability process.