Ground‐Based Observations of VLF Waves as a Proxy for Satellite Observations: Development of Models Including the Influence of Solar Illumination and Geomagnetic Disturbance Levels
Ground‐Based Observations of VLF Waves as a Proxy for Satellite Observations: Development of Models Including the Influence of Solar Illumination and Geomagnetic Disturbance Levels
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甚低频波的地面观测作为卫星观测的代理：开发包括太阳光照和地磁扰动水平影响的模型
DOI：
10.1029/2018ja026407
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Rodger, Craig J.
中科院分区：
文献类型：
--
作者：
Simms, Laura E.;Engebretson, Mark J.;Clilverd, Mark A.;Rodger, Craig J.
VLF（甚低频）波的地面观测经常被用来推断磁层中的VLF活动；然而，由于跨层吸收和亚层衰减，它们并不是卫星高度活动的无偏测量。我们提出了几个控制这些影响的经验模型。利用VLF/ELF记录器实验（VELOX， L=4.6，哈雷，南极洲）的VLF功率谱密度（PSD）预测DEMETER近地轨道VLF PSD。这些模型的验证相关性高达0.764；因此，分布在地球周围的地面VLF接收器可以在该模型的纬度极限（±45-75°）范围内提供外辐射带低频段合唱的覆盖。比较了四个频带（以0.5、1.0、2.0和4.25 kHz为中心）的相关性。在1.0‐kHz信道中，地面和卫星VLF PSD之间的简单线性相关性为0.606（黎明时分）。三次模型的相关性较高（0.638）。由于太阳照射时电离层的吸收和干扰条件下导管场线的中断，VLF对地面的穿透减少了。亚层衰减也降低了从远场线观测到的VLF。这些协变量的加入改善了预测。太阳光照和扰动条件均降低了VLF PSD的地面观测，高功率波穿透地面的比例小于低功率波。在较高的频率（4.25 kHz）下，照明降低波穿透的效果更为明显，而在中频（2.0 kHz）下，效果介于这两个极端之间。
Ground observations of VLF (very low frequency) waves have often been used to infer VLF activity in the magnetosphere; however, they are not an unbiased measure of activity at satellite altitudes due to transionospheric absorption and subionospheric attenuation. We propose several empirical models that control for these effects. VLF power spectral density (PSD) from the VLF/ELF Logger Experiment (VELOX, L=4.6, Halley, Antarctica) is used to predict DEMETER low Earth orbit VLF PSD. Validation correlations of these models are as high as 0.764; thus, ground VLF receivers spaced around the Earth could provide coverage of outer radiation belt lower band chorus over the latitudinal limits of this model (±45–75°). Correlations of four frequency bands (centered at 0.5, 1.0, 2.0, and 4.25 kHz) are compared. The simple linear correlation between ground and satellite VLF PSD in the 1.0‐kHz channel was 0.606 (at dawn). A cubic model resulted in higher correlation (0.638). VLF penetration to the ground is reduced by ionospheric absorption during solar illumination and by disruption of ducting field lines during disturbed conditions. Subionospheric attenuation also reduces VLF observations from distant field lines. Addition of these covariates improved predictions. Both solar illumination and disturbed conditions reduced ground observation of VLF PSD, with higher power waves penetrating to the ground proportionately less than lower power waves. The effect of illumination in reducing wave penetration was more pronounced at higher frequency (4.25 kHz), with the effect at a midrange frequency (2.0 kHz) falling between these two extremes.
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发表时间：
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发表时间：
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