Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability
Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability
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南美洲 VLF 网络 (SAVNET) 的低电离层监测：C 区发生和大气温度变化
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发表时间：
2013
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通讯作者：
G. Fernandez
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作者：
F. Bertoni;J. Raulin;H. R. Gavilán;P. Kaufmann;R. Rodríguez;M. Clilverd;Jorge Samanes Cardenas;G. Fernandez
在固定 VLF 路径上观察到的每日相位测量曲线通常显示瞬态相位超前，随后是日出后约 90 分钟的相位延迟。这表明反射电离层 C 区域在低于正常 D 区域的高度沿终止线发展。 C 区的出现与 20 世纪 60 年代的火箭测量结果一致，显示电子密度最大值在 64 至 68 公里之间，并通过 1980 年代的无线电探测得出。为了正确描述与 C 区域存在相关的相位效应的特性，了解 VLF 路径的亚电离层传播特性非常重要。在本文中，我们分析了 VLF 窄带相位效应的时间特性所呈现的变化，并确定了与南美 VLF 网络接收器观测到的日出时 C 区外观相关的参数。参数曲线出现周期性模式。可以识别两种不同的时间行为模式：一种在三月和十月之间表现出缓慢的变化，另一种在十月和三月之间表现出较快的变化。太阳光照条件和 VLF 路径相对于日出终止线的几何结构在一定程度上解释了缓慢变化的情况。在变化较快的时期，我们在使用宽带发射辐射测量卫星仪器对热层、电离层、中间层能量和动力学以及大气探测进行测量时发现，与大气温度变化有良好的关联，我们认为这与冬季异常大气现象有关。然而，在将参数时间序列与温度曲线进行比较时，没有发现瞬态事件的直接一一对应关系。
Daily profiles of phase measurements as observed on fixed VLF paths generally show a transient phase advance, followed by a phase delay, for about 90 min after sunrise hours. This is indicative of a reflecting ionospheric C region developing along the terminator line at an altitude below the normal D region. The suggested occurrence of a C region is consistent with rocket measurements made in the 1960s, showing a maximum of the electron density between 64 and 68 km, and by radio sounding in the 1980s. In order to correctly describe the properties of the phase effect associated with the presence of a C region, it is important to understand the subionospheric propagation characteristics of the VLF paths. In this paper, we analyze the variations presented by the temporal properties of the VLF narrowband phase effect and determined a parameter associated with the appearance of the C region at sunrise hours observed by receivers from the South America VLF Network. Periodic patterns emerge from the parameter curves. Two distinct temporal behavior regimes can be identified: one exhibiting slow variations between March and October, and another one exhibiting faster variations between October and March. Solar illumination conditions and the geometrical configuration of the VLF paths relative to the sunrise terminator partly explain the slow variation regime. During periods of faster variations, we have observed good association with atmospheric temperature variability found in the measurements of the Thermosphere Ionosphere Mesosphere Energetics and Dynamics and Sounding of the Atmosphere using Broadband Emission Radiometry satellite instrument, which we assume to be related to the winter anomaly atmospheric phenomenon. However, when comparing the parameter time series with temperature curves, no direct one‐to‐one correspondence was found for transient events.