Sunrise effects on VLF signals propagating over a long north-south path
Sunrise effects on VLF signals propagating over a long north-south path
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DOI：
10.1029/1999rs900052
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发表时间：
1999-07-01
期刊：
影响因子：
1.6
通讯作者：
Rodger, CJ
中科院分区：
文献类型：
--
作者：
Clilverd, MA;Thomson, NR;Rodger, CJ
我们提出了一个详细的研究时间的振幅最小值上观察到的12毫米路径从NAA（24 kHz，1兆瓦，卡特勒，缅因州），南极洲的法拉第，在1990 - 1995年期间。(NAA是海军发射机呼号。）这项研究代表了第一个帐户的效果时，日出终止平行于传播路径在一年中的某些时候。由于NAA-Faraday路径在南北子午线的3度范围内，平行方向发生在接近分点的地方，而最大的入射角发生在至点。在至点期间，终止器需要很长的时间才能穿过整个传播路径，因此在几个小时的范围内观察到模态转换效应。然而，在春分点期间，昼夜过渡区的前沿在20分钟内穿过整个传播路径。最小值的时间的解释是一致的模态转换发生的日出终结者穿越NAA-法拉第传输路径在特定的，一致的位置。最小值的出现时间每年都非常一致。长波传播模拟表明，在45 - 75公里的高度在亚电离层波导的夜侧极小值的位置代表的位置时，日侧极小值发生时的大圆路径上的日出终止。
We present a detailed study of the times of amplitude minima observed on the 12-Mm path from NAA (24 kHz, 1 MW, Cutler, Maine) to Faraday, Antarctica, during the period 1990-1995. (NAA is a naval transmitter call sign.) This study represents the first account of the effect of the sunrise terminator when it is parallel to a propagation path at some times of the year. Since the NAA-Faraday path is within 3 degrees of the north-south meridian, parallel orientation happens close to the equinoxes, while the maximum angle of incidence occurs during the solstices. During the solstices the terminator takes a significant length of time to cross the entire propagation path, so modal conversion effects are observed over a range of hours. During the equinoxes, however, the leading edge of the night-day transition region crosses the whole propagation path within 20 min. The interpretation of the timing of minima is consistent with modal conversion taking place as the sunrise terminator crosses the NAA-Faraday transmission path at specific, consistent locations. The timing of minima is remarkably consistent from year to year. Long wave propagation modeling is used to show that the location of nightside minima at an altitude of 45-75 km in the subionospheric waveguide represents the location of the sunrise terminator on the great circle path when dayside minima occur.