Spatial Distribution and Temporal Variations of Occurrence Frequency of Lightning whistlers Observed by VLF/WBA onboard Akebono
Spatial Distribution and Temporal Variations of Occurrence Frequency of Lightning whistlers Observed by VLF/WBA onboard Akebono
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曙号VLF/WBA观测到的闪电哨声发生频率的空间分布和时间变化
DOI：
10.1002/2014rs005523
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发表时间：
2014
期刊：
影响因子：
1.6
通讯作者：
and Y. Goto
中科院分区：
文献类型：
--
作者：
Y. Oike;Y. Kasahara;and Y. Goto
我们统计分析了Akebono上的VLF仪器观测到的15 kHz以下的模拟波形数据中检测到的闪电哨声。我们研究了从1989年到2010年在日本内之浦航天中心获得的大量数据。闪电哨声主要出现在2.雷哨声出现频率的季节变化有两个高峰，分别在7 ~ 8月和12 ~ 1月。由于闪电在夏季最为活跃，一般来说，这两个峰值分别对应于北方和南半球的夏季。出现频率的日变化表明，闪电哨声开始增加，傍晚和保持在一个高的发生水平，通过夜间与磁当地时间（MLT）21左右的峰值。与闪电活动相比，这个峰值向夜侧移动，闪电活动在中午左右开始上升，在下午晚些时候达到峰值。这一变化趋势可能是由于VLF波在白天的电离层中衰减所致。与地面观测的对比研究表明，除了地面观测的峰值出现在午夜之后，而我们的测量结果在MLT中约为21。这种差异定性解释的术语，在地面站测量的闪电哨声通过电离层两次以上的源区和地面站。这些事实为定量评价电离层对雷哨声的吸收效应提供了重要线索。
We statistically analyzed lightning whistlers detected from the analog waveform data below 15 kHz observed by the VLF instruments onboard Akebono. We examined the large amount of data obtained at Uchinoura Space Center in Japan for 22 years from 1989 to 2010. The lightning whistlers were mainly observed inside the L shell region below 2. Seasonal dependence of the occurrence frequency of lightning whistlers has two peaks around July to August and December to January. As lightning is most active in summer, in general, these two peaks correspond to summer in the Northern and Southern Hemispheres, respectively. Diurnal variation of the occurrence frequency showed that lightning whistlers begin to increase in the early evening and remain at a high-occurrence level through the night with a peak around 21 in magnetic local time (MLT). This peak shifts toward nightside compared with lightning activity, which begins to rise around noon and peaks in the late afternoon. This trend is supposed to be caused by attenuation of VLF wave in the ionosphere in the daytime. Comparison study with the ground-based observation revealed consistent results, except that the peak of the ground-based observation appeared after midnight while our measurements obtained by Akebono was around 21 in MLT. This difference is explained qualitatively in terms that lightning whistlers measured at the ground station passed through the ionosphere twice above both source region and the ground station. These facts provide an important clue to evaluate quantitatively the absorption effect of lightning whistler in the ionosphere.