Amplitude variations of VLF radio signals of JXN and DHO transmitters received in Yakutsk during the solar eclipse June 10, 2021

A solar eclipse affects the Earth's upper atmosphere. The eclipse time can be calculated in advance, which allows us to prepare for experiments. Dynamic processes during each specific eclipse depend on the heliogeophysical environment. VLF radio waves can propagate thousands of kilometers in the Earth-ionosphere waveguide. The location of the VLF radio paths determines the space for monitoring the lower ionosphere (as a part of the upper atmosphere). We applied a method of studying the amplitude variation of VLF radio signals from DHO (23.4 kHz, 53.08° N, 7.62° E) and JXN (16.4 kHz, 66.97° N, 13.87° E) transmitters received in Yakutsk. The most part of these radio paths is located along the Arctic territory of Eurasia. The diurnal VLF amplitude variations of the DHO и JXN signals from June 7 to 13 are explained by the solar ionizing flux variation, the higher-order modes interference during the passage of the rising and setting terminators along the elements of the radio paths, and the transmitters operating mode. During the solar eclipse of June 10, 2021, the minimum average ratio value of the open part of the solar disk area to the full disk area was 0.532 (11:39:18 UTC) and 0.411 (11:33:00 UTC) along the DHO - Yakutsk and JXN - Yakutsk radio paths, respectively. The eclipse effect appeared as an amplitude increase at the maximum of 1.62 dB (11:39:18 UTC) and 1.4 dB (11:26:42 UTC) for the DHO and JXN signals, respectively. Furthermore, our data provide the low VLF receivers manufacturing costs and the ability to cover large areas make the VLF registration a convenient tool for sounding the lower ionosphere over the hard-to-reach and sparsely populated areas.

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