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<p>We present the results of studies of simultaneous ground-based and spacecraft observations of quasiperiodic VLF emissions. About 20 events were selected in which a one-to-one correspondence between the elements of quasi-periodic emissions onboard the Van Allen Probes spacecraft and at the Kannuslehto ground-based observatory (Finland, 67.74°N, 26.27°E; McIlwain parameter <i>L</i> ≈ 5.5) was observed. This correspondence occurred over a wide range of latitudes (~ 20°) and longitudes (~ 90°) at distances of up to 3000 km between the geomagnetic projection of the spacecraft trajectory to the Earth and the ground-based station. By using multicomponent wave field measurements onboard Van Allen Probes spacecraft, we found the sections of their orbits at which the VLF waves propagated almost along the geomagnetic field and the energy flux (Poynting vector) was directed away from the geomagnetic equator. Using the data on the energetic electron distribution function obtained by the same spacecraft we calculated the growth rate of the cyclotron instability of whistler-mode waves in the magnetosphere. Comparison of the results of these calculations with the results of multicomponent VLF wave measurements allowed us to find probable generation regions of quasi-periodic emissions. It is shown that these regions are clustered in the <i>L</i>-shell interval from 4 to 5.5, and their characteristic radial size is Δ<i>L</i> ≈ 0.1–0.5, which is much smaller than the size of the quasi-periodic emission observation region (Δ<i>L</i> ≈ 1–3).</p>

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Simultaneous Observations of Quasi-Periodic VLF Emissions by Spacecraft and on the Ground and Localization of Their Generation Region

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • A. G. Demekhov,
  • E. E. Titova,
  • A. A. Lyubchich,
  • D. L. Pasmanik,
  • J. Manninen,
  • A. V. Larchenko

摘要

We present the results of studies of simultaneous ground-based and spacecraft observations of quasiperiodic VLF emissions. About 20 events were selected in which a one-to-one correspondence between the elements of quasi-periodic emissions onboard the Van Allen Probes spacecraft and at the Kannuslehto ground-based observatory (Finland, 67.74°N, 26.27°E; McIlwain parameter L ≈ 5.5) was observed. This correspondence occurred over a wide range of latitudes (~ 20°) and longitudes (~ 90°) at distances of up to 3000 km between the geomagnetic projection of the spacecraft trajectory to the Earth and the ground-based station. By using multicomponent wave field measurements onboard Van Allen Probes spacecraft, we found the sections of their orbits at which the VLF waves propagated almost along the geomagnetic field and the energy flux (Poynting vector) was directed away from the geomagnetic equator. Using the data on the energetic electron distribution function obtained by the same spacecraft we calculated the growth rate of the cyclotron instability of whistler-mode waves in the magnetosphere. Comparison of the results of these calculations with the results of multicomponent VLF wave measurements allowed us to find probable generation regions of quasi-periodic emissions. It is shown that these regions are clustered in the L-shell interval from 4 to 5.5, and their characteristic radial size is ΔL ≈ 0.1–0.5, which is much smaller than the size of the quasi-periodic emission observation region (ΔL ≈ 1–3).