Национальный исследовательский университет «Высшая школа экономики»
Нижний Новгород, Россия
Нижний Новгород, Россия
Нижний Новгород, Россия
A threshold condition has been established for excitation of VLF electromagnetic radiation with a chorus structure of the dynamic spectrum in the daytime magnetosphere using the BPA (Beam Pulse Amplifier) mechanism for amplifying short noise electromagnetic pulses. The kappa distribution was used as a model function of the electron velocity distribution in the magnetosphere. Calculations performed for this distribution have shown that the threshold for excitation of chorus largely depends on the electron plasma parameter equal to the ratio of gas-kinetic pressure of electrons to magnetic pressure. This pattern is not contradicted by the dependence of the probability of excitation of chorus on the degree of magnetic field irregularity, which we derived from observations made by the Van Allen Probe spacecraft. It is sharp fluctuations in the magnetic field strength near its local minima outside the plasmasphere where the radiation under study can be excited. If there is an irregularity, the probability of detecting chorus is >70 %; and if there is no or very low irregularity, the probability of the absence of any emissions is ~80 %. The results indicate a common reason for the excitation of chorus and the magnetic field irregularity — a small but finite value of the plasma parameter.
VLF emissions, chorus, wave-particle interaction, data analysis, middle magnetosphere
1. Artsimovich L.A., Sagdeev R.Z. Plasma Physics for Physicists. Moscow, Atomizdat Publ., 1979, 313 p. (In Russian).
2. Agapitov O., Blum L.W., Mozer F.S., Bonnell J.W., Wygant J. Chorus whistler wave source scales as determined from multipoint Van Allen Probe measurements. Geophys. Res. Lett. 2017, vol. 44, pp. 2634–2642. DOI:https://doi.org/10.1002/2017GL072701.
3. Bell T.F., Inan U.S., Hague N., Pickett J.S. Source regions of banded chorus. Geophys. Res. Lett. 2009, vol. 36, L11101. DOI:https://doi.org/10.1029/2009GL037629.
4. Benson R.F., Vicas A.F., Osherovich V.A., Fainberg J., Purser C.M., Adrian M.L., et al. Magnetospheric electron-velocity-distribution function information from wave observations. J. Geophys. Res.: Space Phys. 2013, vol. 118, pp. 5039–5049. DOI:https://doi.org/10.1002/jgra.50459.
5. Bespalov P.A., TrakhtengertsV.Yu. Cyclotron instability of the Earth radiation belts. Reviews of Plasma Physics. 1986, vol. 10, pp. 155-292. Consultants Bureau, New York.
6. Bespalov P., Savina O. An excitation mechanism for discrete chorus elements in the magnetosphere. Ann. Geophys. 2018, vol. 36, pp. 1201–1206. DOI:https://doi.org/10.5194/angeo-36-1201-2018.
7. Bespalov P.A., Savina O.N. On the linear theory of oblique magnetospheric chorus excitation. J. Atmos. Solar-Terr. Phys. 2019, vol. 185, pp. 58–67. DOI:https://doi.org/10.1016/j.jastp.2019.01.016.
8. Bespalov P.A., Savina O.N. Electromagnetic pulse amplification in a magnetized nearly stable plasma layer. Results in Physics. 2021, vol. 28, aid. 104607. DOI:https://doi.org/10.1016/j.rinp.2021.104607.
9. Bespalov P.A., Savina O.N., Zharavina P.D. Special Features of Chorus Excitation by Means of the Beam-Pulse-Amplifier Mechanism in Ducts of Enhanced and Depleted Cold-Plasma Density with Refraction Reflection. Cosmic Res. 2022, vol. 60, pp. 15–22. DOI:https://doi.org/10.1134/S0010952522010026.
10. Fu X., Cowee M.M., Friedel R.H., Funsten H.O., Gary S.P., Hospodarsky G.B., et al. Whistler anisotropy instabilities as the source of banded chorus: Van Allen Probes observations and Particle-in-Cell simulations. J. Geophys. Res. 2014, vol. 119, pp. 8288–8298. DOI:https://doi.org/10.1002/2014JA020364.
11. Ginzburg V.L. The propagation of electromagnetic waves in plasmas. New York, Pergamon Press, 1970, 615 p.
12. Helliwell R.A. Whistlers and Related Ionospheric Phenomena. Stanford Univ. Press, Stanford, 1965.
13. Helliwell R.A. The role of the Gendrin mode of VLF propagation in the generation of magnetosphericemis-sions. Geophys. Res. Lett. 1995, vol. 22, pp. 2095–2098. DOI: 10.1029/ 95GL02003.
14. Horne R.B., Thorne, R.M. Potential waves for relativistic electron scattering and stochastic acceleration during magnetic storms. Geophys. Res. Lett. 1998, vol. 25, pp. 3011–3014. DOI:https://doi.org/10.1029/98GL01002.
15. Kasahara Y., Miyoshi Y., Omura Y., Verkhoglyadova O.P., Nagano I., Kimura I., Tsurutani B.T. Simultaneous satellite observations of VLF chorus, hot and relativistic electrons in a magnetic storm “recovery” phase. Geophys. Res. Lett. 2009, vol. 36, L01106. DOI:https://doi.org/10.1029/2008GL036454.
16. Kletzing C.A., Kurth W.S., Acuna M., MacDowall R.J., Torbert R.B.,•Averkamp T., et al. The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP. Space Sci. Rev. 2013, vol. 179, pp. 127–181. DOI:https://doi.org/10.1007/s11214-013-9993-6.
17. Meredith N.P., Cain M., Horne R.B., Thorne R.M., Summers D., Anderson R.R. Evidence for chorus-driven electron acceleration to relativistic energies from a survey of geomagnetically disturbed periods. J. Geophys. Res. 2003, vol. 108, 1248. DOI:https://doi.org/10.1029/2002JA009764.
18. Miyoshi Y., Saito S., Seki K., Nishiyama T., Kataoka R., Asamura K., et al. Relation between fine structure of energy spectra for pulsating aurora electrons and frequency spectra of whistler mode chorus waves. J. Geophys. Res. 2015, vol. 120, pp. 7728–7736. DOI:https://doi.org/10.1002/2015JA021562.
19. Nishimura Y., Bortnik J., Li W., Thorne R.M., Lyons L.R., Angelopoulos V., et al. Identifying the Driver of Pulsating Aurora. Science. 2010, vol. 330, pp. 81–84. DOI: 10.1126/ science.1193186.
20. Omura Y., Katoh Y., Summers D. Theory and simulation of the generation of whistler-mode chorus. J. Geophys. Res. 2008, vol. 113, A04223. DOI:https://doi.org/10.1029/2007JA012622.
21. Summers D., Thorne R. M., Xiao F. Relativistic theory of wave-particle resonant diffusion with application to electron acceleration in the magnetosphere. J. Geophys. Res. 1998, vol. 103, pp. 20487–20500. DOI:https://doi.org/10.1029/98JA01740.
22. Trakhtengerts V.Y. Magnetosphere cyclotron maser: Backward wave oscillator generation regime. J. Geophys. Res. 1995, vol. 100, pp. 17205–17210. DOI:https://doi.org/10.1029/95JA00843.
23. Zhou C., Li W., Thorne R.M., Bortnik J., Ma Q., An X., et al. Excitation of dayside chorus waves due to magnetic field line compression in response to interplanetary shocks. J. Geophys. Res.: Space Phys. 2015, vol. 120, pp. 8327–8338. DOI:https://doi.org/10.1002/2015JA021530.
24. URL: http://emfisis.physics.uiowa.edu/Flight/ (accessed March 24, 2024).
