Earth and Planetary Science

ULF Pulsations as a Driver of Relativistic Electrons: Pros and Cons

Vyacheslav Pilipenko

Plasma Physics Department, Space Research Institute, Moscow 117997, Russia

Olga Kozyreva

Laboratory of Near‑Earth Environment, Institute of Physics of the Earth, Moscow 123242, Russia

Vladimir Belakhovsky

Auroral Phenomena Laboratory, Polar Geophysical Institute, Apatity 184209, Russia Institute of Solar‑Terrestrial Physics, Irkutsk 664033, Russia

DOI: https://doi.org/10.36956/eps.v4i1.1310

Received: 23 October 2024 | Revised: 13 January 2025 | Accepted: 8 February 2025 | Published Online: 13 March 2025

---

Abstract

Ultralow frequency (ULF) waves in the Pc5 band have been suggested as a possible intermediary transferring energy from high‑speed streams of the solar wind to magnetospheric electrons. Although ULF waves are not the only mechanism of accelerating electrons up to relativistic energies, nonetheless they are an essential element of the electron energization process, though their role has not been finally established yet. Among observational facts regarding the interrelationships between Pc5 wave activity and electron dynamics, we discuss the following pro and con factors related to the ULF‑associated energization mechanisms: The correlation of electron fluxes at the geosta‑tionary orbit and the Pc5 wave power; The correspondence between the azimuthal phase velocities of toroidal and poloidal Pc5 waves and the electron magnetic drift; The correspondence between the latitudinal structure of Pc5 waves and the outer radiation belt. Consideration of these facts does not allow one to unambiguously resolve the issues concerning the role of ULF waves in the magnetospheric electron energization. We suggest that the acceleration of electrons by ULF disturbances may occur not in a regime of “geoserfotron” with Pc5 waves (match of the azimuthal velocities of waves and drifting electrons), but rather in a regime of “geosynchrotron” with transit‑time acceleration by substorm‑related Pi3 pulsations.

Keywords: Outer Radiation Belt; Relativistic Electrons; Auroral Oval; ULF Pulsations

---

References

[1] Pilipenko, V., Yagova, N., Romanova, N., et al., 2006. Statistical relationships between the satellite anomalies at geostationary orbits and high-energy particles. Advances in Space Research. 37(6), 1192–1205.

[2] Li, X., Baker, D.N., Temerin, M., et al., 1997. Are energetic electrons in the solar wind the source of the outer radiation belt? Geophysical Research Letters. 24(8), 923–926. DOI: https://doi.org/10.1029/97GL00543

[3] Kuznetsov, S.N., Yushkov, B.Y., Kudela, K., et al., 2005. Dynamics of the Earth's radiation belts during the magnetic storm of November 6th, 2001. Advances in Space Research. 36, 1997–2002.

[4] Zong, Q., Wang, Y., Yuan, C., et al., 2011. Fast acceleration of “killer” electrons and energetic ions by interplanetary shock stimulated ULF waves in the inner magnetosphere. Chinese Science Bulletin. 56(N12), 1188–1201.

[5] Reeves, G.D., Baker D.N., Belian R.D., et al., 1998. The global response of relativistic radiation belt electrons to the January 1997 magnetic cloud. Geophysical Research Letters. 17, 3265–3268.

[6] Kanekal, S.G., Baker D.N., Blake J.B., et al., 1999. Magnetospheric response to magnetic cloud (coronal mass ejection) events: Relativistic electron observations from SAMPEX and Polar. Journal of Geophysical Reserach. 104(A11), 24885–24894. DOI: https://doi.org/10.1029/1999JA900239.

[7] Vassiliadis, D., Klimas A.J., Weigel R.S., et al., 2003. Structure of Earth’s outer radiation belt inferred from long-term electron flux dynamics. Geophysical Research Letters. 30(19), 2015. DOI: https://doi.org/10.1029/2003GL017328

[8] Belakhovsky, V.B., Pilipenko, V.A., Antonova, E.E., et al., 2023. Relativistic electron flux growth during storm and non-storm periods as observed by ARASE and GOES satellites. Earth Planets Space. 75(1), 189.

[9] Fok, M.H., Moore, T.E., Spjeldvik, W., 2001. Rapid enhancement of radiation belt electron fluxes due to substorm dipolarization of the geomagnetic field. Journal of Geophysical Research. 106(A3), 3873–3881.

[10] Glocer, A., Fok, M.-C., Nagai, T., et al., 2011. Rapid rebuilding of the outer radiation belt. Journal of Geophysical Research. 116(A9), A09213.

[11] Lazutin, L.L., 2013. Injection of relativistic electrons into the internal magnetosphere during magnetic storms: Connection with substorms. Geomagnetism and Aeronomy. 53(6), 716–732.

[12] Kim, H-J, Chan, A.A., Wolf, R.A., et al., 2000. Can substorms produce relativistic outer belt electrons? Journal of Geophysical Research. 105(A4), 7721–7735.

[13] Mathie, R.A., Mann, I.R., 2000. A correlation between between extended intervals of ULF wave power and storm-time geosynchronous relativistic electron flux enhancements. Geophysical Research Letters. 27(20), 3261–3264.

[14] Tan, L.C., Fung, S.F., Shao, X., 2004. Observation of magnetospheric relativistic electrons accelerated by Pc5 ULF waves. Geophysical Research Letters. 31(14), L14802.

[15] Mann, I.R., Lee, E.A., Claudepierre, S.G., et al., 2016. Discovery of the action of a geophysical synchrotron in the Earth’s Van Allen radiation belts. Nature Communications. 4(1), 2795.

[16] Zhao, H., Li X., 2013. Inward shift of outer radiation belt electrons as a function of Dst index and the influence of the solar wind on electron injections into the slot region. Journal of Geophysical Research: Space Physics. 118(2), 756–764.

[17] Bakhareva, M.F., Dmitriev, A.V., 2002. Statistical Alfvenic electron acceleration in outer magnetosphere. Geomagnetism and Aeronomy. 42(1), 18–27.

[18] Shprits, Y.Y., Elkington, S.R., Meredith, N.P., et al., 2008. Review of modeling of losses and sources of relativistic electrons in the outer radiation belt I: Radial transport. Journal of Atmospheric and Solar-Terrestrial Physics. 70(14), 1679–1693.

[19] Su, Z., Zhu, H., Xiao, F., et al., 2015. Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons. Nature Communications. 6(1), 10096.

[20] Shprits, Y.Y., Subbotin, D.A., Meredith, N.P., et al., 2008. Review of modeling of losses and sources of relativistic electrons in the outer radiation belt II: Local acceleration and loss. Journal of Atmospheric and Solar-Terrestrial Physics. 70(14), 1694–1713.

[21] Meredith, N.P., Horne, R.B., Iles, R.H.A., et al., 2002. Outer zone relativistic electron acceleration associated with substorm-enhanced whistler mode chorus. Journal of Geophysical Research. 107(A7), SMP 29-1–SMP 29-14.

[22] Horne, R.B., Thorne R.M., Shprits, Y.Y., et al., 2005. Wave acceleration of electrons in the Van Allen radiation belts. Nature. 437(7056), 227–230.

[23] Tverskoy, B.A., 1997. Formation mechanism for the structure of the magnetic-storm ring current, Geomagn. Aeronomy, 37(N5), 555.

[24] Elkington, S.R., 2003. Resonant acceleration and diffusion of outer zone electrons in an asymmetric geomagnetic field. Journal of Geophysical Research. 108(A3), 1116.

[25] Ukhorskiy, A.Y., Sitnov, M.I., Takahashi, K., et al., 2009. Radial transport of radiation belt electrons due to stormtime Pc5 waves. Annales Geophysicae. 27, 2173–2181.

[26] Degeling, A.W., 2007. The effect of ULF compressional modes and field line resonances on relativistic electron dynamics. Planetary and Space Science. 55(6), 731–742.

[27] Sitnov, M.I., 1988. Maximum energy of particles in serfotron in the unlimited acceleration regime. Technical Physics Letters (“Pisma v Zhurnal Tekhnicheskoi Fiziki”). 14(1), 89–92.

[28] Antonova, E.E., Kirpichev, I.P., Stepanova, M.V., et al., 2009. Topology of the high latitude magnetosphere during large magnetic storms and the main mechanisms of relativistic electron acceleration. Advances in Space Research. 43(4), 628–633.

[29] Antonova, E.E., Stepanova, M.V., 2015. The problem of the acceleration of electrons of the outer radiation belt and magnetospheric substorms. Earth, Planets and Space. 67(1), 148.

[30] Tverskoy, B.A., 1968. Dynamics of the Earth radiation belts (in Russian: "Dinamika Radiatsionnykh Poyasov Zemli") Moscow. pp. 1–185.

[31] Tverskaya, L.V., Pavlov, N.N., Blake, J.B., et al., 2003. Predicting the L-position of the storm-injected relativistic electron belt. Advances in Space Research. 31(4), 1039–1044.

[32] Kleimenova, N.G., Kozyreva, O.V., 2009. Penetration of Pc5 geomagnetic pulsations to unusually low latitudes during the recovery phase of a superstrong magnetic storm of October 31, 2003. Geomagnetism and Aeronomy. 49(8), 1199–1203.

[33] Potapov, A., Guglielmi, A., Tsegmed, B., et al., 2006. Global Pc5 event during 29-31 October 2003 magnetic storm. Advances in Space Research. 38(8), 1582–1586.

[34] Marin, J., Pilipenko, V., Kozyreva, O., et al., 2014. Global Рс5 pulsations during strong magnetic storms: excitation mechanisms and equatorward expansion. Annales Geophysicae. 32(4), 319–331.

[35] Martines-Bedenko, V.A., Pilipenko, V.A., et al., 2022. Conjugate properties of Pi3/Ps6 pulsations according to Antarctica-Greenland observations. Russian Journal of Earth Sciences. 22(4), ES4006.

[36] O’Brien, T.P., McPherron, R.L., Sornette, D., et al., 2001. Which magnetic storms produce relativistic electrons at geosynchronous orbit? Journal of Geophysical Research. 106(A8), 15533–15544.

[37] Pilipenko, V.A., Kozyreva O.V., Engebretson M.J., et al., 2017. ULF wave power index for the space weather and geophysical applications: A review. Russian Journal of Earth Sciences. 17(N2), ES1004.

[38] Romanova, N., Pilipenko, V. 2008. ULF wave indices to characterize the solar wind – magnetosphere interaction and relativistic electron dynamics. Acta Geophysica. 57(1), 158–170.

[39] Antonova, E.E., Stepanova, M.V., Moya, P.S., et al., 2018. Processes in auroral oval and outer electron radiation belt. Earth Planets Space. 70(1), 127.

[40] Kozyreva, O.V., Pilipenko V.A., Engebretson M.J., et al., 2016. Correspondence between the ULF wave power distribution and auroral oval. Solar-Terrestrial Physics. 2(2), 46–65.

[41] Claudepierre, S. G., et al. (2013), Van Allen Probes observation of localized drift resonance between poloidal mode ultra-low frequency waves and 60 keV electrons, Geophysical Research Letters. 40, 4491–4497. DOI: https://doi.org/10.1002/grl.50901

[42] Tan, L.C., Shao, X, Sharma, A.S., Fung, S.F., 2011. Relativistic electron acceleration by compressional mode ULF waves: Evidence from correlated Cluster, LANL spacecraft, and ground-based magnetometer measurements. Journal of Geophysical Research. 116(A7), A07226.

[43] O’Brien, T.P., Lorentzen, K.R., Mann, I.R., et al., 2003. Energization of relativistic electrons in the presence of ULF power and MeV microbursts: Evidence for dual ULF and VLF acceleration. Journal of Geophysical Research. 108(A8), 1329.