Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 33, 1431-1442, 2015
https://doi.org/10.5194/angeo-33-1431-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
20 Nov 2015
Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms
M. Georgiou1,2, I. A. Daglis1, E. Zesta3, G. Balasis2, I. R. Mann4, C. Katsavrias1, and K. Tsinganos1,2 1Department of Physics, University of Athens, Panepistimiopoli Zografou, Athens, 15784, Greece
2Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Vas. Pavlou & I. Metaxa, Penteli, 15236, Greece
3Goddard Space Flight Center, National Aeronautics and Space Administration, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
4Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada
Abstract. Geospace magnetic storms, driven by the solar wind, are associated with increases or decreases in the fluxes of relativistic electrons in the outer radiation belt. We examine the response of relativistic electrons to four intense magnetic storms, during which the minimum of the Dst index ranged from −105 to −387 nT, and compare these with concurrent observations of ultra-low-frequency (ULF) waves from the trans-Scandinavian IMAGE magnetometer network and stations from multiple magnetometer arrays available through the worldwide SuperMAG collaboration. The latitudinal and global distribution of Pc5 wave power is examined to determine how deep into the magnetosphere these waves penetrate. We then investigate the role of Pc5 wave activity deep in the magnetosphere in enhancements of radiation belt electrons population observed in the recovery phase of the magnetic storms. We show that, during magnetic storms characterized by increased post-storm electron fluxes as compared to their pre-storm values, the earthward shift of peak and inner boundary of the outer electron radiation belt follows the Pc5 wave activity, reaching L shells as low as 3–4. In contrast, the one magnetic storm characterized by irreversible loss of electrons was related to limited Pc5 wave activity that was not intensified at low L shells. These observations demonstrate that enhanced Pc5 ULF wave activity penetrating deep into the magnetosphere during the main and recovery phase of magnetic storms can, for the cases examined, distinguish storms that resulted in increases in relativistic electron fluxes in the outer radiation belts from those that did not.

Citation: Georgiou, M., Daglis, I. A., Zesta, E., Balasis, G., Mann, I. R., Katsavrias, C., and Tsinganos, K.: Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms, Ann. Geophys., 33, 1431-1442, https://doi.org/10.5194/angeo-33-1431-2015, 2015.
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Short summary
Our study demonstrates a remarkable association between the earthward penetration of ULF waves and radiation belt electron enhancements during four magnetic storms that occurred in 2001. In the past, ULF waves had been observed at unusual depths during rare superstorms. But ULF wave activity, reaching magnetic shells as low as 2, was also observed during relatively intense storms when it played a key role in diffusing electrons radially inward and thereby accelerating them to higher energies.
Our study demonstrates a remarkable association between the earthward penetration of ULF waves...
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