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Ann. Geophys., 25, 801-814, 2007
www.ann-geophys.net/25/801/2007/
© European Geosciences Union 2007

Multi-spacecraft observation of plasma dipolarization/injection in the inner magnetosphere

S. V. Apatenkov¹, V. A. Sergeev¹, M. V. Kubyshkina¹, R. Nakamura², W. Baumjohann², A. Runov², I. Alexeev³, A. Fazakerley³, H. Frey⁴, S. Muhlbachler⁵, P. W. Daly⁵, J.-A. Sauvaud⁶, N. Ganushkina⁷, T. Pulkkinen⁷, G. D. Reeves⁸, and Y. Khotyaintsev^9
1Institute of Physics, St. Petersburg State University, St. Petersburg, Russia
²Space Research Institute, Austrian Academy of Sciences, Graz, Austria
³Mullard Space Science Laboratory, University College London, UK
⁴Space Science Laboratory, Berkeley, USA
⁵Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany
⁶Centre d'Etude Spatiale des Rayonnements, Toulouse, France
⁷Finnish Meteorological Institute, Helsinki, Finland
⁸Los Alamos National Laboratory, USA
⁹Swedish Institute of Space Physics, Uppsala, Sweden

Abstract. Addressing the origin of the energetic particle injections into the inner magnetosphere, we investigate the 23 February 2004 substorm using a favorable constellation of four Cluster (near perigee), LANL and Geotail spacecraft. Both an energy-dispersed and a dispersionless injection were observed by Cluster crossing the plasma sheet horn, which mapped to 9–12 R_E in the equatorial plane close to the midnight meridian. Two associated narrow equatorward auroral tongues/streamers propagating from the oval poleward boundary could be discerned in the global images obtained by IMAGE/WIC. As compared to the energy-dispersed event, the dispersionless injection front has important distinctions consequently repeated at 4 spacecraft: a simultaneous increase in electron fluxes at energies ~1..300 keV, ~25 nT increase in B_Z and a local increase by a factor 1.5–1.7 in plasma pressure. The injected plasma was primarily of solar wind origin. We evaluated the change in the injected flux tube configuration during the dipolarization by fitting flux increases observed by the PEACE and RAPID instruments, assuming adiabatic heating and the Liouville theorem. Mapping the locations of the injection front detected by the four spacecraft to the equatorial plane, we estimated the injection front thickness to be ~1 R_E and the earthward propagation speed to be ~200–400 km/s (at 9–12 R_E). Based on observed injection properties, we suggest that it is the underpopulated flux tubes (bubbles with enhanced magnetic field and sharp inner front propagating earthward), which accelerate and transport particles into the strong-field dipolar region.

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Citation: Apatenkov, S. V., Sergeev, V. A., Kubyshkina, M. V., Nakamura, R., Baumjohann, W., Runov, A., Alexeev, I., Fazakerley, A., Frey, H., Muhlbachler, S., Daly, P. W., Sauvaud, J.-A., Ganushkina, N., Pulkkinen, T., Reeves, G. D., and Khotyaintsev, Y.: Multi-spacecraft observation of plasma dipolarization/injection in the inner magnetosphere, Ann. Geophys., 25, 801-814, 2007.   Bibtex   EndNote   Reference Manager