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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L12105, doi:10.1029/2007GL029915, 2007

Ultralow frequency modulation of energetic particles in the dayside magnetosphere

Q.-G. Zong

Center for Atmospheric Research, University of Massachusetts-Lowell, Massachusetts, USA
Institute of Space Physics and Applied Technology, Peking University, Beijing, China


X.-Z. Zhou

Center for Atmospheric Research, University of Massachusetts-Lowell, Massachusetts, USA
Institute of Space Physics and Applied Technology, Peking University, Beijing, China


X. Li

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA


P. Song

Center for Atmospheric Research, University of Massachusetts-Lowell, Massachusetts, USA


S. Y. Fu

Institute of Space Physics and Applied Technology, Peking University, Beijing, China


D. N. Baker

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA


Z. Y. Pu

Institute of Space Physics and Applied Technology, Peking University, Beijing, China


T. A. Fritz

Center For Space Physics, Boston University, Boston, Massachusetts, USA


P. Daly

Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany


A. Balogh

Space and Atmospheric Physics Group, Imperial College, London, UK


H. Réme

Centre D'Etude Spatiale des Rayonnements, Toulouse, France


Abstract

Energetic electron and ion (electrons: 30 keV to 500 keV, protons: 30 keV to 1.5 MeV) flux variations associated with ultralow frequency (ULF) waves in the dayside magnetosphere were observed during the CLUSTER's perigee pass near 0900 MLT on Oct. 31, 2003. The ULF modulation terminated where higher frequency fluctuations appeared, as the CLUSTER spacecraft entered the plasmasphere boundary layer (PBL) where the plasma ion density was elevated. In the region from L ∼ 5.0 to 10, the periods of the ion flux modulation and the electron flux modulation are same but out-of-phase. The observed magnetic ULF pulsations are dominated by the toroidal mode, along with a relatively weaker poloidal wave. A 90° phase shift between the radial electric field and the azimuthal magnetic field indicates that dominating toroidal standing waves observed at the southern hemisphere are a fundamental harmonic. This study shows that the modulation of the electron flux is dominated by the toroidal mode in the region of L > 7.5. The observations made in this analysis suggest the excitation of the energetic electron drift resonance at around 127 keV.

Received 6 March 2007; accepted 1 June 2007; published 29 June 2007.

Keywords: ULF wave; energetic particle; radiation belt.

Index Terms: 2752 Magnetospheric Physics: MHD waves and instabilities (2149, 6050, 7836); 2720 Magnetospheric Physics: Energetic particles: trapped; 2778 Magnetospheric Physics: Ring current; 2768 Magnetospheric Physics: Plasmasphere; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 524392 bytes)

Citation: Zong, Q.-G., et al. (2007), Ultralow frequency modulation of energetic particles in the dayside magnetosphere, Geophys. Res. Lett., 34, L12105, doi:10.1029/2007GL029915.