American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 525661 bytes)

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, A11212, doi:10.1029/2005JA011043, 2005

Multiple spacecraft observations of energetic ions during a high solar wind pressure event

Jiasheng Chen

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


Theodore A. Fritz

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


Robert B. Sheldon

National Space Science and Technology Center, NASA Marshall Space Flight Center, Huntsville, Alabama, USA


Abstract

On 28 June 1999 the Wind spacecraft (near the forward libration point) observed a large solar wind pressure spike from 0445 UT to 0600 UT. The Polar satellite at 7 hours magnetic local time detected an energetic particle event in the high-altitude region associated with turbulent diamagnetic cavities from 0512 UT to 0627 UT. The particles and cavities are very similar to those that were previously found in the high-altitude dayside cusp region. They are independent of both the solar wind velocity and the interplanetary magnetic field (IMF) vectors. The enhancements of the magnetic field fluctuations in the ultra-low frequency range measured by the Wind were also observed by the Polar. Most of the time, during the event period, the IMF had a duskward component, suggesting that cusp diamagnetic cavities also existed in the postnoon sector in the Northern Hemisphere. Energetic ions of both ionospheric origin and solar wind origin were observed by the Polar spacecraft during this event period. The He++/H+ ratio in the diamagnetic cavities was a factor of four higher than in the quasi-trapping region before the event onset, while the He+/He++ ratio in the cavities was more than one order of the magnitude lower. In this event, the measured cusp ions had energies up to 4 MeV. No clear relationship between the cusp energetic ion flux and the IMF cone angle was found. The Interball 1 spacecraft located just upstream of the bow shock in the prenoon sector measured an upstream ion event from about 0516 UT to 0600 UT. The onset of the energetic ions observed by Interball 1 in the upstream event was the same for different energies; the ion energy spectra were independent of the solar wind velocity and their intensities were independent of the bow shock geometry and the solar wind density. The energetic ion event onset was first detected in the cusp by Polar at 0512 UT, then near the bow shock in the prenoon by Interball 1 at 0516 UT, and then in the far upstream by Wind at 0523 UT. The measured energetic ion intensity decreased with increasing distance from the cusp diamagnetic cavities. These observational facts together with the IMF directions suggest that (1) this large solar wind pressure event produced an extremely large diamagnetic cavity (>10 R E ) within the magnetosphere, (2) the bow shock was not the main source of both the cusp and upstream energetic ions, and (3) the upstream energetic ions most likely came from the cusp.

Received 2 February 2005; accepted 9 August 2005; published 11 November 2005.

Keywords: cusp energetic particles; upstream ion events; wave/particle interaction; magnetospheric configuration and dynamics; bow shock; interplanetary magnetic fields.

Index Terms: 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2706 Magnetospheric Physics: Cusp; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2134 Interplanetary Physics: Interplanetary magnetic fields; 2720 Magnetospheric Physics: Energetic particles: trapped.

Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 525661 bytes)

Citation: Chen, J., T. A. Fritz, and R. B. Sheldon (2005), Multiple spacecraft observations of energetic ions during a high solar wind pressure event, J. Geophys. Res., 110, A11212, doi:10.1029/2005JA011043.