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Ann. Geophys., 22, 1033-1046, 2004
www.ann-geophys.net/22/1033/2004/
© European Geosciences Union 2004
A comparison between ion characteristics observed by the POLAR and DMSP spacecraft in the high-latitude magnetosphere
T. J. Stubbs1,2, M. Lockwood3, P. Cargill1, M. Grande3, B. Kellett3, and C. Perry3
1Space & Atmospheric Physics, The Blackett Laboratory, Imperial College London, UK
2Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
3Space Science Department, Rutherford Appleton Laboratory, Oxfordshire, UK
Abstract. We study here the injection and transport of ions in the convection-dominated region of
the Earth's magnetosphere. The total ion counts from the CAMMICE MICS instrument
aboard the POLAR spacecraft are used to generate occurrence probability distributions
of magnetospheric ion populations. MICS ion spectra are characterised by both the peak
in the differential energy flux, and the average energy of ions striking the detector. The
former permits a comparison with the Stubbs et al. (2001) survey of He2+ ions of solar
wind origin within the magnetosphere. The latter can address the occurrences of various
classifications of precipitating particle fluxes observed in the topside ionosphere by
DMSP satellites (Newell and Meng, 1992). The peak energy occurrences are consistent
with our earlier work, including the dawn-dusk asymmetry with enhanced occurrences
on the dawn flank at low energies, switching to the dusk flank at higher energies. The
differences in the ion energies observed in these two studies can be explained by drift
orbit effects and acceleration processes at the magnetopause, and in the tail current
sheet. Near noon at average ion energies of ≈1keV, the cusp and open LLBL occur
further poleward here than in the Newell and Meng survey, probably due to convection-
related time-of-flight effects. An important new result is that the pre-noon bias
previously observed in the LLBL is most likely due to the component of this population
on closed field lines, formed largely by low energy ions drifting earthward from the tail.
There is no evidence here of mass and momentum transfer from the solar wind to the
LLBL by non-reconnection coupling. At higher energies ≈2–20keV), we
observe ions mapping to the auroral oval and can distinguish between the boundary and
central plasma sheets. We show that ions at these energies relate to a transition from
dawnward to duskward dominated flow, this is evidence of how ion drift orbits in the
tail influence the location and behaviour of the plasma populations in the
magnetosphere.
Key words. Magnetospheric physics (magnetopause, cusp
and boundary layers; magnetosphere-ionosphere interactions;
magnetospheric configuration and dynamic)
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