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| Titel |
Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument |
| VerfasserIn |
T. Asikainen, K. Mursula |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 23, no. 6 ; Nr. 23, no. 6 (2005-09-15), S.2217-2230 |
| Datensatznummer |
250015298
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| Publikation (Nr.) |
 copernicus.org/angeo-23-2217-2005.pdf |
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| Zusammenfassung |
In this paper we study the fluxes of energetic protons (30–4000 keV) and
electrons (20–400 keV) in the exterior cusp and in the adjacent
high-latitude dayside plasma sheet (HLPS) with the Cluster/RAPID instrument.
Using two sample orbits we demonstrate that the Cluster observations at
high latitudes can be dramatically different because the satellite orbit
traverses different plasma regions for different external conditions.
We make a statistical study of energetic particles in the exterior cusp and
HLPS by analysing all outbound Cluster dayside passes in February and
March, 2002 and 2003.
The average particle fluxes in HLPS are
roughly three (protons) or ten (electrons) times larger than in the
exterior cusp. This is also true on those Cluster orbits where both
regions are visited within a short time interval.
Moreover, the total electron fluxes, as well as proton fluxes
above some 100 keV, in these two regions correlate with each other.
This is true even for fluxes in every energy channel when considered separately.
The spectral indices of electron and proton
fluxes are the same in the two regions. We also examine the possible
dependence of particle fluxes at different energies on the external (solar
wind and IMF) and internal (geomagnetic) conditions.
The energetic proton fluxes (but not electron fluxes) in the cusp
behave differently at low and high energies.
At low energies (<70 keV), the fluxes increase strongly with the
magnitude of IMF By.
Instead, at higher energies the proton fluxes in the cusp
depend on substorm/geomagnetic activity.
In HLPS proton fluxes, irrespective of energy, depend
strongly on the Kp and AE indices.
The electron fluxes in HLPS depend both on the <Kp index and
the solar wind speed.
In the cusp the electron fluxes mainly depend on the solar wind speed,
and are higher for northward than southward IMF.
These results give strong evidence in favour of the idea
that the high-latitude dayside plasma sheet is the main source of energetic
particles in the exterior cusp. Energetic particles can reach HLPS
from the near-Earth tail. The closed field
lines of HLPS act as storage for these particles. Direct diffusion
(for electrons and high-energy protons) and magnetic reconnection in the
high-latitude magnetopause near HLPS (for low energy protons) control the number of particles
released into the exterior cusp.
Note that this explanation, in contrast to other suggested theories,
works both for the energetic protons and electrons in the exterior cusp.
Keywords. Magnetospheric physics (Magnetopause, cusp
and boundary layers; Solar wind-magnetosphere interactions)
– Space plasma physics (magnetic reconnection) |
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