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| Titel |
Investigation of the outer and inner low-latitude boundary layers |
| VerfasserIn |
T. M. Bauer, R. A. Treumann, W. Baumjohann |
| 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 ; 19, no. 9 ; Nr. 19, no. 9, S.1065-1088 |
| Datensatznummer |
250014317
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| Publikation (Nr.) |
 copernicus.org/angeo-19-1065-2001.pdf |
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| Zusammenfassung |
We analyze 22 AMPTE/IRM
crossings of the day-side low-latitude boundary layer for which a dense outer
part can be distinguished from a dilute inner part. Whereas the plasma in the
outer boundary layer (OBL) is dominated by solar wind particles, the partial
densities of solar wind and magnetospheric particles are comparable in the
inner boundary layer (IBL). For 11 events we find a reasonable agreement
between observed plasma flows and those predicted by the tangential stress
balance of an open magnetopause. Thus, we conclude that, at least in these
cases, the OBL is formed by a local magnetic reconnection. The disagreement
with the tangential stress balance in the other 11 cases might be due to
reconnection being time-dependent and patchy. The north-south component of the
proton bulk velocity in the boundary layer is, on average, directed toward high
latitudes for both low and high magnetic shear across the magnetopause. This
argues clearly against the possibility that the dayside low-latitude boundary
layer is populated with solar wind plasma primarily from the cusps.
"Warm", counterstreaming electrons that originate primarily from the
magnetosheath and have a field-aligned temperature that is higher than the
electron temperature in the magnetosheath by a factor of 1–5, are a
characteristic feature of the IBL. Profiles of the proton bulk velocity and the
density of hot ring current electrons provide evidence that the IBL is on
closed field lines. Part of the IBL may be on newly opened field lines. Using
the average spectra of electric and magnetic fluctuations in the boundary
layer, we estimate the diffusion caused by lower hybrid drift instability,
gyroresonant pitch angle scattering, or kinetic Alfvén wave turbulence. We
find that cross-field diffusion cannot transport solar wind plasma into the OBL
or IBL at a rate that would account for the thickness ( ~ 1000 km) of these
sublayers. On the duskside, the dawn-dusk component of the proton bulk velocity
in the IBL and magnetosphere is, on average, directed from the nightside toward
local noon. Formation of the IBL may also be due to mechanisms operating in the
magnetotail.
Key words. Magnetospheric physics
(magnetopause, cusp and boundary layer; magnetospheath) |
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