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| Titel |
Dayside isotropic precipitation of energetic protons |
| VerfasserIn |
V. A. Sergeev, G. R. Bikkuzina, P. T. Newell |
| 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 ; 15, no. 10 ; Nr. 15, no. 10, S.1233-1245 |
| Datensatznummer |
250012970
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| Publikation (Nr.) |
 copernicus.org/angeo-15-1233-1997.pdf |
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| Zusammenfassung |
| Recently it has been shown that isotropic
precipitation of energetic protons on the nightside is caused by a non-adiabatic
effect, namely pitch-angle scattering of protons in curved magnetic field lines
of the tail current sheet. Here we address the origin of isotropic proton
precipitation on the dayside. Computations of proton scattering regions in the
magnetopheric models T87, T89 and T95 reveal two regions which contribute to the
isotropic precipitation. The first is the region of weak magnetic field in the
outer cusp which provides the 1–2° wide isotropic precipitation on closed field
lines in a ~2–3 hour wide MLT sector centered on noon. A second zone is
formed by the scattering on the closed field lines which cross the nightside
equatorial region near the magnetopause which provides isotropic precipitation
starting ≈ 1.5–2 h MLT from noon and which joins smoothly the precipitation
coming from the tail current sheet. We also analyzed the isotropic proton
precipitation using observations of NOAA low altitude polar spacecraft. We find
that isotropic precipitation of >30 to >80 keV protons continues around
noon forming the continuous oval-shaped region of isotropic precipitation. Part
of this region lies on open field lines in the region of cusp-like or mantle
precipitation, its equatorward part is observed on closed field lines. Near noon
it extends ~1–2° below the sharp boundary of solar electron fluxes (proxy of
the open/closed field line boundary) and equatorward of the cusp-like auroral
precipitation. The observed energy dispersion of its equatorward boundary
(isotropic boundary) agrees with model predictions of expected particle
scattering in the regions of weak and highly curved magnetic field. We also
found some disagreement with model computations. We did not observe the
predicted split of the isotropic precipitation region into separate nightside
and dayside isotropic zones. Also, the oval-like shape of the isotropic boundary
has a symmetry line in 10–12 MLT sector, which with increasing activity rotates
toward dawn while the latitude of isotropic boundary is decreasing. Our
conclusion is that for both dayside and nightside the isotropic boundary
location is basically controlled by the magnetospheric magnetic field, and
therefore the isotropic boundaries can be used as a tool to probe the
magnetospheric configuration in different external conditions and at different
activity levels. |
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