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| Titel |
3-D-geocoronal hydrogen density derived from TWINS Ly-α-data |
| VerfasserIn |
J. H. Zoennchen, U. Nass, G. Lay, H. J. Fahr  |
| 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 ; 28, no. 6 ; Nr. 28, no. 6 (2010-06-01), S.1221-1228 |
| Datensatznummer |
250016839
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1221-2010.pdf |
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| Zusammenfassung |
Based on Ly-α-line-of-sight measurements
taken with two Ly-α detectors onboard of the
satellite TWINS1 (Two Wide-angle Imaging Neutral-atom Spectrometers)
density profiles of the exospheric, neutral geocoronal hydrogen were derived
for the time period between summer solstice and fall equinox 2008. With the
help of specifically developed inversion programs from Ly-α
line of sight intensities the three-dimensional density
structure of the geocoronal hydrogen at geocentric distances r>3 RE could be derived for the period mentioned characterized by very
low solar 10.7 cm radiofluxes of ≈65–70 [10−22 W m−2 Hz−1]. The time-variable,
solar "line-centered"-Ly-α-flux was extracted on the basis of
daily (terrestrial) NGDC 10.7 cm radioflux data using the models from
Barth et al. (1990) and Vidal-Madjar (1975).
The results for the geocoronal H-densities are compared here
both with theoretical calculations based on a Monte-Carlo model by Hodges
(1994) and with density profiles obtained with the Geocoronal Imager (GEO)
by Østgaard and Mende (2003). In our results we find a remarkably more
pronounced day-/night-side asymmetry which clearly hints to the existence of
a hydrogen geotail (i.e. a tail structure with comparatively higher hydrogen
densities on the night side of the earth for geocenctric distances >4 RE), and a only weakly pronounced polar depletion.
These unexpected features we try to explain by new models in the near future. The derived 3-D-H-density
structures are able to explain the line-of-sight (LOS) dependent Ly-α intensity variations for all LOS seen up to now
with TWINS-LAD. The presented results are valid for the region with
geocentric distances 3 RE<r<7 RE
and are based on the reasonable assumption of an optically thin H-exosphere
with respect to resonant Ly-α-scattering allowing the use of single
scattering calculations. |
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