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| Titel |
Exospheric hydrogen density distributions for equinox and summer solstice observed with TWINS1/2 during solar minimum |
| VerfasserIn |
J. H. Zoennchen, U. Nass, 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 ; 31, no. 3 ; Nr. 31, no. 3 (2013-03-19), S.513-527 |
| Datensatznummer |
250019011
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| Publikation (Nr.) |
 copernicus.org/angeo-31-513-2013.pdf |
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| Zusammenfassung |
| The Lyman-α Detectors (LAD) on board the two
TWINS 1/2-satellites allow for the simultaneous stereo imaging of the resonant
emission glow of the H-geocorona from very different orbital positions.
Terrestrial exospheric atomic hydrogen (H) resonantly scatters solar
Lyman-α (121.567 nm) radiation. During the past solar minimum,
relevant solar parameters that influence these emissions were quite stable.
Here, we use simultaneous LAD1/2-observations from TWINS1 and TWINS2 between
June 2008 and June 2010 to study seasonal variations in the H-geocorona. Data
are combined to produce two datasets containing (summer) solstice and
(combined spring and fall) equinox emissions. In the range from 3 to 10
Earth
radii (RE), a three-dimensional (3-D) mathematical model is used that allows
for density asymmetries in longitude and latitude. At lower geocentric
distances (< 3 RE), a best fitting r-dependent (Chamberlain,
1963)-like model is adapted to enable extrapolation of our information to
lower heights. We find that dawn and dusk H-geocoronal densities differ by up
to a factor of 1.3 with higher densities on the dawn side. Also, noon
densities are greater by up to a factor of 2 compared to the dawn and dusk
densities. The density profiles are aligned well with the Earth–Sun line and
there are clear density depletions over both poles that show additional
seasonal effects. These solstice and equinox empirical fits can be used to
determine H-geocoronal densities for any day of the year for solar minimum
conditions. |
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