 |
| Titel |
Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission |
| VerfasserIn |
J. H. Zoennchen, U. Nass, H. J. Fahr  |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 33, no. 3 ; Nr. 33, no. 3 (2015-03-27), S.413-426 |
| Datensatznummer |
250121184
|
| Publikation (Nr.) |
 copernicus.org/angeo-33-413-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| Circumterrestrial Lyman-α column brightness observations above 3
Earth radii (Re) have been used to derive separate 3-D neutral
hydrogen density models of the Earth's exosphere for solar minimum (2008,
2010) and near-solar-maximum (2012) conditions. The data
used were measured by Lyman-α detectors (LAD1/2) onboard each of
the TWINS satellites from very different orbital positions with respect to
the exosphere. Exospheric H atoms resonantly scatter the near-line-center
solar Lyman-α flux at 121.6 nm. Assuming optically thin conditions
above 3Re along a line of sight (LOS), the scattered
LOS-column intensity is proportional to the LOS H-column density. We found
significant differences in the density distribution of the terrestrial
exosphere under different solar conditions. Under solar maximum conditions
we found higher H densities and a larger spatial extension compared to solar
minimum. After a continuous, 2-month decrease in (27 day averaged) solar activity,
significantly lower densities were found. Differences in shape and
orientation of the exosphere under different solar conditions exist.
Above 3 Re, independent of solar activity, increased
H densities appear on the Earth's nightside shifted towards dawn. With
increasing distance (as measured at 8Re) this feature is
shifted westward/duskward by between −4 and −5° with
respect to midnight. Thus, at larger geocentric distance the exosphere
seems to be aligned with the aberrated Earth–solar-wind line, defined by the
solar wind velocity and the orbital velocity of the Earth. The results
presented in this paper are valid for geocentric distances between
3 and 8Re. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|