Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission
Circumterrestrial Lyman-α column brightness observations above 3 Earth radii (<i>R</i><sub>e</sub>) 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....
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-03-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/33/413/2015/angeo-33-413-2015.pdf |
| _version_ | 1811257685921759232 |
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| author | J. H. Zoennchen U. Nass H. J. Fahr |
| author_facet | J. H. Zoennchen U. Nass H. J. Fahr |
| author_sort | J. H. Zoennchen |
| collection | DOAJ |
| description | Circumterrestrial Lyman-α column brightness observations above 3
Earth radii (<i>R</i><sub>e</sub>) 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 3<i>R</i><sub>e</sub> 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 <i>R</i><sub>e</sub>, independent of solar activity, increased
H densities appear on the Earth's nightside shifted towards dawn. With
increasing distance (as measured at 8<i>R</i><sub>e</sub>) 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 8<i>R</i><sub>e</sub>. |
| first_indexed | 2024-04-12T18:01:17Z |
| format | Article |
| id | doaj.art-4c83dcdc631a4be4ba5e2f7ce05e84b7 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-04-12T18:01:17Z |
| publishDate | 2015-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-4c83dcdc631a4be4ba5e2f7ce05e84b72022-12-22T03:22:08ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762015-03-013341342610.5194/angeo-33-413-2015Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo missionJ. H. Zoennchen0U. Nass1H. J. Fahr2Argelander Institut für Astronomie, Astrophysics Department, University of Bonn, Auf dem Huegel 71, 53121 Bonn, GermanyArgelander Institut für Astronomie, Astrophysics Department, University of Bonn, Auf dem Huegel 71, 53121 Bonn, GermanyArgelander Institut für Astronomie, Astrophysics Department, University of Bonn, Auf dem Huegel 71, 53121 Bonn, GermanyCircumterrestrial Lyman-α column brightness observations above 3 Earth radii (<i>R</i><sub>e</sub>) 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 3<i>R</i><sub>e</sub> 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 <i>R</i><sub>e</sub>, independent of solar activity, increased H densities appear on the Earth's nightside shifted towards dawn. With increasing distance (as measured at 8<i>R</i><sub>e</sub>) 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 8<i>R</i><sub>e</sub>.https://www.ann-geophys.net/33/413/2015/angeo-33-413-2015.pdf |
| spellingShingle | J. H. Zoennchen U. Nass H. J. Fahr Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission Annales Geophysicae |
| title | Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission |
| title_full | Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission |
| title_fullStr | Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission |
| title_full_unstemmed | Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission |
| title_short | Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission |
| title_sort | terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the twins stereo mission |
| url | https://www.ann-geophys.net/33/413/2015/angeo-33-413-2015.pdf |
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