The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data
Circumterrestrial Lyman-<i>α</i> column brightness observations from 3–8 Earth radii (<i>R</i><sub>e</sub>) have been used to study temporal density variations in the exospheric neutral hydrogen as response to geomagnetic disturbances of different strength, i.e...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2017-02-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/35/171/2017/angeo-35-171-2017.pdf |
| _version_ | 1819132016592945152 |
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| author | J. H. Zoennchen U. Nass H. J. Fahr J. Goldstein J. Goldstein |
| author_facet | J. H. Zoennchen U. Nass H. J. Fahr J. Goldstein J. Goldstein |
| author_sort | J. H. Zoennchen |
| collection | DOAJ |
| description | Circumterrestrial Lyman-<i>α</i> column brightness observations from
3–8 Earth radii (<i>R</i><sub>e</sub>) have been used to study temporal density
variations in the exospheric neutral hydrogen as response to geomagnetic
disturbances of different strength, i.e., Dst peak values between −26 and
−147 nT. The data used were measured by the two Lyman-<i>α</i> detectors
(LAD1/2) onboard both TWINS satellites between the solar minimum of 2008 and
near the solar maximum of 2013. The solar Lyman-<i>α</i> flux at 121.6 nm is
resonantly scattered near line center by exospheric H atoms and measured by
the TWINS LADs. Along a line of sight (LOS), the scattered LOS-column
intensity is proportional to the LOS H column density, assuming optically
thin conditions above 3 <i>R</i><sub>e</sub>. In the case of the eight analyzed
geomagnetic storms we found a significant increase in the exospheric
Lyman-<i>α</i> flux between 9 and 23 % (equal to the same increase in
H column density Δ<i>n</i><sub>H</sub>) compared to the undisturbed case short
before the storm event. Even weak geomagnetic storms (e.g., Dst peak values
≥ −41 nT) under solar minimum conditions show increases up to
23 % of the exospheric H densities. The strong H density increase in the
observed outer exosphere is also a sign of an enhanced H escape flux during
storms. For the majority of the storms we found an average time shift of about
11 h between the time when the first significant dynamic solar wind
pressure peak (<i>p</i><sub>SW</sub>) hits the Earth and the time when the
exospheric Lyman-<i>α</i> flux variation reaches its maximum. The results
show that the (relative) exospheric density reaction of Δ<i>n</i><sub>H</sub>
have a tendency to decrease with increasing peak values of Dst index or the
Kp index daily sum. Nevertheless, a simple linear correlation between Δ<i>n</i><sub>H</sub> and these two geomagnetic indices does not seem to exist. In
contrast, when recovering from the peak back to the undisturbed case,
the Kp index daily sum and the Δ<i>n</i><sub>H</sub> essentially show
the same temporal recovery. |
| first_indexed | 2024-12-22T09:24:42Z |
| format | Article |
| id | doaj.art-cadb00a43cf54af594dc1cc2ca93c42c |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-22T09:24:42Z |
| publishDate | 2017-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-cadb00a43cf54af594dc1cc2ca93c42c2022-12-21T18:31:06ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762017-02-013517117910.5194/angeo-35-171-2017The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> dataJ. H. Zoennchen0U. Nass1H. J. Fahr2J. Goldstein3J. Goldstein4Argelander 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, GermanySouthwest Research Institute, San Antonio, Texas, USAUniversity of Texas, San Antonio, San Antonio, Texas, USACircumterrestrial Lyman-<i>α</i> column brightness observations from 3–8 Earth radii (<i>R</i><sub>e</sub>) have been used to study temporal density variations in the exospheric neutral hydrogen as response to geomagnetic disturbances of different strength, i.e., Dst peak values between −26 and −147 nT. The data used were measured by the two Lyman-<i>α</i> detectors (LAD1/2) onboard both TWINS satellites between the solar minimum of 2008 and near the solar maximum of 2013. The solar Lyman-<i>α</i> flux at 121.6 nm is resonantly scattered near line center by exospheric H atoms and measured by the TWINS LADs. Along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H column density, assuming optically thin conditions above 3 <i>R</i><sub>e</sub>. In the case of the eight analyzed geomagnetic storms we found a significant increase in the exospheric Lyman-<i>α</i> flux between 9 and 23 % (equal to the same increase in H column density Δ<i>n</i><sub>H</sub>) compared to the undisturbed case short before the storm event. Even weak geomagnetic storms (e.g., Dst peak values ≥ −41 nT) under solar minimum conditions show increases up to 23 % of the exospheric H densities. The strong H density increase in the observed outer exosphere is also a sign of an enhanced H escape flux during storms. For the majority of the storms we found an average time shift of about 11 h between the time when the first significant dynamic solar wind pressure peak (<i>p</i><sub>SW</sub>) hits the Earth and the time when the exospheric Lyman-<i>α</i> flux variation reaches its maximum. The results show that the (relative) exospheric density reaction of Δ<i>n</i><sub>H</sub> have a tendency to decrease with increasing peak values of Dst index or the Kp index daily sum. Nevertheless, a simple linear correlation between Δ<i>n</i><sub>H</sub> and these two geomagnetic indices does not seem to exist. In contrast, when recovering from the peak back to the undisturbed case, the Kp index daily sum and the Δ<i>n</i><sub>H</sub> essentially show the same temporal recovery.https://www.ann-geophys.net/35/171/2017/angeo-35-171-2017.pdf |
| spellingShingle | J. H. Zoennchen U. Nass H. J. Fahr J. Goldstein J. Goldstein The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data Annales Geophysicae |
| title | The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data |
| title_full | The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data |
| title_fullStr | The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data |
| title_full_unstemmed | The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data |
| title_short | The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data |
| title_sort | response of the h geocorona between 3 and 8 i r i sub e sub to geomagnetic disturbances studied using twins stereo lyman i α i data |
| url | https://www.ann-geophys.net/35/171/2017/angeo-35-171-2017.pdf |
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