STARE velocities: the importance of off-orthogonality and ion motions
A 3.5-h morning event of joint EISCAT/STARE observations is considered and the differences between the observed STARE velocities and the electron drift components (EISCAT) are studied. We find that the STARE-Finland radar velocity was larger than the EISCAT convec-tion component for a prolon...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2003-03-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/21/729/2003/angeo-21-729-2003.pdf |
| _version_ | 1819264181695676416 |
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| author | M. Uspensky M. Uspensky A. Koustov P. Janhunen R. Pellinen D. Danskin S. Nozawa |
| author_facet | M. Uspensky M. Uspensky A. Koustov P. Janhunen R. Pellinen D. Danskin S. Nozawa |
| author_sort | M. Uspensky |
| collection | DOAJ |
| description | A 3.5-h morning event of
joint EISCAT/STARE observations is considered and the differences between the
observed STARE velocities and the electron drift components (EISCAT) are
studied. We find that the STARE-Finland radar velocity was larger than the
EISCAT convec-tion component for a prolonged period of time. In addition, a
moderate 5–20° offset between the EISCAT convection azimuth and the
corresponding STARE estimate was observed. We show that both the STARE-Finland
radar velocity "over-speed" and the offset in the azimuth can be
explained by fluid plasma theory, if the ion drift contribution to the
irregularity phase velocity is taken into account under the condition of a
moderate backscatter off-orthogonality. We call such an explanation the
off-orthogonal fluid approach (OOFA). In general terms, we found that the
azimuth of the maxi-mum irregularity phase velocity <b><i>V</i></b><sub><i>ph</i></sub>
is not collinear with the <b><i>V<sub>E × B</sub></i></b> electron flow
direction, but differs by 5–15°. Such an azimuth offset is the key factor,
not only for the explanation of the Finland velocity overspeed, but also for
the revisions of the velocity cosine rule, traditionally accepted in the STARE
method at large flow angles. We argue that such a rule is only a rough
approximation. The application of the OOFA to the STARE l-o-s velocities gives
a reasonable agreement with the EISCAT convection data, implying that ion
motions and the non-orthogonality of backscatter are important to consider for
VHF auroral echoes. The data set discussed had the STARE velocity magnitudes,
which were 1.5–2 times smaller than the electron <b><i>V<sub>E × B</sub></i></b>
velocities, as was found earlier by Nielsen and Schlegel (1983).<br><br><b>Key words. </b>Ionospheric
irregularities; plasma waves and instabilities; auroral ionosphere |
| first_indexed | 2024-12-23T20:25:24Z |
| format | Article |
| id | doaj.art-772565f57dc744bbb81b4752a18931a9 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-23T20:25:24Z |
| publishDate | 2003-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-772565f57dc744bbb81b4752a18931a92022-12-21T17:32:24ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762003-03-012172974310.5194/angeo-21-729-2003STARE velocities: the importance of off-orthogonality and ion motionsM. Uspensky0M. Uspensky1A. Koustov2P. Janhunen3R. Pellinen4D. Danskin5S. Nozawa6Finnish Meteorological Institute, Geophisycal Research, P.O. Box 503, FIN-00101, Helsinki, Finlandon leave from Murmansk State Technical University, Sportivnaya 13, Murmansk, 183010, RussiaInstitute of Space and Atmospheric Studies, Universtity of Saskatchewan, Saskatoon, S7N 5E2, CanadaFinnish Meteorological Institute, Geophisycal Research, P.O. Box 503, FIN-00101, Helsinki, FinlandFinnish Meteorological Institute, Geophisycal Research, P.O. Box 503, FIN-00101, Helsinki, FinlandInstitute of Space and Atmospheric Studies, Universtity of Saskatchewan, Saskatoon, S7N 5E2, CanadaSolar-Terrestrial Environment Laboratory, Nagoya University, 3-13 Honohara, Toyokawa, Aichi 442, JapanA 3.5-h morning event of joint EISCAT/STARE observations is considered and the differences between the observed STARE velocities and the electron drift components (EISCAT) are studied. We find that the STARE-Finland radar velocity was larger than the EISCAT convec-tion component for a prolonged period of time. In addition, a moderate 5–20° offset between the EISCAT convection azimuth and the corresponding STARE estimate was observed. We show that both the STARE-Finland radar velocity "over-speed" and the offset in the azimuth can be explained by fluid plasma theory, if the ion drift contribution to the irregularity phase velocity is taken into account under the condition of a moderate backscatter off-orthogonality. We call such an explanation the off-orthogonal fluid approach (OOFA). In general terms, we found that the azimuth of the maxi-mum irregularity phase velocity <b><i>V</i></b><sub><i>ph</i></sub> is not collinear with the <b><i>V<sub>E × B</sub></i></b> electron flow direction, but differs by 5–15°. Such an azimuth offset is the key factor, not only for the explanation of the Finland velocity overspeed, but also for the revisions of the velocity cosine rule, traditionally accepted in the STARE method at large flow angles. We argue that such a rule is only a rough approximation. The application of the OOFA to the STARE l-o-s velocities gives a reasonable agreement with the EISCAT convection data, implying that ion motions and the non-orthogonality of backscatter are important to consider for VHF auroral echoes. The data set discussed had the STARE velocity magnitudes, which were 1.5–2 times smaller than the electron <b><i>V<sub>E × B</sub></i></b> velocities, as was found earlier by Nielsen and Schlegel (1983).<br><br><b>Key words. </b>Ionospheric irregularities; plasma waves and instabilities; auroral ionospherehttps://www.ann-geophys.net/21/729/2003/angeo-21-729-2003.pdf |
| spellingShingle | M. Uspensky M. Uspensky A. Koustov P. Janhunen R. Pellinen D. Danskin S. Nozawa STARE velocities: the importance of off-orthogonality and ion motions Annales Geophysicae |
| title | STARE velocities: the importance of off-orthogonality and ion motions |
| title_full | STARE velocities: the importance of off-orthogonality and ion motions |
| title_fullStr | STARE velocities: the importance of off-orthogonality and ion motions |
| title_full_unstemmed | STARE velocities: the importance of off-orthogonality and ion motions |
| title_short | STARE velocities: the importance of off-orthogonality and ion motions |
| title_sort | stare velocities the importance of off orthogonality and ion motions |
| url | https://www.ann-geophys.net/21/729/2003/angeo-21-729-2003.pdf |
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