Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude
We have observed a number of strong echoes with the European incoherent-scatter (EISCAT) UHF (930-MHz) radar at angles 83.5° and 78.6° with the geomagnetic field and at about 100-km altitude north in the auroral zone. The echoes are short-lived and occur in single 2- or 10-s data dumps. They are off...
Published in: | Annales Geophysicae |
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Springer Verlag
1996
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Online Access: | https://doi.org/10.1007/s00585-996-1328-4 https://noa.gwlb.de/receive/cop_mods_00037669 https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00037623/angeo-14-1328-1996.pdf https://angeo.copernicus.org/articles/14/1328/1996/angeo-14-1328-1996.pdf |
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ftnonlinearchiv:oai:noa.gwlb.de:cop_mods_00037669 2023-05-15T16:04:39+02:00 Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude Malnes, E. Bjørnå, N. Hansen, T. L. 1996-12 electronic https://doi.org/10.1007/s00585-996-1328-4 https://noa.gwlb.de/receive/cop_mods_00037669 https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00037623/angeo-14-1328-1996.pdf https://angeo.copernicus.org/articles/14/1328/1996/angeo-14-1328-1996.pdf eng eng Springer Verlag Annales Geophysicae -- http://www.bibliothek.uni-regensburg.de/ezeit/?1458425 -- https://www.ann-geophys.net/ -- https://www.ann-geophys.net/volumes.html -- http://link.springer.com/journal/585 -- 1432-0576 https://doi.org/10.1007/s00585-996-1328-4 https://noa.gwlb.de/receive/cop_mods_00037669 https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00037623/angeo-14-1328-1996.pdf https://angeo.copernicus.org/articles/14/1328/1996/angeo-14-1328-1996.pdf https://open-access.net/ uneingeschränkt info:eu-repo/semantics/openAccess article Verlagsveröffentlichung article Text doc-type:article 1996 ftnonlinearchiv https://doi.org/10.1007/s00585-996-1328-4 2022-02-08T22:43:25Z We have observed a number of strong echoes with the European incoherent-scatter (EISCAT) UHF (930-MHz) radar at angles 83.5° and 78.6° with the geomagnetic field and at about 100-km altitude north in the auroral zone. The echoes are short-lived and occur in single 2- or 10-s data dumps. They are offset by 125–130 kHz with respect to the transmitted frequency. In most cases the offset compares well with the frequency of gyro lines in the incoherent-scatter spectrum, as given by the standard linear dispersion relation. But sometimes the measured offsets deviate significantly from the model calculations, and the interpretation in terms of gyro lines becomes questionable. The discrepancy could possibly be explained by local deviations in the magnetic field from the model (IGRF 1987), which are generated by incoming particle beams. A more serious problem with the gyro-line theory is how the line can be excited at altitudes where the collisional damping is substantial. The high intensity and short lifetime of the signal point to a fast-growing plasma instability as the likely excitation mechanism, if the gyro-line interpretation is correct. The cause of the instability could be the same particle beams as those causing the disturbances in the magnetic field. Alternatively, the observations may be interpreted as meteor head echoes. The large Doppler shifts, the short lifetimes and the altitudes of the signals support this explanation. The main difficulty is that the distribution of measured offsets appears to be different in magnetically active conditions and in less active conditions. Also, the occurrence of echoes does not seem to follow the expected changes in meteor density. More observations in different conditions are needed to decide between the two interpretations. As it is, we are inclined to believe in the meteor head echo theory, the objections to the gyro-line theory being more fundamental. Article in Journal/Newspaper EISCAT Niedersächsisches Online-Archiv NOA Annales Geophysicae 14 12 1328 1342 |
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article Verlagsveröffentlichung Malnes, E. Bjørnå, N. Hansen, T. L. Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude |
topic_facet |
article Verlagsveröffentlichung |
description |
We have observed a number of strong echoes with the European incoherent-scatter (EISCAT) UHF (930-MHz) radar at angles 83.5° and 78.6° with the geomagnetic field and at about 100-km altitude north in the auroral zone. The echoes are short-lived and occur in single 2- or 10-s data dumps. They are offset by 125–130 kHz with respect to the transmitted frequency. In most cases the offset compares well with the frequency of gyro lines in the incoherent-scatter spectrum, as given by the standard linear dispersion relation. But sometimes the measured offsets deviate significantly from the model calculations, and the interpretation in terms of gyro lines becomes questionable. The discrepancy could possibly be explained by local deviations in the magnetic field from the model (IGRF 1987), which are generated by incoming particle beams. A more serious problem with the gyro-line theory is how the line can be excited at altitudes where the collisional damping is substantial. The high intensity and short lifetime of the signal point to a fast-growing plasma instability as the likely excitation mechanism, if the gyro-line interpretation is correct. The cause of the instability could be the same particle beams as those causing the disturbances in the magnetic field. Alternatively, the observations may be interpreted as meteor head echoes. The large Doppler shifts, the short lifetimes and the altitudes of the signals support this explanation. The main difficulty is that the distribution of measured offsets appears to be different in magnetically active conditions and in less active conditions. Also, the occurrence of echoes does not seem to follow the expected changes in meteor density. More observations in different conditions are needed to decide between the two interpretations. As it is, we are inclined to believe in the meteor head echo theory, the objections to the gyro-line theory being more fundamental. |
format |
Article in Journal/Newspaper |
author |
Malnes, E. Bjørnå, N. Hansen, T. L. |
author_facet |
Malnes, E. Bjørnå, N. Hansen, T. L. |
author_sort |
Malnes, E. |
title |
Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude |
title_short |
Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude |
title_full |
Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude |
title_fullStr |
Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude |
title_full_unstemmed |
Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude |
title_sort |
anomalous echoes observed with the eiscat uhf radar at 100-km altitude |
publisher |
Springer Verlag |
publishDate |
1996 |
url |
https://doi.org/10.1007/s00585-996-1328-4 https://noa.gwlb.de/receive/cop_mods_00037669 https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00037623/angeo-14-1328-1996.pdf https://angeo.copernicus.org/articles/14/1328/1996/angeo-14-1328-1996.pdf |
genre |
EISCAT |
genre_facet |
EISCAT |
op_relation |
Annales Geophysicae -- http://www.bibliothek.uni-regensburg.de/ezeit/?1458425 -- https://www.ann-geophys.net/ -- https://www.ann-geophys.net/volumes.html -- http://link.springer.com/journal/585 -- 1432-0576 https://doi.org/10.1007/s00585-996-1328-4 https://noa.gwlb.de/receive/cop_mods_00037669 https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00037623/angeo-14-1328-1996.pdf https://angeo.copernicus.org/articles/14/1328/1996/angeo-14-1328-1996.pdf |
op_rights |
https://open-access.net/ uneingeschränkt info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.1007/s00585-996-1328-4 |
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Annales Geophysicae |
container_volume |
14 |
container_issue |
12 |
container_start_page |
1328 |
op_container_end_page |
1342 |
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1766400260645584896 |