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| Titel |
Long term observations of polar mesospheric echoes at Andøya |
| VerfasserIn |
Ralph Latteck, Irina Strelnikova, Toralf Renkwitz, Svenja Sommer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134340
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| Publikation (Nr.) |
 EGU/EGU2016-15050.pdf |
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| Zusammenfassung |
| Polar mesosphere summer echoes (PMSE) are strong enhancements of received signal power
at very high radar frequencies occurring at altitudes between about 80 and 95 km at polar
latitudes during summer. These echoes are caused by inhomogeneities in the electron
density of the radar Bragg scale within the plasma of the cold summer mesopause
region in the presence of negatively charged ice particles. Thus the occurrence
of PMSE contains information about mesospheric temperature and water vapour
content but also depends on the ionisation due to solar electromagnetic radiation
and precipitating high energetic particles. Continuous observations of PMSE have
been done on the North-Norwegian island Andøya (69.3∘N, 16.0∘E) since 1994
using different VHF radars. The PMSE occurrence rate is positively correlated
with the geomagnetic Ap index, however not correlated with the solar Lyman α
radiation and shows a significant positive trend during the time interval from 1994 until
2012. VHF radar echoes have been observed also during winter times but in the mid
mesosphere from about 55 to 85 km altitude. These so called polar mesosphere winter
echoes (PMWE) have been observed continuously at Andøya since 2004 using the
ALWIN VHF radar (until 2008) and the Middle Atmosphere Alomar Radar System
MAARSY (since 2011). Using the more sensitive MAARSY compared to the previous
VHF radar systems operated at the site, results in more detections characterized by
smaller volume reflectivity values down to 4 ⋅ 10−18m−1. The end of the winter
season is now hard to determine since mesospheric echoes have also been observed
below altitudes of 80 km during non winter months, particularly around the end
of May, i.e. the beginning of the polar mesospheric summer echo season. These
observations indicate that the physical mechanism for creating the lower mesospheric
echoes is present during the early summer months as well. We present results from
long term observations of polar mesospheric echoes at Andøya during summer and
winter time and discuss the observations with respect to the radar systems used
at the location but with a focus on the results recently obtained with MAARSY. |
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