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| Titel |
Characteristics of Poker Flat Incoherent Scatter Radar (PFISR) naturally enhanced ion-acoustic lines (NEIALs) in relation to auroral forms |
| VerfasserIn |
R. G. Michell, T. Grydeland, M. Samara |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 32, no. 10 ; Nr. 32, no. 10 (2014-10-29), S.1333-1347 |
| Datensatznummer |
250121126
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| Publikation (Nr.) |
 copernicus.org/angeo-32-1333-2014.pdf |
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| Zusammenfassung |
| Naturally enhanced ion-acoustic lines (NEIALs) have been observed with the
Poker Flat Incoherent Scatter Radar (PFISR) ever since it began operating in
2006. The nearly continuous operation of PFISR since then has led to a large
number of NEIAL observations from there, where common-volume, high-resolution
auroral imaging data are available. We aim to systematically distinguish the
different types of auroral forms that are associated with different NEIAL
features, including spectral shape and altitude extent. We believe that
NEIALs occur with a continuum of morphological characteristics, although we
find that most NEIALs observed with PFISR fall into two general categories.
The first group occurs at fairly low altitudes – F region or below – and
have power at, and spread between, the ion-acoustic peaks. The second group
contains the type of NEIALs that have previously been observed with the
EISCAT radars, those that extend to high altitudes (600 km or more) and
often have large asymmetries in the power enhancements between the two
ion-acoustic shoulders. We find that there is a correlation between the auroral
structures and the type of NEIALs observed, and that the auroral structures
present during NEIAL events are consistent with the likely NEIAL generation
mechanisms inferred in each case. The first type of NEIAL – low altitude –
is the most commonly observed with PFISR and is most often associated with
active, structured auroral arcs, such as substorm growth phase, and onset arcs
and are likely generated by Langmuir turbulence. The second type of NEIAL –
high altitude – occurs less frequently in the PFISR radar and is associated
with aurora that contains large fluxes of low-energy electrons, as can happen
in poleward boundary intensifications as well as at substorm onset and is
likely the result of current-driven instabilities and in some cases Langmuir
turbulence as well. In addition, a preliminary auroral photometry analysis
revealed that there is an anticorrelation between the altitude of the NEIALs
and the calculated energy of the electrons, which is consistent with the
hypotheses presented here regarding generation mechanisms. |
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