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| Titel |
High resolution observations of sporadic-E layers within the polar cap ionosphere using a new incoherent scatter radar experiment |
| VerfasserIn |
B. Damtie, T. Nygrén, M. S. Lehtinen, A. Huuskonen |
| 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 ; 20, no. 9 ; Nr. 20, no. 9, S.1429-1438 |
| Datensatznummer |
250014463
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| Publikation (Nr.) |
 copernicus.org/angeo-20-1429-2002.pdf |
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| Zusammenfassung |
High resolution
observations of sporadic-E layers using a new experiment with the EISCAT
(European Incoherent SCATter) Svalbard radar (ESR) are presented. The
observations were made by means of a new type of hardware, which was connected
in parallel with the standard receiver. The radar beam was aligned with the
geomagnetic field. The experiment applies a new modulation principle. Two phase
codes, one with 22 bits and the other with 5 bits, were transmitted at separate
frequencies. Each bit was further modulated by a 5-bit Barker code. The basic
bit length of both transmissions was 6 µs. Instead of storing the lagged
products of the ionospheric echoes in the traditional way, samples of both the
transmitted pulses and the ionospheric echoes were taken at intervals of 1 µs
and stored on hard disk. The lagged products were calculated later in an
off-line analysis. In the analysis a sidelobe-free Barker decoding technique
was used. The experiment produces range ambiguities, which were removed by
mathematical inversion. Sporadic-E layers were observed at 105–115 km
altitudes, and they are displayed with a 150-m range resolution and a 10-s time
resolution. The layers show sometimes complex shapes, including triple peaked
structures. The thickness of these sublayers is of the order of 1–2 km and
they may be separated by 5 km in range. While drifting downwards, the sublayers
merge together to form a single layer. The plasma inside a layer is found to
have a longer correlation length than that of the surrounding plasma. This may
be an indication of heavy ions inside the layer. The field-aligned ion velocity
is also calculated. It reveals shears in the meridional wind, which suggests
that shears probably also exist in the zonal wind. Hence the wind shear
mechanism is a possible generation mechanism of the layer. However,
observations from the coherent SuperDARN radar indicate the presence of an
ionospheric electric field pointing in the sector between west and north. Thus,
the layer could also be produced by the electric field mechanism. This means
that both mechanisms may be active simultaneously. Their relative importance
could not be determined in this study.
Key words. Ionosphere; polar
ionosphere, instruments and techniques |
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