Cristin-resultat-ID: 431914
Sist endret: 13. april 2004, 14:23
NVI-rapporteringsår: 2004
Resultat
Vitenskapelig artikkel
2004

Interferometric radar observations of filamented structures due to plasma instabilities and their relation to dynamic auroral rays

Bidragsytere:
  • Tom Grydeland
  • Erik Mårten Blixt
  • Unni Pia Løvhaug
  • Tor Hagfors
  • Cesar La Hoz og
  • Trond S. Trondsen

Tidsskrift

Annales Geophysicae
ISSN 0992-7689
e-ISSN 1432-0576
NVI-nivå 1

Om resultatet

Vitenskapelig artikkel
Publiseringsår: 2004
Volum: 22
Hefte: 4
Sider: 1115 - 1132
Open Access

Importkilder

Isi-ID: 134450196

Klassifisering

Emneord

Ionosfærefysikk, nordlys • Radarinterferometri

Beskrivelse Beskrivelse

Tittel

Interferometric radar observations of filamented structures due to plasma instabilities and their relation to dynamic auroral rays

Sammendrag

Several explanations have been proposed for Naturally Enhanced ion-acoustic Echoes observed at mid- and high-latitude Incoherent Scatter observatories. A decisive measure for distinguishing between these explanations, is whether or not simultaneously observed up- and down-shifted enhancement occur simultaneously, or if they are the result of temporal and/or spatial averaging. The EISCAT Svalbard Radar has two antennas in the same radar system, which can be used as an interferometer when pointed parallel. In observations from 2002-01-17 between 06:46:10 and 06:46:30 UT, we used this possibility, in combination with direct sampling of the received signals, to yield measurements of naturally enhanced ion-acoustic echoes with sufficiently high resolution to resolve such averaging, if any. For the first time, radar interferometry has been employed to estimate the sizes of coherent structures. The observations were coordinated with an image intensified video camera with a narrow field of view. Together this forms the initial study on the causal relationships between enhanced echoes and fine structure in the auroral activity on sub-kilometer, sub-second scales. The results confirm that the enhanced echoes originate from very localised regions (~300 m perpendicular to the magnetic field at 500 km altitude) with varying range distribution, and with high time variability (?200 ms). The corresponding increase in scattering cross-section, up to 50 dB above incoherent scattering, eliminates theoretical explanations based on marginal stability. The simultaneously observed up- and down-shifted enhanced shoulders, when caused by sufficiently narrow structures to be detected by the interferometer technique, originate predominantly from the same volume. These results have significant impact on theories attempting to explain the enhancements, in particular it is found that the ion-electron two-stream mechanism favoured by many authors is an unlikely candidate to explain the observations. The video data has helped establish a clear correlation between the enhanced echoes and auroral activity, on sub-second time scales, showing a threshold connection between the auroral intensity and the triggering of the radar enhancements. It appears that the up- and down-shifted enhanced echoes correlate with fine auroral structures in different ways.

Bidragsytere

Tom Grydeland

  • Tilknyttet:
    Forfatter
    ved Institutt for fysikk og teknologi ved UiT Norges arktiske universitet

Mårten Blixt

Bidragsyterens navn vises på dette resultatet som Erik Mårten Blixt
  • Tilknyttet:
    Forfatter
    ved Institutt for fysikk og teknologi ved UiT Norges arktiske universitet

Unni Pia Løvhaug

  • Tilknyttet:
    Forfatter
    ved Institutt for fysikk og teknologi ved UiT Norges arktiske universitet

Tor Hagfors

  • Tilknyttet:
    Forfatter

Cesar Augusto Vergara La Hoz

Bidragsyterens navn vises på dette resultatet som Cesar La Hoz
  • Tilknyttet:
    Forfatter
    ved Institutt for fysikk og teknologi ved UiT Norges arktiske universitet
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