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| Titel |
On recent developments in E-region irregularity simulationsand a summary of related theory |
| VerfasserIn |
P. Janhunen  |
| 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 ; 13, no. 7 ; Nr. 13, no. 7, S.791-806 |
| Datensatznummer |
250011922
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| Publikation (Nr.) |
 copernicus.org/angeo-13-791-1995.pdf |
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| Zusammenfassung |
| Theoretical and simulation approaches to
E-region irregularities (gradient drift and Farley-Buneman instabilities) are
reviewed, and an account is given of some relevant observations. A new hybrid
linear dispersion relation is also derived and presented. The most important
problem that cannot be explained by more straightforward theories is the
saturation of the phase velocity to the ion acoustic speed (Cs
saturation). This phenomenon is well-known from equatorial electrojet radar
observations. Recent particle simulations have yielded an interesting new
explanation for the (Cs saturation, which has been named flow
angle stabilization: the phase velocity is not actually (Cs
saturated, but the flow angle distribution of the spatial power spectrum is
highly asymmetric. The asymmetry is such that the most intense waves propagate
at the k·E < 0 edge of the linearly unstable sector, and thus the
phase velocity of the most intense waves is close to (Cs.
Depending on the level of larger scale turbulence, the radar observes varying
degrees of (Cs saturation. If the larger scale turbulence
level is high (equatorial electrojet case), the local flow angle fluctuates, and
there are always sub-regions within the scattering volume with local flow angles
favourable for the detection of the most intense waves. Under these conditions,
the spectra show (Cs saturation. If the larger scale
turbulence level is lower, there will not always be enough mixing of the flow
angle for even the most intense waves to be observed. In these cases, the mean
Doppler shift will be proportional to the electric field, i.e. it will obey the
linear theory. |
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