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| Titel |
Complexity in the scaling of velocity fluctuations in the high-latitude F-region ionosphere |
| VerfasserIn |
M. L. Parkinson |
| 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 ; 26, no. 9 ; Nr. 26, no. 9 (2008-09-12), S.2657-2672 |
| Datensatznummer |
250016217
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| Publikation (Nr.) |
 copernicus.org/angeo-26-2657-2008.pdf |
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| Zusammenfassung |
| The temporal scaling properties of F-region velocity
fluctuations, δvlos, were characterised over 17 octaves of temporal scale
from τ=1 s to <1 day using a new data base of 1-s time resolution SuperDARN
radar measurements. After quality control, 2.9 (1.9) million fluctuations
were recorded during 31.5 (40.4) days of discretionary mode soundings using
the Tasmanian (New Zealand) radars. If the fluctuations were statistically
self-similar, the probability density functions (PDFs) of δvlos would collapse
onto the same PDF using the scaling Ps (δvs, τ)=ταP (δvlos, τ)
and δvs=δvlosτ−α where α is the scaling exponent. The
variations in scaling exponents α and multi-fractal behaviour were estimated
using peak scaling and generalised structure function (GSF) analyses, and a
new method based upon minimising the differences between re-scaled
probability density functions (PDFs). The efficiency of this method enabled
calculation of "α spectra", the temporal spectra of scaling exponents from
τ=1 s to ~2048 s. The large number of samples enabled calculation of
α spectra for data separated into 2-h bins of MLT as well as two main
physical regimes: Population A echoes with Doppler spectral width <75 m s−1
concentrated on closed field lines, and Population B echoes with
spectral width >150 m s−1 concentrated on open field lines. For all
data there was a scaling break at τ~10 s and the similarity of the
fluctuations beneath this scale may be related to the large spatial
averaging (~100 km×45 km) employed by SuperDARN radars. For
Tasmania Population B, the velocity fluctuations exhibited approximately
mono fractal power law scaling between τ~8 s and 2048 s (34 min), and
probably up to several hours. The scaling exponents were generally less than
that expected for basic MHD turbulence (α=0.25), except close to magnetic
dusk where they peaked towards the basic MHD value. For Population A, the
scaling exponents were larger than for Population B, having values generally
in the range expected for basic MHD and Kolmogorov turbulence (α=0.25–0.33).
The α spectra exhibited complicated variations with MLT and τ which must be
related to different physical processes exerting more or less influence. |
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