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Ann. Geophys., 24, 1851-1859, 2006
www.ann-geophys.net/24/1851/2006/
© European Geosciences Union 2006
Statistical properties of ionospheric stimulated electromagnetic emissions
R. L. Karlsson1, T. D. Carozzi2, L. Norin1, J. E. S. Bergman3, and B. Thidé3,4
1Department of Astronomy and Space Physics, Uppsala University, Box 515, SE-751 20 Uppsala, Sweden
2Space Science Centre, University of Sussex, Brighton, BN1 9QT, UK
3Swedish Institute of Space Physics, Uppsala, Box 537, SE-751 21 Uppsala, Sweden
4LOIS Space Centre, Växjö University, SE-35195 Växjö, Sweden
Abstract. We have analysed the statistical properties of the stimulated electromagnetic
emissions (SEE) spectral features in the steady state, reached after a long
period of continuous HF pumping of the ionosphere in experiments performed at
the Sura ionospheric radio research facility in Russia. Using a digital
filter bank method, we have been able to analyse complex valued signals
within narrow frequency bands. Each of the SEE spectral features are thereby
separated into a number of narrow spectral components. Statistical tests were
performed for all these spectral components and the distributions of the
spectral amplitudes and phases were evaluated. Also, a test for sinusoidal
components was performed. These tests showed that all observed SEE features
were indistinguishable from coloured Gaussian noise. The test results exclude
that the SEE features can be the result of a single isolated coherent
process, but does not rule out that there could be many statistically independent
parametric wave-wave processes taking place simultaneously at various parts
of the HF-pumped ionosphere, as long as the superposition from all these is
incoherent. Furthermore, from the test results, we cannot exclude the
possibility that the waveforms of some, or all, of the SEE features may be
chaotic.
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