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Statistical properties of ionospheric stimulated electromagnetic emissions
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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2006 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, no 7, 1851-1859 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2006. Vol. 24, no 7, 1851-1859 p.
Keyword [en]
ionosphere, active experiments, ionospheric irregularities, space plasma physics, wave-wave interactions
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-93427ISI: 000240367200008OAI: oai:DiVA.org:uu-93427DiVA: diva2:166896
Available from: 2005-09-07 Created: 2005-09-07 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Theory and Applications of Tri-Axial Electromagnetic Field Measurements
Open this publication in new window or tab >>Theory and Applications of Tri-Axial Electromagnetic Field Measurements
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polarisation, which was first studied in optics, is a fundamental property of all electromagnetic fields. A convenient way to describe the polarisation of two dimensional electromagnetic fields is given by the Stokes parameters. This thesis deals with different aspects of wave polarisation and electromagnetic field measurements. A generalisation of the Stokes parameters to three dimensions is presented. The theory has been used to develop methods and systems for obtaining the polarisation parameters of electromagnetic waves. The methods can be applied for a wide range of electromagnetic fields, measured both on ground and onboard satellites. The applications include, e.g., direction-finding, polarisation analysis, radar, and several examples in the field of wireless communication. Further applications are given in the analysis of satellite data, where a whistler wave is considered. Whistlers are circularly polarised electromagnetic waves propagating in the magnetosphere along the geomagnetic field. Dispersion in the magnetospheric plasma make the whistler frequencies travel at different speeds and the signal takes the form of a chirp. From instantaneous polarisation analysis of the whistler´s magnetic wave field, the normal to the polarisation plane is obtained and found to precess around the geomagnetic field. A statistic analysis of ionospheric stimulated electromagnetic emissions (SEE) is also presented. SEE is generated by injecting a powerful high frequency radio wave into the ionosphere. It is shown that the SEE features have a statistical behaviour indistinguishable from the amplitude and phase distributions of narrow-band Gaussian noise. The results suggests that SEE cannot be explained by simple coherent processes alone. Finally, an expression for the complex Poynting theorem is derived for the general case of anharmonic fields. It is found that the complex Poynting theorem, for real fields and sources, is not a conservation law of the imaginary part of electromagnetic energy.

Place, publisher, year, edition, pages
Uppsala: Institutionen för astronomi och rymdfysik, 2005. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 88
Keyword
Space and plasma physics, polarisation, polarization, Stokes parameters, antenna, radio waves, whistler wave, SEE, direction-finding, statistics, Poynting theorem, Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-5916 (URN)91-554-6327-4 (ISBN)
Public defence
2005-09-30, Polhemsalen, 10134, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 14:00
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Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved

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