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Ionospheric plasma density irregularities measured by stimulated electromagnetic emission
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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2008 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A9, A09314- p.Article in journal (Refereed) Published
Abstract [en]

It is well known that ionospheric plasma turbulence can be conveniently generated by controlled injection of powerful high-frequency radio beams from the ground. Irradiation of the ionosphere with such radio waves leads to the formation of plasma density structures, striations, and the generation of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission (SEE). In this paper we present experimental results of the dependence of SEE on decreasing excitation levels of the striations. In the experiments the frequency of the injected radio beam was varied near the fifth harmonic of the local ionospheric electron gyro frequency. We use the SEE measurements to obtain transverse length scales of the striations involved in the generation of the SEE. Our results show that different spectral features of the SEE display different temporal dynamics, suggesting that they are related to striations with different transverse length scales (1 less than or similar to L-perpendicular to less than or similar to 25 m).

Place, publisher, year, edition, pages
2008. Vol. 113, no A9, A09314- p.
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-97796DOI: 10.1029/2008JA013338ISI: 000259398700002OAI: oai:DiVA.org:uu-97796DiVA: diva2:172869
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Secondary Electromagnetic Radiation Generated by HF Pumping of the Ionosphere
Open this publication in new window or tab >>Secondary Electromagnetic Radiation Generated by HF Pumping of the Ionosphere
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electromagnetic waves can be used to transmit information over long distances and are therefore often employed for communication purposes. The electromagnetic waves are reflected off material objects on their paths and interact with the medium through which they propagate. For instance, the plasma in the ionosphere can refract and even reflect radio waves propagating through it.

By increasing the power of radio waves injected into the ionosphere, the waves start to modify the plasma, resulting in the generation of a wide range of nonlinear processes, including turbulence, in particular near the reflection region. By systematically varying the injected radio waves in terms of frequency, power, polarisation, duty cycle, inclination, etc. the ionosphere can be used as an outdoor laboratory for investigating fundamental properties of the near-Earth space environment as well as of plasma turbulence. In such ionospheric modification experiments, it has been discovered that the irradiation of the ionosphere by powerful radio waves leads to the formation of plasma density structures and to the emission of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission. These processes are highly repeatable and have enabled systematic investigations of the nonlinear properties of the ionospheric plasma.

In this thesis we investigate features of the plasma density structures and the secondary electromagnetic radiation. In a theoretical study we analyse a certain aspect of the formation of the plasma structures. The transient dynamics of the secondary radiation is investigated experimentally in a series of papers, focussing on the initial stage as well as on the decay. In one of the papers we use the transient dynamics of the secondary radiation to reveal the intimate relation between certain features of the radiation and structures of certain scales. Further, we present measurements of unprecedentedly strong secondary radiation, attributed to stimulated Brillouin scattering, and report measurements of the secondary radiation using a novel technique imposed on the transmitted radio waves.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 576
Keyword
space physics, ionospheric modification experiments, plasma turbulence, stimulated electromagnetic emission, ionospheric irregularities, radio waves, parametric processes, thermal parametric instability, transient dynamics, wave-wave interactions
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-9393 (URN)978-91-554-7344-0 (ISBN)
Public defence
2008-12-12, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
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Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2011-01-21Bibliographically approved

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Astronomy and Space PhysicsSwedish Institute of Space Physics, Uppsala Division
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