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Recovery of the ponderomotive parametric instability after long pumping of the ionosphere
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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2007 (English)In: Advances in Space Research, ISSN 0273-1177, Vol. 40, no 3, 377-383 p.Article in journal (Refereed) Published
Abstract [en]

We show that during high frequency (HF) pumping of the overhead ionosphere with a pump wave frequency slightly above the local fifth electron gyroharmonic, when one switches the pump wave from continuous pumping to low duty cycle pulse pumping, the stimulated electromagnetic emission (SEE) features related to the ponderomotive parametric instability (PPI) near the pump wave reflection point, such as the ponderomotive narrow continuum and the narrow continuum maximum, recover and become dominating in the SEE spectra after a few seconds after the switch. Simultaneously, the ionospherically reflected pump wave signal exhibits a recovery of ponderomotive self-action and the damped quasi-periodical oscillations (spikes) of the reflected pump wave, also related to the PPI development. The intensity of the down-shifted maximum (DM) feature in the SEE spectra increases for about 1–2 s after the switch to the pulse mode, but later, together with PPI related phenomena recovery, the DM intensity decreases noticeably. The phenomena described are attributed to the relaxation of small-scale irregularities (striations). The latter provide strong scattering of the pump wave into upper hybrid waves, strong shielding of the pump wave reflection point, and generation of the upper-hybrid related DM feature.

Place, publisher, year, edition, pages
2007. Vol. 40, no 3, 377-383 p.
Keyword [en]
HF pumping of the ionosphere, Stimulated electromagnetic emissions, Ponderomotive and thermal parametric instabilities
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-97794DOI: 10.1016/j.asr.2007.04.067ISI: 000253589400013OAI: oai:DiVA.org:uu-97794DiVA: diva2:172867
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2011-03-24Bibliographically 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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 576
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
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
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2011-01-21Bibliographically approved

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