| 1. |
- Carozzi, TD, et al.
(författare)
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Full polarimetry measurements of stimulated electromagnetic emissions: First results
- 2001
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. - 0148-0227. ; 106:A10, s. 21395-21407
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Tidskriftsartikel (refereegranskat)abstract
- A theory and technique for the measurement of the full state of polarization (SOP) for wideband electromagnetic HF emissions from the ionosphere are introduced. The technique was employed in a recent experiment at the Sura ionospheric HF pumping facility
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| 2. |
- Frolov, V.L., Grach, S.M., Erukhimov, L.M., Komrakov, G.P., Sergeev, E.N., Thidé, B., Carozzi, T.
(författare)
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Investigation of the Temporal Evolution of the Broad Upshifted Maximum (BUM)
- 1996
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Ingår i: Radiophysics and Quantum Electronics. ; 39, s. 241-254
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Frolov, V.L., Grach, S.M., Erukhimov, L.M., Komrakov, G.P., Sergeev, E.N., Thidé, B., Carozzi, T.
(författare)
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Peculiarities in the Evolution of the BUM of Stimulated Radio Emission of the Ionosphere
- 1996
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Ingår i: Radiophysics and Quantum Electronics. ; 39, s. 352-371
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Kotov, P. V., et al.
(författare)
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Recovery of the ponderomotive parametric instability after long pumping of the ionosphere
- 2007
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 40:3
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Norin, Lars, et al.
(författare)
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Ionospheric plasma density irregularities measured by stimulated electromagnetic emission
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:A9, s. A09314-
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Tidskriftsartikel (refereegranskat)abstract
- 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).
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| 6. |
- Norin, Lars, et al.
(författare)
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On the linear stage of thermal parametric instabilities in the ionosphere excited by HF pumping near electron gyroharmonics
- 2006
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 38:11, s. 2527-2532
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Tidskriftsartikel (refereegranskat)abstract
- Thresholds and growth rates of the thermal parametric instability in the ionosphere were studied taking into account the regular inhomogeneity (altitude dependence) of the plasma density and of the magnetic field strength. A noticeable decrease of the pump wave threshold power and an increase of the growth rate occurs when f0 approaches the double resonance frequency fd = nfce(zd) = fUH(zd), zd being the altitude for double resonance. Particularly, the threshold power decreases relative to the non-resonant case by a factor 3-7 at |f0 - fd(zd)| ≲ 15 kHz for n = 3 and up to a factor 3 for n = 4. The instability growth rate can increase with a factor of 103-104 relative to the non-resonant case. The decrease of the threshold and increase of the growth rate occur for quite small scales of the striations, l⊥ ∼ 1 m for n = 3 and l⊥ ∼ 0.5 m for n = 4.
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| 7. |
- Norin, Lars, et al.
(författare)
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Transient dynamics of secondary radiation from an HF pumped magnetized space plasma
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 119:A9
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Tidskriftsartikel (refereegranskat)abstract
- In order to systematically analyze the transient wave and radiation processes that are excited when a high-frequency (HF) radio wave is injected into a magnetized space plasma, we have measured the secondary radiation, or stimulated electromagnetic emission (SEE), from the ionosphere, preconditioned such that geomagnetic field-aligned plasma irregularities are already present. The transient dynamics experiments were made using a duty cycle of the HF radio wave of 200 ms (180 ms on and 20 ms off) and 100 ms (80 ms on and 20 ms off) for various frequencies near the fifth harmonic of the local ionospheric electron cyclotron frequency. Within the first 10 ms after the radio pulse turn-on, frequency downshifted structures of the SEE exhibit an overshoot with a maximum at 3 ms < t < 8 ms, whereas the upshifted spectral components do not exhibit this feature. The relative magnitude of the overshoot is strongly dependent on the frequency offset of the pump from the harmonic of the electron cyclotron frequency. A transient blue-shifted frequency component is identified. This component is upshifted from the pump by 14 kHz < Δ f< 55 kHz and exists only within the first 10 ms after the radio pulse turn-on. On a longer time scale we analyze the amplitude modulation, or "ringing," of the reflected radio wave, (also known as "quasi-periodic oscillations" or "spikes"). The ringing has a frequency of the order 15-20 Hz and we show that this phenomenon is also present in the SEE sidebands and is synchronized with the ringing of the reflected HF wave itself.
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