Nonlinear phenomena in the ionosphere

Gurevich, A. V.

doi:10.3367/ufnr.0120.197610f.0319

Cited by 189 publications

(273 citation statements)

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“…Although not immediately apparent from Figure 1, detailed analysis shows that the optical emission appears to descend in the same way (not shown). The descent in altitude is probably due to the increase in electron temperature [Gustavsson et al, 2001;Rietveld et al, 2003], which reduces the electron recombination rate [Robinson, 1989;Gurevich, 1978] thereby effectively increasing the local plasma density. Since the HF reflection altitude is a function of electron density, it must therefore descend.…”

Section: Observations and Resultsmentioning

confidence: 99%

Novel artificial optical annular structures in the high latitude ionosphere over EISCAT

Kosch

Rietveld

Senior

et al. 2004

Geophysical Research Letters

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The EISCAT low‐gain HF facility has been used repeatedly to produce artificially stimulated optical emissions in the F‐layer ionosphere over northern Scandinavia. On 12 November 2001, the high‐gain HF facility was used for the first time. The pump beam zenith angle was moved in 3° steps along the north‐south meridian from 3°N to 15°S, with one pump cycle per position. Only when pumping in the 9°S position were annular optical structures produced quite unexpectedly. The annuli were approximately centred on the pump beam but outside the −3 dB locus. The optical signature appears to form a cylinder, which was magnetic field‐aligned, rising above the pump wave reflection altitude. The annulus always collapsed into the well‐known optical blobs after ∼60 s, whilst descending many km in altitude. All other pump beam directions produced optical blobs only. The EISCAT UHF radar, which was scanning from 3° to 15°S zenith angle, shows that enhanced ion‐line backscatter persisted throughout the pump on period and followed the morphology of the optical signature. These observations provide the first experimental evidence that Langmuir turbulence can accelerate electrons sufficiently to produce the optical emissions at high latitudes. Why the optical annulus forms, and for only one zenith angle, remains unexplained.

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Section: Observations and Resultsmentioning

confidence: 99%

Novel artificial optical annular structures in the high latitude ionosphere over EISCAT

Kosch

Rietveld

Senior

et al. 2004

Geophysical Research Letters

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“…The temperature dependence of the recombination rate can be found by noting that the dominant positive ions in the lower ionosphere (z < 85 km) are water cluster ions H + (H 2 O) n . Their electron-ion recombination rate a depends on the number of water molecules in the cluster, with an average value given by [Gurevich, 1978;Johnsen, 1993] a ¼ a 0 300K=T e ð Þ 0:6 ; a 0 ¼ 2:5 Â 10 À6 cm 3 =s ð2Þ…”

Section: Efficiency Enhancement Physicsmentioning

confidence: 99%

Enhanced ionospheric ELF/VLF generation efficiency by multiple timescale modulated heating

Milikh

Papadopoulos

2007

Geophysical Research Letters

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[1] It is shown theoretically that for high power HF ionospheric heaters, such as the current HAARP heater, the HF to VLF conversion can increase significantly by using a two-timescale heating. A long heating pulse, t p % 1 minute, is followed over the same timescale period by modulation at the desired ELF/VLF frequency. The long pulse reduces the electron-ion recombination coefficient, resulting in increased ambient electron density and current density. The efficiency increases due to the increase in the current density over the time t p . Besides, the more efficient heating results from sharpening of the ambient density profile at the modified height that reduces low altitude self-absorption. It is shown that following the long preheating pulse by amplitude modulated heating at VLF frequencies can result in efficiency increase of up to 7 dB over the non-preheated case. In addition to the theory the letter describes proof-ofprinciple experiments using the completed HAARP.

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“…This allows us to neglect the inertial terms in the hydrodynamic velocity equation, as well as thermal and kinetic effects. The complete system of equations, describing low-frequency quasi-neutral os-cillations in a weakly ionized plasma takes then the following form [Gurevich, 1978] Expressions for the components of tensor be, Di, (re, and &i, are determined in the kinetic theory of a weakly ionized plasma [Gurevich, 1978]. We'll use for them the following elementary theory approximate expressions, taking into account also, that in the lower part of E region electrons are strongly magnetized ( Here qh,,, is a Fourier transformation of electric field potential (10).…”

Section: Turbulence Of Ionospheric Plasmamentioning

confidence: 99%

Ionospheric turbulence induced in the lower part of the E region by the turbulence of the neutral atmosphere

Gurevich¹,

Borisov²,

Zybin³

1997

J. Geophys. Res.

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Abstract. Strong large-scale oscillations of the electric field and plasma density observed on rockets in the lower part of the ionospheric E layer and the scattering of low-frequency radar waves (f _< 10 MHz) in the same region of ionosphere are not well explained by the existing theories. We explore here a new mechanism of the excitation of plasma turbulence in the lower part of the E region, connected with the turbulent motion of neutral atmosphere. The problem is solved in a fluid approximation. The spectrum of induced fluctuations of electron and ion densities and electric field is determined and analyzed. The cross section for scattering of radio waves from the lower ionosphere is determined. IntroductionPlasma turbulence exists in the E region of the ionosphere beginning from heights between 70 and 80 km. Ionospheric turbulence is excited most efficiently in the auroral and equatorial regions. It is also regularly observed in the midlatitude ionosphere. The vast observational material, obtained mostly by radio scattering and in situ measurements from rockets, is summarized in a textbook [Kelley, 1989] Atmospheric TurbulenceAtmospheric turbulence at the heights 70 •< z •< 100 km is generated by neutral winds, gravity, and tidal waves. It is reg-379

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Nonlinear phenomena in the ionosphere

Cited by 189 publications

References 0 publications

Novel artificial optical annular structures in the high latitude ionosphere over EISCAT

Novel artificial optical annular structures in the high latitude ionosphere over EISCAT

Enhanced ionospheric ELF/VLF generation efficiency by multiple timescale modulated heating

Ionospheric turbulence induced in the lower part of the E region by the turbulence of the neutral atmosphere

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