Determination of low energy photoelectron distribution from plasma line measurements at Saint Santin

Kofman, W.; Lejeune, Gérard

doi:10.1016/0032-0633(80)90111-7

Cited by 13 publications

(10 citation statements)

References 22 publications

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“…Enhancements of the intensity of plasma lines above the thermal level have been observed in the F region of the ionosphere at several incoherent scatter radar facilities [Yngvesson and Perkins, 1968 Lejeune, 1980]. In these cases the suprathermal electrons responsible for the enhancements are local or conjugate photoelectrons created by solar ionization, Observations of plasma line spectra in the auroral E region have recently been made with the Chatanika incoherent scatter radar [Wickwar, 1978;Kofman and Wickwar, 1980].…”

Section: Introductionmentioning

confidence: 99%

“…They have helped to define and resolve problems involving self-consistent calculations of electron temperatures [Carlson et al, 1977], anisotropy in upshifted and downshifted plasma line intensities , and the existence of large electron fluxes in the F region near the intersection of the thermal and photoelectron populations [Kofman and Lejeune, 1980]. This paper presents a first attempt to compare auroral E region observations to theoretical predictions.…”

Section: Introductionmentioning

confidence: 99%

“…In the auroral region, some of these questions focus on the role of collisionless processes in determining the secondary electron spectra [Papadopoulos and Coffey, 1974;Matthews et al, 1976;Papadopoulos and Rowland, 1978]. Uncertainties in the collision cross sections for low-energy electrons have arisen because of inconsistencies in the estimates of the energy required to heat thermal electrons to observed temperatures [Carlson et al, 1977;Kofman and Lejeune, 1980]. Experimental and theoretical considerations have indicated that the modeling procedures and the cross sections in the energy range between thermal and suprathermal electrons are of questionable validity [Kofman and Lejeune, 1980; Ashihara and Takyanagi, 1974; Jasperse, 1976Jasperse, , 1977.…”

Section: Introductionmentioning

confidence: 99%

“…Uncertainties in the collision cross sections for low-energy electrons have arisen because of inconsistencies in the estimates of the energy required to heat thermal electrons to observed temperatures [Carlson et al, 1977;Kofman and Lejeune, 1980]. Experimental and theoretical considerations have indicated that the modeling procedures and the cross sections in the energy range between thermal and suprathermal electrons are of questionable validity [Kofman and Lejeune, 1980; Ashihara and Takyanagi, 1974; Jasperse, 1976Jasperse, , 1977. Finally, the large electron-neutral collision frequencies at low altitudes suggest that they must also be included in the basic calculation of plasma line intensities.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Auroral plasma lines: A first comparison of theory and experiment

Oran¹,

Wickwar²,

Kofman³

et al. 1981

J. Geophys. Res.

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In this preliminary report on low-energy (0.3 to 3 eV) secondary electrons in the auroral E layer (90 to 150 km), we compare intensities of plasma lines observed with the Chatanika radar to theoretical predictions obtained from a detailed numerical model. The model calculations are initiated with a flux of energetic auroral primary electrons which enter the atmosphere and lose energy to electrons, ions, and neutrals through a combination of elastic and inelastic collisions. This flux is chosen in order that the total calculated ionization rate matches one that is deduced from the radar measurements. From these same calculations the steady state secondary electron flux is deduced as a function of altitude, energy, and pitch angle. This flux is used to calculate plasma line intensities which are then compared with observed intensities. Initial comparisons suggest that the plasma line theory, when applied to low altitudes, must include the effect of electron-neutral collisions. When this is done, the good agreement obtained between theory and experiment indicates the promise of this approach for the study of low-energy auroral electrons.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Auroral plasma lines: A first comparison of theory and experiment

Oran¹,

Wickwar²,

Kofman³

et al. 1981

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…The enhancement process of the plasma line is well understood theoretically Yngvesson and Perkins, 1968;BjùrnaÊ et al, 1982;BjùrnaÊ and Trulsen, 1986) and has been con®rmed by measurements both during daytime Yngvesson and Perkins, 1968;Lejeune and Kofman, 1977;Kofman and Lejeune, 1980) and in auroral conditions Kirkwood et al, 1995). The problem of estimating the ®eld-aligned electron net current from an incoherent scatter Doppler measurement of the electron plasma lines has also been studied for some time (Vidal-Madjar et al, 1975;Bauer et al, 1976;Showen, 1979), yet the work on the subject has progressed rather slowly, partly due to experimental problems (the spectra needs to be estimated) and partly due to the lack of theoretical understanding.…”

Section: Introductionmentioning

confidence: 77%

Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines

Guio

Lilensten

1999

Ann. Geophys.

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Abstract. In an incoherent scattering radar experiment, the spectral measurement of the so-called up-and downshifted electron plasma lines provides information about their intensity and their Doppler frequency. These two spectral lines correspond, in the backscatter geometry, to two Langmuir waves travelling towards and away from the radar. In the daytime ionosphere, the presence of a small percentage of photoelectrons produced by the solar EUV of the total electron population can excite or damp these Langmuir waves above the thermal equilibrium, resulting in an enhancement of the intensity of the lines above the thermal level. The presence of photo-electrons also modi®es the dielectric response function of the plasma from the Maxwellian and thus in¯uences the Doppler frequency of the plasma lines. In this paper, we present a high time-resolution plasma-line data set collected on the EISCAT VHF radar. The analysed data are compared with a model that includes the e ect of a suprathermal electron population calculated by a transport code. By comparing the intensity of the analysed plasma lines data to our model, we show that two sharp peaks in the electron suprathermal distribution in the energy range 20±30 eV causes an increased Landau damping around 24.25 eV and 26.25 eV. We have identi®ed these two sharp peaks as the e ect of the photoionisation of N 2 and O by the intense¯ux of monochromatic HeII radiation of wavelength 30.378 nm (40.812 eV) created in the chromospheric network and coronal holes. Furthermore, we see that what would have been interpreted as a mean Doppler drift velocity for a Maxwellian plasma is actually a shift of the Doppler frequency of the plasma lines due to suprathermal electrons.

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Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines

Guio

Lilensten

1999

Ann Geophysicae

View full text Add to dashboard Cite

In an incoherent scattering radar experiment, the spectral measurement of the so-called up-and downshifted electron plasma lines provides information about their intensity and their Doppler frequency. These two spectral lines correspond, in the backscatter geometry, to two Langmuir waves travelling towards and away from the radar. In the daytime ionosphere, the presence of a small percentage of photoelectrons produced by the solar EUV of the total electron population can excite or damp these Langmuir waves above the thermal equilibrium, resulting in an enhancement of the intensity of the lines above the thermal level. The presence of photo-electrons also modi®es the dielectric response function of the plasma from the Maxwellian and thus in¯uences the Doppler frequency of the plasma lines. In this paper, we present a high time-resolution plasma-line data set collected on the EISCAT VHF radar. The analysed data are compared with a model that includes the eect of a suprathermal electron population calculated by a transport code. By comparing the intensity of the analysed plasma lines data to our model, we show that two sharp peaks in the electron suprathermal distribution in the energy range 20±30 eV causes an increased Landau damping around 24.25 eV and 26.25 eV. We have identi®ed these two sharp peaks as the eect of the photoionisation of N 2 and O by the intense¯ux of monochromatic HeII radiation of wavelength 30.378 nm (40.812 eV) created in the chromospheric network and coronal holes. Furthermore, we see that what would have been interpreted as a mean Doppler drift velocity for a Maxwellian plasma is actually a shift of the Doppler frequency of the plasma lines due to suprathermal electrons.

show abstract

Determination of low energy photoelectron distribution from plasma line measurements at Saint Santin

Cited by 13 publications

References 22 publications

Auroral plasma lines: A first comparison of theory and experiment

Auroral plasma lines: A first comparison of theory and experiment

Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines

Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines

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