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

Abstract

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.

Incoherent Scatter Radar Studies of Daytime Plasma Lines

“…Also, Fredriksen et al (1989) demonstrated that electron temperature could be determined with simultaneous EISCAT observations at VHF and UHF, and performed a detailed study of PEPL intensity versus angle relative to the geomagnetic field B. The PEPL phase energy spectrum has been interpreted within the context of the photoelectron spectrum and several key experimental/theoretical issues have been examined (Cicerone 1974;Oran et al 1978Kofman and Lejeune 1980;Bjørnå and Kirkwood 1986;Guio and Lilensten 1999). Similar measurements have also been used to determine PEPL energy loss and transport versus PEPL energy (Cicerone et al 1973;Abreu and Carlson 1977).…”

Effect of loss-cone distribution on the generation of whistler waves in the magnetosphere

“…Recently, Mace (1998Mace ( , 1999 explained the observed whistler bursts of the low to intermediate frequencies obtained in stream of earth's bow shock and the foreshock by considering a kappa distribution which makes the plasma more unstable for whistler wave than Maxwellian distribution with suprathermal electrons. Recently, it was found that suprathermal electron in bi-Maxwellian distribution modify the intensity and Doppler frequencies of electron plasma lines (Guio and Lilensten, 1999). Our results of emitted frequencies are found in the range of (0.59-2:03 kHz) for kappa distribution and are smaller than those of Maxwellian distribution (0.87-2:30 kHz).…”

An Overview of Ionosphere—Thermosphere Models Available for Space Weather Purposes

“…This is performed by solving a stationary kinetic Boltzmann transport equation. TRANSSOLO (Lummerzheim and Lilensten 1994;Guio and Lilensten 1999;Lilensten and Blelly 2002) is a kinetic transport model developed for research as a physics code and has been made operational recently. The main output is the electron distribution function as a function of energy, altitude and range From this physical parameters, production rates (ions or excitation states) may be computed, from which the emission lines are deduced.…”