Temperatures in the upper ionosphere and plasmasphere

Abstract

Modeling of the topside ionosphere requires a knowledge of the electron and ion temperatures (Te and T,.) as a function of height. Data in the International Reference Ionosphere (IRI) model are sometimes conflicting, and extend only up to 3000 km. An exact, analytic solution is found for the variation of Te along a magnetic field line, making full allowance for changes in the cross section and inclination of the tube of force. The downward heat flux is assumed to decrease smoothly with height, becoming zero at the top of the field line. Changes in the Coulomb cross section increase plasmaspheric temperatures by 6-8 %. For a given field line, the temperature profile is defined by two parameters, taken as the temperature To and gradient Go at a reference height of 400 km. Results are fitted to satellite data, for mean day and night conditions, at intervals of 5 o in latitude and heights from 400 to 8000 km. Diurnal changes are reproduced using sunrise and sunset transitions that are matched to observed values. Seasonal changes in Te are generally less than experimental errors. A solar activity variation of 30-40% is required, at low heights, to match the change in neutral temperature. Exospheric temperatures must also increase by 10-20 %, near solar maximum. A first-order correction is derived for high-latitude heating during periods of magnetic activity. Values of T• are calculated from the Te profile and the neutral temperature Tn, giving results that agree well with mean observations. The use of physically acceptable temperature profiles, fitted to the often conflicting satellite data, should give more consistent results for most purposes. IntroductionThere is a continuing need for knowledge of the electron density at heights above the peak of the ionosphere, to calculate the effect of the Earth's environment on the propagation of radio signals. Global maps of the electron density N m, at the peak of the ionospheric F2 layer, have been constructed for some years. The International Reference Ionosphere model (IRI-90) [Rawer and Bilitza, 1989; Bilitza, 1990] calculates N m using spherical harmonic coefficients derived from a large number of ionosonde observations [Rush et al., 1989]. The peak height h,,,F2 is also obtained from global coefficients based on data from the worldwide ionosonde network. Results give a reasonable representation of observed changes with latitude, longitude, local time, season and solar flux. Above the peak of the F2 layer, the variation of electron density with height is controlled closely by the effects of diffusion [e.g., Titheridge, 1976a, 1991]. The gradient dNe/dh then depends primarily on the electron and ion temperatures (Te and T/), and the height of the transition from O + to H + (or He +) ions.The IRI model includes an approximate representation for the electron density variation at heights above h,,•2, up to 1000 km, but this is rather simplified with a number of unsatisfactory features. No attempt is made to predict the changes above 1000 km. , 1985, 1991]. T• is defined by g...

A new global empirical model of the electron temperature with the inclusion of the solar activity variations for IRI

“…Epstein-step functions are used to transition from one region to the next thus generating a continuous analytical representation of the T e gradient and integration then results in the final T e formula. For future upgrades of the IRI model physics-based field aligned profile functions as for example deduced by Bilitza (1975), Titheridge (1998), or Truhlik et al (2009b could bring further improvement.…”

Magnetosonic resonances in the magnetospheric plasma

“…If the resonance peaks for the Alfven waves are also present in the system, however, the above features of the hodograph behavior may indicate the presence of resonant SMS waves. The only exception is the region inside the plasmasphere on the magnetic shells L < 2, where T e ≈ 2T i (Titheridge, 1998). The decrement of SMS waves is relatively small here so that resonant SMS oscillations can be observed directly.…”

DC Langmuir Probe for Measurement of Space Plasma: A Brief Review

“…Past measurement was done at night, or when the electrode was in the shadow of the satellite during the daytime (Rich et al 1979). As a result of this situation, the amount of data accumulated was small, and no systematic measurement was done before 1989 (Titheridge 1998). To overcome this problem, we applied a second-harmonic method to -120 ˚, 120˚ -180˚, 180˚ -240˚, 240˚-300˚, and 300˚ -360˚, respectively.…”

“…The secondary electrons from the satellite itself have much higher energy than thermal electrons, and they do not affect the T e value. The instrument was deployed in the Japanese auroral study satellite "AKEBONO", and it produced the first systematic T e measurement up to 8,000 km (Balan et al 1996a, b;Titheridge 1998;Kutiev et al 2002). Figs.…”