Abstract
Abstract. A set of EISCAT UHF and VHF observations is used for calibrating a coupled fluid-kinetic model of the ionosphere. The data gathered in the period 1200- 2400 UT on 24 March 1995 had various intervals of interest for such a calibration. The magnetospheric activity was very low during the afternoon, allowing for a proper examination of a case of quiet ionospheric conditions. The radars entered the auroral oval just after 1900 UT: a series of dynamic events probably associated with rapidly moving auroral arcs was observed until after 2200 UT. No attempts were made to model the dynamical behaviour during the 1900–2200 UT period. In contrast, the period 2200–2400 UT was characterised by quite steady precipitation: this latter period was then chosen for calibrating the model during precipitation events. The adjustment of the model on the four primary parameters observed by the radars (namely the electron concentration and temperature and the ion temperature and velocity) needed external inputs (solar fluxes and magnetic activity index) and the adjustments of a neutral atmospheric model in order to reach a good agreement. It is shown that for the quiet ionosphere, only slight adjustments of the neutral atmosphere models are needed. In contrast, adjusting the observations during the precipitation event requires strong departures from the model, both for the atomic oxygen and hydrogen. However, it is argued that this could well be the result of inadequately representing the vibrational states of N2 during precipitation events, and that these factors have to be considered only as ad hoc corrections.
Highlights
For more than half a century, much theoretical work has been carried out to derive the basic transport equationsCorrespondence to: P.-L
There still remains some unsolved and important uncertainties: for instance, the O>-O resonant collision frequency remains an object of disagreement by a factor of nearly 2 between its theoretical expression as predicted by the most recent studies (Banks and Kockarts, 1973; Pesnell et al, 1993, 1994) and its indirect measurement in the ionosphere (Burnside et al, 1987; Salah, 1993; Davis et al, 1995, and references therein)
The results from the dynasonde placed at the EISCAT Tromsosite showed that the calibration constant for the UHF measurements was good within less than 15%, and the UHF can be thereby considered as calibrated for the 24 March
Summary
For more than half a century, much theoretical work has been carried out to derive the basic transport equations. Et al.: Calibration of a numerical ionospheric model with EISCAT observations of energetic photo- or precipitating-electrons flows through the ambient thermal plasma and is responsible for local energy deposition on the thermal electrons in the lower part of the ionosphere (&100—200 km; Schunk and Nagy, 1978). It was shown by Blelly and Schunk (1993) and by Blelly and Alcayde (1994) that they can contribute to a significant part of the energy transport from the magnetosphere into the topside ionosphere.
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