Estimation of the value of the electric field in the upper ionosphere before an earthquake

Summary Plasma parameters were measured by the Intercosmos 24 satellite at altitudes between 2300 km and 2500 km about 40 hours prior to the strong shock of the Iranian earthquake of 6 July 1990. Anomalous concentrations of light ions and electrons were observed mainly above the active seismic zone up to two days before the shock (Boková et al., 1993, 1994). This paper presents a model which, with the use of the anomalous electric field, is able to describe the observed changes of light ion concentrations in the plasmasphere above regions of imminent seismic events. The value of the intensity of the anomalous electric field, required to explain the observed changes, is estimated. For the seismic event analyzed intensity of the anomalous electric field is comparable with the value of the ambipolar electric field, but of opposite direction.