Sunrise and sunset effects on solar heating in the Jovian thermosphere and ionosphere

We present some calculations on the effects of oblateness on the solar heating process as considered in the Jovian Ionospheric Model by Achilleos et al. (1998). Since Jupiter has significant oblateness we have to use a new approach for the investigation of sunrise/sunset variations in the Jovian ionosphere, We introduce the modified Chapman function (Che) and point to its importance for the sunrise and sunset time periods where this function significantly deviates from the "classic" Chapman function (Ch). Because of the dependence of the Che function on latitude and solar declination we have included latitudinal variations in all thermospheric and ionospheric parameters. The Jovian Ionospheric Model assumes plane stratified atmospheric layers. We consider one part of this model., the solar heating, and more precisely take into account the shape of the planetary body. We model it with a rotational ellipsoid and calculate the optical depth parameter, used in evaluation of the neutral volume heating rate due to solar radiation. We use secants for the flat model, the Ch function for spherical model, and the Che function for the ellipsoidal model. We use all other physical inputs of the Jovian Ionospheric Model to explore the effects due to oblateness only. Calculations show that only the modified Chapman function Che can really describe sunrise/sunset and latitudinal variations in the Jovian thermosphere and ionosphere. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.