Study of the Behaviour of the Topside Ionosphere during Sunrise from Alouette-I & Alouette-II Satellite Data

Abstract

The electron density profiles obtained by the Alouette-I and Alouette-II topside sounders are used to study the sunrise behaviour of the topside ionosphere. Remarkable changes occur in the plasma scale height profiles at higher altitudes in the winter hemisphere even before the local sunrise, indicating significant heating due to conjugate photoelectrons. It is also possible to derive the upward velocity of plasma, due to thermal expansion after the sunrise, from the plasma scale height profiles. The scale height profiles do not indicate either significant changes in plasma temperature during sunrise period or the presence of a temperature gradient in the high latitude topside ionosphere.