The Tromsّ dynasonde

A description, history and the capabilities of an ionospheric sounder in the auroral zone near Tromsّ, Norway are presented, together with some scientific applications. The sounder, which is of the dynasonde type, has provided a data set which has improved dramatically in quantity, quality and information content. A similar sounder is planned to be installed in the polar cap near Longyearbyen on Spitsbergen.