FINE-STRUCTURE OF THE HIGH-LATITUDE IONOSPHERE IN THE CLEFT AND CUSP

The results of studies of the fine structure and dynamic processes in the high-latitude ionosphere in the cleft and cusp region by the data of complex radiophysical observations on high-latitudinal paths are pr esented. They are based on experimental material obtained on board the research vessel 'Professor Vize' during July-September 1990 when the vessel was at the Greenwich meridian and the latitudes 75-78-degrees-N . The distinctive feature of the radiophysical observations on the ves sel was the simultaneous observations by the Doppler method at two fix ed frequencies in the decameter range and by the method of oblique sou nding of the ionosphere at a frequency sweeping the range from 3.5 to 27.5 MHz. From the observations, the typical feature of the cleft and the cusp has been found to be the presence of wave processes of variou s periods from 30-40 s to 3-8 min. It is suggested that the emergence of typical negative tracks on the dynamic spectra of HF signals is rel ated to the ionospheric manifestations of flux transfer events.