HIGH-LATITUDE DIGISONDE MEASUREMENTS AND THEIR RELEVANCE TO IRI

Digisondes operating at high latitudes provide new insights into the structure and dynamics of the polar cap and auroral ionosphere. These instruments derive the electron density profiles from vertical incidence ionograms, and the horizontal and vertical plasma velocities using the interferometric Doppler imaging drift technique. Multi-beam and polarization measurements in the ionogram unambiguously define the critical frequency of the E and F layers even in the presence of spread F and large scale patches. Occurrence of the patches is controlled by the configuration of the polar cap convection pattern which in turn is driven by the Bz and By components of the interplanetary magnetic field. To specify the UT and seasonal variations of the polar cap F region for IRI requires the knowledge of the prevailing convection pattern. This paper describes the applied techniques to measure profiles and drifts at high latitudes and the status of the analysis on polar cap patches and their transport across the polar cap.