Spatial and temporal distribution of the total electron content inferred from beacon-satellite observations and Kharkiv incoherent scatter radar data

Abstract

Model-experiment intercomparisons have allowed us to assess the IRI-2001 errors in representing the latitudinal and diurnal variations in the electron density, the total electron content, and in the electron and ion temperatures over Eastern Europe. The main cause of these errors is the difference between the variations in the ionospheric parameters over Eastern Europe and those over the western hemisphere where the database for the IRI-2001 was mainly collected. In order to improve the IRI-2001 and to develop a regional ionospheric model, we have developed a technique for deriving maps of total electron content by jointly analyzing incoherent scatter radar (ISR) data and dual-frequency Doppler shift measurements from navigation satellites. The ISR data were collected near Kharkiv city (49.6°N, 36.6°E), and the dual-frequency signals from navigation satellites in circular polar orbits at the altitude of about 1000km were received at the Kharkiv V. Karazin National University Radiophysical Observatory (49.6°N, 36.3°E). The calculated total electron content maps span the 35°–65°N geographic latitude range and the 24-h local time range. These maps represent all known features of diurnal and latitudinal total electron content variations at middle and subauroral latitudes, and in particular, they represent the local latitudinal maximum in total electron content. It is distinctly displayed at 50°N geographic latitude, exists almost always, and corresponds to a point at which the Hough function for the semi-diurnal tidal mode (m=2, n=4) assumes maximum, although it is at present unclear which of the physical processes may lie in the basis of this correspondence. The results obtained also indicate that tidal and planetary-scale waves act to noticeably modify the temporal and spatial variability of TEC, including that under quiet conditions.