Signature of polar cap inhomogeneities in vertical sounding data

The typical feature of the vertical ionogram, which is produced by local enhancements of electron density (patches and arcs), is investigated. The polar patches drift from the dayside of the Earth across the magnetic pole in accordance with convection flow patterns at speeds of a few hundred meters per second. Patches are typically about 500km in length in the dawn-to-dusk direction, but they range from 200 to 1000km and exhibit electron density enhancements of up to a factor of 10 above background. A model of the ionosphere with irregularities (midlatitude trough, auroral oval, polar cap patches, and Sun-aligned arcs) was developed in collaboration with the University of Leicester (UK). Based on this model, the vertical ionograms for different time and geophysical conditions were simulated. The ionograms were classified by types of the trace shapes. The results of simulation are very reminiscent of the main characteristics of the ionograms observed in high latitude. It is believed that the variations of the model parameters may be employed to estimate the real parameters of the high-latitude ionospheric inhomogeneities.