Long-term Scintillations in the Dayside Cusp and Polar Cap Locations and its Impact on Trans-ionospheric Satellite Communication Links at VHF

This study provides the first long-term scintillation statistics at 250 MHz from 2000-2005 at the cusp at two longitudes, namely in Sondrestorm, Greenland and in NyAlesund, Svalbard, the former remaining in sunlight during winter whereas the latter is in darkness. The interpretation of statistics at these stations are, however, quite complex since the quasi-stationary satellites observed, combined with the observing geometry, yield a data base in which different magnetic latitude ranges (polar, auroral and sub-auroral) are explored during different times of day and seasons with no easy way to separate these variables. Ionospheric plasma from midlatitudes entering the dayside cusp region are structured through shear flows or gradient drift instability mechanisms and during the passage of the plasma through the central polar cap the anti-sunward convection continually structures the plasma by the gradient drift instability mechanism until it transits into the nightside auroral oval. The structured plasma scatters signals from satellites and introduces scintillations of signal amplitude and degrades the quality of a communication link. Overall, maximum scintillation occurrence at the cusp is observed at the two equinoxes and the December solstice with the minimum occurrence noted in Jun-July. In addition, both the magnitude of scintillation and percent occurrence decline with declining sunspot number. Earlier, long-term statistics for Thule, a polar cap location, were shown in Basu et al. (Radio Sc., 1988). Though the peak sunspot values of solar cycle 23 are lower than those in the 1979 time period, there is favorable comparison of scintillation occurrence and seasonal variability for similar sunspot periods at Thule. The study provides a quantitative measure of degradation in satellite to ground or satellite to aircraft communication links at VHF in the polar region due to structured ionospheric plasma.