DISTRIBUTION OF IRREGULARITIES IN ANTARCTIC IONOSPHERE .2. DIURNAL MAGNETIC AND SOLAR CYCLE EFFECTS

Radio signals from the satellite S-66 were recorded at Scott Base (78°S) from October 1964 to February 1968. Fluctuations in the polarisation angle of the received signals show the amplitude of small-scale variations in the electron content along the ray path. Results from 12,000 transits are used to map the changes occurring over much of the Antarctic ionosphere. In equinox there is a large diurnal variation with a maximum near local sunset. There is no overall diurnal change in summer, at sunspot minimum, although the density of irregularities is reduced near 05.00 and 18.00 local time. The winter results are similar except for an additional production of irregularities throughout most of the Antarctic near 04.00 U.T. (corresponding to local noon near the corrected geomagnetic pole). At sunspot maximum the degree of irregularity increases considerably in all seasons, and shows a definite peak near 06.00 U.T. in agreement with F-region and electron precipitation observations. In the polar cap zone, at geomagnetic latitudes greater than 80°, the degree of irregularity shows a large diurnal variation in summer and winter (but not in equinox) with a maximum near sunset. The polar peak shows at latitudes near 80° as an increase in the degree of irregularity from 03.00 to 15.00 local geomagnetic time in summer, and 07.00 to 17.00 in winter. Averaged over the whole of the observed area the ionosphere is most irregular about 12 hr before a maximum in magnetic activity. The degree of irregularity then decreases, reaching a minimum about 1 day after the maximum magnetic activity and returning to normal in a further 3 days. © 1969.