Results of ten years' ionospheric drift measurements in the l.f. range

Abstract

Abstract From systematic observations at two stations in Central Europe it can be shown that closely spaced receiver drift measurements at low frequencies are a useful technique for continuous observation of night-time drift motions in the lower ionosphere. In excellent accordance with radar meteor drift results the prevailing drift has been found to be directed towards E or SE in winter and summer, with a strong semi-diurnally rotating drift component superimposed. Drastic seasonal anomalies of drift direction have been observed every year for some weeks during spring and autumn, consisting of a temporary reversal of the prevailing drift towards SW and of a simultaneous anomaly in the phase of the semi-diurnal component. In most cases the individual drift directions, obtained simultaneously at two stations, separated by a distance of about 300 km, are nearly identical, thus indicating the significance of such observations and the systematic large-scale character of the observed wind systems. First indications have been found for a probable sunspot cycle dependence of drift direction and drift velocity in the lower ionosphere, and for an anomaly in the drift direction associated with a strong stratospheric warming event.