Wave-like structures in the variation of ionospheric absorption

Abstract

In winter 1971/1972, a very clear wave-like structure with a period of about 7 days was found in the day-to-day variation of ionospheric absorption L ( cos χ = 0.2) obtained from recordings of the diurnal variation of absorption on the circuit Norddeich-Lindau (2.61 MHz; 52.6°N; 8.7°E); χ solar zenith angle. It is suggested that this particular pattern, which did not appear clearly in earlier winters, was due to special conditions in the lower atmosphere in winter 1971/1972. A similar and nearly coinciding pattern appeared also in the data obtained from the circuit Aranjuez-Balerma in Spain (2.83 MHz; 38.6°N; 5.2°W) some 1900 km from Lindau. Periods of 20–25 days were also found in the data of some European stations, and a period of 25 days in the data of Japanese stations.