1. Possible modulation effects in the foF2 variations in the periodic range 30–200 hours;Altadill;Bulg. Geophys. J.,1993
2. Solar cycle and seasonal behaviour of quasi-two and five-day oscillations in the time variations of foF2;Apostolov;Ann. Geofis.,1994
3. Bloomfield, P., , Fourier Analysis of Time Series: An Introduction, John Wiley, New York, 1976,
4. Study of periodic components of wind velocity in the lower thermosphere above the equator (in Russian);Bulgakov;Geomagn. Aeron.,1973
5. Observation of the quasi two-day wave;Craig;J. Atmos. Terr. Phys.,1981