DOES THE QBO AND THE MT. PINATUBO VOLCANIC-ERUPTION AFFECT THE GRAVITY-WAVE ACTIVITY IN THE LOWER IONOSPHERE

All existing data (similar to 6 years) on gravity wave activity, infer red from the nighttime A3 (oblique incidence on the ionosphere) radio wave absorption measurements in the lower ionosphere on 270 kHz at Pru honice in Central Europe, have been exploited to get information on th e effects of QBO phases and the Mt. Pinatubo volcanic eruption on the gravity wave activity in the winter half of the year. There appears to be an enhancement of gravity wave activity in the two winters just af ter the strong volcanic eruption of Mt. Pinatubo. This enhancement is remarkable for long-period waves (T = 2-3 hours). No clear effect of t he phase of QBO on the level of gravity wave activity has been found; a possible effect of QBO on the correlations between gravity wave acti vities in individual period bands is indicated. The results are limite d by a relatively short data series; however, no more data will be ava ilable.