Origin and development of vertical propagating oscillations with periods of planetary waves in the ionospheric F region

Starting from previous results of vertical propagating 6.5-day oscillations observed in the F region of the ionosphere during 1998, we investigated th eir possible forcing from both the planetary wave activity of the neutral w inds in the mesosphere/lower thermosphere and the geomagnetic activity. For this purpose we used the electron density profiles and geomagnetic field c omponents obtained at Observatori de I'Ebre station (40.8 degreesN, 0.5 deg reesE), the mesopause region neutral wind data obtained at Collm Observator y (52 degreesN, 15 degreesE) and the 3-hourly geomagnetic index Ap. From th e four events of 6.5-day oscillations observed in the ionosphere, we found that two of them are contemporary with two events of 6.5-day period in the neutral winds and the coherency between the neutral winds and ionosphere va riations at 6.5-day periods is very large. The other ionospheric events are contemporary with the existence of two geomagnetic storms and the coherenc y between the ionospheric and geomagnetic activity variations is very large at periods of 6.5 days. The potential mechanisms linking the geomagnetic a ctivity variations and the planetary wave activity of the neutral winds in the mesosphere/lower thermosphere with the wave events observed in the iono sphere are discussed in order to explain the possible origin of the ionosph eric waves. (C) 2001 Elsevier Science Ltd. All rights reserved.