Vertical propagating signatures of wave-type oscillations (2-and 6.5-days)in the ionosphere obtained from electron-density profiles

We investigate the meteorology of wave-type oscillations in the period rang e of 2- and 6.5-days observed in the middle latitude ionosphere at the alti tude range from 170 to 230 lan during 1998, with an emphasis on their verti cal propagation characteristics. The true height electron density profiles obtained at the Observatori de l'Ebre station (40.8 degreesN, 0.5 degreesE) have been used for this purpose. We found several events with occurrence o f wave packets with periods near 2- and 6.5-days during the summer half-yea r. These events display a clear vertical progression in the ionospheric F r egion, with vertical wavelengths larger than 100 km. The events exist with upward or downward propagation and the different values between the phase a nd group velocities indicate the degree of dispersion that the ionosphere i ntroduces on their propagation. The potential mechanisms linking the planet ary wave activity in the mesosphere/lower thermosphere with the wave events observed in the ionosphere are discussed in order to evaluate the most lik ely mechanism. (C) 2001 Elsevier Science Ltd. All rights reserved.