Vertical development of the 2-day wave in the midlatitude ionospheric F region

The altitude development of the 2-day wave in the ionospheric F region (fro m 170 to 230 km) has been investigated from the true height electron densit y profiles obtained at Observatori de l'Ebre station (40.8 degrees N, 0.5 d egrees E). We found five time intervals of enhanced activity of the 2-day w ave, bursts type, during 1995. The altitude variations of the 2-day wave pe riod, amplitude, and phase are presented. The phase and group velocities of the wave are evaluated for each case. The observed changes in the electron density indicate three types of dominant vertical propagation of the 2-day wave in the F region: (I) upward propagation of the wave, (2) simultaneous 2-day oscillation of the electron density at all altitude range under stud y, and (3) downward propagation of the wave. The potential mechanisms propo sed for explaining the vertical propagation of the 2-day wave in the ionosp heric F region are discussed in order to evaluate the most likely mechanism .