Vertical structure of a gravity wave like oscillation in the ionosphere generated by the solar eclipse of August 11, 1999

The dependence in altitude and time of the ionospheric electron density and its altitude variations during the solar eclipse of August 11, 1999, have been studied. The true height electron density profiles recorded at the Obs ervatori de l'Ebre station (40.8 degrees N, 0.5 degrees E) during a rapid s equence vertical ionospheric sounding campaign have been used. A gravity wa ve like oscillation in the ionosphere has been characterized after the maxi mum of solar occultation by the Moon. The event is clearly seen in both the plasma frequency and in the altitude variations of the F region in the alt itude range from 150 to 250 km, and it has a dominant oscillating period T= 57.5 min. The oscillation activity linked with the gravity wave event is fo und to exist in the variations of the ionospheric parameters, being coheren t with the oscillations characterized in the plasma frequency variations. T he source-origin of the event was located around the transition region betw een F, and FZ layers and from that altitude the wave propagates vertically drawing energy upwards and downwards simultaneously. The decreasing/increas ing solar ionizing radiation and the cooling/heating processes linked with the solar eclipse are discussed as a possible mechanism to explain the grav ity wave event observed in the electron density and dynamics of the ionosph ere.