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 Observatori de l'Ebre station (40.8° N, 0.5° E) during a rapid sequence vertical ionospheric sounding campaign have been used. A gravity wave like oscillation in the ionosphere has been characterized after the maximum 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 altitude 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 found to exist in the variations of the ionospheric parameters, being coherent with the oscillations characterized in the plasma frequency variations. The source-origin of the event was located around the transition region between F₁ and F₂ layers and from that altitude the wave propagates vertically drawing energy upwards and downwards simultaneously. The decreasing/increasing solar ionizing radiation and the cooling/heating processes linked with the solar eclipse are discussed as a possible mechanism to explain the gravity wave event observed in the electron density and dynamics of the ionosphere.