SIMULATION OF A GRAVITY-WAVE OVER THE MIDDLE AND UPPER-ATMOSPHERE RADAR

We previously reported the observation of the passage of a gravity wave over the middle and upper atmosphere (MU) radar at nighttime during the strong magnetic storm of February 6-8, 1986, and suggested that the electron density changes seen in the F layer may have been due to the existence of an influx of ionization from above and the modulation of the assimilation of this flux into the ambient ionosphere by the wave-modulated neutral atmosphere. We use a simple, one-dimensional ionospheric model to investigate this possibility. We impose a flux into the top of the ionosphere and a temporal wavelike modulation of the neutral densities and compute the resulting equilibrium nighttime F layer density. We find that our mechanism reproduces qualitatively the wave behavior observed with the MU radar. To match the amplitude of the waves observed, however, we were compelled to impose a combination of large changes in the background level of the neutral molecular densities and in the wave amplitudes of the neutral densities. This process should be routinely considered in the interpretation of wave structure in the nighttime ionosphere.