Effects of auroral arcs on the generation of gravity waves in the auroral F-region

The relationship between auroral activity and the generation of gravity waves (GWs) in the auroral F-region (150–300 km) was investigated using data from the European Incoherent Scatter (EISCAT) radar and an all-sky camera at Kilpisjärvi (69.0° N, 20.8° E). The oscillations of neutrals observed with the EISCAT radar on 1 March 1995 had a dominant oscillation period of 24 min, which is longer than the typical Brunt-Väisälä period in the auroral F-region (≅ 13 min). According to the equation of the dispersion relation for GWs, the horizontal phase-velocity and the horizontal wavelength of the observed oscillations were about 110 m/s and about 160 km, respectively. The observed oscillations showed a downward propagation of the phase with time. Although we could not find conclusive evidence that the observed oscillations were GWs, the estimated characteristics of the observed oscillations were typical ones for the medium-scale GWs. The all-sky images showed that the auroral arc extended in an almost zonal direction near the source region estimated from the values of the observed wave-parameters. When the oscillations were compared with ones calculated using the Francis model, the phase lines of the modeled GWs showed agreement with those of the observed oscillations. Although we could not rule out the possibility of generating the observed oscillations by meteorological sources, enhancements of electromagnetic energy in association with the arc are considered to be strong candidate source to generate the observed oscillations.