Generation of atmospheric gravity waves associated with auroral activity in the polar F region

Relations between auroral activities and the generation of neutral-wind osc illations in the polar F region (150-300 km) were investigated using data f rom the European Incoherent Scatter (EISCAT) radar, the all-sky auroral cam era, and the IMAGE (International Monitor for Auroral Geomagnetic Effects) magnetograms. We dealt with two cases: observations on March 1, 1995 (case 1), and on March 29, 1995 (case 2). For both cases the field-aligned compon ent of the neutral-wind velocity estimated from EISCAT radar data had domin ant oscillation periods of 20-30 min, which are longer than the typical Bru nt-Vaisala period in the polar F region ( similar or equal to 13 min). The observed oscillations showed the downward propagation of the phase with tim e. These properties on the oscillation period and the phase are general one s of atmospheric gravity waves (AGWs). For case 1 the all-sky auroral image s obtained at Kilpisjarvi showed the auroral arc extending in an almost zon al direction near a distance estimated using wave parameters derived from t he equation of the dispersion relation for AGWs applicable to the observed oscillations. This suggested that the auroral arc appeared to be the effect ive generator of the observed oscillations. The comparison of observed phas e lines with predicted ones using models by Francis [1974] and Kato et al. [1977] showed agreements between the two for both cases. The comparison sug gests that effective parameters of the wave source in characterizing neutra l-wind oscillations would be the horizontal distribution of the wave source and the distance between the observing point and the source region. It was concluded that geomagnetic activities on March 1 and 29, 1995, in northern Scandinavia significantly related to the generation of the observed oscill ations. The conclusion implies that geomagnetic activities at high latitude s are an important source to generate AGWs, as indicated by previous theore tical studies.