Propagation of the Pressure Waves Produced by Auroras

Abstract

As shown in previous paper (Maeda and Watanabe), periodic heating around E-region in the polar upper atmosphere by auroral particles can be regarded as the source of very long acoustic type atmospheric pressure waves observable at the ground. It was shown, however, that these pressure waves attenuate rapidly outside the source in the isothermal atmosphere. On the other hand, in the actual atmosphere, these waves propagate horizontally through the ducting, which consists of two channels, corresponding to the atmospheric temperature minima at the mesopause and the tropopause, respectively. It is shown that for the propagation of 100sec waves, upper channel is effective in summertime, while lower one is effective in winter in the polar upper atmosphere. It is also shown that the traveling pressure waves associated with auroral activity is not necessarily limited in the acoustic mode, but sometimes extended to gravity (thermobaric) mode. This is partly due to the existence of large positive lapes rates layers such as upper part of stratosphere and in the thermosphere. As a consequence, clear sinusoidal oscillations, which appear occasionally with periods of group velocity minima (around 5min), can be ascribed to Airy phase. As an example, the data obtained at the NBS-stations in Washington, D. C. on July 15, 1960 are shown with its preliminary results of power spectrum.