Pulsating Aurorae and Infrasonic Waves in the Polar Atmosphere

Abstract

Pulsating aurorae are proposed as a source of the infrasonic waves associated with geomagnetic activity reported by Chrzanowski et al. One of the most plausible mechanisms for generating these long period pressure waves is the periodic heating of the upper air around the 100-km level by auroral bombardment, during pulsating visual aurorae. To see the energetic relation between source input and pressure change at sea level, some theoretical calculations are performed with a simple model of auroral distribution in an isothermal atmosphere. At least 100 erg cm⁻² sec⁻¹ of energy flux variation at auroral height is necessary to produce surface pressure amplitudes of the order of 1 dyne cm⁻² in this model. The intensity of the pressure waves in this model decreases rapidly outside of the region of auroral activity, indicating the importance of sound-ducts in the upper atmosphere for the propagation of these long period sonic waves.