Pulsating Radio Auroral Echoes

Abstract

PULSATING auroral echoes have been described¹ which accompany sudden commencements, and attention has been directed to the fact that the periods of repetition of these echoes are close to those predicted for the bounce periods of hydromagnetic waves along the geomagnetic line of force terminating in the echo region. More exactly, the bounce periods considered are those for waves having angular frequencies ω which are considerably less than Ω₀ the minimum (equatorial plane) particle cyclotron frequency along the field line. Thus there can be an apparent agreement between echo period and hydromagnetic bounce period for ω ≃ 0 up to ω ≃ 0.1 Ω₀, beyond which the travel time increases as ω → Ω0.