Aspect angle dependence of mean Doppler velocities of 1‐m auroral plasma waves

Abstract

The mean phase velocity of 1‐m unstable plasma waves, excited by the two‐stream instability in the auroral E region, has been measured as a function of aspect angle. The normalized function is consistent with the predicted variation of the phase velocity at threshold of the instability. To reconcile the observations with theoretical predictions of the functional relationship for excitation far beyond threshold, an effective electron collision frequency 6 times the electron‐neutral collision frequency is required.