Nonlinear saturation and angular rotation of instabilities in the E layer


  • J. Weinstock,

  • T. D. Rognlien


Two plasma instabilities have been identified as causing small-scale irregularities in the equatorial E layer. These instabilities are referred to as the two-stream and gradient drift instabilities. Here a unified calculation is made of the saturated density amplitudes of these instabilities. The present nonlinear saturation mechanism is referred to as perturbed orbits or diffusing orbits. The density fluctuations required for this saturation are roughly 10% for the gradient drift instability and 1% for the two-stream instability. This agrees with rocket measurements over India. In addition, a calculation is made of the frequency shift of two-stream waves. This shift is a nonlinear effect due to the slowing down of electrons by the unstable waves, and could be viewed as an enhanced friction. It is shown that this frequency shift will cause the angular spectrum of the two-stream waves to be rotated upwards or downwards, depending on the direction of the electrojet. Such rotations have been observed by radar.