Low‐frequency electrostatic turbulence in the polar cap E region

Electrostatic turbulent fluctuations in a broad frequency band were observed in the polar cap E region over Greenland by an instrumented rocket payload. The fluctuations were detected by potential‐difference measurements on two sets of boom‐mounted spherical probes. The direction and magnitude of the phase velocity of the fluctuations are determined by standard correlation techniques. The driving mechanism for the turbulence is identified as the Farley‐Buneman instability. A characteristic velocity close to the sound speed is deduced while the direction of propagation deviates slightly from the E 0 × B 0 direction. A correlation time of 20–150 ms along the rocket trajectory is determined, indicating that the fluctuations are essentially statistically independent for altitude separations of >50 m. A conditional analysis of the signals indicates that to a good approximation they can be described by Gaussian statistics. The data exclude the possibility of wave steepening as a saturation mechanism for the linear instability. It is thus unlikely that wave energy is cascaded toward short wavelengths to be dissipated there.