The vertical wave number spectrum of topside equatorial spread F: Estimates of backscatter levels and implications for a unified theory


  • M. C. Kelley,

  • R. C. Livingston,

  • C. L. Rino,

  • R. T. Tsunoda


A wave number spectrum for plasma density fluctuations in decaying equatorial spread F covering 5 orders of magnitude in spatial scale and 12 orders of magnitude in spectral power is presented. The outer scale is found, as is the spectral transition between a shallow spectral form (slope < 2) at intermediate scales and a steep spectrum at smaller scales. The characteristic features of the spectrum are discussed and related to the physical processes operating in several regimes. A unified model is discussed involving aeronomic effects and neutral atmospheric dynamics at the largest scales, a generalized Rayleigh-Taylor plasma instability at intermediate scales, and a cascade of wave energy involving drift waves at transitional wavelengths. Open questions still remain concerning free energy sources near 1 km wavelength and at wavelengths less than a meter. Estimates of backscatter levels using the plasma density fluctuation spectra are consistent with Jicamarca and Altair radar observations except in topside regions of low plasma density, where in situ data at very short wavelengths are needed.