On the hierarchy of processes contributing to equatorial spread F

Unstable plasma stratification in the twilight equatorial F region ionosphere is subject to plasma instabilities known collectively as equatorial spread F. Small-scale irregularities in electron density give rise to coherent VHF and UHF radio scatter during spread F while in situ spacecraft detect intermediate- and large-scale plasma structures. The authors present data from observations made over three years at the Jicamarca Radio Observatory and from the summer 1990 CRRES/EQUIS campaign which involved the Cornell 50 MHz radar interferometer (CUPRI) and the Altair UHF radar at Kwajalein, MI. Radar findings are correlated with spread F data from sounding rockets launched during the EQUIS project and from the Atmospheric Explorer E satellite. A review of fundamental fluid theory for the ionospheric interchange instability emphasizes dissipative and non-local effects that restrict linear instability to intermediate-scale wavelengths. A nonlinear fluid theory incorporating three wave interactions extends the range of instability to transitional and small scales, and renormalization group analysis offers a way to evaluate enhanced transport due to these nonlinearly excited modes. At large scales, circumstantial evidence suggests that internal gravity waves seed plasma upwellings and initiate topside spread F. Density and electric field spectra measured by the spread F sounding rockets exhibit inertial-convective and inertial-diffusive subranges. A model of quasi one-dimensional plasma turbulence reproduces the spectral indices and breaking scales observed by the rockets. Density power spectra from 30 AE-E orbits also possess convective and diffusive subranges, but their characteristic scale sizes are about 10 times larger than the rocket's. One-dimensional rocket and satellite power spectra combine to form a two-dimensional spectral model of F region irregularities which predicts VHF radar scattering cross-sections