A review of recent results on spread F theory

Although ionospheric Spread F was discovered four decades ago, only in the past few years has significant progress been made in the theoretical explanation of such phenomena. In particular, considerable effort has been expended to explain equatorial Spread F and the attendant satellite signal propagation scintillation phenomena. The present review dwells mainly in this low latitude area. The various linear plasma instabilities thought to initiate equatorial Spread F are discussed. Recent theoretical and numerical simulation studies of the nonlinear evolution of the collisional Rayleigh-Taylor instability in equatorial Spread F is reviewed. Analytical studies of rising equatorial Spread F bubbles in the collisional and collisionless Rayleigh-Taylor regime are discussed, as well as the nonlinear saturation of instabilities in these two regimes. Current theories on very small scale size irregularities observed by radar backscatter during equatorial Spread F and their relation to the larger wavelength scintillation causing irregularities are discussed. Application of turbulent theory to equatorial Spread F phenomena is reviewed and remaining problems to be dealt with at equatorial latitudes are summarized.