Weak-scattering theory for ionospheric scintillation

The VHF scintillations recorded at Varanasi (geomag. lat.4147558N; geomag. long.4154 7E) are mostly weak scintillations. Using a thin phase screen model for ionospheric irregularities, under the approximation of weak-scattering theory, attempts have been made to evaluate theoretically the time evolution of the scintillation index, S4, for different models of electron densities. The present formulation is used to study the impact of turbulence strength, Cs , and its outer scale length L0 on the variation of the scintillation index S4 . The S4 index increases with the increase in spectral index n but decreases with increasing outer scale length L0. Diurnal, seasonal and solar-cycle variations of the S4 index have also been studied and it is found that S4 lies between 0.2 and 0.9 as the Sun passes through solar maxima to solar minima. The results are found to be in good agreement with those reported by other workers