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Weak-scattering theory for ionospheric scintillation

The VHF scintillations recorded at Varanasi (geomag. lat.=14°55'N; geomag. long. =154 °E) 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, S 4 , for different models of electron densities. The present formulation is used to study the impact of turbulence strength, C s , and its outer scale length L 0 on the variation of the scintillation index S 4 . The S 4 index increases with the increase in spectral index ν but decreases with increasing outer scale length L 0 . Diurnal, seasonal and solar-cycle variations of the S 4 index have also been studied and it is found that S 4 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.