Power-law wavenumber spectrum deduced from ionospheric scintillation observations

Abstract

Ionospheric scintillation observations near Boulder, Colorado, from the radio source Cygnus A were spectral analyzed at 26 MHz. The scintillation spectral features are used to calculate the diffraction effects and hence deduce the F-region irregularity wavenumber spectrum for sizes from about 4 to 0.6 km. The wavenumber spectrum on many occasions follows a power-law variation PN(κx) ∝ κx−βH+1, where βH typically varies from 3 to 4. An example based on the Gaussian spectrum shows that the extrapolation to radio frequencies much higher than 26 MHz will not explain the observed equatorial and auroral scintillations. Abrupt changes in electron density are required to support the higher-wavenumber spectral densities that cause these higher-frequency scintillations. These abrupt density changes can be represented by a power-law wavenumber spectrum. The scintillation-deduced power-law variation agrees with in-situ density spectra measurements from the Ogo 6 satellite. Several production mechanisms that follow a power-law variation are discussed. The measurement of the wavenumber spectrum will help explain the mechanism that produces small-scale irregularities.