<title>Spectra of strong scintillation caused by large-scale anisotropic stratospheric irregularities, in spacecraft-based observations</title>

Abstract

Numerical methods are used to investigate one- and two-dimentional spectra of strong scintillation caused by atmospheric irregularities associated with the internal gravity waves. Calculations are based on the model of statistically uniform phase screen. The irregularities possess specific features: their spectra are anisotropic and they are much larger than the size of a Fresnel zone in the observation plane. The conditions are specified under which the theory of small perturbations can be applied to calculate weak-scintillation spectra. It is shown that large-scale part of the scintillation spectra can be appropriately described using the theory of perturbations even for strong scintillation, when the rms value of the relative intensity fluctuations β₀ , calculated with the perturbations method, equals 10. At the same time, the perturbations method is not applicable for the description of the small-scale portion of scintillation spectra even at β₀ >0.3. It was found that the product of 1-D spectral density and a wave number has a "plateau" interval. The level of this plateau depends only on the parameter β₀ , provided that this parameter is smaller than one-third of the squared anisotropy coefficient. Within the interval of large wave numbers, the maximum point of the scintillation spectra is formed, with the value of 0.242. The conditions are formulated for small-scale part of the spectrum to become normal; under these conditions, the scintillation spectrum is equal to that of the squared coherence function on the phase screen.