Abstract
Abstract. In this paper, we consider possibilities for studying the anisotropy of small-scale air density irregularities using satellite observations of bi-chromatic stellar scintillations during tangential occultations. Estimation of the anisotropy coefficient (the ratio of the characteristic horizontal to vertical scales) and other atmospheric parameters is based on the comparison of simulated/theoretical and experimental auto-spectra and coherency spectra of scintillation. Our analyses exploit a 3-D model of the spectrum of atmospheric inhomogeneities, which consists of anisotropic and isotropic components. For the anisotropic component, a spectral model with variable anisotropy is used. Using stellar scintillation measurements by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers, estimates of the anisotropy coefficient are obtained for atmospheric irregularities with vertical scales of 8–55 m at altitudes of 43–30 km. It is shown that the anisotropy increases from about 10 to 50 with increasing vertical scales.
Highlights
Random irregularities of air density and temperature, which are generated by internal gravity waves (GWs) and turbulence, cause fluctuations in light intensity when a star is observed through the atmosphere
The model of saturated gravity waves is used for description of the anisotropic component, and the Kolmogorov model is used for the description of the isotropic component (Gurvich and Brekhovskikh, 2001; Gurvich and Kan, 2003b)
This method allows reconstructing all parameters of the 3-D spectral model, except for the anisotropy coefficient η of the anisotropic component (η is defined as a ratio of characteristic horizontal to vertical scale) and η = Const 1 was assumed in retrievals
Summary
Random irregularities of air density and temperature, which are generated by internal gravity waves (GWs) and turbulence, cause fluctuations in light intensity (scintillation) when a star is observed through the atmosphere. Stellar scintillation measurements on board the orbital station MIR (Alexandrov et al, 1990; Gurvich and Kan, 2003a, b) have shown that there are two types of irregularities in the stratosphere: relatively large anisotropic irregularities and small-scale isotropic ones Based on these data, an empirical model of the 3-D wave-number spectrum of air density irregularities has been developed. The main objective of the present paper is to estimate the anisotropy coefficient of small-scale irregularities by measuring the horizontal spectra of chromatic scintillations of stars during tangential occultation by GOMOS/ENVISAT.
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