Strong turbulence and atmospheric waves in stellar occultations

Many of the problems of stellar occultation observations stem from the difficulty of determining the effects of realistic atmospheric structure on the lightcurves. General techniques for producing model lightcurves for a variety of realistic atmospheric irregularities, including turbulence and inertia-gravity waves, are presented and applied. Using numerical simulations which model the propagation of a wave through a phase-changing screen, the limit of strong scintillations for one-dimensional, Kolmogorov-like turbulence, both for a point source and for extended sources, is investigated in some detail, and significant departures from the behavior in the weak scintillation regime are found. The results are compared with published analytical results and recent occultation data. The effects of large-scale atmospheric waves with realistic horizontal structure are examined, and the reliability of the numerical inversion method of retrieving the true atmospheric vertical structure under circumstances of strong ray crossing and horizontal inhomogeneities is assessed. The simulations confirm that large-scale layered features of the atmosphere are accurately recovered; horizontally inhomogeneous structures (including turbulence) with coherence scale $\text{L ? (2πRH)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (where R = planetary radius and H = scale height) have little effect on the derived temperature profiles. It is concluded that analysis of occultations may eventually allow us to determine both the quasiglobal atmospheric structure and the statistical characteristics of small-scale refractivity variations.