The Structure of Titan's Stratosphere from the 28 Sgr Occultation

Abstract

at immersion and at emersion, at latitudes ranging from 46• S to 20• N, and are thus global features of the stratosphere. The profiles of temperature gradients exhibit a clear cutoff at the adiabatic lapse rate, indicating that fluctuations lead to marginal convective instabilities. Although ray crossing can also cause an apparent cutoff of the temperature gradients, we estimate it probably does not play an important role in the observed cutoff, at least for the larger structures under study. The vertical power spectra of fluctuations show a general power law behavior, with an exponent close to −3, between vertical wavelengths of ∼5 and 50 km. The finite stellar diameter and ray crossings can distort the real spectra, and we can only conclude that the original power spectra have slopes between −2 and −3. The horizontal structure of the atmosphere exhibits typical aspect (horizontal-to-vertical) ratios of 15-45, with a tail in the distribution with values as high as 100-200 for some structures. Finally, the horizontal spectrum of fluctuations is a power law with an exponent close to −4 (between horizontal wavelengths of ∼25 and 250 km), if we assume it is separable from the vertical spectrum.

Adaptive optics imaging of a stellar occultation by Titan

“…Nevertheless, an intensive photometric observing campaign led to 19 separate lightcurves, which were synthesized to create a sparsely-sampled map of the stellar flux across Titan's shadow. 7,8 The structure of the central flash recorded in these lightcurves was then modeled to provide a first estimate the zonal winds in Titan's lower stratosphere.…”

Observation and reduction of mutual events in the solar system

“…Indeed, besides spacecraft needs, it is necessary to predict star occultations by natural satellites (see, e.g., Sicardy et al 1999), or to detect a secular accelerations in the motion of these bodies, consequences of tidal effects.…”

A Fourier Optics Method for Calculating Stellar Occultation Light Curves by Objects With Thin Atmospheres

“…Elliot & Young (1992) extended the inversion to small planets (objects whose atmospheric scale heights were significant fractions of their radii). Sicardy et al (1999) developed a raytracing code that is used to fit candidate atmospheres to occultation light curves by forward modeling. French & Lovelace (1983) and Cooray & Elliot (2003) looked at intensity fluctuations in occultation light curves to determine whether they are caused by density fluctuations (turbulence versus gravity waves) or caustics caused by ray-crossing situations (e.g., due to the macroscopic figure of an object's atmosphere).…”