Analysis of light curves from the 2003 Nov 14 occultation by Titan of TYC 1343-1855-1

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 17-18).We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u', g', and i' (358, 487, and 758 nm, respectively). The occultation probed latitudes 2°S and 1°N during immersion and emersion, respectively. A prominent central flash was present in only the i' filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i' profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396 ± 7 km and 401 ± 20 km (u' immersion and emersion); 354 ± 7 km and 387 ± 7 km (g' immersion and emersion); and 336 ± 5 km and 318 ± 4 km (i' immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3 ± 0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541-563].by Angela M. Zalucha.S.M

The effect of topography on the Martian atmospheric circulation and determining Pluto's atmospheric thermal structure from stellar occultations

Thesis (Ph. D. in Atmospheric Science)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 143-152).Previous work with Mars General Circulation Models (MGCMs) has shown that the north-south slope in Martian topography causes asymmetries in the Hadley cells at equinox and in the annual average. To quantitatively solve for the latitude of the dividing streamline and poleward boundaries of the cells, the Hadley cell model of Lindzen and Hou [1988, J. Atmos Sci. 45, 216-2427] was modified to include topography. The model was thermally forced by Newtonian relaxation to an equilibrium temperature profile calculated with daily averaged solar forcing at constant season. Two sets of equilibrium temperatures were considered that either contained the effects of convection or did not. When convective effects were allowed, the presence of the slope component shifted the dividing streamline upslope, qualitatively similar to a change of season in the original Lindzen and Hou [1988 (flat) model. The modified model also confirmed that the geometrical effects of the slope are much smaller than the thermal effects of the slope on the radiative-convective equilibrium temperature aloft. The results are compared to a simple MGCM forced by Newtonian relaxation to the same equilibrium temperature profiles, and the two models agree except at the winter pole near solstice. The simple MGCM results for radiative-convective forcing also show an asymmetry between the strengths of the Hadley cells at northern summer and northern winter solstices. The Hadley cell weakens with increasing slope steepness at northern summer solstice, but has little effect on the strength at northern winter solstice. In the second part, a radiative-conductive model from Strobel et al. [1996, Icarus 120, 266-289] was used to least-squares fit Pluto stellar occultation light curve data. This model predicted atmospheric temperature based on surface temperature, surface pressure, surface radius, and methane and carbon monoxide mixing ratios, from which model light curves were able to be calculated. The model improves upon previous techniques for deriving Pluto's atmospheric thermal structure from stellar occultation light curves by calculating temperature (as a function of height) caused by heating and cooling by species in Pluto's atmosphere, instead of a general assumption that temperature follows a power law with height or some other idealized function. Fits were able to be performed for model surface radius, surface pressure, and methane mixing ratio with one of the 2006 datasets and for surface pressure and methane mixing ratio for other datasets from the years 1988, 2002, 2006, and 2008. It was not possible to fit for carbon monoxide mixing ratio and surface temperature because the light curves are not sensitive to these parameters. The model surface radius, under the assumption of a stratosphere only (i.e. no troposphere) model and radiative equilibrium, was determined to be 1180 +20/-10 kin, where the error bars are those from the formal least-squares fit and errors on the closest approach distance. The methane mixing ratio results are more scattered with time and are in the range of 0.18% to 1.78%. The surface pressure results show an increasing trend with time, although it is not as dramatic as the factor of 2 from previous studies. Finally, I demonstrate with a preliminary Pluto general circulation model the importance of the effect of atmospheric circulation on temperature and surface pressure.by Angela Marie Zalucha.Ph.D.in Atmospheric Scienc