Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8134597 | Icarus | 2018 | 14 Pages |
Abstract
We have developed a seasonal radiative-dynamical model of Titan's stratosphere to investigate the temporal variation of temperatures in the 0.2-4 mbar range observed by the Cassini/CIRS spectrometer. The model incorporates gas and aerosol vertical profiles derived from Cassini/CIRS and Huygens/DISR data to calculate the radiative heating and cooling rate profiles as a function of time and latitude. At 20°S in 2007, the heating rate is larger than the cooling rate at all altitudes, and more specifically by 20-35% in the 0.1-5 mbar range. A new calculation of the radiative relaxation time as a function of pressure level is presented, leading to time constants significantly lower than previous estimates. At 6°N around spring equinox, the radiative equilibrium profile is warmer than the observed one at all levels. Adding adiabatic cooling in the energy equation, with a vertical upward velocity profile approximately constant in pressure coordinates below the 0.02-mbar level (corresponding to 0.03-0.05 cm sâ1 at 1 mbar), allows us to reproduce the observed profile quite well. The velocity profile above the â¼0.5-mbar level is however affected by uncertainties in the haze density profile. The model shows that the change in insolation due to Saturn's orbital eccentricity is large enough to explain the observed 4-K decrease in equatorial temperatures around 1 mbar between 2009 and 2016. At 30°N and S, the radiative model predicts seasonal variations of temperature much larger than observed. A seasonal modulation of adiabatic cooling/heating is needed to reproduce the temperature variations observed from 2005 to 2016 between 0.2 and 4 mbar. At 1 mbar, the derived vertical velocities vary in the range â0.05 (winter solstice) to 0.16 (summer solstice) cm sâ1 at 30°S, â0.01 (winter solstice) to 0.14 (summer solstice) cm sâ1 at 30°N, and 0.03-0.07 cm sâ1 at the equator.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Space and Planetary Science
Authors
Bruno Bézard, Sandrine Vinatier, Richard K. Achterberg,