Spatial and temporal variations in Titan's surface temperatures from Cassini CIRS observations |
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| Authors: | V Cottini CA Nixon DE Jennings R de Kok NA Teanby PGJ Irwin FM Flasar |
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| Institution: | 1. Department of Astronomy, University of Maryland at College Park, College Park, MD 20742, USA;2. NASA Goddard Space Flight Center, Solar System Exploration Division, Planetary Systems Laboratory—Code 693, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA;3. SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands;4. Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford OX1 3PU, UK |
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| Abstract: | We report a wide-ranging study of Titan's surface temperatures by analysis of the Moon's outgoing radiance through a spectral window in the thermal infrared at 19 μm (530 cm?1) characterized by lower atmospheric opacity. We begin by modeling Cassini Composite Infrared Spectrometer (CIRS) far infrared spectra collected in the period 2004–2010, using a radiative transfer forward model combined with a non-linear optimal estimation inversion method. At low-latitudes, we agree with the HASI near-surface temperature of about 94 K at 10°S (Fulchignoni et al., 2005). We find a systematic decrease from the equator toward the poles, hemispherically asymmetric, of ～1 K at 60° south and ～3 K at 60° north, in general agreement with a previous analysis of CIRS data (Jennings et al., 2009), and with Voyager results from the previous northern winter. Subdividing the available database, corresponding to about one Titan season, into 3 consecutive periods, small seasonal changes of up to 2 K at 60°N became noticeable in the results. In addition, clear evidence of diurnal variations of the surface temperatures near the equator are observed for the first time: we find a trend of slowly increasing temperature from the morning to the early afternoon and a faster decrease during the night. The diurnal change is ～1.5 K, in agreement with model predictions for a surface with a thermal inertia between 300 and 600 J m?2 s?1/2 K?1. These results provide important constraints on coupled surface–atmosphere models of Titan's meteorology and atmospheric dynamic. |
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