Determinations of Titan's Methane and Haze Variability

Details Determinations of Titan's Methane and Haze Variability Determinations of Titan's Methane and Haze Variability

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.3304p&link_type=abstract

American Astronomical Society, DPS meeting #41, #33.04

Physics

Optics

Scientific paper

Titan's atmosphere presents a complex and variable meteorology, with a variety of methane clouds detected in ground-based and Cassini near-IR observations. Its thick haze has been observed to vary seasonally, producing a strong variable effect on the radiative balance, dynamics and chemistry of the atmosphere. To understand how the methane cycle and the atmospheric variability, it becomes necessary to measure the methane and haze distribution.
In this work, we analyze complementary observations to constrain the variation of the methane and haze: 1) ground-based spectra that resolve the variation of the CH3D band at 1600 nm, obtained with the Near Infrared Spectrograph (NIRSPEC) with adaptive optics at the Keck II telescope, constrain the methane abundance in the lowest 10 kmof the atmosphere. 2) Cassini VIMS (Visual and Infrared Mapping Spectrometer) observations at 400-1600 nm sampleregions of varied methane and haze optical depths, enough to partially constrain the profiles of the haze, and the upper tropospheric (20-50 km altitude) methane.
The CH3D observations show no methane variation larger than 20% below 10 km altitude over 32S-32N latitudes. In the VIMS observations there is an ambiguity between the methane and haze abundances. The observations can be reproduced with no methane variation, and a haze density increase of 60% between 20S and 10S. The largest methane variation allowed by the data, derived assuming no haze variation with latitude, is a drop of 60% over latitudes 27S to 19N.
To further constrain the range of possible methane and haze profiles, we also present an initial analysis of VIMS limb observations, which resolve the vertical structure of the atmosphere, and thus separate the spectral changes that originate at the troposphere (mostaffected by the methane) from those that originate at the stratosphere (most affected by the haze). Work supported by NASA, CAPES and FAPESP.

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