Titan's Haze Extinction Vertical Profiles Retrieved from Cassini/CIRS Limb Spectra

Aerosols in Titan's atmosphere play an important role in the radiative budget through the absorption of the UV and visible solar flux (heating of the stratosphere) and through their infrared emission (cooling of the atmosphere). Therefore the spatial distribution of haze, mainly governed by dynamics, has an impact on the temperature field and the radiative forcing, which in turn, affects the dynamics.

We investigated the thermal emission of the haze recorded by the Composite InfraRed Spectrometer (CIRS) aboard Cassini in the mid-infrared spectral region 600-1400 cm-1 (16.7 to 7 microns). We used nadir and limb spectra to retrieve vertically-resolved information in the range 120-300 km.

Préviously, an analysis of the Voyager data in this range by Coustenis and Bézard (1995, Icarus 115, 126-140) only provided a measurement of the haze absorption in the lower stratosphere with no vertical resolution and was limited to four wavenumbers (650, 900, 1000 and 1100 cm-1).

We determined the vertical profiles of the haze extinction (particle number density times cross section) from CIRS limb spectra acquired during sequences at given latitudes. These spectra were retrieved simultaneously by using a linear constrained inversion algorithm of the radiative transfer equation. This work was done for about 15 wavenumbers, which allows us to constrain the spectral variation of the haze opacity. We studied several latitudes in the northern and southern hemispheres in order to investigate the variation with latitude of the vertical extinction profiles and of the spectral characteristics of the haze opacity.