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Water Vapor in Titan's Stratosphere from Cassini/CIRS Far-infrared SpectraSince the first detection of water vapor in Titan's stratosphere by disk-average observations from the Infrared Space Observatory (Coustenis et al. 1998) we report here the successful detection of stratospheric water vapor using the Cassini Composite Infrared Spectrometer (CIRS, Flasar et al. 2004). CIRS senses water emissions in the far infrared spectral region near 50 microns, which we have modeled using two independent radiative transfer codes (NEMESIS, Irwin et al 2008 and ART, Coustenis et al. 2007, 2010). From the analysis of nadir spectra we have derived a mixing ratio of (0.14 0.05) ppb at an altitude of 97 kilometers, which corresponds to an integrated (from 0 to 600 kilometers) surface normalized column abundance of (3.7 plus or minus 1.3) x 10(exp 14) molecules per square centimeter. In the latitude range 80 S to 30 N we see no evidence for latitudinal variations in these abundances within the error bars. Using limb observations, we obtained mixing ratios of (0.13 plus or minus 0.04) ppb at an altitude of 115 kilometers and (0.45 plus or minus 0.15) ppb at an altitude of 230 kilometers, confirming that the water abundance has a positive vertical gradient as predicted by photochemical models (e.g. Lara et al. 1996, Wilson and Atreya 2004, Horst et al. 2008); retrieved scaling factors (from approximately 0.1 to approximately 0.6) to the water profile suggested by these models show that water vapor is present in Titan stratosphere with less abundance than predicted.
Document ID
20120013575
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Cottini, V. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Nixon, C. A. (Maryland Univ. College Park, MD, United States)
Jennings, D. E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Anderson, C. M. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Gorius, N. (Catholic Univ. of America Washington, DC, United States)
Bjoraker, G. L. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Coustenis, A. (Observatoire de Paris France)
Teanby, N. A. (Bristol Univ. United Kingdom)
Achterberg, R. K. (Maryland Univ. College Park, MD, United States)
Bezard, B. (Observatoire de Paris France)
de Kok, R. (Space Research Organization Netherlands Utrecht, Netherlands)
Lellouch, E. (Observatoire de Paris France)
Irwin, J. (Oxford Univ. Oxford, United Kingdom)
Flasar, F. M. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Bampasidis, G. (Athens Univ. Greece)
Date Acquired
August 26, 2013
Publication Date
January 1, 2012
Subject Category
Astronomy
Report/Patent Number
GSFC.JA.6393.2012
Report Number: GSFC.JA.6393.2012
Distribution Limits
Public
Copyright
Public Use Permitted.

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