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Two boundary layers in Titan’s lower troposphere inferred from a climate model

Nature Geoscience volume 5, pages 106–109 (2012)Cite this article

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Abstract

Saturn’s moon Titan has a dense atmosphere, but its thermal structure is poorly known. Conflicting information has been gathered on the nature, extent and evolution of Titan’s planetary boundary layer—the layer of the atmosphere that is influenced by the surface—from radio-occultation observations by the Voyager 1 spacecraft1 and the Cassini orbiter2, measurements by the Huygens probe3,4,5 and by dune-spacing analyses6. Specifically, initial analyses of the Huygens data suggested a boundary layer of 300 m depth with no diurnal evolution4, incompatible with alternative estimates of 2–3 km (refs 1, 2, 6). Here we use a three-dimensional general circulation model7, albeit not explicitly simulating the methane cycle, to analyse the dynamics leading to the thermal profile of Titan’s lowermost atmosphere. In our simulations, a convective boundary layer develops in the course of the day, rising to an altitude of 800 m. In addition, a seasonal boundary of 2 km depth is produced by the reversal of the Hadley cell at the equinox, with a dramatic impact on atmospheric circulation. We interpret fog that had been discovered at Titan’s south pole earlier8 as boundary layer clouds. We conclude that Titan’s troposphere is well structured, featuring two boundary layers that control wind patterns, dune spacing and cloud formation at low altitudes.

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Figure 1: Thermal structure of the first kilometres at the Huygens landing site, measured by the Huygens Atmospheric Structure Instrument and simulated by the GCM.
Figure 2: Simulated diurnal evolution of dry convection in the first kilometre during one typical Titan day at the Huygens site.
Figure 3: Simulated averaged potential-temperature profiles giving the seasonal evolution of the thermal structure for the first kilometres.

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Acknowledgements

We are grateful to F. Forget and R. Wordworth for advice and corrections to the paper. We thank N. Rochetin for discussions of the terrestrial climate. This study was supported by an Agence Nationale de la Recherche grant.

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Authors and Affiliations

  1. Laboratoire de Météorologie Dynamique, IPSL, CNRS/UPMC, Box 99, 75252 Paris Cedex 05, France

    Benjamin Charnay & Sébastien Lebonnois

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  1. Benjamin Charnay
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  2. Sébastien Lebonnois
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Contributions

S.L. and B.C. developed this version of the model. B.C. ran and analysed simulations. B.C. and S.L. wrote the manuscript.

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Correspondence to Benjamin Charnay.

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The authors declare no competing financial interests.

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Charnay, B., Lebonnois, S. Two boundary layers in Titan’s lower troposphere inferred from a climate model. Nature Geosci 5, 106–109 (2012). https://doi.org/10.1038/ngeo1374

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