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Locally enhanced precipitation organized by planetary-scale waves on Titan

Nature Geoscience volume 4, pages 589–592 (2011)Cite this article

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Abstract

Saturn’s moon Titan exhibits an active weather cycle that involves methane1,2,3,4,5,6,7,8. Equatorial and mid-latitude clouds can be organized into fascinating morphologies on scales exceeding 1,000 km (ref. 9). Observations include an arrow-shaped equatorial cloud that produced detectable surface accumulation, probably from the precipitation of liquid methane10. An analysis of an earlier cloud outburst indicated an interplay between high- and low-latitude cloud activity, mediated by planetary-scale atmospheric waves11. Here we present a combined analysis of cloud observations and simulations with a three-dimensional general circulation model of Titan’s atmosphere, to obtain a physical interpretation of observed storms, their relation to atmosphere dynamics and their aggregate effect on surface erosion. We find that planetary-scale Kelvin waves arise naturally in our simulations, and robustly organize convection into chevron-shaped storms at the equator during the equinoctial season. A second and much slower wave mode organizes convection into southern-hemisphere streaks oriented in a northwest–southeast direction, similar to observations9. As a result of the phasing of these modes, precipitation rates can be as high as twenty times the local average in our simulations. We conclude that these events, which produce up to several centimetres of precipitation over length scales exceeding 1,000 km, play a crucial role in fluvial erosion of Titan’s surface.

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Figure 1: Titan’s clouds (right) are organized by planetary-scale waves that dominate storm activity in model simulations (centre).
Figure 2: Simulated precipitation and surface wind patterns in selected events during the equinoctial season (left column) and derived from statistical analysis (right column).
Figure 3: Space–time variability of simulated equatorial winds and precipitation averaged over ±10° latitude in the Titan GCM.

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Acknowledgements

E.P.T. is supported by NASA’s Cassini–Huygens mission.

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Authors and Affiliations

  1. Earth & Space Sciences, Atmospheric & Oceanic Sciences, University of California, Los Angeles, California 90095, USA

    Jonathan L. Mitchell

  2. Astronomy Department, University of California, Berkeley, California 94720, USA

    Máté Ádámkovics

  3. Department of Meteorology (MISU), Stockholm University, 106 91 Stockholm, Sweden

    Rodrigo Caballero

  4. Bert Bolin Centre for Climate Research, Stockholm University, 106 91 Stockholm, Sweden

    Rodrigo Caballero

  5. Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723, USA

    Elizabeth P. Turtle

Authors
  1. Jonathan L. Mitchell
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  2. Máté Ádámkovics
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  3. Rodrigo Caballero
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  4. Elizabeth P. Turtle
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Contributions

J.L.M. contributed experiment design, performed GCM simulation analysis, and wrote the manuscript. M.Á. and J.L.M. developed the algorithm for simulating clouds from the GCM, and M.Á. contributed radiative transfer analysis of the GCM. R.C. contributed the statistical analysis of the GCM simulation and J.L.M. and R.C. interpreted the model dynamics. E.P.T. contributed analysis of Cassini ISS cloud images.

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Correspondence to Jonathan L. Mitchell.

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Mitchell, J., Ádámkovics, M., Caballero, R. et al. Locally enhanced precipitation organized by planetary-scale waves on Titan. Nature Geosci 4, 589–592 (2011). https://doi.org/10.1038/ngeo1219

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