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3 - Thermal structure of Titan's troposphere and middle atmosphere
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- By F. M. Flasar, NASA/Goddard Space Flight Center, R. K. Achterberg, University of Maryland, P. J. Schinder, Cornell University
- Edited by Ingo Müller-Wodarg, Imperial College London, Caitlin A. Griffith, University of Arizona, Emmanuel Lellouch, Observatoire de Paris, Meudon, Thomas E. Cravens, University of Kansas
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- Book:
- Titan
- Published online:
- 05 January 2014
- Print publication:
- 24 February 2014, pp 102-121
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Summary
3.1 Introduction
The thermal structure of an atmosphere is a product of radiative processes and dynamical transports. Indeed, the study of the distribution of temperature and pressure (as well as of winds and humidity) and its temporal behavior has played a key role in the development of terrestrial meteorology (Brunt, 1939). The distribution of gaseous constituents, produced by photo- or ion-chemistry, can affect atmospheric temperatures, if the gases are radiatively active, as does the distribution of clouds and aerosols. The redistribution of trace gases, clouds, and aerosols by atmospheric motions can materially affect an atmosphere's thermal structure.
Like Earth, Titan has a well defined troposphere, stratosphere, and mesosphere (the latter two layers comprise the middle atmosphere). Figure 3.1 depicts representative temperature profiles for the two atmospheres. Barometric pressure is used as the vertical coordinate. In these units the terrestrial and Titan profiles look roughly similar, except that Earth is much warmer, and its stratopause is at a higher pressure. Were the two sets of profiles depicted using geometric height instead of pressure as the vertical coordinate, Titan's temperature profile would look much more extended. This is mainly because its surface gravitational acceleration (g = 1.34 m s-2) is 14 percent that of Earth. Indeed, because Titan's atmosphere is so extended, the decrease of gravity with altitude matters.
4 - The general circulation of Titan's lower and middle atmosphere
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- By S. Lebonnois, Lawrence Livermore National Laboratory, F. M. Flasar, NASA/Goddard Space Flight Center, T. Tokano, Universität Zu Köln, C. E. Newman, Ashima Research
- Edited by Ingo Müller-Wodarg, Imperial College London, Caitlin A. Griffith, University of Arizona, Emmanuel Lellouch, Observatoire de Paris, Meudon, Thomas E. Cravens, University of Kansas
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- Book:
- Titan
- Published online:
- 05 January 2014
- Print publication:
- 24 February 2014, pp 122-157
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Summary
4.1 Introduction
The atmosphere of Titan shares a specific circulation feature with the atmosphere of Venus, the so-called superrotation. Most of the middle and lower atmosphere rotates significantly faster than the underlying solid body, with maximum zonal winds in the winter stratosphere of ~200 m/s. This chapter focuses on this dominant feature, through discussions of all aspects of Titan's atmospheric dynamics. In such a complex system, interactions are strong among atmospheric circulation, temperature structure, composition of the atmosphere, and clouds and haze distributions. Therefore, close links are made with other chapters of this book: Chapter 3 for temperature structure, Chapter 5 for composition, and Chapters 6 and 8 for clouds and haze distributions.
The altitude region covered by this chapter goes from the surface to the detached haze layer, a peculiar feature located at the top of the haze completely covering Titan (see Chapter 8), at an altitude of roughly 500 km. This region includes the troposphere, the stratosphere, and the lower mesosphere (see Chapter 3). The troposphere goes from the surface up to ~40 km (the tropopause), where the coldest temperatures are found on Titan. In this region, the atmospheric system includes the cycle of methane, presenting features similar to the hydrological system in the Earth atmosphere (see Chapters 5 and 6). The stratosphere goes from the tropopause to the stratopause, where temperatures peak, located at altitudes around 250 to 300 km (around 0.1 mbar).