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Abstract Saturn’s largest moon, Titan, has an Earth-like volatile cycle, but with methane playing the role of water and surface liquid reservoirs geographically isolated at high latitudes. We recreate Titan’s characteristic dry hydroclimate at the equator of an Earth-like climate model without seasons and with water as the condensable by varying a small set of planetary parameters. We use three observationally motivated criteria for Titan-like conditions at the equator: 1) the peak in surface specific humidity is not at the equator, despite it having the warmest annual-mean temperatures; 2) the vertical profile of specific humidity in the equatorial column is nearly constant through the lower troposphere; and 3) the relative humidity near the surface at the equator is significantly lower than saturation (lower than 60%). We find that simply reducing the available water at the equator does not fully reproduce Titan-like conditions. We additionally vary the rotation period and volatility of water to mimic Titan’s slower rotation and more abundant methane vapor. Longer rotation periods coupled with a dry equatorial surface meet fewer of the Titan-like criteria than equivalent experiments with shorter rotation periods. Experiments with higher volatility of water meet more criteria than those with lower volatility, with some of those with the highest volatility meeting all three, demonstrating that an Earth-like planet can display Titan-like climatology by changing only a few physical parameters.
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Seasons, Shorelines, and Their Effects on the Tropical Circulation and Hydrological Cycle
Abstract This work is a direct continuation of McKinney et al., who attempted to create a planet with Earth-like temperatures and physical properties but with precipitation and circulation patterns that were Titan-like. McKinney et al. attempted to do so by changing only three basic planetary parameters: the ratio of dry land to ocean on the surface, the rotation period, and the volatility of the condensable. Each of these parameters is varied from an Earth-like value to a Titan-like one to analyze the climate transition between these two planetary archetypes. In this work, we expand on McKinney et al. by including a seasonal cycle and increasing the number of diagnostic criteria for determining Titan-like dynamics. The simulations use Earth-like obliquity and an Earth-like solar constant. We find that the presence of a dry land strip extending to at least 55°N/S is most effective at creating Titan-like climatic conditions on an otherwise Earth-like planet, such as high-latitude summer precipitation maxima and a low-humidity equator. In contrast, slow rotation and high atmospheric vapor abundance have minimal climatic impacts despite being characteristic features of Titan. Our experiments show that it is not difficult to produce distinctly Titan-like features in an Earth-like GCM with minimal changes to its fundamental parameters. This suggests that Earth-like planets could have a large range of global climate states throughout their history just through changes in topography. Similarly, Titan may have experienced more Earth-like climate states in periods where its tropics were wetter.
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- Award ID(s):
- 2310364
- PAR ID:
- 10533209
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 81
- Issue:
- 8
- ISSN:
- 0022-4928
- Format(s):
- Medium: X Size: p. 1475-1494
- Size(s):
- p. 1475-1494
- Sponsoring Org:
- National Science Foundation
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