(a) Surface temperature Ts (filled contours) for surface pressure ps = 5 bar and global mean surface optical depth τ = 5. The topography is plotted in blue dashed lines with a contour interval of 1000 m from 1000 m to 5000 m. The horizontal red dashed lines indicate the zone for tropical averaging (see Section 2.2). (b) Same as (a), but for the case with ps = 0.01 bar and τ = 0.01. The horizontal white dashed lines indicate the tropical averaging zone. (c) Relative surface lapse rate, γ (defined in Eq. 5), as a function of greenhouse effect, τ , and atmospheric thickness, ps. The data is sampled on a log-scale grid with τ = 0.003, 0.01, 0.1, 0.3, 1, 3, 5 and ps = 0.01, 0.1, 1, 5 bar. (d) The dependence of γ on τ when ps = 1 bar. Red solid (def): default simulation, obliquity equals zero, no atmospheric condensation, idealized topography, sensible heat flux enabled. Blue solid (obl20): as def, but with obliquity set to 20◦ . Blue dotted (atmo cond): as def, but with obliquity set to 20◦ , and a CO2-like atmospheric condensation is enabled. Magenta (MOLA): as def, but with Mars Orbiter Laser Altimeter topography. Cyan solid (w/o SH): as def, but with sensible heat flux disabled. Red dotted (2-column model): calculations from the simple two-column model (see Section 3.4). (e) As (d), but with varying ps and fixed τ = 0.1. Cyan dotted (fixed ρ in SH): as def, but the value of air density, ρ, is held fixed at the reference value for a 1-bar atmosphere in Eq. (3). — astro-ph.EP
Understanding surface temperature is important for habitability. Recent work on Mars has found that the dependence of surface temperature on elevation (surface lapse rate) converges to zero in the limit of a thin CO2 atmosphere.
However, the mechanisms that control the surface lapse rate are still not fully understood. It remains unclear how the surface lapse rate depends on both greenhouse effect and surface pressure. Here, we use climate models to study when and why “mountaintops are cold”.
We find the tropical surface lapse rate increases with the greenhouse effect and with surface pressure. The greenhouse effect dominates the surface lapse rate transition and is robust across latitudes. The pressure effect is important at low latitudes in moderately opaque atmospheres. A simple model provides insights into the mechanisms of the transition. Our results suggest that topographic cold-trapping may be important for the climate of arid planets.
Bowen Fan, Malte F. Jansen, Michael A. Mischna, Edwin S. Kite
Comments: 14 pages, 4 figures; accepted for publication on Geophysical Research Letters Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Geophysics (physics.geo-ph) Cite as: arXiv:2311.10151 [astro-ph.EP] (or arXiv:2311.10151v1 [astro-ph.EP] for this version) Submission history From: Bowen Fan [v1] Thu, 16 Nov 2023 19:12:56 UTC (2,388 KB) https://arxiv.org/abs/2311.10151 Astrobiology,
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