Abstract
Abstract Central stages in the evolution of rocky, potentially habitable planets may play out under atmospheric conditions with a large inventory of nondilute condensable components. Variations in condensate retention and accompanying changes in local lapse rate may substantially affect planetary climate and surface conditions, but there is currently no general theory to effectively describe such atmospheres. In this article, expanding on the work by Li et al., we generalize the single-component moist pseudoadiabat derivation in Pierrehumbert to allow for multiple condensing components of arbitrary diluteness and retained condensate fraction. The introduction of a freely tunable retained condensate fraction allows for a flexible, self-consistent treatment of atmospheres with nondilute condensable components. To test the pseudoadiabat’s capabilities for simulating a diverse range of climates, we apply the formula to planetary atmospheres with compositions, surface pressures, and temperatures representing important stages with condensable-rich atmospheres in the evolution of terrestrial planets: a magma ocean planet in a runaway greenhouse state; a post-impact, late-veneer-analog planet with a complex atmospheric composition; and an Archean Earth-like planet near the outer edge of the classical circumstellar habitable zone. We find that variations in the retention of multiple nondilute condensable species can significantly affect the lapse rate and in turn outgoing radiation and the spectral signatures of planetary atmospheres. The presented formulation allows for a more comprehensive treatment of the climate evolution of rocky exoplanets and early Earth analogs.
Highlights
The vertical temperature structure of an atmosphere is a primary determinant of planetary climate and surface evolution
In the case where the atmosphere is composed of a dry component mixed with “wet” components that can condense under the local temperature/pressure conditions, the latent heat released by condensation partially offsets the cooling by expansion work, leading to a “moist adiabat” with a lapse rate that is less steep than would be the case under dry conditions
We derive a moist pseudoadiabatic lapse rate formula that allows for any number of condensables, each with arbitrary diluteness and arbitrary retained condensate fraction, and we apply the formula to a set of test cases to illustrate the behavior of terrestrial atmospheres with multiple condensable components and variable retained condensate fraction
Summary
The vertical temperature structure of an atmosphere is a primary determinant of planetary climate and surface evolution. Ingersoll (1969) exploited entropy conservation to derive both an adiabat (with all condensate retained in the column) and a pseudoadiabat (with instantaneous rainout of all condensate) to describe atmospheres with a single nondilute condensable component in the context of modeling Venus undergoing a runaway greenhouse effect. Weidenschilling & Lewis (1973) used energy conservation to derive a single-component moist pseudoadiabat to model the Jovian planets, and Pierrehumbert (2010) took the same approach during a pedagogical discussion of atmospheric thermodynamics. We apply the energy conservation approach to derive a lapse rate formula that allows for multiple condensing components and the specification of arbitrary retained condensate fractions. For atmospheres with dilute condensable components, regardless of retained condensate fraction, the temperature–pressure profiles produced by this formula differ negligibly from those produced by the fully reversible adiabat derived in Li et al (2018).
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