A Numerical Study of Convection in a Condensing CO2 Atmosphere under Early Mars-Like Conditions

Abstract

Cloud convection of a CO 2 atmosphere where the major constituent condenses is numerically investigated under a setup idealizing a possible warm atmosphere of early Mars, utilizing a two-dimensional cloudresolving model forced by a fixed cooling profile as a substitute for a radiative process. The authors compare two cases with different critical saturation ratios as condensation criteria and also examine sensitivity to number mixing ratio of condensed particles given externally.When supersaturation is not necessary for condensation, the entire horizontal domain above the condensation level is continuously covered by clouds irrespective of number mixing ratio of condensed particles. Horizontal-mean cloud mass density decreases exponentially with height. The circulations below and above the condensation level are dominated by dry cellular convection and buoyancy waves, respectively. When 1.35 is adopted as the critical saturation ratio, clouds appear exclusively as intense, short-lived, quasiperiodic events. Clouds start just above the condensation level and develop upward, but intense updrafts exist only around the cloud top; they do not extend to the bottom of the condensation layer. The cloud layer is rapidly warmed by latent heat during the cloud events, and then the layer is slowly cooled by the specified thermal forcing, and supersaturation gradually develops leading to the next cloud event. The periodic appearance of cloud events does not occur when number mixing ratio of condensed particles is large.

Convection modeling of pure-steam atmospheres

“…Our simulations show that the atmospheric domain is generally comprised of two characteristic regions -a relatively quiescent, stratified upper condensing region and a vigorously convecting lower dry region, separated by the first condensation level. This is similar to those found in 2D convection simulations of Yamashita et al (2016). We start with describing horizontal-mean properties of the simulations.…”

“…demonstrated the novelty on large-scale dynamics arisen from mass transport by precipitation and constraints from the condensation thermodynamics, then presented general circulation models (GCMs) in nondilute conditions. Yamashita et al (2016) performed two-dimensional convection modeling for a pure-CO 2 atmosphere in Martian conditions. Ding & Pierrehumbert (2018) further demonstrated the importance of horizontal heat transport in determining global surface temperature variation of pure-steam atmospheres.…”

Troposphere-to-mesosphere microphysics of carbon dioxide ice clouds in a Mars Global Climate Model

“…Despite the limitations of a one-dimensional model, (Listowski et al, 2014) showed that an additional source of condensation nuclei (CN) was required in the mesosphere. One study of cloud-resolving simulations on CO 2 condensation has been performed for the Early Mars climate (Yamashita et al, 2016), but none in the current conditions of Martian polar regions. Moreover, the respective roles of topography (Tobie et al, 2003;Colaprete and Toon, 2002) and convection (Colaprete et al, 2008) in driving cloud formation and snowfall in the polar regions remain to be determined, as does the coupling of CO 2 and H 2 O cycles through heterogeneous nucleation of CO 2 on H 2 O crystals.…”

Moist Convection Is Most Vigorous at Intermediate Atmospheric Humidity

“…A longstanding challenge in climate science is to improve the crude treatment of such convective phenomena in general circulation models, which hampers predictions of critical quantities such as changes in local precipitation and the sensitivity of Earth's climate to CO 2 . Looking beyond Earth, there is strong evidence that moist convection-that is, convection coupled to phase changes of a condensible substance-factors into the past and present evolution of the majority of solar system atmospheres, including Venus (Kasting 1988), Mars (Wordsworth 2016;Yamashita et al 2016), Jupiter (Gierasch et al 2000), Saturn (Li & Ingersoll 2015), the ice giants (Hueso et al 2020), and Titan (Schneider et al 2012). Therefore, in order improve our understanding of contemporary Earth's climate and planetary climates more generally, there is a clear need to deepen and generalize our understanding of moist convective physics.…”