Hierarchical Modeling of Solar System Planets with Isca

Abstract

We describe the use of Isca for the hierarchical modeling of Solar System planets, with particular attention paid to Earth, Mars, and Jupiter. Isca is a modeling framework for the construction and use of models of planetary atmospheres at varying degrees of complexity, from featureless model planets with an atmosphere forced by a thermal relaxation back to a specified temperature, through aquaplanets with no continents (or no ocean) with a simple radiation scheme, to near-comprehensive models with a multi-band radiation scheme, a convection scheme, and configurable continents and topography. By a judicious choice of parameters and parameterization schemes, the model may be configured for fairly arbitrary planets, with stellar radiation input determined by astronomical parameters, taking into account the planet's obliquity and eccentricity. In this paper, we describe the construction and use of models at varying levels of complexity for Earth, Mars and Jupiter using the primitive equations and/or the shallow water equations.Atmosphere 2019, 10, 803 2 of 21 with a nominal troposphere that in some respects is quite Earth-like: its temperature falls from about 320 K at its base to 53 K at its top, possibly containing both water and ammonia/methane clouds.Beyond our Solar System, there are likely billions of planets in our galaxy alone, with over 4000 confirmed planets at the time of writing (NASA Exoplanet Archive [7]). Many of these planets are undoubtedly similar to those mentioned above, but some surely different-tidally-locked "Hot-Jupiters", being but one example class [8,9].Given such a diversity-a diversity far greater than that of the stars around which the planets orbit-the question arises as to how such planets should be modeled. On Earth, we may reasonably seek to model Earth's atmosphere and climate in some detail using very complex models-such as comprehensive General Circulation Models (GCMs) or Earth System Models (ESMs)-in which we seek to put the most realistic representation of physical and chemical (and sometimes biological) processes possible. Such models are extensions of those used for weather forecasting and, similar to weather forecast models, one goal is to be as quantitatively accurate as possible.However, several factors suggest that such an approach is not always ideal for planetary atmospheres:

Terrestrial evaporation and global climate: lessons from Northland, a planet with a hemispheric continent

“…Simulations with "jello" continents in an Earth-like configuration generally capture the presentday climate well (Geen et al 2018;Thomson and Vallis 2019), but might be too idealized for studying precipitation change in response to CO 2 forcing in some tropical regions such as the Amazon basin (Pietschnig et al 2019). While the reduction in evaporation due to the presence of land leads to cooling in TRACMIP, similar to what we see from Aqua to NorthlandDark or from NorthlandBright to NorthlandDry, the mechanisms for the cooling are different.…”

“…equivalent to a 2m mixed layer ocean). This is larger than the heat capacity of land on Earth, but Isca simulations with realistic continents have been shown to compare well with reanalyses when these heat capacities are used (Thomson and Vallis 2019;Geen et al 2018). The roughness length is 0.2 mm, and is uniform over land and ocean in our simulations.…”

SimCloud version 1.0: a simple diagnostic cloud scheme for idealized climate models

“…We also use the scheme in an idealized GCM, Isca (Vallis et al, 2018), configured with a realistic distribution of continents to explore the geographical variability of the cloud schemes. Idealized models have a number of advantages in investigating physical processes, especially when set within a hierarchy connecting them to more comprehensive models (e.g., Maher et al, 2019;Thomson and Vallis, 2019). We find that a relative-humidity scheme alone is unable to capture the subtropical low cloud distribution but that this can be readily improved by the addition of a scheme that takes into account inversion strength.…”

“…The convection parameterization used in this study is the simplified Betts-Miller scheme from Frierson (2007). The SOCRATES (Suite of Community Radiation Codes based on Edwards & Slingo) radiation scheme (Edwards and Slingo, 1996;Manners et al, 2015) is employed for the radiation transfer calculation as in Thomson and Vallis (2019). Spectral files with 9 longwave bands and 6 shortwave bands are used, which are those used in the Unified Model's Global Atmosphere version 7 (Walters et al, 2019).…”

SimCloud version 1.0: a simple diagnostic cloud scheme for idealized climate models

“…The prognostic approach is to explicitly calculate the cloudrelated variables (e.g., cloud water content) based on associated physical processes that constitute to the source and sink terms in the prognostic equations (e.g., Tiedtke, 1993). Statistical cloud schemes calculate the cloud fraction and condensate content consistently once the sub-grid probability density functions (PDFs) of certain variables, such as total water specific humidity, are determined (e.g., Sommeria and Deardorff, 1977;Smith, 1990;Tompkins, 2002;Park et al, 2014;Qin et al, 2018;Tsang and Vallis, 2018).…”