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Volume 11, issue 3 | Copyright
Geosci. Model Dev., 11, 843-859, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model description paper 06 Mar 2018

Model description paper | 06 Mar 2018

Isca, v1.0: a framework for the global modelling of the atmospheres of Earth and other planets at varying levels of complexity

Geoffrey K. Vallis1, Greg Colyer1, Ruth Geen1, Edwin Gerber2, Martin Jucker3, Penelope Maher1, Alexander Paterson1, Marianne Pietschnig1, James Penn1, and Stephen I. Thomson1 Geoffrey K. Vallis et al.
  • 1University of Exeter, Department of Mathematics, Exeter, UK
  • 2New York University, Courant Institute, New York, USA
  • 3University of Melbourne, School of Earth Sciences, Melbourne, Australia

Abstract. Isca is a framework for the idealized modelling of the global circulation of planetary atmospheres at varying levels of complexity and realism. The framework is an outgrowth of models from the Geophysical Fluid Dynamics Laboratory in Princeton, USA, designed for Earth's atmosphere, but it may readily be extended into other planetary regimes. Various forcing and radiation options are available, from dry, time invariant, Newtonian thermal relaxation to moist dynamics with radiative transfer. Options are available in the dry thermal relaxation scheme to account for the effects of obliquity and eccentricity (and so seasonality), different atmospheric optical depths and a surface mixed layer. An idealized grey radiation scheme, a two-band scheme, and a multiband scheme are also available, all with simple moist effects and astronomically based solar forcing. At the complex end of the spectrum the framework provides a direct connection to comprehensive atmospheric general circulation models.

For Earth modelling, options include an aquaplanet and configurable continental outlines and topography. Continents may be defined by changing albedo, heat capacity, and evaporative parameters and/or by using a simple bucket hydrology model. Oceanic Q fluxes may be added to reproduce specified sea surface temperatures, with arbitrary continental distributions. Planetary atmospheres may be configured by changing planetary size and mass, solar forcing, atmospheric mass, radiation, and other parameters. Examples are given of various Earth configurations as well as a giant planet simulation, a slowly rotating terrestrial planet simulation, and tidally locked and other orbitally resonant exoplanet simulations.

The underlying model is written in Fortran and may largely be configured with Python scripts. Python scripts are also used to run the model on different architectures, to archive the output, and for diagnostics, graphics, and post-processing. All of these features are publicly available in a Git-based repository.

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Short summary
The models that are used to describe the atmospheres of Earth and other planets are often very complicated. Although this is necessary for such things as weather prediction, it does not help in understanding. Furthermore, when studying other planets, there are insufficient data to warrant the use of complicated models. We have developed a framework that allows the construction of models of appropriate complexity for the problem at hand, and thus helps to actually model these atmospheres.
The models that are used to describe the atmospheres of Earth and other planets are often very...