Abstract
Abstract. We describe and evaluate version 2.1 of the Community Ice Sheet Model (CISM). CISM is a parallel, 3-D thermomechanical model, written mainly in Fortran, that solves equations for the momentum balance and the thickness and temperature evolution of ice sheets. CISM's velocity solver incorporates a hierarchy of Stokes flow approximations, including shallow-shelf, depth-integrated higher order, and 3-D higher order. CISM also includes a suite of test cases, links to third-party solver libraries, and parameterizations of physical processes such as basal sliding, iceberg calving, and sub-ice-shelf melting. The model has been verified for standard test problems, including the Ice Sheet Model Intercomparison Project for Higher-Order Models (ISMIP-HOM) experiments, and has participated in the initMIP-Greenland initialization experiment. In multimillennial simulations with modern climate forcing on a 4 km grid, CISM reaches a steady state that is broadly consistent with observed flow patterns of the Greenland ice sheet. CISM has been integrated into version 2.0 of the Community Earth System Model, where it is being used for Greenland simulations under past, present, and future climates. The code is open-source with extensive documentation and remains under active development.
Highlights
As mass loss from the Greenland and Antarctic ice sheets has accelerated (Shepherd et al, 2012; Church et al, 2013; Hanna et al, 2013; Shepherd et al, 2017), climate modelers have recognized the importance of dynamic ice sheet models (ISMs) for predicting future mass loss and sea level rise (Vizcaino, 2014)
We describe and evaluate the Community Ice Sheet Model (CISM) version 2.1, a higher-order model that evolved from the Glimmer model (Rutt et al, 2009)
– Velocity: Glide solves the SIA only, but Glissade can solve several Stokes approximations, including the SIA, SSA, a depth-integrated higher-order approximation based on Goldberg (2011), and a 3-D higher-order approximation based on Blatter (1995) and Pattyn (2003)
Summary
As mass loss from the Greenland and Antarctic ice sheets has accelerated (Shepherd et al, 2012; Church et al, 2013; Hanna et al, 2013; Shepherd et al, 2017), climate modelers have recognized the importance of dynamic ice sheet models (ISMs) for predicting future mass loss and sea level rise (Vizcaino, 2014). – It should solve a range of Stokes approximations, including the SIA, SSA, and higher-order approximations Velocity solvers for these approximations are included in a new dynamical core called Glissade. – It should run efficiently – supporting whole-ice-sheet applications even on small platforms – and should scale to hundreds of processor cores, enabling century- to millennial-scale simulations with higher-order solvers at grid resolutions of ∼ 5 km or finer. Changes between versions 2.0 and 2.1 have been made primarily to support robust, accurate, and efficient Greenland ice sheet simulations, both as a stand-alone model and in CESM. These changes include a depth-integrated higherorder velocity solver We summarize the model results and suggest directions for future work (Sect. 6)
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