Model for Prediction Across Scales-Land Ice version 6: A variable resolution ice sheet model for Earth system modeling using Voronoi grids

We introduce a new, variable resolution land ice model built using the Model for Prediction Across Scales (MPAS) -- a mature framework for developing variable resolution Earth System Model components -- as well as the Trilinos and Albany solver libraries.  The Model for Prediction Across Scales-Land Ice (MPASLI) ice sheet model uses variable resolution, unstructured Voronoi grids on a plane or sphere.  MPASLI includes a Blatter-Pattyn three-dimensional, first-order momentum balance solver by linking to the Albany/FELIX velocity solver referenced above, as well as an explicit shallow ice velocity solver. Evolution of ice geometry and tracers is handled through an explicit first-order horizontal advection scheme with vertical remapping. Evolution of ice temperature is treated using operator splitting of vertical diffusion and horizontal advection and can be configured to use either a temperature or enthalpy formulation.  MPASLI includes a mass-conserving subglacial hydrology model that supports distributed and/or channelized drainage and can optionally be coupled to ice dynamics. Options for calving include "eigencalving", which assumes calving rate is proportional to extensional` strain rates.
MPASLI is evaluated against commonly used exact solutions and community benchmark experiments and shows the expected accuracy. We report first results for the MISMIP3d benchmark experiments for a Blatter-Pattyn type model and show that results fall in-between those of models using Stokes flow and L1L2 approximations. We demonstrate running the model for a realistic Antarctic Ice Sheet problem for 2000 years at 20 km resolution.  MPASLI is the glacier component of the Energy Exascale Earth System Model (E3SM) version 1, and we describe current and planned coupling to other components.