Abstract
Abstract. We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).
Highlights
In order to understand the evolution of ice sheets, especially with respect to their contribution to sea-level rise, there is a need for numerical models which are able to capture the dynamics of sheet-shelf systems as a whole
PISM-PIK is based on the Parallel Ice Sheet Model (PISM; Bueler and Brown, 2009), which is a threedimensional thermodynamically-coupled shallow model using a finite-difference discretization
To avoid the zero velocity contribution of the ocean box adjacent to the last shelf box, when computing the staggered velocity at the calving front, we use the unstaggered shallow shelf approximation (SSA) velocity from this last shelf box and the front stress boundary condition. The properties of this alternative scheme for the pure-shallow ice approximation (SIA) mass continuity problem have been tested by comparison to the similarity solution described by Halfar (1983), and the deviations of this solution when using the PISM-PIK scheme are of the same order of magnitude as the ones when using the PISM base version (Bueler et al, 2005)
Summary
In order to understand the evolution of ice sheets, especially with respect to their contribution to sea-level rise, there is a need for numerical models which are able to capture the dynamics of sheet-shelf systems as a whole. We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research (PIK), a new hybrid model for marine ice sheets It combines the two approximations by adding the SIA and the SSA velocity on the whole sheet and shelf system in order to incorporate the different flow regimes in sheet, streams and shelves in a universal manner. PISM-PIK is based on the Parallel Ice Sheet Model (PISM; Bueler and Brown, 2009), which is a threedimensional thermodynamically-coupled shallow model using a finite-difference discretization These models are innovative in using the SSA as a sliding law for grounded ice, thereby avoiding discontinuities at the onset of sliding, and provide a framework for consistently modeling sheet-shelf systems. Speaking, PISMPIK is implemented as derived classes of the C++ code of the open-source Parallel Ice Sheet Model (PISM), version stable0.2 (The PISM authors, 2011)
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