Ice-Sheet / Ocean Interaction Model for Greenland Fjords Using High-Order Discontinuous Galerkin Methods

Synopsis: This interdisciplinary project focuses on the physics of ice-sheet/ocean interaction in the pan-Arctic region to advance understanding and prediction of (i) increased mass loss from the margins of the Greenland ice sheet (GrIS), (ii) the contribution of increased freshwater flux from the GrIS, to sea level rise and (iii) its impact on the North Atlantic circulation and climate. It aims to address one of the key outstanding challenges in modeling studies of climate change and sea level rise related to the physics of ice-sheet/ocean interaction in narrow, elongated fjords around Greenland and in other polar regions. Intellectual Merit: We propose to build a separate, high-resolution module for use in Earth System models (ESMs) to realistically represent the fjord bathymetry and coastlines and the fine-scale processes occurring within the fjord and at the ice shelf interface, using discontinuous Galerkin (DG) methods. We will develop a non-hydrostatic, DG model for the equations governing the physics of the problem, leveraging the machinery developed for the Non-hydrostatic Unified Model of the Atmosphere (NUMA; Kelly and Giraldo 2012). We will account for the stationary ice-shelf with sub-shelf ocean interaction, basal melting and subglacial meltwater influx, with boundary conditions at the surface to account for floating sea ice. We will first test this fjord DG (FDG) module in a single fjord (e.g. Sermilik Fjord) and validate its performance. FDG will be interfaced with a CPL7 coupler, which will be used to prescribe boundary conditions for the module emulating coupling with full climate model. Following successful completion of this project, FDG can be used within the Accelerated Climate Modeling for Energy (ACME) project. It can be expanded to many fjords around Greenland, and made available for general use in the Community Earth System Model (CESM) and in other ESMs. Broader Impact: This project will develop and test a new module, allowing two-way coupling of ice-sheet and ocean to account for currently missing, small-scale processes and ice-sheet/ocean interactions in narrow, elongated fjords, for use in global and regional ESMs. It will complement both ice-sheet and ocean modeling efforts within CESM and ACME, involving several DOE laboratories. This project leverages existing successful research by the PIs in both high resolution climate modeling and advanced mathematical methods to address increasing societal needs for improved seasonal to decadal arctic climate predictions. It will also facilitate progress in understanding and prediction of climate change and sea-level rise by improving the realism of simulations for ice-sheet/ocean interactions, while reducing the computational cost of running a single ocean model (OGCM) with grid cell resolution varying by 4-5 orders of magnitude (from ~100 km to meters) required to account for fjord and large scale ocean dynamics. It will also narrow the range of spatial scales over which the existing and new ocean sub-grid parameterizations will need to operate to simulate both the large scale ocean circulation and small scale processes in glacial fjords at decadal/millennial time scales. The FDG module will be implemented, tested and readily applicable to any future ocean (e.g. MPAS-Ocean) and ice-sheet models. This module can be expanded to handle non-stationary ice-shelf effects using dynamic mesh adaptation techniques already developed for NUMA. As such, this project directly addresses key requirements of the DOE Biological and Environmental Research (BER) program, especially the Climate and Environmental Sciences subprogram, aimed at understanding the basic physical processes of the Earth's System and at enhancement and evaluation of the quantitative models necessary to predict natural climatic variability at global and regional scales. It also responds to the Scientific Discovery through Advanced Computing (SciDAC) program goals by developing and testing of a model for coupling of ice-sheet and ocean model components using computationally advanced methods. Furthermore, much of the new technology being proposed herein (high-order DG methods, adaptivity, implicit solvers, etc.) overlap with many of the state-of-the-art techniques mentioned in the recent DOE ASCR report entitled 'Applied Mathematics Research in Exascale Computing' (Dongarra et al. 2014). Finally, this project addresses key processes of ocean-fjord-glacier-climate interactions identified in the recent report from the US CLIVAR/NSF workshop on 'Understanding the Responses of Greenland's Marine-Terminating Glaciers to Oceanic and Atmospheric Forcing' (Heimbach et al. 2014). References: Dongarra, J., J. Hittinger, J. Bell, L. Chacon, R. Falgout, M. Heroux, P. Hovland, E. Ng, C. Webster, S. Wild (2014), Applied Mathematics Research for Exascale Computing, U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research Program, Heimbach, P., F. Straneo, O. Sergienko, and G. Hamilton (2014), International workshop on understanding the response of Greenland's marine-terminating glaciers to oceanic and atmospheric forcing: Challenges to improving observations, process understanding and modeling, US CLIVAR Report 2014-1, U.S. CLIVAR Project Office, Washington, DC 20005. Kelly, J. F., and Giraldo, F. X. (2012). Continuous and discontinuous Galerkin methods for a scalable three-dimensional nonhydrostatic atmospheric model: Limited-area mode. J. Comput. Phys. , 231 (24), 7988-8008.