Modeling Ice-Ocean Interactions with Non-hydrostatic Unified Model of the Ocean (NUMO).

Ice-sheet/ocean interaction in Greenland is one of the key outstanding challenges in climate modeling, yet present-day climate models are not able to resolve fine-scale processes in the fjords. This is due to orders of magnitude difference in spatial scales between the open ocean (~1000km) and fjord (<1km) as well as small-scale processes at the glacier terminus (~1m), complicated bathymetry and coastline. The most recent computational studies of fjord circulation focused on simplified box-like domains (e.g., Slater et al., 2015).

Non-hydrostatic Unified Model of the Ocean (NUMO) is being developed to provide the scientific community with a tool capable of simulating ocean circulation in Greenland fjords while accounting for the complex domain geometry and the range of scales. The model uses fully three-dimensional unstructured mesh and high-order element-based Galerkin method to discretize the Boussinesq approximation of incompressible Navier-Stokes equations. A vital aspect of the model is the ability to capture the ice/ocean interface with high-resolution mesh while keeping the remainder of the domain relatively coarse. At the ice/ocean boundary, we model melting by solving three fundamental equations representing freezing-point of seawater dependence of salinity and pressure, and balance of heat and salinity fluxes.

We will discuss the validation of the model on a range of test cases with increasing complexity and present recent developments and challenges. Those include modeling process from GIS bathymetry information (e.g., BedMachine 3.0, Morlighem et al., 2017), through 3D geometry modeling, meshing, and simulations.

References:

Morlighem, M., Williams, C. N., Rignot, E., An, L., Arndt, J. E., Bamber, J. L., ... & Fenty, I. (2017). BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multibeam echo sounding combined with mass conservation. Geophysical Research Letters, 44(21), 11-051.

Slater, D. A., Nienow, P. W., Cowton, T. R., Goldberg, D. N., & Sole, A. J. (2015). Effect of near-terminus subglacial hydrology on tidewater glacier submarine melt rates. Geophysical Research Letters, 42(8), 2861-2868