Adding Ice Shelves Improves the Accuracy of Global Tidal Models
The coastlines and water depth of oceans influence global tides, just as the shape and thickness of a violin’s wood determines its musical vibrations. Ocean simulations with realistic continents and bottom depth can model tides by including external forces imposed by the sun and the moon. Ice shelves are floating decks of ice that protrude from the Antarctic continent. Below these ice shelves are large ocean cavities, which influence tides in the Southern Ocean and throughout the globe. This work adds the geometry of ice shelf cavities to global ocean simulations. The researchers compared the model results to the sea surface height observed by satellites and tide gauges around Antarctica. Adding ice shelf cavities substantially improves the model accuracy.
Global simulations with and without ice shelves were compared at global uniform resolutions of 64 to 8 km grid cells, with a single variable resolution mesh of 45 to 5 km grid cells. Researchers analyzed the results for characteristics of the five largest tidal constituents. Adding ice shelves reduced errors compared to satellite observations by up to 50% near Antarctica and 5 – 10% globally. The variable-resolution mesh produced significantly lower errors than the uniform resolution simulations. Tidal modeling is important for coastal inundation studies of future climates, so validation against observations and improved accuracy is a critical first step.
Oceanic tides are seldom represented in Earth system models due to the need for high horizontal resolution to accurately represent the associated waves near coasts. Recently, the ability to model tides was added to the Model for Prediction Across Scales-Ocean (MPAS-Ocean), the ocean component within the Energy Exascale Earth System Model developed by the Department of Energy. MPAS-Ocean circumvents the resolution limits by using variable-resolution global meshes, allowing fine grid cells to be added to critical regions such as coastlines.
This work adds the geometry of ice shelf cavities to these global ocean simulations. Tidal constituents calculated using MPAS-Ocean were evaluated against long-term satellite observations of sea surface height. The addition of ice shelves substantially lowers the error in the Southern Ocean and even improves the accuracy of forecasted tides far from the ice shelves. These modifications to MPAS-Ocean will enable further studies with potential future Antarctic ice shelf geometries, sea ice distributions, and sea level rise to investigate the impact of climate change on coastal communities.