In this framework, two months of support are granted in 2020 to NERSC (Bergen, Norway) to improve the numerical efficiency of the existing neXtSIM–NEMO (sea ice–ocean) coupling interface.

The neXtSIM sea ice model is unique in that it uses a Lagrangian mesh that moves with the motion of the ice it simulates. As the ice drifts the mesh becomes successively more deformed until it must be adapted in order to maintain mesh integrity. This adaptation is done locally, replacing those mesh elements that have become too deformed and possibly some of their neighbours. Through this process the mesh is continually updated, requiring among other things frequent recalculations of interpolation weights used in the coupled model. The strong physical coupling between the ice and the ocean also requires the numerical coupling to be as frequent as possible (preferably every ocean time-step). All of this requires an efficient method to calculate interpolation weights for a conservative interpolation of fields being exchanged between neXtSIM and an ocean model.

The task proposed is to take advantage of the parallel weight calculation in OASIS3-MCT and implement an efficient recalculation of the interpolation weights every coupling timestep, opening the way to dynamic coupling. This development will also improve the numerical efficiency if neXtSIM is coupled to other ocean models or an atmosphere model.