Toward global-scale data assimilation using SWOT: Requirements for global hydrodynamics models

The measurement of spatially distributed water surface elevation (WSE) at the global scale, which is planned by "Surface Water and Ocean Topography (SWOT) mission", will bring lots of fresh knowledge on global-scale terrestrial water circulation especially when observed WSE is merged into global hydrodynamics modes by data assimilation. In this paper, we discussed the predictability of WSE by a global hydrodynamics model, which is required as a dynamic core for global-scale data assimilation using SWOT. From the comparison against WSE observed by the altimeter on Envisat, we found that the up-to-date global hydrodynamics model is able to reproduce the seasonal variations of WSE in the Amazon River, though predicted WSE still has errors due to the uncertainties in topographic parameters and sub-grid-scale dynamics of the model. Reduction of these uncertainties is required along with the development of the algorithm itself for achieving global scale data assimilation of WSE.