Reconstructing Upper Ocean Vertical Velocity Field from Sea Surface Height in the Presence of Unbalanced Motion

Reconstructability of upper-ocean vertical velocity w and vorticity zeta fields from high-resolution sea surface height (SSH) data is explored using the global 1/48 degrees horizontal-resolution MITgcm output in the context of the forthcoming Surface Water and Ocean Topography (SWOT) mission. By decomposing w with an omega equation of the primitive equation system and by taking into account the measurement design of the SWOT mission, this study seeks to reconstruct the subinertial, balanced w and zeta signals. By adopting the effective surface quasigeostrophic (eSQG) framework and applying to the Kuroshio Extension region of the North Pacific, we find that the target and reconstructed fields have a spatial correlation of similar to 0.7 below the mixed layer for w and 0.7-0.9 throughout the 1000-m upper ocean for zeta in the error-free scenario. By taking the SWOT sampling and measurement errors into account, the spatial correlation is found to decrease to 0.4-0.6 below the mixed layer for w and 0.6-0.7 for zeta, respectively. For both w and zeta reconstruction, the degradation due to the SWOT errors is more significant in the surface layer and for smaller-scale signals. The impact of errors lessens with the increasing depth and lengthening horizontal scales.