The contribution of SWOT to the mesoscale eddy activity estimation

Mesoscale eddies play a significant role in transporting heat, salinity, and nutrients. The sea surface height (SSH) mapped by nadir data, limited by the spatial coverage and resolved wavelength of SSH observations, cannot fully resolve eddies with wavelengths smaller than 150 km. However, with the launch of the Surface Water and Ocean Topography (SWOT) mission, the spatial coverage and resolved wavelength of SSH observations have been significantly improved, resulting in an enhancement in the effective spatial resolution of SSH maps. Here, we further investigate the effect of the enhancement brought by SWOT on the study of mesoscale eddies. As the long wavelength error, which can introduce spurious signals during SSH mapping, remains in the level-3 SWOT ocean product, we propose an interpolation method to reduce LWE, thereby ensuring the accuracy of mesoscale eddy reconstruction. Two versions of SSH maps were generated by the proposed method, one using both nadir data and SWOT data, and the other using only nadir data. With the contribution of SWOT data, more mesoscale eddies with scales smaller than 150 km are reconstructed in the SSH maps, with a corresponding increase in eddy kinetic energy (EKE) up to 0.01 m²/s². In the Kuroshio, where the mean EKE is about 0.12 m²/s², the EKE increases by about 6%, whereas it increases by 20% in the California Currents (with a mean EKE of 0.014 m²/s²) and by 35% for the Open Ocean (with a mean EKE of 0.004 m²/s²). As the mean EKE decreases, the contribution of SWOT to the study of mesoscale eddies becomes more pronounced. Notably, the significant increase in EKE in the Open Ocean is accompanied by additional monthly variations in EKE.