Enhanced resolution capability of SWOT sea surface height measurements and their application in monitoring ocean dynamics variability

Abstract. The wavenumber spectrum of sea surface height along ground profiles is commonly determined to quantify the magnitude of detectable ocean dynamics features by altimetry missions. In this paper, wavenumber spectra were calculated and compared for HY-2B, SARAL/AltiKa, Sentinel-3A, and SWOT (Surface Water and Ocean Topography). The wavenumber power spectral density (PSD) of sea surface height (SSH) was averaged using weighted methods across multiple along-track profiles within defined boxes. The deduced resolution capabilities were also compared and analysed, evaluated using the relevant definition of one-dimensional mesoscale resolution capability. We verified that the latest wide-swath SWOT mission offers significantly improved measurements. For example, in the vicinity of the Kuroshio, the one-dimensional mesoscale resolution of SWOT is about 25 km, twice the resolution capability of conventional satellites. In addition, the quality of measurements declined obviously over regions where the eddy kinetic energy becomes larger. Finally, the scale of change in global ocean dynamics between 60° N and 60° S was analysed using cross-power-spectrum analysis based on SWOT data from two 21 d cycles. The results showed significant geographic and temporal variations in the ocean dynamics variability scales, which are mainly relative to sea state variability. The regions with large scales of ocean dynamics variability are concentrated in oceans with strong currents and unstable sea states, such as the Kuroshio Current, the Gulf Stream, and the Antarctic Circumpolar Current. In addition, the scale of ocean dynamics variability is not necessarily large where eddy kinetic energy is large, such as the Equator and the Northwest Indian Ocean Current area. Ocean dynamics variability also varies across seasons. Meanwhile, SWOT 1 d repeat cycle data were also utilized to analyse the sub-mesoscale variability of the ocean.