Can satellite altimetry observe coastally trapped waves on sub-monthly timescales?

Abstract. Coastally trapped waves (CTWs) are a major cause of sub-seasonal coastal sea level variability. While they have mostly been studied using numerical models, observational evidence is limited due to the sparse spatial coverage of the tide gauge network and the limitations of satellite altimetry gridded maps, which arise from the interpolation of sparse along-track data. The simultaneous operation of multiple altimetry missions, advancements in processing technologies, the advent of wide-swath altimetry, and the development of new interpolation techniques have the potential to significantly improve the monitoring of CTWs. In this study, we analyze three months of sea level data from satellite altimetry to evaluate the new capabilities for detecting sub-monthly variability, comparing the results to tide gauge data and an ocean model in Eastern Australia, an area known for its dominance of CTWs at these time scales. The results demonstrate that in the study area, the correlation between tide gauges and coastal daily sea level grids from satellite altimetry exceeds 0.5, even when considering time series filtered to capture only sub-monthly variability. CTWs are generally well detected, though discrepancies remain, particularly in terms of amplitude, wavelength and period.