FY 2024

Validation of OSCAR surface currents in the western Arctic marginal seas against Saildrone observations

Chi, N.-H., D. Zhang, and C. Zhang

Earth Space Sci., 10(11), e2022EA002612, doi: 10.1029/2022EA002612, View open access article online at Wiley/AGU (external link) (2023)

The western Arctic marginal seas undergo large seasonal variation, but are very challenging to observe directly due to sea ice and shallow depths. Deployments of several saildrone uncrewed surface vehicles in the summers of 2018 and 2019 provided unique opportunities to validate the satellite-derived near surface currents, Ocean Surface Current Analysis Real-time (OSCAR), in the western Arctic marginal seas against in situ upper ocean current measurements. Overall, OSCAR current is biased low (by 5.3 cm/s) with significant noise. Higher vector correlation estimated by the cosine similarity and speed differences often occur where stronger currents (often topography-steered) are observed. Such differences reveal that the data set resolvability depends on spatial and temporal resolutions, smoothing, and latitudes, suggesting that OSCAR is able to depict the major current systems but significantly underestimates their strength. Poorer vector correlation occurs at weaker current regimes (<10 cm/s), over the shallow Hanna Shoal, near fresher water due to ice melt and river discharge. The latter two water class regimes highlight the importance of salinity contribution to the buoyancy force which is neglected in the OSCAR formulation.

Plain Language Summary. It is challenging to make direct measurements in the western Arctic marginal seas, which undergo large seasonal swings, because of the sea ice and shallow depths. We validate the satellite-derived surface current product, Ocean Surface Current Analysis Real-time (OSCAR), against observations from saildrone uncrewed surface vehicles in the western Arctic marginal seas cruising in summers of 2018 and 2019. Overall, OSCAR current is biased low and noisy. Higher current direction relation and speed differences often occur where stronger currents are observed. Such differences suggest that the reliability of OSCAR depends on several factors. It also suggests that OSCAR is able to depict the major current systems but significantly underestimates their strength. Poorer current direction relation occurs at weaker current regimes, over the shallow Hanna Shoal, near fresher water due to ice melt and river discharge. The latter two regimes highlight the importance of salinity information, which however, is neglected in the OSCAR model.