Abstract:

Satellite observations provide broad ocean coverage for variables essential to weather and climate research, but their accuracy can be difficult to evaluate under extreme environmental conditions, when conventional in situ observations are sparse or unavailable. NOAA’s use of uncrewed observing systems, particularly Saildrones deployed during hurricanes, provides a unique opportunity to evaluate satellite-observed sea surface salinity (SSS) under these challenging conditions and supports NOAA’s Weather-Ready Nation goal. This NERTO project quantified the agreement between satellite SSS and in situ Saildrone observations and further investigated how SSS changes spatially and temporally during hurricane encounters. The analysis focused on Atlantic hurricanes observed during NOAA Saildrone missions from 2021–2024 and integrated Saildrone measurements with SMAP Level-2B and Level-3 CAP Version 5.0 SSS products and IBTrACS storm-track and intensity data. Satellite–Saildrone matchups and residual statistics were used to evaluate agreement, while observations were transformed into a dynamic storm-relative coordinate system based on hurricane motion. SSS responses were examined before (−72 to −12 h), during (−12 to +12 h), and after (+12 to +72 h) the closest storm approach, and by normalized distance from the storm center and left-front, right-front, left-rear, and right-rear quadrants. Results showed that satellite–Saildrone agreement varies under hurricane conditions and that hurricane-induced SSS responses are spatially and temporally heterogeneous rather than characterized by a single uniform freshening or salinification response. Post-storm SSS exhibited greater variability, with distinct responses among storm-relative quadrants.