Results of the Mini-Adaptive Sampling Test Run (MASTR) Experiment: Autonomous Vehicles, Drifters, Floats, ROCIS, and HF-Radar, to Improve Loop Current System Dynamics and Forecasts in the Deepwater Gulf of México

Abstract We report the preliminary results of the international MASTR (Mini-Adaptive Sampling Test-Run) Experiment of the UGOS (Understanding the Gulf Ocean Systems) Program, which simultaneously deployed multiple autonomous measurement platforms (i.e., ocean buoyancy gliders, subsurface floats, surface drifters) and high-frequency coastal radar in the Deepwater south-eastern Gulf of México. The state-of-the-art ocean observing technologies provide near-real-time surface and subsurface co-located temperature, salinity and velocity observations and were assessed for improvements to the predictive capability of multiple federal and industry operational ocean circulation models. Six ocean buoyancy gliders were deployed in the western Yucatan Strait near Mahahual, México - four of the gliders were deployed in January 2024, two gliders were deployed from July thru November 2023. The summer and fall 2023 glider data was assimilated into the NOAA RTOFS numerical model and significantly improved the model performance to accurately represent the vertical hydrographic structure of the inflowing water from the Caribbean Sea to the Gulf of México via the Yucatan Strait. The high-frequency radar system deployed near Cancun, México was operational throughout the experiment. Radar observations of surface velocity during fall 2023 observed the passage of extreme weather events, including Hurricane Idalia (26 August – 2 September). Additionally, the hi-frequency radar observed the spatial and temporal position of the Yucatan Current speed core as the Loop Current System in the Gulf of México evolved from a retracted state to an extended state, to a detached state, with numerous reattachment sequences. The research underscores the complexity of the four-dimensional structure of the Loop Current system and the spatial and temporal evolution of the circulation in response to topographic, tidal, geostrophic, ageostrophic, and wind forcing. Additional observations from airborne and subsurface observational platforms reveal sub-mesoscale variability and the correlation between surface and subsurface current patterns.