Image_1_Assessing the potential impact of assimilating total surface current velocities in the Met Office’s global ocean forecasting system.pdf

• Main Authors: Jennifer Waters, Matthew J. Martin, Michael J. Bell, Robert R. King, Lucile Gaultier, Clément Ubelmann, Craig Donlon, Simon Van Gennip
• Format: Still Image
• Language: unknown
• Published: 2024
• Subjects: Oceanography; Marine Biology; Marine Geoscience; Biological Oceanography; Chemical Oceanography; Physical Oceanography; Marine Engineering; data assimilation; observing system simulation experiment; ocean prediction; total surface current velocities; satellite velocities; ESA A-TSCV project; Antarctic; Antarc*; Sea ice
• Online Access: https://doi.org/10.3389/fmars.2024.1383522.s001; https://figshare.com/articles/figure/Image_1_Assessing_the_potential_impact_of_assimilating_total_surface_current_velocities_in_the_Met_Office_s_global_ocean_forecasting_system_pdf/25738299

Accurate prediction of ocean surface currents is important for marine safety, ship routing, tracking of pollutants and in coupled forecasting. Presently, velocity observations are not routinely assimilated in global ocean forecasting systems, largely due to the sparsity of the observation network. Several satellite missions are now being proposed with the capability to measure Total Surface Current Velocities (TSCV). If successful, these would substantially increase the coverage of ocean current observations and could improve accuracy of ocean current forecasts through data assimilation. In this paper, Observing System Simulation Experiments (OSSEs) are used to assess the impact of assimilating TSCV in the Met Office’s global ocean forecasting system. Synthetic observations are generated from a high-resolution model run for all standard observation types (sea surface temperature, profiles of temperature and salinity, sea level anomaly and sea ice concentration) as well as TSCV observations from a Sea surface KInematics Multiscale monitoring (SKIM) like satellite. The assimilation of SKIM like TSCV observations is tested over an 11 month period. Preliminary experiments assimilating idealised single TSCV observations demonstrate that ageostrophic velocity corrections are not well retained in the model. We propose a method for improving ageostrophic currents through TSCV assimilation by initialising Near Inertial Oscillations with a rotated incremental analysis update (IAU) scheme. The OSSEs show that TSCV assimilation has the potential to significantly improve the prediction of velocities, particularly in the Western Boundary Currents, Antarctic Circumpolar Current and in the near surface equatorial currents. For global surface velocity the analysis root-mean-square-errors (RMSEs) are reduced by 23% and there is a 4-day gain in forecast RMSE. There are some degradations to the subsurface in the tropics, generally in regions with complex vertical salinity structures. However, outside of the tropics, improvements ...