Performances of the new Copernicus Marine Service global ocean monitoring and forecasting real-time high-resolution system

Abstract

<p>Since October 2016, and in the framework of Copernicus Marine Service, Mercator Ocean International delivered in real-time daily services (weekly analyses and daily 10-day forecasts) with a global 1/12° high resolution (eddy-resolving) system. In this system, oceanic observations were assimilated in the model using a reduced-order Kalman filter method. Along track altimeter Sea Level Anomaly (SLA), satellite sea surface temperature (SST) and sea ice concentration, and in situ temperature and salinity vertical profiles were jointly assimilated to estimate the initial conditions for numerical ocean forecasting. A 3D-VAR scheme was also used to better control the slowly evolving large-scale biases in temperature and salinity.</p> <p>A major release of this analysis and forecasting system is available since November 2022 with the following main changes and updates:</p> <ul> <li>A new version of NEMO ocean and sea ice models (new numerical schemes, coherent bulk formulation with the atmospheric forcing, multi-categories sea ice model);</li> <li>Higher spatial and temporal resolution (1/10° - 1 hour) atmospheric forcing from IFS ECMWF analyses and forecasts;</li> <li>A new assimilated SST observation (assimilation of L3 ODYSSEA SST high resolution product instead of L4 OSTIA gridded product);</li> <li>A new Mean Dynamic Topography for SLA assimilation;</li> <li>A different parametrization of the model error covariance with a new anomalies base deduced from the Mercator Ocean reanalysis at 1/12°;</li> <li>A 4D extension of the data assimilation scheme allowing a better spatiotemporal continuity of mesoscale structures;</li> <li>The assimilation of “super-observations” to filter out noisy data and scales that the model does not resolve;</li> <li>The use of satellite-based monthly estimates of the Global Mean Sea Level to better constrain the ocean mass and the steric height.</li> </ul> <p>This presentation shows how some identified weaknesses present in the previous system have been improved. It also highlights the new system’s performance in terms of analysis and forecast skills, of representation of mesoscale activity, of mass/steric distribution and of representation of the equatorial dynamics. The new system is very close to SLA observations with a forecast RMS difference below 5 cm (best analysis is around 4 cm). The description of the ocean water masses is also very accurate and departure from in situ temperature and salinity observations are generally below 0.3 °C and 0.05 PSU. In addition, a global comparison with independent (not assimilated) velocity measurements shows that the location of the main currents is accurately represented.</p>