Operational assimilation of glider temperature and salinity for an improved description of the Cyprus eddy

The authors demonstrate how assimilation of hydrographic data from a single ocean glider can significantly improve short-term regional forecasts. An operational data assimilation system for the Eastern Mediterranean is described and evaluated for a six-month numerical experiment consisting of two nearly-identical hydrodynamic model runs. In the assimilative run, glider profiles of temperature and salinity were assimilated daily into a high resolution ocean forecast, after an initial spin up of one week. In the control run, the same initial and boundary conditions were used to produce an operational forecast, but without assimilation of in situ data. While both runs were similar for most of the time and most of the domain, significant differences were found mostly near the region of assimilation, particularly when the glider passed through the anticyclonic Cyprus eddy, but also far away. The spatial scale at which the assimilation of the glider data improved the forecast is up to 40-50 km around the glider. Root mean square differences of the misfits between the temperature and salinity observations and the model background field at those locations were approximately 15% lower in the assimilative run. Improvements in the forecasting capability of surface currents were found and would provide a significant improvement of predictive capacity for applications such as pollutant spreading or offshore operational safety.