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Use in real time of profiler data in an operational forecast system.

    Soap is the oceanic forecasting system used by Shom to elaborate defense‑related products for French Navy ships. It has been routinely operated, in successive versions, since April 1998. In its present implementation over the Northeast Atlantic, the system relies on two predictive models, operated daily with real time forcing and data assimilation.

    The upper ocean model is a one-dimensional finite difference mixed layer model with Turbulent Kinetic Energy closure scheme [2]. It uses as input meteorological analyses and forecasts of surface heat fluxes, net radiative fluxes and wind stress in order to predict evolution of temperature profile up to 2 days ahead within the 0-400 m upper layer of the ocean. A QG circulation model assimilating sea surface height measurements in real time [1] gives analysis and forecast of the circulation in the intermediate and deep layers, from which hydrological properties are inferred.

    A full 3D hydrological description of the ocean state is achieved by building up the mixed layer on top of the QG-derived profiles using the mixed layer features (temperature, depth,) provided by the upper ocean model.

     The system is run daily and gives analysis of the current state of the ocean (nowcast) and evolution to come in the next 48 hours  (forecast). Maps below show nowcast and forecast of the surface temperature field and the mixed layer depth. They are updated every two days.

        Analyzed Sea surface Temperature            48-H forecast of sea surface temperature

                Analyzed Mixed layer depth                  48-H forecast of the mixed layer depth

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    The bottom of the mixed layer is computed as the level associated with a "strong" variation in the vertical temperature gradient. The algorithm uses a smoothed temperature gradient profile and look for maximum values exceeding a given threshold. Threshold values have been tuned with different thermal ocean conditions and range from 0.003°C/m to 0.06°C/m depending on the maximum vertical gradient computed for each profile. Those points flagged as potential bottom mixed layer, are then classified according to their depth (mixed layer is not expected bellow 600m) and logical link with other selected points on the profile (the thermocline, first minimum of sound speed,…) to only retain - if any- one single point identified as the bottom of the mixed layer.

[1]     E. Blayo, J. Verron and J-M Molines : Assimilation of Topex/Poseidon altimeter data into a circulation model of the North Atalntic, J. Geophys. Res., 99 (C12), 24691-24705, 1994.