Observed and Modelled Mixed-Layer Properties on the Continental Shelf of Sardinia (Mediterranean Sea)
Helmholtz-Zentrum Geesthacht Centre for Materials und Coa stal Research (HZG), Max-Planck-Straße 1, 21502 Geesthacht, Germany
Received: 21 Oct 2016 – Accepted for review: 27 Oct 2016 – Discussion started: 28 Oct 2016
Abstract. The Regional Ocean Modeling System (ROMS) has been employed to explore the sensitivity of the forecast skill of mixed-layer properties to the initial conditions, boundary conditions, and vertical mixing parameterisations. The initial and lateral boundary conditions were provided by the Mediterranean Forecasting System (MFS) or by the MERCATOR global ocean circulation model via one-way nesting; the initial conditions were additionally updated by the assimilation of observations. Nowcasts and forecasts from the weather forecast models COSMO-ME and COSMO-IT, partly melded with observations, served as surface boundary conditions. The vertical mixing was parameterised by the GLS (Generic Length Scale) scheme (Umlauf et al. 2003) in four different setups. All ROMS forecasts were validated against observations which were taken during the REP14-MED oceanographic survey to the west of Sardinia. Nesting ROMS in MERCATOR and updating the initial conditions by data assimilation provided the best agreement of the predicted mixed-layer temperature and the mixed-layer depth with time series from a moored thermistor chain. Further improvement was obtained by the usage of COSMO-ME atmospheric forcing which was melded with real observations, and by the application of the k − ε vertical mixing scheme with increased vertical eddy diffusivity. The predicted temporal variability of the mixed-layer temperature was reasonably well correlated with the observed variability in the frequency range above one cycle per day, while the modelled variability of the mixed-layer depth exhibited only agreement with the observations near the diurnal frequency peak. For the forecasted horizontal variability, reasonable agreement was found with observations from a ScanFish section, but only for the mesoscale wavenumber band; the observed sub-mesoscale variability was not reproduced by ROMS.
Onken, R.: Observed and Modelled Mixed-Layer Properties on the Continental Shelf of Sardinia (Mediterranean Sea), Ocean Sci. Discuss., doi:10.5194/os-2016-85, in review, 2016.