SHORT DESCRIPTION

CMEMS MED-MFC logo

The Mediterranean Forecasting System (MedFS) is a numerical ocean prediction system that produces analyses, reanalyses and short term forecasts for the entire Mediterranean Sea and its Atlantic ocean adjacent areas (see Fig. 1). MedFS became operational in the late 90’s and was developed in the VI and VII EU and National Framework programs (Pinardi et al., 2003, Pinardi and Coppini 2010, Tonani et al 2014) and since 2015 is part of the Copernicus Marine Service (CMEMS). MedFS is developed and operationally maintained by CMCC since 2018 providing regular and systematic information about the physical state of the Mediterranean Sea. The service is available 24 hours a day, 365 days a year.

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Figure 1: Mediterranean Sea numerical domain and bathymetry [m].

MedFS is a coupled hydrodynamic-wave model with data assimilation component. The model horizontal grid resolution is 1/24˚ (4 km approximately) and is resolved over 141 unevenly spaced vertical levels (Clementi et al., 2017a) and is nested in the Atlantic Ocean through the Copernicus global ocean analyses and forecasting system (https://marine.copernicus.eu/). The Nucleus for European Modelling of the Ocean (NEMO, https://www.nemo-ocean.eu/) is used to produce the hydrodynamic fields and the third-generation wave model WaveWatch-III (WW3, https://polar.ncep.noaa.gov/waves/wavewatch) provides the wave component. Ocean measurements from satellites (Sea Level Anomaly - SLA) and in situ temperature and salinity vertical profiles (ARGO, CTD and XBT) are assimilated weekly with a daily cycle.

The CMEMS MedFS catalogue (https://marine.copernicus.eu/services-portfolio/access-to-products/) offers offers a Near Real Time product – analysis and forecast – of monthly, daily and hourly 3D temperature, salinity, currents; 2D sea level; 2D de-tided sea level; mixed layer depth; bottom temperature; 15 minutes sea surface height and currents (Clementi et al., 2021, DOI: https://doi.org/10.25423/CMCC/MEDSEA_ANALYSISFORECAST_PHY_006_013_EAS6)

ANALYSIS AND FORECASTING SYSTEM

THE MEDFS MODELING SYSTEM

The Mediterranean Sea analysis and forecasting numerical core of the NRT system (MedFS) is based on the NEMO v3.6 ocean general circulation model (Nucleus for European Modelling of the Ocean, https://www.nemo-ocean.eu/), coupled with the wave model WaveWatch3 (https://polar.ncep.noaa.gov/waves/wavewatch) and includes an OceanVAR scheme for assimilating available observations. The model horizontal grid resolution is 1/24˚ (~4 km) and is resolved over 141 unevenly spaced vertical levels.

The hydrodynamic model NEMO v3.6 has been implemented in the Mediterranean Sea using a non-linear explicit free surface formulation solved by a time-splitting scheme. It uses vertical partial cells to fit the bottom depth shape and a vertical time-varying z* coordinate system. The model solves the 8 major Mediterranean tidal components (M2, S2, N2, K2, K1, O1,P1, Q1), in addition, tidal forcing is applied along the lateral boundaries in the Atlantic Ocean by means of tidal elevation and currents.The model is forced by momentum, water and heat fluxes interactively computed by bulk formulae using the 1/10° horizontal-resolution operational analysis and forecast fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) at varying temporal resolution (1-hr for the first 3 days of forecast, 3-hr for the following 3 days of forecast and 6-hr for the last 4 days of forecast and for the analysis). The water balance is computed as Evaporation minus Precipitation and Runoff. The evaporation is derived from the latent heat flux, precipitation is provided by ECMWF, while the runoff of the 39 rivers implemented is provided by monthly mean datasets except for the Po river runoff which is provided as daily mean observations (ARPAE, www.arpae.it). The model is nested in the Atlantic within the daily analysis and forecast CMEMS GLO-MFC product at 1/12° horizontal resolution, while the Dardanelles Strait boundary conditions are provided by the analysis and forecast CMEMS GLO-MFC product and the daily climatological values provided in Maderich et al. (2015). The topography is derived from the GEBCO 30arc-second grid filtered and manually modified in critical areas.

The wave model WW3 implemented in the Mediterranean Sea solves the wave action balance equation in slowly varying depth domain and currents considering a superposition of the following source/sink terms: wind input growing actions (based on Janssen’s quasi-linear theory of wind-wave generation: Janssen, 1989, 1991), a dissipation source term based on Hasselmann (1974) whitecapping theory according to Komen et al. (1984) and nonlinear resonant wave-wave interactions modelled using the Discrete Interaction Approximation (DIA, Hasselmann et al., 1985). The spectral discretization has been achieved through 30 frequency bins ranging from 0.05 Hz (20 s) to 0.79 Hz (1.25 s) and 24 equally distributed directional bins. The wave model takes into consideration the surface currents for wave refraction but assumes no interactions with the ocean bottom.

NEMO-WW3 coupling is achieved as following:-NEMO provides every hour estimates of Air-Sea Temperature difference and Sea Surface Currents to WW3, which returns back to NEMO the neutral component of the Surface Drag Coefficient (Figure 2) taking into account the wave induced effect at the air-sea interface (Clementi et al., 2017c).

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Figure 2: The current-wave coupling scheme.

The MedFS data assimilation System

The data assimilation system of MedFS is based on a three-dimensional variational assimilation scheme (OceanVAR), originally developed for the Mediterranean Sea by Dobricic and Pinardi (2008) and later extended for the global ocean by Storto et al. (2015) implemented with a specific background error correlation matrix formulation.

The assimilated data includes: along tracksatelite Sea Level Anomaly (SLA), in situ temperature profiles by VOS XBTs (Voluntary Observing Ship-eXpandable Bathythermograph), in situ temperature and salinity profiles by ARGO floats and from different survey CTD profiles. Satellite objectively analysed Sea Surface Temperature (SST) is used for the correction of surface heat fluxes. All the assimilated observations are provided by the CMEMS Thematic Assembly Centers (https://marine.copernicus.eu/).

The MedFS System evaluation

The quality assessment of the system is monitored weekly by the calculation of the root mean square differences between observations and model background fields (so-called misfits) for SLA, temperature and salinity: http://oceanlab.cmcc.it/mfs-evaluation/

Moreover, daily mean temperature, salinity and sea level fileds are compared to insitu fixed moorings observations: https://evalid.cmcc.it/evaluation/calval/

The MedFS data quality control and rejection are performed during a pre-processing phase and during the assimilation phase.

Pre-processing Quality checks on Temperature and Salinity ARGO vertical profiles and on SLA tracks include:

ARGO QC1 Check on the date and location quality flags: only the profiles with both flags equal to 1 are taken into account
ARGO QC2 Out of the Mediterranean Sea region
ARGO QC3 Retain only ascending profiles (descending are rejected)
ARGO QC4 Check on the values of the quality flags of pressure, temperature and salinity for each depth: if one of the flags is not equal to 1, the layer is deleted
ARGO QC5 Check on the values of the temperature and salinity, data outside the following ranges are rejected: 0<T<35 ; 0<S<45
ARGO QC6 Check on the thermocline: if distance between two subsequent measurements of temperature and salinity in the first 300 meters is larger than 40 m, the profile is rejected.
ARGO QC7 Measurement between 0 and 2 m are rejected
SLA QC1 Check on the values of date, latitude, longitude, sea level anomaly and DAC: if one of these values is equal to missing value the measurement of sea level anomaly is rejected. Check on the quality flag of sea level anomaly: if the flag is not equal to 1 the measurement of sea level anomaly is rejected.

The Processing chain

The MedFS processing system consists of two cycles: a daily cycle for the production of forecast data, and a weekly cycle for the production of analysis data. A sketch representing the production cycle is represented in Figure 3.

The analysis fields are produced weekly, on Tuesday, for the previous 14 days with a daily assimilation cycle.

The 10-days daily forecast fields (including first 5-days hourly forecasts) are produced every day. The forecast is initialized by a hindcast every day except Tuesday, when the analysis is used instead of the hindcast.

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Figure 3: Production cycle scheme.

The MedFS NRT product catalogue is available at https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=MEDSEA_ANALYSISFORECAST_PHY_006_013

How to cite the product:

Clementi, E., Aydogdu, A., Goglio, A. C., Pistoia, J., Escudier, R., Drudi, M., Grandi, A., Mariani, A., Lyubartsev, V., Lecci, R., Cretí, S., Coppini, G., Masina, S., & Pinardi, N. (2021). Mediterranean Sea Physical Analysis and Forecast (CMEMS MED-Currents, EAS6 system) (Version 1) [Data set]. Copernicus Monitoring Environment Marine Service (CMEMS). DOI: https://doi.org/10.25423/CMCC/MEDSEA_ANALYSISFORECAST_PHY_006_013_EAS6

Essential references