Mediterranean Forecasting System: Forecast and analysis assessment through skill scores

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Abstract

This paper describes the first evaluation of the quality of the forecast and analyses produced at the basin scale by the Mediterranean ocean Forecasting System (MFS) (http://gnoo.bo.ingv.it/mfs). The system produces short-term ocean forecasts for the following ten days. Analyses are produced weekly using a daily assimilation cycle. The analyses are compared with independent data from buoys, where available, and with the assimilated data before the data are inserted. In this work we have considered 53 ten days forecasts produced from 16 August 2005 to 15 August 2006. The forecast skill is evaluated by means of root mean square error (rmse) differences, bias and anomaly correlations at different depths for temperature and salinity, computing differences between forecast and analysis, analysis and persistence and forecast and persistence. The Skill Score (SS) is defined as the ratio of the rmse of the difference between analysis and forecast and the rmse of the difference between analysis and persistence. The SS shows that at 5 and 30 m the forecast is always better than the persistence, but at 300 m it can be worse than persistence for the first days of the forecast. This result may be related to flow adjustments introduced by the data assimilation scheme. The monthly variability of SS shows that when the system variability is high, the values of SS are higher, therefore the forecast has higher skill than persistence. We give evidence that the error growth in the surface layers is controlled by the atmospheric forcing inaccuracies, while at depth the forecast error can be interpreted as due to the data insertion procedure. The data, both in situ and satellite, are not homogeneously distributed in the basin; therefore, the quality of the analyses may be different in different areas of the basin.

Figures

  • Fig. 1. MFSTEP production cycle. Every Tuesday (J) a ten-day forecast (d1, d2, d3, d4, d5, d6, d7, d8, d9, d10) is produced. It is initialised by an analysis generated by the past sequence of 15 intermittent daily data assimilation cycles.
  • Table 1. Mean values of rmse AN-buoy, AN-Argo and AN-XBT at surface and different depths. The mean is computed over the considered year.
  • Fig. 3a. Rms of Analysis-Persistence (AP, Eq. 3), ForecastPersistence (FP, Eq. 4) and Analysis-Forecast-(AF, Eq. 2) for Temperature (left panel) and Salinity (right panel) at the depths of 5, 30 and 150 m. The rmse is a mean of the 53 ten-day forecast cycles from August 2005 to 2006.
  • Fig. 3b. Vertical profile of spatially and annual averaged of error standard deviation estimated from the background error covariances of the OI scheme and rmse of Analysis-Forecast (AF) for Temperature (top panel) and Salinity (bottom panel).
  • Fig. 4. Upper Panel: normalised rms of the difference between ECMWF atmospheric forecast and analyses fields. The value is a mean of the 53 ten-day forecast cycles. The value of the rms is normalised by the standard deviation of each atmospheric field considered. The atmospheric fields considered are: Mean Sea Level Pressure (m.s.l.), Air Temperature at 2 m (T2M), Dew-point Temperature at 2 m (T2MD), zonal and meridional wind speed at 10 m (U10M and V10M) and the Cloud Cover (CLC). Bottom Panel: AF of the model heat fluxes (total upward heat flux and shortwave radiation flux) and momentum (meridional and zonal wind stress).
  • Fig. 5. Skill Score (SS, Eq. 5) for salinity (triangle) and Temperature (circle) at the depths of 5 m (dashed line), 30 m (dash dotted line) and 150 m (continuos line). The SS is a mean of the 53 ten-day forecast cycles from August 2005 to 2006.
  • Fig. 6. Bias for the difference between forecast and analysis (Eq. 6) of Temperature (top panel) and Salinity (bottom panel) at 5, 30, 150, 300 and 600 m. The profiles for the ten days of forecast are labelled as d1, d2, d3, d4, d5, d6, d7, d8, d9 and d10 in the corresponding legend.
  • Fig. 7. Anomaly correlation (AC, Eq. 5) of Temperature (left panel) and Salinity (right panel) at the depths of 5 m, 30, 150 m, 300 m and 600 m.

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APA

Tonani, M., Pinardi, N., Fratianni, C., Pistoia, J., Dobricic, S., Pensieri, S., … Nittis, K. (2009). Mediterranean Forecasting System: Forecast and analysis assessment through skill scores. Ocean Science, 5(4), 649–660. https://doi.org/10.5194/os-5-649-2009

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