Mediterranean Forecasting System: forecast and analysis assessment through skill scores

M Tonani,K Nittis,N Pinardi,S Dobricic,C Fratianni,J Pistoia,S Pensieri,M De Alfonso

doi:10.5194/os-5-649-2009

Abstract

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.

Highlights

The aim of this study is to evaluate the accuracy of the forecast produced at the basin scale by the Mediterranean ocean Forecasting System (MFS), developed during MFSPilot Projetc,MFSPP (Pinardi et al, 2003) and MFS-Toward Environmental Predictions, MFSTEP projects
The results of this paper provide the first comprehensive assessment of the accuracy of the real time ocean forecasting system implemented in the Mediterranean Sea
This work is the first attempt to estimate the quality of the forecast produced during the MFSTEP project and will be useful in the future to define the forecast evaluation protocol

Summary

Introduction

The aim of this study is to evaluate the accuracy of the forecast produced at the basin scale by the Mediterranean ocean Forecasting System (MFS), developed during MFSPilot Projetc,MFSPP (Pinardi et al, 2003) and MFS-Toward Environmental Predictions, MFSTEP projects. The starting fields for the initialization of the forecast are taken as the instantaneous field at 12:00 a.m. of Tuesday (J) resulting from the chain of daily analyses done each week for the previous 15 days. The assimilation cycle is daily and all the data sets are assimilated intermittently at the end of each day after misfits (differences between forecast first guesses and observations) are computed at the time and location of the observations. (1) Maps of the position and of the vertical profiles of assimilated XBT and Argo data, maps of the along track assimilated SLA values and the animation of the last seven days of daily SST from satellite. WhereXFC (t) is the daily mean values of temperature or salinity from the forecast and analysis respectively at each forecast day t, with t=d1, d2,.

Rmse of observations and analyses

Forecast evaluation

Findings

Conclusions