The INGV-CMCC Seasonal Prediction System: improved ocean initial conditions

The development of the INGV (Istituto Nazionale di Geofisica e Vulcanologia)-CMCC (Centro
Euro-Mediterraneo per i Cambiamenti Climatici) Seasonal Prediction System (SPS) is
documented. In this SPS the ocean initial conditions estimation includes a Reduced Order
Optimal Interpolation procedure for the assimilation of temperature and salinity profiles
at the global scale. Nine member ensemble forecasts have been produced for the period
1991-2003 for two starting dates per year in order to assess the impact of the subsurface
assimilation in the ocean for initialization.
Comparing the results with control simulations (i.e.: without assimilation of subsurface
profiles during ocean initialization), we showed that the improved ocean initialization increases
the skill in the prediction of tropical Pacific SSTs in our system for boreal winter
forecasts. Considering the forecast of the El Ni˜no 1997-1998, the data assimilation in the
ocean initial conditions leads to a considerable improvement in the representation of its onset
and development.
Our results indicate a better prediction of global scale surface climate anomalies for the
forecasts started in November, probably due to the improvement in the tropical Pacific. For
boreal winter, in both tropics and extra tropics, we show significant increases in the capability
of the system to discriminate above normal and below normal temperature anomalies.

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