Role of the Ocean Observing System in an End-to-End Seasonal Forecasting System

There is clear demand for reliable forecasts of climate at seasonal time scales for a variety of societal applications. This paper discusses the role of ocean observations in the different components of a seasonal forecasting system, namely the initialization of the ocean, coupled model development and calibration of model output, concluding that the maintenance and enhancement of the current observing system is of paramount importance for further progress in seasonal forecasting. It is shown that the assimilation of ocean observations improves the skill of seasonal forecasts. Results indicate that no observing system is redundant. Independent observations, not directly assimilated, are necessary for the improvement of assimilation methods and numerical models, thus increasing the information content of the observations. Forecast calibration requires long observational records to produce historical ocean initial conditions. These are equivalent to ocean re-analyses, which, continuously brought up to real-time, allow the monitoring of relevant climate variables. The current forecasting systems are not making optimal use of the existing observations, in particular in regions where model error is large and/or where the initialization is inadequate. This is particularly noticeable in the equatorial Atlantic. Improvements in numerical models and initialization strategies are needed to exploit the full potential of current and future observing systems.