Impact of observations on ocean forecasts

Assessing the impact of observations on ocean forecasts and reanalyses: Part 2, Regional applications

Abstract

Ocean forecast and reanalysis systems routinely assimilate ocean observations to constrain ocean models to predict the three-dimensional ocean circulation. Under GODAE OceanView the operational ocean modelling community has developed a suite of global ocean forecast and analysis systems. Each system has a critical dependence on ocean observations – routinely assimilating observations of in situ temperature and salinity, and satellite sea-level anomaly and sea surface temperature. This paper demonstrates the value and impact of ocean observations to three global eddy-permitting forecast systems, one eddy-permitting analysis system, and two seasonal prediction systems. All systems have been used to assess the impact of Argo profiles, including scenarios with no Argo data, and a degraded Argo array – unanimously concluding that Argo is a critical data set – the most critical for seasonal prediction, and as critical as satellite altimetry, the most important data type, for eddy-permitting applications. Most systems also show that TAO data are as important as Argo in the tropical Pacific, and that XBT data has an impact that is comparable to other data types in the vicinity of XBT transects. It is clear that no currently available data type is redundant. By contrast, the components of the global ocean observing system complement each other remarkably well, providing sufficient information to monitor and forecast the global ocean.