Ocean Response to Atmospheric Forcing by the ERA-20C Climate Reanalysis Within the ERA-CLIM2 Project

The response of the ocean heat content to the atmospheric forcing over the 20th century is investigated within the European Centre for Medium-range Weather Forecasts (ECMWF) ocean assimilation system. Ocean simulations and assimilation experiments are conducted using surface forcing from the ERA20C climate reanalysis produced at ECMWF. Analyses show that long-term trends in ocean heat content are sensitive to the choice of the initial conditions, spin-up methodology, changes in the observing system and constraint at the air-sea interface. A set of ocean experiments is used to discriminate model drift from low-frequency climate signals. Links between low frequency signals in ocean heat content, atmospheric forcing and modes of variability such as the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation are then investigated.