Dealing with discontinuous meteorological forcing in operational ocean modelling: a case study using ECMWF-IFS and GETM (v2.5)

Abstract

Meteorological data providers release updated forecasts several times per day – at the forecast epochs. The first time step (t=0) of each forecast, the so-called analysis step, is updated by a data-assimilation process so that the meteorological fields at this time in general do not match the fields from the previous forecast. Seen from the perspective of oceanographic modelling, the analysis step represents a possible discontinuity in the model forcing. Unless care is taken, this “meteorological discontinuity” may generate spurious waves in the ocean model. The problem is examined and quantified for a single meteorological model: the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). A simple straightforward solution is suggested to overcome the forcing discontinuity and the effect on two particular ocean models is examined: the FCOO NA3 (North Atlantic 3 nm) storm-surge model and the NS1C (North Sea–Baltic Sea 1 nm) circulation model.