Detection of oceanographic fronts using empirical orthogonal functions

Oceanographic fronts are boundaries between water masses with differences in hydrography. Often the presence of fronts coincide with oceanographic currents. The detection of fronts has traditionally been carried out by looking for sudden horizontal changes in the sea surface temperature or salinity. Applications involving temperature or salinity alone, may therefore overlook significant oceanic fronts. Also some fronts may be more exaggerated below the sea surface and therefore missed by approaches that rely on sea surface values only. Here we suggest a parametrical approach that combines both salinity and temperature profiles simultaneously using empirical orthogonal functions. This ensures that both salinity and temperature based fronts may be detected even if they are present below the sea surface. The suggested parametrisation allows the user to customise the emphasis on salinity or temperature, and even put an emphasis on particular depth regions. The method is demonstrated on data from two different dynamical ocean models. The same parametrisation is used for both data sets. No calibration or tuning was required and the resulting fronts are comparable. The method is also applied on a full year of data with unchanged parametrisation. The detected fronts exhibit expected behaviour, which builds confidence in the methods robustness and versatility.