32 FIG. 17. Time series of surface current magnitude and direction calculated by the di?erent hydrodynamic models in point P2. Current direction is measured in degrees counterclockwise from east. 3.3.3. Quantitative comparison An objective comparison between calculated sea surface temperature (SST) fields and satellite observations was carried out to evaluate closeness between hydrodynamic model fields and to then assess which model may provide the most realistic picture of circulation. SST fields have been used since they can be more easily handled than current fields (i.e. it is a scalar instead of a vectorial field). Moreover, SST can be easily obtained from satellite observations. Finally, SST is essential in determining baroclinic circulation and a good SST description is required in order to have a realistic representation of circulation. The SST gridded fields averaged for the first week of April 2011 were provided by 7 regional models and one local model. In this exercise only regional models are analysed. The models are: (1) HYCOM (Hybrid Coordinate Ocean Model); (2) JAEA (University of Kyoto); (3) JCOPE2; (4) MARS; (5) NCOM; (6) SELFE; (7) SYMPHONIE. The hydrodynamic models used are brie?y described in Annex XI, except for SELFE which is provided in Annex IV.