Surface current observations made by high-frequency radar in the Monterey Bay region during August 2003 are
assimilated using a three-dimensional variational data assimilation scheme developed for the Regional Ocean Modeling
System (ROMS-DAS). The observed upwelling and relaxation surface currents in Monterey Bay are well recovered in
the analysis. A new mapping method based on ROMS-DAS is also proposed. This method is based on a variational
algorithm for the calculation of stream function and velocity potential from given velocity fields, and has the ability to
interpolate vectors over any irregular domain.