Observation impact and sensitivity analysis applied to ocean circulation estimates using 4D-Var

The impact of individual observation platforms during analysis-forecast cycles of the California Current System (CCS) will be assessed using the Regional Ocean Modeling System (ROMS) 4-Dimensional Variational (4D-Var) data assimilation system. The contribution of the observations to increments in the alongshore transport of the CCS and the cross-shelf transport associated with coastal upwelling will be considered and discussed. The majority of ocean observations are in the form of satellite measurements of SST and sea surface height (~90%). The remaining 10% or so are in form of subsurface hydrographic data. However, despite the relatively small percentage of subsurface observations, we will demonstrate that these data often exert considerable influence on the CCS transport estimates resulting from 4D-Var.