An assessment of data requirements for quasigeostrophic nowcasts and hindcasts of a mesoscale eddy field in the California Current System with application to fall transition

Abstract

An extensive Ocean Prediction Through Observation, Modeling, and Analysis (OPTOMA) domain, off Northern and Central California, was surveyed in November 1986, during OPTOMA 23. Surface dynamic height (SDH), sea surface temperature (SST), and other fields were mapped with a Gandin objective analysis (OA) model; stream function nowcasts and hindcasts of the mesoscale oceanic field were generated by a quasigeostrophic (QG) model, initialized and updated with OA fields of dynamic topography. The westward propagation, at 5-to-10 km/day, of an anticyclone was the predominant mesoscale event; cyclonic features were quasi-stationary. The Generalized Digital Environmental Model had accurate averages and ranges of values, but was not representative of the mesoscale field, Because the mesoscale field did not change much over the ten-day period, persistence fields scored well. QG hindcasts were most sensitive to data density, The transition in the autumn of 1986 in the California Current System was a chronic event; winds favorable for upwelling fluctuated and diminished in late Oct. but occurred during short periods through Dec. A balance of alongshore pressure gradient and wind stress at Monterey shifted from a maximum southward in late Nov. to maximum northward two weeks later. The northward nearshore flow was observed in satellite imagery, SDH and SSH OA fields, and in QG hindcasts.