Observations and modeling of the shelf circulation north of the Monterey Bay during August 2006

Abstract

In August of 2006 the Adaptive Sampling and Prediction (ASAP) experiment was conducted near the northern Monterey Bay. Multiple assets including aircraft, autonomous vehicles, moorings, and numerical models were used to gain a better understanding of three-dimensional upwelling centers. Data were collected at two separate mooring locations using Acoustic Doppler Current Profilers (ADCPs) during the experiment. The focus of this thesis is to determine the effects of local wind forcing on the ocean circulation and provide a comparison between the data collected at the mooring locations and numerical predictions for the region. Upwelling and relaxation events are used as the basis for understanding the local wind forcing. Upwelling typically results in equatorward flow while relaxation events typically result in poleward flow. Several different types of analyses were used to determine the effects of the local wind forcing. A visual analysis was performed with stick vector plots and component plots of the rotated time series that compared the wind with the data from the water column. Two methods of cross correlation, component correlations and vector correlations, were exploited as well as a spectral analysis of the wind and ADCP data. Finally the coherence and phase between the wind and currents were examined. Based on the analysis it became evident that the currents were forced by both wind and non-local events such as eddies, meanders, and the large-scale alongshelf pressure gradient. Associated with the ASAP experiment, the Harvard Ocean Prediction System (HOPS), the Regional Ocean Modeling System (ROMS), and the Navy Coastal Ocean Model (NCOM) provided nowcasts that were compared with the mooring data to determine their accuracy and precision. Overall, in the beginning of August the models provided reasonable representations of the flow patterns at the mooring locations. The prediction error increased towards the end of August which was possibly related to data assimilation techniques and more non-local forcing at that time. The military application of this thesis is that accurate current prediction by ocean models will benefit amphibious operations, special warfare operations, and mine warfare in the littoral zone.