Dynamics of Low-frequency fluctuations in San Francisco Bay due to upwelling

Low-frequency dynamics of San Francisco Bay during the 1999 upwelling event is analyzed using observations of wind, surface elevations, and currents, and a principal component analysis is carried out on the observations to distinguish between barotropic and baroclinic components of the low-frequency fluctuations. The source of these low-frequency fluctuations is then determined with the SUNTANS model which is forced using local winds and offshore low-frequency surface observations. The results show that local wind forcing generates 5-10 cm/s currents in the direction of the winds in the shallows and 2-3 cm/s currents against winds in deep water. The offshore forcing, on the other hand, induces predicted current speeds of 1-2 cm/s in the shallows and negligible currents in deeper waters. The simulations also show that the local winds and bathymetric variability drive transverse circulation in the Bay similar to topographic gyres seen in lakes.