Comparisons of upwelling and relaxation events in the Monterey Bay area

Abstract

Observations show significant differences in circulation patterns of upwelling and relaxation events that occurred in the Monterey Bay during two Autonomous Ocean Sampling Network field experiments in August 2003 and 2006. During the 2003 experiment, circulation exhibited more typical patterns associated with upwelling/relaxation: the development of the southward flowing jet and pair of cyclonic (inside of the bay) and anticyclonic (outside of the bay) circulations during upwelling and the development of the northward flow along the coast during relaxation of winds. During the upwelling event of 2006, the southward flow was weaker and shallower than in 2003. The second relaxation event of 2006 was significantly different from the first relaxation event of 2006 and the relaxation event of 2003: a southward flow was present along the entrance to the bay and this southward flow penetrated into the subsurface up to around 50 m at the mooring location. Two reasons for the observed differences in upwelling and relaxation events of 2003 and 2006 are identified in the paper: weaker winds in August 2006 than in August 2003 and strong positive sea surface height anomalies propagating poleward along the coast during 2006. The 2003 field program included an extensive sampling of the bay and surrounding areas with a fleet of underwater gliders, while during 2006 program, the extensive sampling was conducted in the area of upwelling center to the north of the Monterey Bay. During the 2003 field program, the Monterey Bay model was able to reproduce observed surface and subsurface features with assimilation of glider observations. However, during the 2006 field program, the assimilation of glider data from the upwelling center to the north of the Monterey Bay had minimal impact on model simulations of observed features to the south of the upwelling center.