Upwelling jet separation in the California Current System

The California Current System is characterized by summertime wind-driven upwelling, high biological productivity, and an intense equatorward upwelling jet. The upwelling jet is generally located close to shore to the north of Cape Blanco (43 degrees N), but it separates from the coast at the cape during summer extending farther offshore downstream of the separation point. Jet separation results in a wider region influenced by cold, nutrient-rich upwelled waters, strongly affecting biological productivity, mesoscale activity, and air-sea interactions. Flow-topography interactions are thought to play a dominant role in jet separation. Here, we use a high-resolution ocean model to show that the wind stress curl is a dominant forcing controlling jet separation, and that separation can occur independently of flow-topography interactions. While jet separation occurs in simulations with realistic wind stress curl and modified topography with no submarine banks or capes, jet separation is substantially reduced when the wind stress curl is removed, even in the presence of realistic topography. This novel insight indicates that future changes in winds, as the predicted delay in the seasonal development of wind stress curl intensifications, may result in substantial changes in ocean circulation in the California Current System.