Anomalously warm July 2005 in the northern California Current: Historical context and the significance of cumulative wind stress

[1] In the northern California Current, the onset of the 2005 upwelling season was five weeks later than usual, and well-established upwelling with a cold surface signature did not occur until about seven weeks after this. As part of the joint US-Canada Pacific hake survey, from 14–16 July 2005 we occupied the Newport Hydrographic line at 44.65°N, from the Oregon coast to 83 km offshore. Instead of the cold surface layer expected in July, we observed anomalously warm water. For example, 10-m temperature at the shelf station NH-5 was the warmest ever recorded in July at this location: 6.2°C above average, with observations back to 1961. We explore the pivotal role played by cumulative (time-integrated) wind forcing in the development of upwelling, in both 2005 and previous years. We find that 80% of July surface layer (0–30 m) interannual temperature variance can be explained by cumulative upwelling index from the spring transition.