Seasonal and interannual variability in along‐slope oceanic properties off the US West Coast: Inferences from a high‐resolution regional model

Abstract

AbstractA 6 year, 2009–2014 simulation using a 2 km horizontal resolution ocean circulation model of the Northeast Pacific coast is analyzed with focus on seasonal and interannual variability in along‐slope subsurface oceanic properties. Specifically, the fields are sampled on the isopycnal surface kg m−3 that is found between depths of 150 and 300 m below the ocean surface over the continental slope. The fields analyzed include the depth , temperature , along‐slope current , and the average potential vorticity PV between 26.5 and 26.25 kg m−3. Each field is averaged in the cross‐shore direction over the continental slope and presented as a function of the alongshore coordinate and time. The seasonal cycle in shows a coherent upwelling‐downwelling pattern from Mexico to Canada propagating to the north with a speed of 0.5 m s−1. The anomalously deep ( m) displacement in spring‐summer 2014 is forced by the southern boundary condition at 24°N as a manifestation of an emerging strong El Niño. The seasonal cycle in is most pronounced between 36°N and 53°N indicating that subarctic waters are replaced by warmer Californian waters in summer with the speed close 0.15 m s−1, which is consistent with earlier estimates of the undercurrent speed and also present analyses. The seasonal patterns and anomalies in and find confirmation in available long‐term glider and shipborne observations. The PV seasonality over the slope is qualitatively different to the south and north of the southern edge of Heceta Bank (43.9°N).