Slope and Shelf Flow Anomalies Off Oregon

Slope and Shelf Flow Anomalies Off Oregon Influenced by the El Niño Remote Oceanic Mechanism in 2014–2016

Adapted and condensed by OOI from Kurapov et al., 2022, doi.org/10.1029/2022JC018604.

Time series of the daily averaged meridional current component at the Oregon shelf location, averaged in the vertical between 60 and 70 m below the surface: (red) ADCP data and (black) model.  Data from before 2015 come from various moorings maintained at the NH-10 site.  Data after 2015 come from the OOI Oregon shelf site. The model reproduces the observed variability over the entire 10-year period very well, except for episodes in Dec 2010 and Oct 2013. Overall, no systematic biases or trends are found. See Fig. 7 Kurapov et al. (2022).

Kurapov et al. analyze outputs of a regional ocean circulation model to demonstrate the measurable impact of the El Niño remote oceanic forcing mechanism along the US West Coast during the major heat wave period of 2014–2016. The 2-km horizontal resolution model, based on the Regional Ocean Modeling System (ROMS), was run for the period of 2009–2018. Though the model does not assimilate observations, it performs well by comparison with time series data (including OOI data, Figure above) explaining observed variability on temporal scales from several days to seasonal and interannual.

The El Niño-related oceanic anomalies provided by a global state estimate are introduced in the regional model at the southern boundary at 24N. These propagate alongshore with coastally trapped waves (CTWs) and influence the variability off Oregon (41°–46°N). In particular, CTWs are evident in the subsurface along-slope current, v_s, and in the depth of the 26.5 kg m³ isopycnal surface over the slope, z_26.5. In summer 2014 and 2015, vs anomalies are positive (northward) and z_26.5 anomalies are negative (deeper) along the US West Coast. In addition to the CTW patterns, z_26.5 anomalies also exhibit slow-moving features associated with undercurrent widening, separation, and subsurface eddy variability. Over the Oregon shelf, El Niño conditions contributed to the sharp weakening of the southward alongshore current throughout the water column in July 2014 and 2015, despite the near-average southward, upwelling-favorable winds.

Kurapov, A. L., Rudnick, D. L., Cervantes, B. T., & Risien, C. M. (2022). Slope and shelf flow anomalies off Oregon influenced by the El Niño remote oceanic mechanism in 2014–2016. J. Geophys. Res.: Oceans, 127, e2022JC018604. doi.org/10.1029/2022JC018604.