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

Abstract

A 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 σ=26.5 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 z26.5, temperature T26.5, along‐slope current v26.5, and the average potential vorticity PV between σ = 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 z26.5 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 ( −20 m) z26.5 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 T26.5 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 v26.5 analyses. The seasonal patterns and anomalies in z26.5 and T26.5 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).

Volume and Heat Budgets in the Coastal California Current System: Means, Annual Cycles, and Interannual Anomalies of 2014–16

“…As discussed in Zaba et al (2018), the 3-month assimilation window used here is shorter than that of a former long-term (2007-10) version of CASE Todd et al 2011Todd et al , 2012Verdy et al 2014) to increase model controllability of eddy variability. This 3-month window is longer than that of other CCS modeling studies (Chao et al 2018;Kurapov et al 2017;Neveu et al 2016) to capture the continuous evolution of ocean dynamics over monthly time scales. A shorter assimilation window (on the order of days) would likely result in solutions closer to the data constraints with smaller but more frequent increments.…”

OceanGliders: A Component of the Integrated GOOS

“…Many combinations of using glider data for verification or assimilation of forecast or hindcast models have been tried in many regions around the world. For example, off California, Kurapov et al (2017) used glider data (Rudnick et al, 2017) to verify a forecast model, while Chao et al (2018) assimilated the same glider data to create forecasts. Temperature and salinity data from these gliders were assimilated into a state estimate (Todd et al, 2011a(Todd et al, , 2012Zaba et al, 2018), while velocity data were not assimilated so they could be used for verification.…”

Better Regional Ocean Observing Through Cross-National Cooperation: A Case Study From the Northeast Pacific

“…The accuracy of the oceanic forecasts is improved through assimilation of surface currents measured by land-based coastal radars, and satellite sea surface temperature and satellite sea-surface height (Kurapov et al, 2011;Yu et al, 2012). This methodology was transitioned to NOAA where the West Coast Operational Forecast System (WCOFS), spanning the entire United States West Coast, is being developed and tested (Kurapov et al, 2017). FIGURE 3 | Numerical ocean circulation model nowcast of sea surface temperature off the Pacific Northwest.…”