Particle Trajectories in an Eastern Boundary Current

By ooistaff | November 1, 2022 |

Adapted and condensed by OOI from Wong-Ala et al., 2022, doi:/10.1016/j.jmarsys.2022.103757

To study the transport and dispersal of marine organisms during spawning, Wong-Ala* et al. developed and applied a Lagrangian particle tracking (LPT) model to compare and contrast particle drift patterns during the spring transition off the Oregon coast. They studied the Oregon coast as it has distinct upwelling and downwelling regimes and variable shelf width. They contrasted years (2016–18) using Regional Ocean Modeling System (ROMS) with different horizontal spatial resolutions (2 km, 250 m). They found the finer spatial resolution model significantly increased retention along the Oregon coast. Particles in the 250 m ROMS were advected to depth at specific times and locations for each simulated year, coinciding with the location and timing of a strong and shallow alongshore undercurrent that is not present in the 2 km ROMS. Additionally, ageostrophic dynamics close to shore, in the bottom boundary layer, and around headlands not present in the coarser model emerged in the 250 m resolution model. They concluded that the higher horizontal model resolution and bathymetry generated well-resolved mesoscale and submesoscale features (e.g., surface, subsurface, and nearshore jet) that vary annually. These results have implications for modeling the dispersal, growth, and development of coastal organisms with dispersing early life stages.

Figure 1: (Fig 9 from Wong-Ala et al. (2022). Comparison of u-velocity (zonal velocity) data between the 250 m ROMS and an inshore mooring and shelf mooring off the Oregon coast collecting data at seven meters depth. The panel is organized by year: 2016 (row 1), 2017 (row 2), 2018 (row 3), and location of data collection: inshore (column 1) and shelf (column 2). In April 2018, there are no data available from the shelf mooring ADCP.

The model applied by Wong-Ala assimilates satellite sea surface temperature and along-track altimetry. Model atmospheric forcing is from the NOAA North American Mesoscale Model (NAM). To validate their model, Wong-Ala et al., used OOI Endurance Array time series data from 2016 to 2018 from the Oregon inshore and shelf moorings (CE01ISSM and CE02SHSM). They compared available OOI zonal and meridional velocities, temperature, and salinity to model output of these parameters for the month of April in each year when they ran their model (Figure 1). They found the modeled currents and temperature from the 250 m ROMS model closely follow the observed data from inshore and shelf moorings compared to the 2 km ROMS. The 250 m ROMS modeled currents and observed currents at the inshore mooring are similar for all three years (Figure 1).

They also found that the 250 m ROMS modeled temperature and observed data are similar in 2017 at the inshore and shelf location. In April 2017 and 2018, the modeled temperature from the 250 m ROMS is about 1 °C cooler than the observed temperatures.

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*Wong-Ala is a PhD student at Oregon State University. She is a Pacific Islander.

Reference:A. T. K. Wong-Ala, Ciannelli, L., Durski, S. M., and Spitz, Y., Particle trajectories in an eastern boundary current using a regional ocean model at two horizontal resolutions, Journal of Marine Systems, vol. 233, p. 103757, 2022. https://doi.org/10.1016/j.jmarsys.2022.103757.