Observations of Near-Inertial Surface Currents at Palau

Siegelman, Mika; Merrifield, M. A.; Firing, Eric; MacKinnon, Jennifer A.; Alford, Matthew H.; Voet, Gunnar; Wijesekera, H. W.; Schramek, Travis; Zeiden, Kristin L.; Terrill, Eric

doi:10.5670/oceanog.2019.413

Cited by 6 publications

(6 citation statements)

References 39 publications

(44 reference statements)

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“…Palau is well suited for studies of such processes because its islands and submarine ridges are situated between the westward North Equatorial Current (NEC) and the eastward North Equatorial Countercurrent (NECC; Figure 1a). In Palau, wake eddies from 1 to 100 km scales and lee waves at 1‐km scales have been observed and modeled at the north and south points along with some estimates of their dissipation and drag on the total flow, which is often a combination of tidal, inertial, and lower‐frequency flows (Andres et al., 2020; Gopalakrishnan & Cornuelle, 2019; Johnston, MacKinnon, et al., 2019; MacKinnon et al., 2019; Merrifield et al., 2019; Rudnick et al., 2019; Siegelman et al., 2019; Simmons et al., 2019; St. Laurent et al., 2019; Voet et al., 2020; Wijesekera et al., 2020; Zedler et al., 2019; Zeiden et al., 2019, 2021).…”

Section: Introductionmentioning

confidence: 99%

Stirring and Mixing in the Wake of Angaur and Peleliu Islands, Palau

Johnston

2022

JGR Oceans

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Temperature or salinity variability on isopycnals is referred to as spice, which acts as a tracer in the absence of mixing. The westward North Equatorial Current and eastward North Equatorial Countercurrent are incident upon Palau, where the meridional extent of the topography exceeds 100 km and the thermohaline structure on the up‐ and downstream sides of the islands can be distinct. Westward flow of high salinity water past two islands at the south point of Palau injects a spice anomaly into the wake in the form of a 15 km wide jet with changes of salinity of 0.1 psu across the headland and the jet. With three repeated surveys, several terms in the spice balance are estimated for the jet. Horizontal diffusivity has a typical value of about 11 m2 s−1 for 15‐km length scales, while the vertical diffusivity is about 10−5 m2 s−1 from the balance, with similar maximum estimates for the latter from a shear‐based parameterization. Typical vertical diffusivities at this latitude are about 10−6 m2 s−1, which is the area mean from the shear‐based parameterization. Amidst this typical background diffusion, the spice variance increases linearly in the wake over three successive surveys. The surveys occurred over similar but not identical areas, following the shifting flow. The spice anomaly is detected 100–200 km downstream and is consistent with the mesoscale flow obtained from altimetric absolute geostrophic currents. Spice anomalies are a useful way of tracing flows encountering abrupt topography.

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Section: Introductionmentioning

confidence: 99%

Stirring and Mixing in the Wake of Angaur and Peleliu Islands, Palau

Johnston

2022

JGR Oceans

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“…Our analysis focuses on measurements collected near the Velasco Reef, located in the southwestern Pacific archipelago of Palau. The regional flow is multiscaled and highly variable, influenced by the large‐scale North Equatorial Current and Counter Current (Qiu et al., 2015; Schönau & Rudnick, 2015) as well as smaller‐scale tidal and near‐inertial motions (MacKinnon et al., 2019; Siegelman et al., 2019). There is substantial interest in characterizing the complex turbulent wakes generated by the interaction of these flows with the reef's shallow headland.…”

Section: Introductionmentioning

confidence: 99%

Data‐Driven Identification of Turbulent Oceanic Mixing From Observational Microstructure Data

Couchman

Wynne‐Cattanach

Alford

et al. 2021

Geophysical Research Letters

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Turbulence significantly enhances the vertical transport of heat and other scalars throughout the ocean, playing a vital role in maintaining ocean stratification and driving global currents such as the meridional overturning circulation (Wunsch & Ferrari, 2004). Despite having a leading order effect on ocean dynamics and climate modeling, turbulent processes cannot currently be resolved in ocean circulation models and must therefore be parameterized, typically in terms of an eddy diffusivity (Fox-Kemper et al., 2019;Jayne, 2009). A considerable amount of recent observational, numerical and theoretical work has focused on improving such parametrizations by considering how variations in local flow characteristics influence the "mixing efficiency", defined loosely as the proportion of energy extracted from the larger-scale flow by turbulence that leads to irreversible scalar mixing

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“…The detached eddies can then be detected up to 50 km away and may persist farther downstream. Oscillating flow from inertial motions is also likely important (Siegelman et al, 2019, in this issue), but our surveys were short compared to the inertial period of about four days.…”

Section: Discussionmentioning

confidence: 87%