Stirring and Mixing in the Wake of Angaur and Peleliu Islands, Palau
Abstract
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- May 01, 2022
- Source ID
- 10.1029/2022jc018544
Entities
People
- S. Johnston
Organizations
- Office of Naval Research
- University of California, San Diego