Internal Bore Evolution across the Shelf near Pt. Sal, California, Interpreted as a Gravity Current
Abstract
Off the central California coast near Pt. Sal, a large-amplitude internal bore was observed for 20 h over 10 km cross shore, or 100–10-m water depth (D), and 30 km along coast by remote sensing, 39 in situ moorings, ship surveys, and drifters. The bore is associated with steep isotherm displacements representing a significant fraction ofD. Observations were used to estimate bore arrival timetB, thicknessh, and bore and nonbore (ambient) temperature difference ΔT, leading to reduced gravityg′. Bore speedsc, estimated from mappedtB, varied from 0.25 to 0.1 m s−1fromD= 50 to 10 m. Thehvaried from 5 to 35 m, generally decreased withD, and varied regionally along isobath. The bore ΔTvaried from 0.75° to 2.15°C. Bore evolution was interpreted from the perspective of a two-layer gravity current. Gravity current speedsU, estimated from the local borehandg′, compared well to observed bore speeds throughout its cross-shore propagation. Linear internal wave speeds based on various stratification estimates result in larger errors. On average bore thicknessh=D/2, with regional variation, suggesting energy saturation. From 50- to 10-m depths, observed bore speeds compared well to saturated gravity current speeds and energetics that depend only on water depth and shelf-wide meang′. This suggests that this internal bore is the internal wave analog to a saturated surfzone surface gravity bore. Along-coast variations in prebore stratification explain variations in bore properties. Near Pt. Sal, bore Doppler shifting by barotropic currents is observed.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Dec 01, 2021
- Source ID
- 10.1175/jpo-d-21-0095.1
Entities
Organizations
- Office of Naval Research