Observations of Nonlinear Internal Wave Runup to the Surfzone

Observations of Nonlinear Internal Wave Runup to the Surfzone AbstractThe cross-shore evolution of nonlinear internal waves (NLIWs) from 8 m depth to shore was observed by a dense thermistor array and ADCP. Isotherm oscillations spanned much of the water column at a variety of periods. At times, NLIWs propagated into the surfzone, decreasing temperature by ≈ 1 °C in five minutes. When stratification was strong, temperature variability was strong and coherent from 18 m to 6 m depth at semi-diurnal and harmonic periods. When stratification weakened, temperature variability decreased and was incoherent between 18 m and 6 m depth at all frequencies. In 8 m depth, onshore coherently propagating NLIW events had associated rapid temperature drops (ΔT) up to 1.7°C, front velocity between 1.4 cm s−1 and 7.4 cm s−1 and incidence angles between −5° and 23°. Front position, ΔT, and two-layer equivalent height (zIW) of four events were tracked upslope until propagation terminated. Front position was quadratic in time, and normalized ΔT and zIW both decreased, collapsing as a linearly decaying function of normalized cross-shore distance. Front speed and deceleration are consistent with two-layer upslope gravity current scalings. During NLIW rundown, near-surface cooling and near-bottom warming in 8 m depth coincide with a critical gradient Richardson number, indicating shear-driven mixing. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Physical Oceanography American Meteorological Society

Observations of Nonlinear Internal Wave Runup to the Surfzone

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0485
D.O.I.
10.1175/JPO-D-17-0210.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThe cross-shore evolution of nonlinear internal waves (NLIWs) from 8 m depth to shore was observed by a dense thermistor array and ADCP. Isotherm oscillations spanned much of the water column at a variety of periods. At times, NLIWs propagated into the surfzone, decreasing temperature by ≈ 1 °C in five minutes. When stratification was strong, temperature variability was strong and coherent from 18 m to 6 m depth at semi-diurnal and harmonic periods. When stratification weakened, temperature variability decreased and was incoherent between 18 m and 6 m depth at all frequencies. In 8 m depth, onshore coherently propagating NLIW events had associated rapid temperature drops (ΔT) up to 1.7°C, front velocity between 1.4 cm s−1 and 7.4 cm s−1 and incidence angles between −5° and 23°. Front position, ΔT, and two-layer equivalent height (zIW) of four events were tracked upslope until propagation terminated. Front position was quadratic in time, and normalized ΔT and zIW both decreased, collapsing as a linearly decaying function of normalized cross-shore distance. Front speed and deceleration are consistent with two-layer upslope gravity current scalings. During NLIW rundown, near-surface cooling and near-bottom warming in 8 m depth coincide with a critical gradient Richardson number, indicating shear-driven mixing.

Journal

Journal of Physical OceanographyAmerican Meteorological Society

Published: Jan 23, 2018

References

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