Observations of nonlinear internal waves at a persistent coastal upwelling front

Walter, Ryan; Stastna, Marek; Woodson, C. Brock; Monismith, Stephen G.

doi:10.1016/j.csr.2016.02.007

Cited by 33 publications

(36 citation statements)

References 75 publications

(123 reference statements)

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“…During the early morning when the local winds are absent, a near‐surface warm water mass in the form of a buoyant plume front advects in the northwest direction (i.e., directly into the northern portion of the bay, black arrows in Figure ), resulting in strong near‐surface stratification. The resulting stratification provides an internal wave guide and supports high‐frequency (i.e., 5–30 min period) internal wave activity [ Walter et al ., ]. During the late morning, a local eastward wind develops, peaking in the early afternoon, and subsiding in the late evening.…”

Section: Resultsmentioning

confidence: 99%

“…[] and Walter et al . [] hypothesized that the local winds were responsible for the transcritical generation [see Stastna and Walter , ] of internal waves at the front. Furthermore, the near‐surface temperature spectra falloff rate follows a −3 power law and sharper falloff, implying a scattering of HFIWs toward smaller scales [ Nam and Send , ].…”

Section: Discussionmentioning

confidence: 99%

“…For example, in northern Monterey Bay, a large open coastal embayment located along the central California coast, a persistent coastal upwelling front forms between cold, recently upwelled waters outside the bay and warm, trapped waters inside of the bay that are shadowed (i.e., “upwelling shadow” [ Graham and Largier , ; Woodson et al ., ; Bonicelli et al ., ]) from regional wind forcing by topographic features (i.e., Santa Cruz Mountains) [ Woodson et al ., ]. The upwelling front propagates back and forth along the coast daily due to modulation by strong diurnal wind forcing [ Woodson et al ., ; Walter et al ., ]. In the northern portions of the bay, the local sea breeze is oriented parallel to the coastline, resulting in an offshore Ekman transport of surface waters and local diurnal upwelling [ Woodson et al ., ].…”

Section: Introductionmentioning

confidence: 99%

“…For example, several studies have found that diurnal wind forcing is a major mechanism driving significant temperature oscillations, some of which are on the order of seasonal fluctuations [ Kaplan et al ., ; Woodson et al ., ; Bonicelli et al ., ; Aristizábal et al ., ]. Local winds have also been shown to influence a host of physical processes including local diurnal upwelling [ Woodson et al ., ], inertial current oscillations [ Orlić et al ., ; Lucas et al ., ], internal wave development [ Lerczak et al ., ], local heat budgets [ Suanda et al ., ], modulation of buoyant plume fronts and the subsequent evolution of nonlinear internal waves [ Woodson et al ., ; Walter et al ., ], and local circulation patterns [ Rosenfeld , ; Woodson et al ., ; Bonicelli et al ., ]. From a biological perspective, local diurnal winds have been shown to play a fundamental role in phytoplankton dynamics [ Lucas et al ., ] and spatial patterns of barnacle settlement [ Bonicelli et al ., ], thereby affecting ecosystem productivity and the transport of larvae.…”

Section: Introductionmentioning

confidence: 99%

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Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Walter

Reid

Davis

et al. 2017

J. Geophys. Res. Oceans

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The oceanic response to high‐frequency local diurnal wind forcing is examined in a small coastal embayment located along an understudied stretch of the central California coast. We show that local diurnal wind forcing is the dominant control on nearshore temperature variability and circulation patterns. A complex empirical orthogonal function (CEOF) analysis of velocities in San Luis Obispo Bay reveals that the first‐mode CEOF amplitude time series, which accounts for 47.9% of the variance, is significantly coherent with the local wind signal at the diurnal frequency and aligns with periods of weak and strong wind forcing. The diurnal evolution of the hydrographic structure and circulation in the bay is examined using both individual events and composite‐day averages. During the late afternoon, the local wind strengthens and results in a sheared flow with near‐surface warm waters directed out of the bay and a compensating flow of colder waters into the bay over the bottom portion of the water column. This cold water intrusion into the bay causes isotherms to shoal toward the surface and delivers subthermocline waters to shallow reaches of the bay, representing a mechanism for small‐scale upwelling. When the local winds relax, the warm water mass advects back into the bay in the form of a buoyant plume front. Local diurnal winds are expected to play an important role in nearshore dynamics and local upwelling in other small coastal embayments with important implications for various biological and ecological processes.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Walter

Reid

Davis

et al. 2017

J. Geophys. Res. Oceans

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“…Thus, the sudden changes observed from hydrographic sections B and C within a time span of 6 h suggest that processes influenced by Earth's rotation are potentially less important in the final weakening of the temperature front. Propagating buoyant plumes related to river discharge (Nash and Moum, 2005) or frontal zones in upwelling regimes (Walter et al, 2016) are common dynamical processes in continental shelf regions. In fact, Dale et al (2008) also identified such a pressure-driven gravity current propagating across the front, once the wind forcing had changed.…”

Section: Discussionmentioning

confidence: 99%

Submesoscale CO<sub>2</sub> variability across an upwelling front off Peru

et al. 2017

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Abstract. As a major source for atmospheric CO 2 , the Peruvian upwelling region exhibits strong variability in surface f CO 2 on short spatial and temporal scales. Understanding the physical processes driving the strong variability is of fundamental importance for constraining the effect of marine emissions from upwelling regions on the global CO 2 budget. In this study, a frontal decay on length scales of O(10 km) was observed off the Peruvian coast following a pronounced decrease in down-frontal (equatorward) wind speed with a time lag of 9 h. Simultaneously, the sea-to-air flux of CO 2 on the inshore (cold) side of the front dropped from up to 80 to 10 mmol m −2 day −1 , while the offshore (warm) side of the front was constantly outgassing at a rate of 10-20 mmol m −2 day −1 . Based on repeated ship transects the decay of the front was observed to occur in two phases. The first phase was characterized by a development of coherent surface temperature anomalies which gained in amplitude over 6-9 h. The second phase was characterized by a disappearance of the surface temperature front within 6 h. Submesoscale mixed-layer instabilities were present but seem too slow to completely remove the temperature gradient in this short time period. Dynamics such as a pressure-driven gravity current appear to be a likely mechanism behind the evolution of the front.

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Bed failure induced by internal solitary waves

2017

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The pressure field inside a porous bed induced by the passage of an Internal Solitary Wave (ISW) of depression is examined using high‐accuracy numerical simulations. The velocity and density fields are obtained by solving the Dubreil‐Jacotin‐Long Equation, for a two‐layer, continuously stratified water column. The total wave‐induced pressure across the surface of the bed is computed by vertically integrating for the hydrostatic and nonhydrostatic contributions. The bed is assumed to be a continuum composed of either sand or silt, with a small amount of trapped gas. Results show variations in pore‐water pressure penetrating deeper into more conductive materials and remaining for a prolonged period after the wave has passed. In order to quantify the potential for failure, the vertical pressure gradient is compared against the buoyant weight of the bed. The pressure gradient exceeds this weight for weakly conductive materials. Failure is further enhanced by a decrease in bed saturation, consistent with studies in surface‐wave induced failure. In deeper water, the ISW‐induced pressure is stronger, causing failure only for weakly conductive materials. The pressure associated with the free‐surface displacement that accompanies ISWs is significant, when the water depth is less than 100 m, but has little influence when it is greater than 100 m, where the hydrostatic pressure due to the pycnocline displacement is much larger. Since the pore‐pressure gradient reduces the specific weight of the bed, results show that particles are easier for the flow to suspend, suggesting that pressure contributes to the powerful resuspension events observed in the field.

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Observations of nonlinear internal waves at a persistent coastal upwelling front

Cited by 33 publications

References 75 publications

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Submesoscale CO<sub>2</sub> variability across an upwelling front off Peru

Bed failure induced by internal solitary waves

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Observations of nonlinear internal waves at a persistent coastal upwelling front

Cited by 33 publications

References 75 publications

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Submesoscale CO&lt;sub&gt;2&lt;/sub&gt; variability across an upwelling front off Peru

Bed failure induced by internal solitary waves

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Submesoscale CO<sub>2</sub> variability across an upwelling front off Peru