Time-Varying Across-Shelf Ekman Transport and Vertical Eddy Viscosity on the Inner Shelf

2009 ◽  
Vol 39 (3) ◽  
pp. 602-620 ◽  
Author(s):  
Anthony R. Kirincich ◽  
John A. Barth
Keyword(s):  
Eddy Viscosity ◽  
Dynamic Range ◽  
Wind Forcing ◽  
Larval Transport ◽  
Ekman Transport ◽  
Time Variability ◽  
Inner Shelf ◽  
Ecological Processes ◽  
Event Scale ◽  
Event Time

Abstract The event-scale variability of across-shelf transport was investigated using observations made in 15 m of water on the central Oregon inner shelf. In a study area with intermittently upwelling-favorable winds and significant density stratification, hydrographic and velocity observations show rapid across-shelf movement of water masses over event time scales of 2–7 days. To understand the time variability of across-shelf exchange, an inverse calculation was used to estimate eddy viscosity and the vertical turbulent diffusion of momentum from velocity profiles and wind forcing. Depth-averaged eddy viscosity varied over a large dynamic range, but averaged 1.3 × 10−3 m2 s−1 during upwelling winds and 2.1 × 10−3 m2 s−1 during downwelling winds. The fraction of full Ekman transport present in the surface layer, a measure of the efficiency of across-shelf exchange at this water depth, was a strong function of eddy viscosity and wind forcing, but not stratification. Transport fractions ranged from 60%, during times of weak or variable wind forcing and low eddy viscosity, to 10%–20%, during times of strong downwelling and high eddy viscosity. The difference in eddy viscosities between upwelling and downwelling led to varying across-shelf exchange efficiencies and, potentially, increased net upwelling over time. These results quantify the variability of across-shelf transport efficiency and have significant implications for ecological processes (e.g., larval transport) in the inner shelf.

scholarly journals Effects of Wind Stress and Surface Cooling on Cross-Shore Exchange

2018 ◽  
Vol 48 (11) ◽  
pp. 2627-2647 ◽  
Author(s):  
Xiaodong Wu ◽  
Douglas Cahl ◽  
George Voulgaris
Keyword(s):  
Heat Loss ◽  
Wind Stress ◽  
Loss Rate ◽  
Baroclinic Instability ◽  
Wind Forcing ◽  
Ekman Transport ◽  
Surface Cooling ◽  
Inner Shelf ◽  
Heat Loss Rate ◽  
Shelf Slope

AbstractThe formation of coastal dense shelf water in winter provides the available potential energy (APE) to fuel baroclinic instability. The combined effects of baroclinic instability and wind forcing in driving cross-shelf exchange are investigated using idealized numerical simulations with varied bottom slope, wind stress, and heat loss rate. The results show that under upwelling-favorable winds, the intensity of the instability decreases as the wind stress increases. This is caused primarily by enhanced turbulence frictional dissipation. Under downwelling-favorable winds, an increase in wind stress and/or a decrease in heat loss rate tends to constrain the baroclinic instability, leading to a circulation resembling that driven purely by wind forcing. In the latter case, once a critical value of cross-shore density gradient is reached, isopycnal slumping is initiated, leading to increased vertical stratification and narrowing of the inner shelf. The change in depth of the inner-shelf outer boundary, defined as the location corresponding to the maximum cross-shore gradient of the surface Ekman transport, is proportional to an empirically derived multiparametric quantity , where a2 is a dimensional constant, B0 is a constant heat loss rate, γ = 0.43, f is the Coriolis parameter, α is the shelf slope, B is the heat loss rate, and τ is the wind stress. This relationship is found to hold for cases when instabilities are present.

Larval Transport in the Coastal Zone: Biological and Physical Processes

2018 ◽  
Keyword(s):  
Simulation Models ◽  
Population Connectivity ◽  
Larval Transport ◽  
Larval Abundance ◽  
Transport Mechanisms ◽  
Larval Behavior ◽  
Physical Processes ◽  
Ecological Processes ◽  
Emergent Technologies ◽  
Advection Diffusion

Larval transport is fundamental to several ecological processes, yet it remains unresolved for the majority of systems. We define larval transport, and describe its components, namely, larval behavior and the physical transport mechanisms accounting for advection, diffusion, and their variability. We then discuss other relevant processes in larval transport, including swimming proficiency, larval duration, accumulation in propagating features, episodic larval transport, and patchiness and spatial variability in larval abundance. We address challenges and recent approaches associated with understanding larval transport, including autonomous sampling, imaging, -omics, and the exponential growth in the use of poorly tested numerical simulation models to examine larval transport and population connectivity. Thus, we discuss the promises and pitfalls of numerical modeling, concluding with recommendations on moving forward, including a need for more process-oriented understanding of the mechanisms of larval transport and the use of emergent technologies.

Local wind forcing of the Monterey Bay area inner shelf

2005 ◽  
Vol 25 (3) ◽  
pp. 397-417 ◽  
Author(s):  
Patrick T. Drake ◽  
Margaret A. McManus ◽  
Curt D. Storlazzi
Keyword(s):  
Wind Forcing ◽  
Monterey Bay ◽  
Local Wind ◽  
Inner Shelf ◽  
Bay Area ◽  
Local Wind Forcing

scholarly journals Differential Temperature Sensors: Review of Applications in the Test and Characterization of Circuits, Usage and Design Methodology

Sensors ◽  
2019 ◽  
Vol 19 (21) ◽  
pp. 4815 ◽  
Author(s):  
Enrique Barajas ◽  
Xavier Aragones ◽  
Diego Mateo ◽  
Josep Altet
Keyword(s):  
Integrated Circuits ◽  
Analog Circuits ◽  
Temperature Sensor ◽  
Design Methodology ◽  
Dynamic Range ◽  
Simple Procedure ◽  
High Dynamic Range ◽  
Temperature Sensors ◽  
Time Variability ◽  
Linear Power Amplifier

Differential temperature sensors can be placed in integrated circuits to extract a signature of the power dissipated by the adjacent circuit blocks built in the same silicon die. This review paper first discusses the singularity that differential temperature sensors provide with respect to other sensor topologies, with circuit monitoring being their main application. The paper focuses on the monitoring of radio-frequency analog circuits. The strategies to extract the power signature of the monitored circuit are reviewed, and a list of application examples in the domain of test and characterization is provided. As a practical example, we elaborate the design methodology to conceive, step by step, a differential temperature sensor to monitor the aging degradation in a class-A linear power amplifier working in the 2.4 GHz Industrial Scientific Medical—ISM—band. It is discussed how, for this particular application, a sensor with a temperature resolution of 0.02 K and a high dynamic range is required. A circuit solution for this objective is proposed, as well as recommendations for the dimensions and location of the devices that form the temperature sensor. The paper concludes with a description of a simple procedure to monitor time variability.

The Response of Buoyant Coastal Plumes to Upwelling-Favorable Winds*

2004 ◽  
Vol 34 (11) ◽  
pp. 2458-2469 ◽  
Author(s):  
Steven Lentz
Keyword(s):  
Wind Stress ◽  
Vertical Mixing ◽  
Wind Forcing ◽  
Ekman Transport ◽  
Entrainment Rate ◽  
Buoyant Plume ◽  
Cross Sectional ◽  
Buoyancy Forcing ◽  
Density Anomaly ◽  
Variable Wind

Abstract To better understand the response of a buoyant coastal plume to wind-induced upwelling, a two-dimensional theory is developed that includes entrainment. The primary assumption is that competition between wind-driven vertical mixing and lateral buoyancy forcing in the region where the isopycnals slope upward to intersect the surface results in continual entrainment at the offshore edge of the plume. The theory provides estimates of the buoyant plume characteristics and offshore displacement as a function of time t, given the wind stress, the characteristics of the buoyant plume prior to the onset of the wind forcing, and a critical value for the bulk Richardson number (Ric). The theory predicts that, for t̂ ≡ t/ts, the plume density anomaly decreases as (1 + t̂)−1, the thickness increases as (1 + t̂)1/3, the width increases as (1 + t̂)2/3, and the plume average entrainment rate decreases as (1 + t̂)−2/3. Here ts = 2Ao/(RicUE) is the time for entrainment to double the cross-sectional area of the plume Ao at the onset of the wind forcing, where UE is the Ekman transport. The theory reproduces results from 20 numerical model runs by Fong and Geyer, including their estimates of the plume-average entrainment rate (correlations greater than 0.98 and regression coefficients approximately 1 for plume characteristics and 1.7 for the entrainment rate). The theory, modified to allow for time-variable wind stress, also reproduces the observed response of the buoyant coastal plume from Chesapeake Bay during an 11-day period of upwelling winds in August 1994.

scholarly journals Spatiotemporal Variation in Cross-Shelf Exchange across the Inner Shelf of Monterey Bay, California

2013 ◽  
Vol 43 (8) ◽  
pp. 1648-1665 ◽  
Author(s):  
C. Brock Woodson
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Ekman Transport ◽  
Return Flow ◽  
Monterey Bay ◽  
Coriolis Parameter ◽  
Inner Shelf ◽  
Sea Breezes ◽  
Positive Vorticity ◽  
Ekman Layers ◽  
Current Profiler

Abstract Cross-shelf exchange resulting from wind- and wave-driven flows across the inner shelf has been the focus of a considerable body of work. This contribution extends recent analyses to the central California coastline using 5-yr of moored current observations. Acoustic Doppler Current Profiler (ADCP) data from stations across the Monterey Bay (two in the northern bay and one in the southern bay), in water depths of ~20 m, showed net offshore transport throughout the year. For the northern bay sites, cross-shelf exchange was dominated by Ekman transport driven by along-shelf diurnal sea breezes during the upwelling season. Intense stratification in the northern bay leads to very shallow observed Ekman layers (~5–8 m), and consequently no overlap between bottom and surface Ekman layers within a few hundred meters of the coast. The total transport is less than predicted by theory consistent with models of shallow-water Ekman transport. The observed transport (~42% of full Ekman transport) is shown to be caused by the influence of a positive vorticity that effectively increases the Coriolis parameter. Wave-driven return flow estimated from an offshore buoy was strongly correlated with observed transport during nonupwelling conditions for the northern, outer bay site, but not for the two inner bay sites (northern and southern). In the southern bay, winds and waves have a significantly reduced effect on the cross-shelf exchange. Internal tidal bores are believed to contribute most of the observed cross-shelf exchange in this region.

Alongshelf Variability of Inner-Shelf Circulation along the Central Oregon Coast during Summer

2009 ◽  
Vol 39 (6) ◽  
pp. 1380-1398 ◽  
Author(s):  
Anthony R. Kirincich ◽  
John A. Barth
Keyword(s):  
Momentum Equation ◽  
Wind Forcing ◽  
Spatial And Temporal Variability ◽  
Local Wind ◽  
Inner Shelf ◽  
Oregon Coast ◽  
Bottom Stress ◽  
Shelf Circulation ◽  
Invertebrate Species ◽  
Local Wind Forcing

Abstract The spatial and temporal variability of inner-shelf circulation along the central Oregon coast during the 2004 upwelling season is described using a 70-km-long array of moorings along the 15-m isobath. Circulation at three stations located onshore of a submarine bank differed from that of a station north of the bank, despite the relatively uniform wind forcing and inner-shelf bathymetry present. During upwelling-favorable winds, strong southward alongshelf flow occurred north of the bank, no alongshelf flow occurred onshore of the northern part of the bank, and increasing southward flow occurred onshore of the southern part of the bank. During downwelling-favorable winds, strong northward flow occurred in the inner shelf onshore of the bank while weak flow occurred north of the bank. These alongshelf differences in inner-shelf circulation were due to the effects of the bank, which isolated the inner shelf onshore of the bank from the regional upwelling circulation that was evident at the northernmost station. As a result, circulation onshore of the bank was driven primarily by local wind forcing, while flow north of the bank was only partially driven by local winds. A secondary mode of variability, attributed to the movement of the regional upwelling jet due to remote forcings, contributed the bulk of the variability observed north of the bank. With the time-dependent wind forcing present, acceleration was an important term in the depth-averaged alongshelf momentum equation at all stations. During upwelling, bottom stress and acceleration opposed the wind stress north of the bank, while bottom stress was weaker onshore of the bank where the across-shelf momentum flux and the alongshelf pressure gradient balanced the residual of the acceleration and stresses. During downwelling, waters onshore of the bank surged northward at magnitudes much larger than that found north of the bank. These spatial variations developed as the season progressed and the regional upwelling circulation intensified, explaining known variations in growth and recruitment of nearshore invertebrate species.

scholarly journals Wave-Driven Inner-Shelf Motions on the Oregon Coast*

2009 ◽  
Vol 39 (11) ◽  
pp. 2942-2956 ◽  
Author(s):  
Anthony R. Kirincich ◽  
Steven J. Lentz ◽  
John A. Barth
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Wave Theory ◽  
Velocity Profiles ◽  
Wind Forcing ◽  
Return Flow ◽  
Linear Wave ◽  
Inner Shelf ◽  
Oregon Coast ◽  
Current Profiler ◽  
Water Depths

Abstract Recent work by S. Lentz et al. documents offshore transport in the inner shelf due to a wave-driven return flow associated with the Hasselmann wave stress (the Stokes–Coriolis force). This analysis is extended using observations from the central Oregon coast to identify the wave-driven return flow present and quantify the potential bias of wind-driven across-shelf exchange by unresolved wave-driven circulation. Using acoustic Doppler current profiler (ADCP) measurements at six stations, each in water depths of 13–15 m, observed depth-averaged, across-shelf velocities were generally correlated with theoretical estimates of the proposed return flow. During times of minimal wind forcing, across-shelf velocity profiles were vertically sheared, with stronger velocities near the top of the measured portion of the water column, and increased in magnitude with increasing significant wave height, consistent with circulation due to the Hasselmann wave stress. Yet velocity magnitudes and vertical shears were stronger than that predicted by linear wave theory, and more similar to the stratified “summer” velocity profiles described by S. Lentz et al. Additionally, substantial temporal and spatial variability of the wave-driven return flow was found, potentially due to changing wind and wave conditions as well as local bathymetric variability. Despite the wave-driven circulation found, subtracting estimates of the return flow from the observed across-shelf velocity had no significant effect on estimates of the across-shelf exchange due to along-shelf wind forcing at these water depths along the Oregon coast during summer.

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