scholarly journals Asymmetric Estuarine Responses to Changes in River Forcing: A Consequence of Nonlinear Salt Flux

2015 ◽  
Vol 45 (11) ◽  
pp. 2836-2847 ◽  
Author(s):  
Shih-Nan Chen
Keyword(s):  
Response Time ◽  
Linear Theory ◽  
Nonlinear Effect ◽  
Nonlinear Function ◽  
Power Laws ◽  
Salt Transport ◽  
Salt Flux ◽  
Exchange Flow ◽  
Salinity Field ◽  
The Asymmetry

AbstractA linear theory for estuarine adjustment to river forcing as put forth by MacCready is extended to allow for quantification of nonlinear salt flux induced by gravitational exchange flow. It has been shown that, under a steplike change of river forcing, the estuarine responses are asymmetric, with the salinity field adjusting faster during the rising discharge. The asymmetry arises because the up-estuary salt flux due to exchange flow is a nonlinear function of estuarine length ∝ L−3. During the rising discharge, the estuary is longer, and the salt flux is comparatively less sensitive to the length variations. As a result, the up-estuary salt transport cannot keep pace with the rate of discharge changes, leading to a larger net salt flux and thus a shorter response time. A simple theory accounting for the nonlinear effect is then applied to Hudson-like systems and shown to capture the asymmetric response. The asymmetry is generalizable to other estuarine regimes where up-estuary salt fluxes are expressed as nonlinear power laws.

scholarly journals Estuarine Exchange Flow Quantified with Isohaline Coordinates: Contrasting Long and Short Estuaries

2012 ◽  
Vol 42 (5) ◽  
pp. 748-763 ◽  
Author(s):  
Shih-Nan Chen ◽  
W. Rockwell Geyer ◽  
David K. Ralston ◽  
James A. Lerczak
Keyword(s):  
Pressure Gradient ◽  
Tidal Volume ◽  
Numerical Models ◽  
Physical Space ◽  
Hudson River ◽  
Salt Transport ◽  
Salt Flux ◽  
Exchange Flow ◽  
Volume Flux ◽  
Tidal Excursion

Abstract Isohaline coordinate analysis is used to compare the exchange flow in two contrasting estuaries, the long (with respect to tidal excursion) Hudson River and the short Merrimack River, using validated numerical models. The isohaline analysis averages fluxes in salinity space rather than in physical space, yielding the isohaline exchange flow that incorporates both subtidal and tidal fluxes and precisely satisfies the Knudsen relation. The isohaline analysis can be consistently applied to both subtidally and tidally dominated estuaries. In the Hudson, the isohaline exchange flow is similar to results from the Eulerian analysis, and the conventional estuarine theory can be used to quantify the salt transport based on scaling with the baroclinic pressure gradient. In the Merrimack, the isohaline exchange flow is much larger than the Eulerian quantity, indicating the dominance of tidal salt flux. The exchange flow does not scale with the baroclinic pressure gradient but rather with tidal volume flux. This tidal exchange is driven by tidal pumping due to the jet–sink flow at the mouth constriction, leading to a linear dependence of exchange flow on tidal volume flux. Finally, a tidal conversion parameter Qin/Qprism, measuring the fraction of tidal inflow Qprism that is converted into net exchange Qin, is proposed to characterize the exchange processes among different systems. It is found that the length scale ratio between tidal excursion and salinity intrusion provides a characteristic to distinguish estuarine regimes.

scholarly journals Total Exchange Flow, Entrainment, and Diffusive Salt Flux in Estuaries

2017 ◽  
Vol 47 (5) ◽  
pp. 1205-1220 ◽  
Author(s):  
Tao Wang ◽  
W. Rockwell Geyer ◽  
Parker MacCready
Keyword(s):  
Temporal Variation ◽  
Cross Sections ◽  
Salt Content ◽  
Spring Tide ◽  
Salt Transport ◽  
Salt Flux ◽  
Exchange Flow ◽  
Important Relationship ◽  
Numerical Mixing ◽  
Total Exchange

AbstractThe linkage among total exchange flow, entrainment, and diffusive salt flux in estuaries is derived analytically using salinity coordinates, revealing the simple but important relationship between total exchange flow and mixing. Mixing is defined and quantified in this paper as the dissipation of salinity variance. The method uses the conservation of volume and salt to quantify and distinguish the diahaline transport of volume (i.e., entrainment) and diahaline diffusive salt flux. A numerical model of the Hudson estuary is used as an example of the application of the method in a realistic estuary with a persistent but temporally variable exchange flow. A notable finding of this analysis is that the total exchange flow and diahaline salt flux are out of phase with respect to the spring–neap cycle. Total exchange flow reaches its maximum near minimum neap tide, but diahaline salt transport reaches its maximum during the maximum spring tide. This phase shift explains the strong temporal variation of stratification and estuarine salt content through the spring–neap cycle. In addition to quantifying temporal variation, the method reveals the spatial variation of total exchange flow, entrainment, and diffusive salt flux through the estuary. For instance, the analysis of the Hudson estuary indicates that diffusive salt flux is intensified in the wider cross sections. The method also provides a simple means of quantifying numerical mixing in ocean models because it provides an estimate of the total dissipation of salinity variance, which is the sum of mixing due to the turbulence closure and numerical mixing.

scholarly journals A Numerical Study of Salt Fluxes in Delaware Bay Estuary

2013 ◽  
Vol 43 (8) ◽  
pp. 1572-1588 ◽  
Author(s):  
María Aristizábal ◽  
Robert Chant
Keyword(s):  
River Discharge ◽  
Neap Tide ◽  
Numerical Study ◽  
Spring Tide ◽  
Delaware Bay ◽  
Salt Flux ◽  
Exchange Flow ◽  
Regional Ocean Modeling System ◽  
Salinity Field ◽  
Estuarine Exchange

Abstract The results of a numerical study of Delaware Bay using the Regional Ocean Modeling System (ROMS) are presented. The simulations are run over a range of steady river inputs and used M2 and S2 tidal components to capture the spring–neap variability. Results provide a description of the spatial and temporal structure of the estuarine exchange flow and the salinity field, as well the along-channel salt flux in the estuary. The along-channel salt flux is decomposed into an advective term associated with the river flow, a steady shear dispersion Fe associated with the estuarine exchange flow, and a tidal oscillatory salt flux Ft. Time series of Fe and Ft show that both are larger during neap tide than during spring. This time variability of Ft, which is contrary to existing scalings, is caused by the lateral flows that bring velocity and salinity out of quadrature and the stronger stratification during neap tide, which causes Ft to be enhanced relative to spring tide. A fit for the salt intrusion length L with river discharge Q for a number of isohalines is performed. The functional dependences of L with Q are significantly weaker than Q−1/3 scaling. It is concluded that the response of the salt field with river discharge is due to the dependence of Fe and Ft with Q and the relative importance of Ft to the total upstream salt flux: as river discharge increases, Fe becomes the dominant mechanism. Once Fe dominates, the salt field stiffens because of a reduction of the vertical eddy viscosity with increasing Q.

Glomerulotubular balance in a mathematical model of the proximal nephron

1990 ◽  
Vol 258 (3) ◽  
pp. F612-F626 ◽  
Author(s):  
A. M. Weinstein
Keyword(s):  
Tight Junction ◽  
Proximal Tubule ◽  
Water Permeability ◽  
Water Flux ◽  
Salt Transport ◽  
Salt Flux ◽  
Filtration Fraction ◽  
Epithelial Junctions ◽  
Permeability Increase ◽  
Glomerulotubular Balance

A nonelectrolyte model of proximal tubule epithelium has been extended by the inclusion of a compliant tight junction. Here "compliance" signifies that both the junctional salt and water permeability increase and the salt reflection coefficient decreases in response to small pressure differences from lateral interspace to tubule lumen. In previous models of rat proximal tubule, there has been virtually no sensitivity of isotonic salt transport to changes in peritubular oncotic force. With the inclusion of junctional compliance, decreases in peritubular protein can open the junction and produce a secretory salt flux. Thus the model can represent the "backflux hypothesis," as it was originally put forth (J. E. Lewy and E. E. Windhager, Am. J. Physiol. 214: 943-954, 1968). Additional calculations, simulating a tight junction with negligible water permeability, reveal that the quantitative impact of peritubular protein can be realized whether or not there is substantial junctional water flux. The epithelial model of proximal tubule has also been incorporated into a model of the proximal nephron, complete with glomerulus, peritubular capillary, and interstitium. The interstitial compartment is well mixed and interstitial pressure and osmolality are determined iteratively to achieve balance between tubule reabsorption and capillary uptake. For this model, two domains of operation are identified. When interstitial pressures are low, junctions are closed, and filtration fraction has no effect on proximal reabsorption. When interstitial pressures are relatively elevated, epithelial junctions are open, and proximal salt reabsorption changes in proportion to changes in filtration fraction. In neither domain, however, does the model tubule augment salt flux with isolated increases in luminal flow rate (at constant filtration fraction). The absence of a separate effect of tubule fluid flow on salt transport precludes perfect glomerulotubular balance.

scholarly journals An Application of Simulated Annealing in Compensation of Nonlinearity of Scanners

2019 ◽  
Vol 9 (8) ◽  
pp. 1655 ◽  
Author(s):  
Rayyan Manwar ◽  
Mohsin Zafar ◽  
Adrian Podoleanu ◽  
Mohammad Avanaki
Keyword(s):  
Simulated Annealing ◽  
Response Time ◽  
Optimization Algorithm ◽  
Applied Voltage ◽  
Simulated Annealing Algorithm ◽  
Nonlinear Function ◽  
Signal Shape ◽  
Annealing Algorithm ◽  
Optimal Signal

Galvo scanners are popular devices for fast transversal scanning. A triangular signal is usually employed to drive galvo scanners at scanning rates close to the inverse of their response time where scanning deflection becomes a nonlinear function of applied voltage. To address this, the triangular signal is synthesized from several short ramps with different slopes. An optimization algorithm similar to a simulated annealing algorithm is used for finding the optimal signal shape to drive the galvo scanners. As a result, a significant reduction in the nonlinearity of the galvo scanning is obtained.

scholarly journals Seasonal Arctic sea-ice simulations with a prognostic ice-ocean model

1991 ◽  
Vol 15 ◽  
pp. 45-53 ◽  
Author(s):  
Peter H. Ranelli ◽  
William D. Hibler
Keyword(s):  
Arctic Ocean ◽  
Arctic Basin ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
Salt Transport ◽  
Salt Flux ◽  
The Arctic ◽  
Diagnostic Model ◽  
Quasi Equilibrium ◽  
The Arctic Ocean

A prognostic ice-ocean model of the Arctic, Greenland and Norwegian seas with daily wind and atmospheric forcing is integrated for 30 years to quasi-equilibrium. Three simulations are carried out to investigate the role played by ice deformation and transport in baroclinic adjustment of the Arctic Ocean: a standard run with precipitation and ice transport, a simulation without precipitation and a “thermodynamics only” simulation without ice transport but including precipitation. A diagnostic model is integrated for five years to serve as a comparative control run. Comparison of the vertically integrated stream-function of each of the model runs indicates that the vertical density stratification needed to maintain the circulation of the Arctic Ocean is reduced excessively when precipitation is neglected and artificially enhanced if ice transport out of the basin is ignored. This effect is even more noticeable in the surface currents and is also apparent in a comparison of simulated and observed drifting-buoy tracks. An analysis of the salt budget of the Arctic Ocean indicates that the three main components, salt transport by the ocean, salt flux from the annual cycle of ice, and a fresh-water flux from precipitation and river runoff are approximately of the same magnitude. The main circulation deficiency identified in the simulations is an inadequate flow of Atlantic water into the Arctic Basin through the Fram Strait.

Fractional harmonics in a plasma

1974 ◽  
Vol 11 (2) ◽  
pp. 325-329
Author(s):  
G. J. Lewak ◽  
H. J. Lee
Keyword(s):  
Perturbation Theory ◽  
Linear Theory ◽  
Nonlinear Effect ◽  
Linearized Equations ◽  
Threshold Amplitude

The most common approach to the study of plasma nonlinearities is by a form of perturbation theory which first studies the linearized equations, then evaluates effects of nonlinearities in terms of these linear solutions. Such an approach is probably justifiable for the effect of weak nonlinearities, but will almost certainly miss features that are exclusively nonlinear in nature (i.e. effects which cannot be described by modifying linear theory, or effects which are present only when e.g. a source of disturbances in a plasma reaches a certain threshold amplitude). It is the object of this paper to investigate one possible such nonlinear effect.

Brine-Driven Eddies under Sea Ice Leads and Their Impact on the Arctic Ocean Mixed Layer

2008 ◽  
Vol 38 (1) ◽  
pp. 146-163 ◽  
Author(s):  
Yoshimasa Matsumura ◽  
Hiroyasu Hasumi
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Mixed Layer ◽  
General Circulation ◽  
Salt Transport ◽  
Salt Flux ◽  
The Arctic ◽  
Theoretical Argument ◽  
Ocean Mixed Layer ◽  
The Arctic Ocean

Abstract Eddy generation induced by a line-shaped salt flux under a sea ice lead and associated salt transport are investigated using a three-dimensional numerical model. The model is designed to represent a typical condition for the wintertime Arctic Ocean mixed layer, where new ice formation within leads is known to be one of the primary sources of dense water. The result shows that along-lead baroclinic jets generate anticyclonic eddies at the base of the mixed layer, and almost all the lead-originated salt is contained inside these eddies. These eddies survive for over a month after closing of the lead and transport the lead-originated salt laterally. Consequently, the lead-origin salt settles only on the top of the halocline and is not used for increasing salinity of the mixed layer. Sensitivity experiments suggest that the horizontal scale of generated eddies depends only on the surface forcing and is proportional to the cube root of the total amount of salt input. This scaling of eddy size is consistent with a theoretical argument based on a linear instability theory. Parameterizing these processes would improve representation of the Arctic Ocean mixed layer in ocean general circulation models.

scholarly journals On the meridional ageostrophic transport in the tropical Atlantic

2017 ◽  
Author(s):  
Yao Fu ◽  
Johannes Karstensen ◽  
Peter Brandt
Keyword(s):  
Mixed Layer Depth ◽  
Volume Transport ◽  
Salt Transport ◽  
Salt Flux ◽  
Ekman Transport ◽  
Flux Calculation ◽  
Vertical Scale ◽  
Salinity Data ◽  
The Difference

Abstract. The meridional Ekman volume, heat and salt transport across two trans-Atlantic sections near 14.5° N and 11° S were estimated using wind products, in-situ observations, and model data. A meridional ageostrophic velocity was obtained as the difference between the directly measured total velocity and the geostrophic velocity derived from observations. Wave-like structures exist in the ageostrophic velocity with 60–80 m vertical scale and large horizontal coherence, which are likely associated with near-inertial waves. The meridional Ekman transport estimated by integrating the ageostrophic velocity was 6.2 ± 2.3 Sv northward at 14.5° N and 11.7 ± 2.1 Sv southward at 11° S, which agrees well with the predictions from in-situ wind stress data of 6.7 ± 3.5 Sv at 14.5° N and 13.6 ± 3.3 Sv at 11° S. The top of the pycnocline well represents the penetration depth of the Ekman currents at both sections, which was typically 20 m deeper than the local mixed layer depth. We observed that in the meridional Ekman heat and salt flux calculation, using only the sea surface temperature and salinity data had a negligible impact on the resulting fluxes compared to using temperature and salinity profile data covering the Ekman layer. The errors in the Ekman heat and salt flux calculation were dominated by the uncertainty in the Ekman volume transport estimates.

scholarly journals The Exchange of Water and Salt across the Drogden Sill in Øresund September 1993-November 1994

1996 ◽  
Vol 27 (5) ◽  
pp. 351-368 ◽  
Author(s):  
FI. Jakobsen ◽  
M.J. Lintrup
Keyword(s):  
Time Series ◽  
Water Discharge ◽  
Water Levels ◽  
Salt Transport ◽  
Salt Flux ◽  
Layer System ◽  
Data Analyses ◽  
Baltic Proper ◽  
One Year ◽  
The Baltic

In this paper accurate hourly time series of water and salt transport across the Drogden Sill in Øresund are presented for a period of more than one year. The investigation is based on measured current, salinity and water levels from two fixed stations in the Drogden Channel and the Flinten Channel. The water transport is calculated by the method outlined in Jakobsen and Castejon (1995), which is extended in the present paper to include salt transport. The resulting water and salt transport distributions are given as functions of time or salinity. The data analyses show a net water discharge out of the Baltic Proper across the Drogden Sill of 2.5×103 m3/s and a net salt flux into the Baltic Proper of 58 tonnes/s. The outflow is water with a salinity less than 12 g/kg, while the inflow takes place in the interval from 12 g/kg to 32 g/kg. The Knudsen relations are extended by two equations regarding gross transport, whereby the barotropically pulsating flow of changing salinity may be equated with a corresponding two-layer system of opposing residual fluxes.

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