scholarly journals Thermally driven exchange flow between open water and an aquatic canopy

2009 ◽  
Vol 632 ◽  
pp. 227-243 ◽  
Author(s):  
XUEYAN ZHANG ◽  
HEIDI M. NEPF
Keyword(s):  
Temperature Difference ◽  
Laboratory Experiments ◽  
Open Water ◽  
Scaling Analysis ◽  
Exchange Flow ◽  
Light Penetration ◽  
Constant Heat ◽  
Velocity Scale ◽  
Thermally Driven ◽  
Particle Imaging

Differential solar heating can result from shading by rooted emergent aquatic plants, producing a temperature difference between vegetated and unvegetated regions of a surface water body. This temperature difference will promote an exchange flow between the vegetation and open water. Drag associated with the submerged portion of the plants modifies this exchange, specifically, changing the dominant velocity scale. Scaling analysis predicts several distinct flow regimes, including inertia-dominated, drag-dominated and energy-limiting regimes. After a constant heat source is initiated, the flow is initially inertial, but quickly transitions to the drag-dominated regime. The energy-limiting regime is not likely to occur in the presence of rooted vegetation. Laboratory experiments describe the exchange flow and confirm the scaling analysis. Particle Imaging Velocimetry (PIV) was used to quantify the velocity field. Once the exchange flow enters the drag-dominated regime, the intrusion velocity uV is steady. The intrusion velocity decreases with increasing density of vegetation. The thickness of the intruding layer is set by the length scale of light penetration.

Relation of algal biovolume to chlorophyll a in selected lakes and wetlands in the north-central United States

1995 ◽  
Vol 52 (2) ◽  
pp. 416-424 ◽  
Author(s):  
James W. LaBaugh
Keyword(s):  
United States ◽  
North Dakota ◽  
Chlorophyll A ◽  
Linear Relation ◽  
Algal Biomass ◽  
Open Water ◽  
Light Penetration ◽  
North Central ◽  
The North ◽  
Central United States

Algal chlorophyll a is commonly used as a surrogate for algal biomass. Data from three lakes in western Nebraska, five wetlands in north-central North Dakota, and two lakes in north-central Minnesota represented a range in algal biovolume of over four orders of magnitude and a range in chlorophyll a from less than 1 to 380 mg∙m−3. Analysis of these data revealed that there was a linear relation, log10 algal biovolume = 5.99 + 0.09 chlorophyll a (r2 = 0.72), for cases in which median values of chlorophyll a for open-water periods were less than 20 mg∙m−3. There was no linear relation in cases in which median chlorophyll a concentrations were larger than 20 mg∙m−3 for open-water periods, an occurrence found only in shallow prairies lakes and wetlands for years in which light penetration was the least.

Symmetric Holmboe instabilities in a laboratory exchange flow

2009 ◽  
Vol 636 ◽  
pp. 137-153 ◽  
Author(s):  
EDMUND W. TEDFORD ◽  
R. PIETERS ◽  
G. A. LAWRENCE
Keyword(s):  
Cross Section ◽  
Laboratory Experiments ◽  
Rectangular Cross Section ◽  
Flow Direction ◽  
Phase Speed ◽  
Exchange Flow ◽  
Subcritical Region ◽  
Average Wavelength

Laboratory experiments have been conducted that test the predictions of Holmboe (Geofys. Publ., vol. 24, 1962, pp. 67–112). Symmetric Holmboe instabilities are observed during steady, maximal two-layer exchange flow in a long laboratory channel of rectangular cross-section. Internal hydraulic controls at each end of the channel isolate the subcritical region within the channel from disturbances in the reservoirs. Inside the channel, the instabilities form cusp-like waves that propagate in both directions. The phase speed of the instabilities is consistent with Holmboe's theory and increases along the length of the channel as a result of the gradual acceleration of each layer. This acceleration causes the wavelength of any given instability to increase in the flow direction until it is approximately twice the most amplified wavelength. At this point new waves develop with the result that the average wavelength is almost constant along the length of the channel.

Long-ranged order in a thermally driven system with temperature dependent interactions

Soft Matter ◽  
2022 ◽  
Author(s):  
Rahul Karmakar ◽  
Jaydeb Chakrabarti
Keyword(s):  
Temperature Difference ◽  
Metallic Nanoparticles ◽  
Particle Interaction ◽  
Temperature Dependent ◽  
Driving Situation ◽  
Driven System ◽  
Thermally Driven

Aggregation of macro-molecules under external drive is far from understood. An important driving situation is achieved by temperature difference. The inter-particle interaction in metallic nanoparticles with ligand capping is reported...

scholarly journals A Simple Method Based on Routine Observations to Nowcast Down-Valley Flows in Shallow, Narrow Valleys

2016 ◽  
Vol 55 (7) ◽  
pp. 1497-1511 ◽  
Author(s):  
Gert-Jan Duine ◽  
Thierry Hedde ◽  
Pierre Roubin ◽  
Pierre Durand
Keyword(s):  
Temperature Difference ◽  
Potential Temperature ◽  
Threshold Value ◽  
Simple Relation ◽  
Forecast Verification ◽  
Valley Wind ◽  
Simple Method ◽  
Thermally Driven ◽  
Scale Down ◽  
Valley Flows

AbstractA simple relation to diagnose the existence of a thermally driven down-valley wind in a shallow (100 m deep) and narrow (1–2 km wide) valley based on routine weather measurements has been determined. The relation is based on a method that has been derived from a forecast verification principle. It consists of optimizing a threshold of permanently measured quantities to nowcast the thermally driven Cadarache (southeastern France) down-valley wind. Three parameters permanently observed at a 110-m-high tower have been examined: the potential temperature difference between the heights of 110 and 2 m, the wind speed at 110 m, and a bulk Richardson number. The thresholds are optimized using the wind observations obtained within the valley during the Katabatic Winds and Stability over Cadarache for the Dispersion of Effluents (KASCADE) field experiment, which was conducted in the winter of 2013. The highest predictability of the down-valley wind at the height of 10 m (correct nowcasting ratio of 0.90) was found for the potential temperature difference at a threshold value of 2.6 K. The applicability of the method to other heights of the down-valley wind (2 and 30 m) and to summer conditions is also demonstrated. This allowed a reconstruction of the climatology of the thermally driven down-valley wind that demonstrates that the wind exists throughout the year and is strongly linked to nighttime duration. This threshold technique will make it possible to forecast the subgrid-scale down-valley wind from operational numerical weather coarse-grid simulations by means of statistical downscaling.

Thermally Driven Exchanges between a Coral Reef and the Adjoining Ocean

2006 ◽  
Vol 36 (7) ◽  
pp. 1332-1347 ◽  
Author(s):  
Stephen G. Monismith ◽  
Amatzia Genin ◽  
Matthew A. Reidenbach ◽  
Gitai Yahel ◽  
Jeffrey R. Koseff
Keyword(s):  
Coral Reef ◽  
Gulf Of Aqaba ◽  
Exchange Flow ◽  
Temperature Changes ◽  
Buoyancy Forcing ◽  
Cooling Flow ◽  
Heating And Cooling ◽  
Thermally Driven ◽  
Near Shore ◽  
The 1960S

Abstract In this paper hydrographic observations made over a fringing coral reef at the northern end of the Gulf of Aqaba near Eilat, Israel, are discussed. These data show exchange flows driven by the onshore–offshore temperature gradients that develop because shallow regions near shore experience larger temperature changes than do deeper regions offshore when subjected to the same rate of heating or cooling. Under heating conditions, the resulting vertically sheared exchange flow is offshore at the surface and onshore at depth, whereas when cooling dominates, the pattern is reversed. For summer conditions, heating and cooling are both important and a diurnally reversing exchange flow is observed. During winter conditions, heating occupies a relatively small fraction of the day, and only the cooling flow is observed. When scaled by ΔV, the observed profiles of the cross-shore during cooling velocity collapse onto a single curve. The value of ΔV depends on the convective velocity scale uf and the bottom slope β through the inertial scaling, ΔV ∼ β−1/3uf first proposed by Phillips in the 1960s as a model of buoyancy-driven flow in the Red Sea. However, it is found that turbulent stresses associated with the longshore tidal flows and unsteadiness due to the periodic nature of the buoyancy forcing can act to weaken the sheared exchange flow. Nonetheless, the measured exchange flow transport agrees well with previous field and laboratory work. The paper is concluded by noting that the “thermal siphon” observed on the Eilat reef may be a relatively generic feature of the nearshore physical oceanography of reefs and coastal oceans in general.

scholarly journals Diagnosing Surface Mixed Layer Dynamics from High-Resolution Satellite Observations: Numerical Insights

2013 ◽  
Vol 43 (7) ◽  
pp. 1345-1355 ◽  
Author(s):  
Aurelien L. Ponte ◽  
Patrice Klein ◽  
Xavier Capet ◽  
Pierre-Yves Le Traon ◽  
Bertrand Chapron ◽  
...  
Keyword(s):  
High Resolution ◽  
Mixed Layer ◽  
Vertical Mixing ◽  
Mesoscale Eddy ◽  
Three Dimensional ◽  
Satellite Observations ◽  
Scaling Analysis ◽  
Surface Mixed Layer ◽  
Surface Layers ◽  
Velocity Scale

Abstract High-resolution numerical experiments of ocean mesoscale eddy turbulence show that the wind-driven mixed layer (ML) dynamics affects mesoscale motions in the surface layers at scales lower than O(60 km). At these scales, surface horizontal currents are still coherent to, but weaker than, those derived from sea surface height using geostrophy. Vertical motions, on the other hand, are stronger than those diagnosed using the adiabatic quasigeotrophic (QG) framework. An analytical model, based on a scaling analysis and on simple dynamical arguments, provides a physical understanding and leads to a parameterization of these features in terms of vertical mixing. These results are valid when the wind-driven velocity scale is much smaller than that associated with eddies and the Ekman number (related to the ratio between the Ekman and ML depth) is not small. This suggests that, in these specific situations, three-dimensional ML motions (including the vertical velocity) can be diagnosed from high-resolution satellite observations combined with a climatological knowledge of ML conditions and interior stratification.

Exchange flow between a canopy and open water

2008 ◽  
Vol 611 ◽  
pp. 237-254 ◽  
Author(s):  
MIRMOSADEGH JAMALI ◽  
XUEYAN ZHANG ◽  
HEIDI M. NEPF
Keyword(s):  
Initial Period ◽  
Gravity Current ◽  
Open Water ◽  
Force Balance ◽  
Exchange Flow ◽  
Drag Forces ◽  
Numerical Predictions ◽  
Initial Stage ◽  
Open Region ◽  
Internal Froude Number

This paper theoretically and experimentally investigates the exchange flow due to temperature differences between open water and a canopy of aquatic plants. A numerical model is used to study the interfacial shape, frontal velocity and total volumetric exchange, and their dependence on a dimensionless vegetation drag parameter. The numerical predictions are consistent with the laboratory measurements. There is a short initial period in which the force balance is between buoyancy and inertia, followed by drag-dominated flow for which there is a balance between buoyancy and drag forces. After the initial stage, the gravity current propagating into the canopy takes a triangular shape whereas the current propagating into the open water has almost the classic unobstructed horizontal profile, but with a slowly decreasing depth. Near the edge of the canopy, but in the open region, the flow is found to be critical with a unit internal Froude number. The exchange flow rate and the front speed in the canopy decrease slowly with time whereas the gravity current in the open water has a constant speed. The magnitude of the exchange flow decreases as the canopy drag increases. Empirical equations for the flow properties are presented. A movie is available with the online version of the paper.

scholarly journals Impact of Thermally Driven Turbulence on the Bottom Melting of Ice

2016 ◽  
Vol 46 (4) ◽  
pp. 1171-1187 ◽  
Author(s):  
T. Keitzl ◽  
J. P. Mellado ◽  
D. Notz
Keyword(s):  
Laboratory Experiments ◽  
Scaling Laws ◽  
Rate Increase ◽  
Strong Temperature Dependence ◽  
Far Field ◽  
Field Temperature ◽  
Thermally Driven ◽  
Flow Features ◽  
Ice Water ◽  
Diffusive Layer

AbstractDirect numerical simulation and laboratory experiments are used to investigate turbulent convection beneath a horizontal ice–water interface. Scaling laws are derived that quantify the dependence of the melt rate of the ice on the far-field temperature of the water under purely thermally driven conditions. The scaling laws, the simulations, and the laboratory experiments consistently yield that the melt rate increases by two orders of magnitude, from ⋍101 to ⋍103 mm day−1, as the far-field temperature increases from 4° to 8°C. The strong temperature dependence of the melt rate is explained by analyzing the vertical structure of the flow: For far-field temperatures below 8°C, the flow features a stably stratified, diffusive layer next to the ice that shields it from the warmer, turbulent outer layer. The stratification in the diffusive layer diminishes as the far-field temperature increases and vanishes for far-field temperatures far above 8°C. Possible implications of these results for ice–ocean interfaces are discussed. The drastic melt-rate increase implies that turbulence needs to be considered in the analysis of ice–water interfaces even in shear-free conditions.

scholarly journals Density-driven exchange flow between open water and an aquatic canopy

2008 ◽  
Vol 44 (8) ◽  
Author(s):  
Xueyan Zhang ◽  
Heidi M. Nepf
Keyword(s):  
Open Water ◽  
Exchange Flow
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