Near-surface mixing in a freshwater lake

1991 ◽  
Vol 42 (6) ◽  
pp. 655 ◽  
Author(s):  
L Padman
Keyword(s):  
Heat Content ◽  
Heat Fluxes ◽  
Freshwater Lake ◽  
Wave Number ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
High Wave Number ◽  
Near Surface ◽  
Vertical Heat ◽  
Surface Mixing

Mixing rates in the upper 10 m of a freshwater lake during the spring heating season are examined by means of fine-structure temperature profiles. Dissipation rate, eddy diffusivity, and vertical heat flux are estimated from 'Thorpe reordering' of measured temperature profiles, a technique that allows these parameters to be obtained from the energy-containing scales of the turbulence rather than from the much smaller scales at which kinetic energy dissipation and scalar diffusion actually occur. The estimated vertical heat fluxes agree reasonably well with the seasonal variability of the lake's total heat content and with the observed short-term variability in mixed-layer temperature. These results suggest that satisfactory estimates of turbulent vertical diffusivities in the surface mixing layer can be obtained from Thorpe reordering. This technique can be applied to data that are considerably simpler and cheaper to obtain than are the measurements of microscale shear required for the more usual 'dissipation' method. Concurrent measurements of vertically averaged shear from a nearby surface mooring are used to study the use of Richardson numbers as a parameter in diffusion models. It is shown that considerable mixing can occur even when the Richardson number based on vertical and temporal averages of shear and density gradient is much larger than the assumed critical value of O(1). Therefore, in regions where the shear and strain variances evaluated over a fixed vertical scale cannot be related either observationally or by means of modelled spectra to the unresolved high wave-number variances, the use of diffusivity parametrizations based on measured, averaged Richardson numbers cannot be justified.

On the Accuracy of the Simple Ocean Data Assimilation Analysis for Estimating Heat Budgets of the Near-Surface Arabian Sea and Bay of Bengal*

2005 ◽  
Vol 35 (3) ◽  
pp. 395-400 ◽  
Author(s):  
S S C. Shenoi ◽  
D. Shankar ◽  
S. R. Shetye
Keyword(s):  
Data Assimilation ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Heat Budget ◽  
Heat Content ◽  
Heat Fluxes ◽  
Simple Ocean Data Assimilation ◽  
Near Surface ◽  
Surface Heat Fluxes ◽  
Ocean Data Assimilation

Abstract The accuracy of data from the Simple Ocean Data Assimilation (SODA) model for estimating the heat budget of the upper ocean is tested in the Arabian Sea and the Bay of Bengal. SODA is able to reproduce the changes in heat content when they are forced more by the winds, as in wind-forced mixing, upwelling, and advection, but not when they are forced exclusively by surface heat fluxes, as in the warming before the summer monsoon.

scholarly journals Thermal Regime of Ice Covered Swedish Lakes

1996 ◽  
Vol 27 (1-2) ◽  
pp. 39-56 ◽  
Author(s):  
Lars Bengtsson ◽  
Thorbjörn Svensson
Keyword(s):  
Heat Flux ◽  
Solar Radiation ◽  
Heat Source ◽  
Lake Water ◽  
Heat Budget ◽  
Heat Content ◽  
Heat Fluxes ◽  
Late Winter ◽  
Temperature Profiles ◽  
Early Winter

Temperature conditions and heat fluxes in ice covered lakes are discussed analyzing measurements in eight Swedish lakes. Heat fluxes from sediments and heat fluxes from water to ice are determined from temperature profiles. The contribution of solar radiation is estimated from heat-budget calculations. It is found that the heat content of most of the lakes changes very little when they are ice covered, but that the lake-water temperature slightly increases. All heat fluxes are small. The heat flux from the sediments is the highest flux in early winter, but is later in the winter balanced by the heat loss from the water to the underside of the ice. Solar radiation is an important heat source in late winter, when the snow cover is thin.

scholarly journals Vertical Redistribution of Oceanic Heat Content

2015 ◽  
Vol 28 (9) ◽  
pp. 3821-3833 ◽  
Author(s):  
Xinfeng Liang ◽  
Carl Wunsch ◽  
Patrick Heimbach ◽  
Gael Forget
Keyword(s):  
Heat Flux ◽  
Heat Exchange ◽  
Heat Transport ◽  
Heat Content ◽  
Deep Ocean ◽  
Temporal Variations ◽  
Near Surface ◽  
Carbon 14 ◽  
Vertical Heat ◽  
Vertical Heat Flux

Abstract Estimated values of recent oceanic heat uptake are on the order of a few tenths of a W m−2, and are a very small residual of air–sea exchanges, with annual average regional magnitudes of hundreds of W m−2. Using a dynamically consistent state estimate, the redistribution of heat within the ocean is calculated over a 20-yr period. The 20-yr mean vertical heat flux shows strong variations in both the lateral and vertical directions, consistent with the ocean being a dynamically active and spatially complex heat exchanger. Between mixing and advection, the two processes determining the vertical heat transport in the deep ocean, advection plays a more important role in setting the spatial patterns of vertical heat exchange and its temporal variations. The global integral of vertical heat flux shows an upward heat transport in the deep ocean, suggesting a cooling trend in the deep ocean. These results support an inference that the near-surface thermal properties of the ocean are a consequence, at least in part, of internal redistributions of heat, some of which must reflect water that has undergone long trajectories since last exposure to the atmosphere. The small residual heat exchange with the atmosphere today is unlikely to represent the interaction with an ocean that was in thermal equilibrium at the start of global warming. An analogy is drawn with carbon-14 “reservoir ages,” which range from over hundreds to a thousand years.

scholarly journals THEORY OF EVAPOTRANSPIRATION: 2. Soil and intercepted water evaporation

2011 ◽  
Vol 59 (2) ◽  
pp. 73-84 ◽  
Author(s):  
Anatolij Budagovskyi ◽  
Viliam Novák
Keyword(s):  
Water Flux ◽  
Heat Fluxes ◽  
Water Evaporation ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Net Radiation ◽  
Air Humidity ◽  
Indirect Methods ◽  
The Difference ◽  
Evapotranspiration Estimation

THEORY OF EVAPOTRANSPIRATION: 2. Soil and intercepted water evaporationEvaporation of water from the soil is described and quantified. Formation of the soil dry surface layer is quantitatively described, as a process resulting from the difference between the evaporation and upward soil water flux to the soil evaporating level. The results of evaporation analysis are generalized even for the case of water evaporation from the soil under canopy and interaction between evaporation rate and canopy transpiration is accounted for. Relationships describing evapotranspiration increase due to evaporation of the water intercepted by canopy are presented. Indirect methods of evapotranspiration estimation are discussed, based on the measured temperature profiles and of the air humidity, as well as of the net radiation and the soil heat fluxes.

Seasonal mixed layer heat budget in coastal waters off Angola

2021 ◽  
Author(s):  
Mareike Körner ◽  
Peter Brandt ◽  
Marcus Dengler
Keyword(s):  
Mixed Layer ◽  
Heat Budget ◽  
Heat Content ◽  
Nutrient Supply ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Driving Mechanism ◽  
Near Surface ◽  
Surface Heat Fluxes ◽  
Mixed Layer Heat Budget

<p>The Angolan shelf system represents a highly productive ecosystem that exhibits pronounced seasonal variability. Productivity peaks in austral winter when seasonally prevailing upwelling favorable winds are weakest. Thus, other processes than local wind-driven upwelling contribute to the near-coastal cooling and nutrient supply during this season. Possible processes that lead to changes of the mixed-layer heat content does not only include local mechanism but also the passage of remotely forced coastally trapped waves. Understanding the driving mechanism of changes in the mixed-layer heat content that may be locally or remotely forced are vital for understanding of upward nutrient supply and biological productivity off Angola. Here, we investigate the seasonal mixed layer heat budget by analyzing atmospheric and oceanic causes for heat content variability. We calculate monthly estimates of surface heat fluxes, horizontal advection from near-surface velocities, horizontal eddy advection, and vertical entrainment. Additionally, diapycnal heat fluxes at the mixed-layer base are determined from shipboard and glider microstructure data. The results are discussed in reference to the variability of the eastern boundary circulation, surface heat fluxes and wind forcing.</p>

Midlatitude Moisture Contribution to Recent Arctic Tropospheric Summertime Variability*

2014 ◽  
Vol 27 (15) ◽  
pp. 5693-5707 ◽  
Author(s):  
Frédéric Laliberté ◽  
Paul J. Kushner
Keyword(s):  
High Frequency ◽  
Climate Models ◽  
Heat Content ◽  
Lower Troposphere ◽  
Late Summer ◽  
Heat Fluxes ◽  
The Arctic ◽  
High Frequency Data ◽  
Frequency Data ◽  
Near Surface

Abstract The dynamics of late summer Arctic tropospheric heat content variability is studied using reanalyses. In both trends and interannual variability, much of the August heat content variability in the Arctic midtroposphere can be explained by the total—sensible plus latent—heat content variability at the midlatitude near surface in July. Climate models suggest that this connection is part of the global warming signal in September–November, but in reanalyses the connection is most strongly present in July–August variability and trends. It is argued that heat content signals are propagated from the midlatitude near surface to the Arctic midtroposphere approximately along climatological moist isentropes. High-frequency data reveal that the propagating signal is primarily driven by a few strong meridional heat flux events each summer season. Composite analysis on these events shows that August meridional heat fluxes into the Arctic midtroposphere are succeeded by positive heat content anomalies in the lower troposphere a few days later. This second connection between the Arctic midtroposphere and the Arctic lower troposphere could be sufficient to explain some of the recent Arctic 850-hPa temperature variability north of 75°N.

Measured Temperature Profiles Within the Superheated Boundary Layer Above a Horizontal Surface in Saturated Nucleate Pool Boiling of Water

1965 ◽  
Vol 87 (3) ◽  
pp. 333-340 ◽  
Author(s):  
B. D. Marcus ◽  
D. Dropkin
Keyword(s):  
Boundary Layer ◽  
Temperature Distribution ◽  
Pool Boiling ◽  
Heating Surface ◽  
Heat Fluxes ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Nucleate Pool Boiling ◽  
Average Temperature ◽  
The Heat Transfer Coefficient

Temperature measurements were made within the superheated boundary layer above and adjacent to a horizontal heating surface in saturated, nucleate, pool boiling of water. A microthermocouple probe was used to measure the average temperature profiles and the temperature fluctuations within the boundary layer at heat fluxes from 1000 to 40,000 Btu/hr-sq ft. Correlations are presented for the “extrapolated” thickness of the boundary layer (δ) as well as the temperature distribution within it. It was found that the thickness (δ) could be expressed in terms of the heat-transfer coefficient as: δ = Chd. Also, the behavior of δ with system parameters was found to agree with that predicted by Han and Griffith [3] and Hsu [4] in their theories of nucleation from surface cavities. The temperature distribution in the boundary layer from the surface to 0.57δ was essentially linear and could be expressed: (T − Tb)/(Ts − Tb) = 1 − (y/δ). Above 0.57δ the temperature profile became an inverse power function of the height above the surface: (T − Tb)/(Ts − Tb) = D(y/δ)−a.

AN EXPERIMENTAL AND NUMERICAL STUDY OF HEAT TRANSFER IN A SIMULATED COLLECTOR FOR A SOLAR DRYER

1993 ◽  
Vol 17 (2) ◽  
pp. 145-160
Author(s):  
P.H. Oosthuizen ◽  
A. Sheriff
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Lower Surface ◽  
Local Heat ◽  
Electrical Heating ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Transfer Rates ◽  
Thermocouple Probe

Indirect passive solar crop dryers have the potential to considerably reduce the losses that presently occur during drying of some crops in many parts of the “developing” world. The performance so far achieved with such dryers has, however, not proved to be very satisfactory. If this performance is to be improved it is necessary to have an accurate computer model of such dryers to assist in their design. An important element is any dryer model is an accurate equation for the convective heat transfer in the collector. To assist in the development of such an equation, an experimental and numerical study of the collector heat transfer has been undertaken. In the experimental study, the collector was simulated by a 1m long by 1m wide channel with a gap of 4 cm between the upper and lower surfaces. The lower surface of the channel consisted of an aluminium plate with an electrical heating element, simulating the solar heating, bonded to its lower surface. Air was blown through this channel at a measured rate and the temperature profiles at various points along the channel were measured using a shielded thermocouple probe. Local heat transfer rates were then determined from these measured temperature profiles. In the numerical study, the parabolic forms of the governing equations were solved by a forward-marching finite difference procedure.

scholarly journals Interaction of Very Large Scale Motion of Coherent Structures with Sediment Particle Exposure

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 248
Author(s):  
Sencer Yücesan ◽  
Daniel Wildt ◽  
Philipp Gmeiner ◽  
Johannes Schobesberger ◽  
Christoph Hauer ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Numerical Study ◽  
Local Maximum ◽  
Wave Number ◽  
Exposure Level ◽  
Sediment Particle ◽  
High Wave Number ◽  
Large Scale Motion ◽  
Scale Motion

A systematic variation of the exposure level of a spherical particle in an array of multiple spheres in a high Reynolds number turbulent open-channel flow regime was investigated while using the Large Eddy Simulation method. Our numerical study analysed hydrodynamic conditions of a sediment particle based on three different channel configurations, from full exposure to zero exposure level. Premultiplied spectrum analysis revealed that the effect of very-large-scale motion of coherent structures on the lift force on a fully exposed particle resulted in a bi-modal distribution with a weak low wave number and a local maximum of a high wave number. Lower exposure levels were found to exhibit a uni-modal distribution.

Thermomechanical Coupling of a Hyper-viscoelastic Truck Tire and a Pavement Layer and its Impact on Three-dimensional Contact Stresses

2021 ◽  
pp. 036119812110171
Author(s):  
Angeli Jayme ◽  
Imad L. Al-Qadi
Keyword(s):  
Contact Stress ◽  
Contact Area ◽  
Three Dimensional ◽  
Interaction Model ◽  
Rolling Resistance ◽  
Contact Stresses ◽  
Thermomechanical Coupling ◽  
Temperature Profiles ◽  
Near Surface ◽  
Truck Tire

A thermomechanical coupling between a hyper-viscoelastic tire and a representative pavement layer was conducted to assess the effect of various temperature profiles on the mechanical behavior of a rolling truck tire. The two deformable bodies, namely the tire and pavement layer, were subjected to steady-state-uniform and non-uniform temperature profiles to identify the significance of considering temperature as a variable in contact-stress prediction. A myriad of ambient, internal air, and pavement-surface conditions were simulated, along with combinations of applied tire load, tire-inflation pressure, and traveling speed. Analogous to winter, the low temperature profiles induced a smaller tire-pavement contact area that resulted in stress localization. On the other hand, under high temperature conditions during the summer, higher tire deformation resulted in lower contact-stress magnitudes owing to an increase in the tire-pavement contact area. In both conditions, vertical and longitudinal contact stresses are impacted, while transverse contact stresses are relatively less affected. This behavior, however, may change under a non-free-rolling condition, such as braking, accelerating, and cornering. By incorporating temperature into the tire-pavement interaction model, changes in the magnitude and distribution of the three-dimensional contact stresses were manifested. This would have a direct implication on the rolling resistance and near-surface behavior of flexible pavements.

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