scholarly journals LAGRANGIAN MEASUREMENTS OF TURBULENT DISSIPATION OVER A SHALLOW TIDAL FLAT FROM PULSE COHERENT ACOUSTIC DOPPLER PROFILERS

2012 ◽  
Vol 1 (33) ◽  
pp. 49 ◽  
Author(s):  
Julia C Mullarney ◽  
Stephen M Henderson
Keyword(s):  
High Resolution ◽  
Tidal Flat ◽  
Order Structure ◽  
Measured Velocity ◽  
Near Surface ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Surface Drifters ◽  
Freshwater Plume ◽  
Lagrangian Measurements

We present high resolution (25 mm spatial, 8 Hz temporal) profiles of velocity measured over a shallow tidal flat using pulse-coherent Acoustic Doppler Profilers mounted on surface drifters. The use of Lagrangian measurements mitigated the problem of resolving velocity ambiguities, a problem which often limits the application of high-resolution pulse-coherent profilers. Turbulent dissipation rates were estimated from second-order structure functions of measured velocity. Drifters were advected towards, and subsequently trapped on, a convergent surface front which marked the edge of a freshwater plume. Measured dissipation rates increased as a drifter deployed within the plume approached the front. A drifter then propagated with and along the front as the fresh plume spread across the tidal flats. Near-surface turbulent dissipation measured at the front roughly matched a theoretical mean-shear-cubed relationship, whereas dissipation measured in the stratified plume behind the front was suppressed. After removal of estimates affected by surface waves, near-bed dissipation matched the velocity cubed relationship, although scatter was substantial. Dissipation rates appeared to be enhanced when the drifter propagated across small subtidal channels.

scholarly journals Chemical Signaling in the Turbulent Ocean—Hide and Seek at the Kolmogorov Scale

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 54
Author(s):  
Erik Selander ◽  
Sam T. Fredriksson ◽  
Lars Arneborg
Keyword(s):  
Steady State ◽  
Chemical Cues ◽  
Chemical Properties ◽  
Strong Wind ◽  
Mate Finding ◽  
Surrounding Water ◽  
Near Surface ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Kolmogorov Scale

Chemical cues and signals mediate resource acquisition, mate finding, and the assessment of predation risk in marine plankton. Here, we use the chemical properties of the first identified chemical cues from zooplankton together with in situ measurements of turbulent dissipation rates to calculate the effect of turbulence on the distribution of cues behind swimmers as well as steady state background concentrations in surrounding water. We further show that common zooplankton (copepods) appears to optimize mate finding by aggregating at the surface in calm conditions when turbulence do not prevent trail following. This near surface environment is characterized by anisotropic turbulence and we show, using direct numerical simulations, that chemical cues distribute more in the horizontal plane than vertically in these conditions. Zooplankton may consequently benefit from adopting specific search strategies near the surface as well as in strong stratification where similar flow fields develop. Steady state concentrations, where exudation is balanced by degradation develops in a time scale of ~5 h. We conclude that the trails behind millimeter-sized copepods can be detected in naturally occurring turbulence below the wind mixed surface layer or in the absence of strong wind. The trails, however, shorten dramatically at high turbulent dissipation rates, above ~10−3 cm2 s−3 (10−7 W kg−1)

scholarly journals Turbulence within rain-formed fresh lenses during the SPURS-2 Experiment

2021 ◽  
Author(s):  
Suneil Iyer ◽  
Kyla Drushka
Keyword(s):  
Water Cycle ◽  
Regional Study ◽  
Surface Salinity ◽  
Near Surface ◽  
Turbulent Dissipation ◽  
Wind Speeds ◽  
Dissipation Rates ◽  
Wide Range ◽  
Surface Turbulence ◽  
Primary Driver

AbstractObservations of salinity, temperature, and turbulent dissipation rate were made in the top meter of the ocean using the ship-towed Surface Salinity Profiler as part of the second Salinity Processes in the Upper Ocean Regional Study (SPURS-2) to assess the relationships between wind, rain, near-surface stratification, and turbulence. A wide range of wind and rain conditions were observed in the eastern tropical Pacific Ocean near 10°N, 125°W in summer-autumn 2016 and 2017. Wind was the primary driver of near-surface turbulence and the mixing of rain-formed fresh lenses, with lenses generally persisting for hours when wind speeds were under 5 m s−1 and mixing away immediately at higher wind speeds. Rain influenced near-surface turbulence primarily through stratification. Near-surface stratification caused by rainfall or diurnal warming suppressed deeper turbulent dissipation rates when wind speeds were under 3 m s−1. In one case with 4-5 m s−1 winds, rain-induced stratification enhanced dissipation rates within the stratified layer. At wind speeds above 7-8 m s−1, strong stratification was not observed in the upper meter during rain, indicating that rain lenses do not form at wind speeds above 8 m s−1. Raindrop impacts enhanced turbulent dissipation rates at these high wind speeds in the absence of near-surface stratification. Measurements of air-sea buoyancy flux, wind speed, and near-surface turbulence can be used to predict the presence of stratified layers. These findings could be used to improve model parameterizations of air-sea interactions and, ultimately, our understanding of the global water cycle.

scholarly journals Small-Scale Dispersion in the Presence of Langmuir Circulation

2019 ◽  
Vol 49 (12) ◽  
pp. 3069-3085 ◽  
Author(s):  
Henry Chang ◽  
Helga S. Huntley ◽  
A. D. Kirwan Jr. ◽  
Daniel F. Carlson ◽  
Jean A. Mensa ◽  
...  
Keyword(s):  
Structure Function ◽  
Second Order ◽  
Relative Dispersion ◽  
Small Scale ◽  
Cell Diameter ◽  
Order Structure ◽  
Near Surface ◽  
Surface Dispersion ◽  
Surface Drifters ◽  
Langmuir Cells

AbstractWe present an analysis of ocean surface dispersion characteristics, on 1–100-m scales, obtained by optically tracking a release of bamboo plates for 2 h in the northern Gulf of Mexico. Under sustained 5–6 m s−1 winds, energetic Langmuir cells are clearly delineated in the spatially dense plate observations. Within 10 min of release, the plates collect in windrows with 15-m spacing aligned with the wind. Windrow spacing grows, through windrow merger, to 40 m after 20 min and then expands at a slower rate to 50 m. The presence of Langmuir cells produces strong horizontal anisotropy and scale dependence in all surface dispersion statistics computed from the plate observations. Relative dispersion in the crosswind direction initially dominates but eventually saturates, while downwind dispersion exhibits continual growth consistent with contributions from both turbulent fluctuations and organized mean shear. Longitudinal velocity differences in the crosswind direction indicate mean convergence at scales below the Langmuir cell diameter and mean divergence at larger scales. Although the second-order structure function measured by contemporaneous GPS-tracked surface drifters drogued at ~0.5 m shows persistent r2/3 power law scaling down to 100–200-m separation scales, the second-order structure function for the very near surface plates observations has considerably higher energy and significantly shallower slope at scales below 100 m. This is consistent with contemporaneous data from undrogued surface drifters and previously published model results indicating shallowing spectra in the presence of direct wind-wave forcing mechanisms.

Interpretation of the Contrast of High-Resolution Electron Microscopy Images of Ni4Mo by Means of Simulated Image Maps

1990 ◽  
Vol 48 (1) ◽  
pp. 28-29
Author(s):  
A. Thust ◽  
K. Urban
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Antiphase Boundary ◽  
High Resolution Electron Microscopy ◽  
Foil Thickness ◽  
Order Structure ◽  
Simulated Image ◽  
Resolution Electron ◽  
Fcc Lattice ◽  
Direct Interpretation

The alloy of composition Ni4Mo develops, at temperatures below 860 °C, an ordered Dla-structure which is based on the fcc-lattice. This alloy has been widely investigated with respect to its physical properties and its ordering behaviour. High resolution studies are rare and concentrated mainly on its short-range order structure. The aim of the present work was to develop a detailed understanding of image contrast and to apply the results to antiphase-boundary studies in ordered Ni4Mo by means of a JEOL 4000 EX electron microscope.In high-resolution electron microscopy, depending on defocus and foil thickness, a large variety of different images is obtained. Only a few of these allow a direct interpretation concerning the location and the type of the atoms. By computing a through-focus/through-thickness map (TFTT map) before starting experimental work it is possible to determine the proper conditions at which images can be obtained which are closely related to the projected potential.

scholarly journals Geophysical investigations for stability and safety mitigation of regional crude-oil pipeline near abandoned coal mines

2021 ◽  
Vol 18 (1) ◽  
pp. 145-162
Author(s):  
B Butchibabu ◽  
Prosanta Kumar Khan ◽  
P C Jha
Keyword(s):  
High Resolution ◽  
Crude Oil ◽  
Seismic Refraction ◽  
High Resolution Imaging ◽  
Weak Zone ◽  
Near Surface ◽  
Oil Pipeline ◽  
Refraction Tomography ◽  
Geophysical Investigations ◽  
Resolution Imaging

Abstract This study aims for the protection of a crude-oil pipeline, buried at a shallow depth, against a probable environmental hazard and pilferage. Both surface and borehole geophysical techniques such as electrical resistivity tomography (ERT), ground penetrating radar (GPR), surface seismic refraction tomography (SRT), cross-hole seismic tomography (CST) and cross-hole seismic profiling (CSP) were used to map the vulnerable zones. Data were acquired using ERT, GPR and SRT along the pipeline for a length of 750 m, and across the pipeline for a length of 4096 m (over 16 profiles of ERT and SRT with a separation of 50 m) for high-resolution imaging of the near-surface features. Borehole techniques, based on six CSP and three CST, were carried out at potentially vulnerable locations up to a depth of 30 m to complement the surface mapping with high-resolution imaging of deeper features. The ERT results revealed the presence of voids or cavities below the pipeline. A major weak zone was identified at the central part of the study area extending significantly deep into the subsurface. CSP and CST results also confirmed the presence of weak zones below the pipeline. The integrated geophysical investigations helped to detect the old workings and a deformation zone in the overburden. These features near the pipeline produced instability leading to deformation in the overburden, and led to subsidence in close vicinity of the concerned area. The area for imminent subsidence, proposed based on the results of the present comprehensive geophysical investigations, was found critical for the pipeline.

scholarly journals High Resolution Transmission Electron Microscopy of Metallic Film/Laser-Irradiated Alumina Couples.

1994 ◽  
Vol 357 ◽  
Author(s):  
A. J. Pedraza ◽  
Siqi Cao ◽  
L. F. Allard ◽  
D. H. Lowndes
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Copper Film ◽  
Interfacial Structure ◽  
Diffuse Interface ◽  
Cross Sectional ◽  
Polycrystalline Alumina ◽  
Near Surface ◽  
Transmission Electron

AbstractA near-surface thin layer is melted when single crystal alumina (sapphire) is pulsed laserirradiated in an Ar-4%H2 atmosphere. γ-alumina grows epitaxially from the (0001) face of axalumina (sapphire) during the rapid solidification of this layer that occurs once the laser pulse is over. Cross sectional high resolution transmission electron microscopy (HRTEM) reveals that the interface between unmelted sapphire and γ-alumina is atomistically flat with steps of one to a few close-packed oxygen layers; however, pronounced lattice distortions exist in the resolidified γ-alumina. HRTEM also is used to study the metal-ceramic interface of a copper film deposited on a laser-irradiated alumina substrate. The observed changes of the interfacial structure relative to that of unexposed substrates are correlated with the strong enhancement of film-substrate bonding promoted by laser irradiation. HRTEM shows that a thin amorphous film is produced after irradiation of 99.6% polycrystalline alumina. Formation of a diffuse interface and atomic rearrangements that can take place in metastable phases contribute to enhance the bonding strength of copper to laser-irradiated alumina.

Climate change in the High Mountain Asia simulated with CMIP6 models

2021 ◽  
Author(s):  
Mickaël Lalande ◽  
Martin Ménégoz ◽  
Gerhard Krinner
Keyword(s):  
High Resolution ◽  
Snow Cover ◽  
Climate Models ◽  
Global Climate Models ◽  
Cold Bias ◽  
High Mountain ◽  
The Tibetan Plateau ◽  
Near Surface ◽  
Model Biases ◽  
Snow Cover Extent

<p>The High Mountains of Asia (HMA) region and the Tibetan Plateau (TP), with an average altitude of 4000 m, are hosting the third largest reservoir of glaciers and snow after the two polar ice caps, and are at the origin of strong orographic precipitation. Climate studies over HMA are related to serious challenges concerning the exposure of human infrastructures to natural hazards and the water resources for agriculture, drinking water, and hydroelectricity to whom several hundred million inhabitants of the Indian subcontinent are depending. However, climate variables such as temperature, precipitation, and snow cover are poorly described by global climate models because their coarse resolution is not adapted to the rugged topography of this region. Since the first CMIP exercises, a cold model bias has been identified in this region, however, its attribution is not obvious and may be different from one model to another. Our study focuses on a multi-model comparison of the CMIP6 simulations used to investigate the climate variability in this area to answer the next questions: (1) are the biases in HMA reduced in the new generation of climate models? (2) Do the model biases impact the simulated climate trends? (3) What are the links between the model biases in temperature, precipitation, and snow cover extent? (4) Which climate trajectories can be projected in this area until 2100? An analysis of 27 models over 1979-2014 still show a cold bias in near-surface air temperature over the HMA and TP reaching an annual value of -2.0 °C (± 3.2 °C), associated with an over-extended relative snow cover extent of 53 % (± 62 %), and a relative excess of precipitation of 139 % (± 38 %), knowing that the precipitation biases are uncertain because of the undercatch of solid precipitation in observations. Model biases and trends do not show any clear links, suggesting that biased models should not be excluded in trend and projections analysis, although non-linear effects related to lagged snow cover feedbacks could be expected. On average over 2081-2100 with respect to 1995-2014, for the scenarios SSP126, SSP245, SSP370, and SSP585, the 9 available models shows respectively an increase in annual temperature of 1.9 °C (± 0.5 °C), 3.4 °C (± 0.7 °C), 5.2 °C (± 1.2 °C), and 6.6 °C (± 1.5 °C); a relative decrease in the snow cover extent of 10 % (± 4.1 %), 19 % (± 5 %), 29 % (± 8 %), and 35 % (± 9 %); and an increase in total precipitation of 9 % (± 5 %), 13 % (± 7 %), 19 % (± 11 %), and 27 % (± 13 %). Further analyses will be considered to investigate potential links between the biases at the surface and those at higher tropospheric levels as well as with the topography. The models based on high resolution do not perform better than the coarse-gridded ones, suggesting that the race to high resolution should be considered as a second priority after the developments of more realistic physical parameterizations.</p>

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