scholarly journals Persistence behavior of heat and momentum fluxes in convective surface layer turbulence

2020 ◽  
Vol 32 (11) ◽  
pp. 115107
Author(s):  
Subharthi Chowdhuri ◽  
Thara Prabhakaran ◽  
Tirtha Banerjee
Keyword(s):  
Surface Layer ◽  
Momentum Fluxes ◽  
Persistence Behavior

scholarly journals Seedbank persistence and emergence pattern of Argemone mexicana, Rapistrum rugosum and Sonchus oleraceus in the eastern grain region of Australia

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sudheesh Manalil ◽  
Bhagirath Singh Chauhan
Keyword(s):  
Surface Layer ◽  
Winter Season ◽  
Seed Viability ◽  
Annual Rainfall ◽  
Argemone Mexicana ◽  
Emergence Pattern ◽  
Seed Persistence ◽  
Rapistrum Rugosum ◽  
Persistence Behavior ◽  
Mesh Bag

AbstractA thorough understanding of the emergence pattern and persistence of weed seeds is a prerequisite in framing appropriate weed management options for noxious weeds. In a study conducted at the University of Queensland, Australia, the emergence and seed persistence behavior of three major weeds Sonchus oleraceous, Rapistrum rugosum, and Argemone mexicana were explored with seeds collected from Gatton and St George, Queensland, Australia, with an average annual rainfall of 760 and 470 mm, respectively. Seed persistence was evaluated by placing seeds at the surface layer (0 cm) or buried at 2 and 10 cm depths enclosed in nylon mesh bags and examined their viability for 42 months. In another study, the emergence pattern of four populations, each from these two locations, was evaluated under a rainfed environment in trays. In the mesh-bag study, rapid depletion of seed viability of S. oleraceous from the surface layer (within 18 months) and lack of seed persistence beyond two years from 2 and 10 cm depths were observed. In trays, S. oleraceous germinated 3 months after seeding in response to summer rains and there was progressive germination throughout the winter season reaching cumulative germination ranging from 22 to 29% for all the populations. In the mesh-bag study, it took about 30 months for the viability of seeds of R. rugosum to deplete at the surface layer and a proportion of seeds (5 to 13%) remained viable at 2 and 10 cm depths even at 42 months. Although fresh seeds of R. rugosum exhibit dormancy imposed due to the hard seed coat, a proportion of seeds germinated during the summer months in response to summer rains. Rapid loss of seed viability was observed for A. mexicana from the surface layer; however, more than 30% of the seeds were persistent at 2 and 10 cm depths at 42 months. Notably, poor emergence was observed for A. mexicana in trays and that was mostly confined to the winter season.

scholarly journals Fluxes over Varanasi during intensive observation  period of MONTBLEX-90

MAUSAM ◽  
2022 ◽  
Vol 46 (3) ◽  
pp. 257-262
Author(s):  
T. N. JHA ◽  
K. C. SINHA RAY
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Similarity Theory ◽  
Sensible Heat Flux ◽  
Eddy Correlation ◽  
Observational Period ◽  
Momentum Fluxes ◽  
Moisture Fluxes ◽  
Intensive Observation ◽  
Observation Period

 ABSTRACT. MONTBLEX-90 data for an Intensive Observational Period (IOP) was extracted to investigate the thunderstorm and its impacts on surface layer at Varanasi on 27 July 1990. Sensible heat flux has been computed by profile, aerodynamic and eddy correlation methods. In addition to that. momentum and moisture fluxes have been computed for comparative diagnosis of situations before, at the time and after thunderstorm, Monin-Obukhov similarity theory has been used for quantification of the fluxes. Findings indicate that surface is more buoyant at the time of thunderstorm. Under this influence, maxima of moisture and momentum fluxes occur at the tin1e of thunderstorm. However, heat flux was found to be maximum before the thunderstorm, The results provide an understanding of surface layer turbulent transfer during stable and unstable conditions.    

Observed influence of moist convection and cloudiness on boundary layer wind and momentum flux profiles.

2020 ◽  
Author(s):  
Mariska Koning ◽  
Louise Nuijens ◽  
Fred Bosveld ◽  
Pier Siebesma ◽  
Remco Verzijlbergh ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Wind Shear ◽  
Momentum Flux ◽  
Cloud Cover ◽  
Cloud Layer ◽  
Momentum Transport ◽  
Clear Sky ◽  
Momentum Fluxes ◽  
Wind Profiles

<p>Convective momentum transport (CMT) measurements are scarce, but important to constrain the impacts of CMT on wind profiles, variability of the wind and possibly the large-scale circulation.</p><p>We investigate how wind profiles and momentum fluxes change with cloudiness and convection. With stronger convection, we expect that the wind shear in the lowest 200m, wherein wind turbines are located, reduces. Cumulus days are generally strongly convective and hence well mixed. They are expected to differ from clear-sky days: the boundary layer is deeper, and cumulus may induce a different (thermal) circulation in the sub-cloud layer. Comparing cumulus and other days fairly, we must be mindful of the changes in convection strength with cloud cover, time of the day, seasons, and the wind strength that impacts the wind shear magnitude.</p><p>This study uses nine years of data from the Cabauw observatory, The Netherlands, containing 10-minute averages of wind speed, wind direction, and momentum fluxes from a 200 m tall tower along with cloud-base heights from a ceilometer. Realistic fine-scale Large Eddy Simulation (LES) hindcasts over the same time period and a 5km<sup>3</sup> domain over Cabauw provide insight into the processes at higher altitude. In both observations and LES, days with rooted clouds, which have strong connection to the sub-cloud layer, are separated from clear-sky days and days in which clouds only impact the convection through radiation effects. Days with rooted clouds are subsequently divided into three groups of increasing cloud cover: 5-30% (shallow clouds), 30-70% (somewhat deeper clouds) and >70% (overcast).</p><p>Both observations and LES show that shear in the near-surface wind speed (NSWS) reduces with stronger insolation, which is expected: more insolation causes a more unstable atmosphere, stronger convection, thus more mixing. In a weakly unstable atmosphere, rooted clouds (5-70% cloud cover) generally have better mixed winds (less normalised shear). The NSWS accelerates more from morning to afternoon on these days, indicating that not only the mixing is stronger, but also that downward mixing of higher momentum by the clouds affects the wind in the lowest 200m. If this is true, the assumption of Monin-Obukhov Similarity Theory (MOST) that large convective eddies are not important in the surface layer, does not hold. This possibly has a great impact on surface-flux parametrizations based on MOST, which are used by many numerical models, from local and mesoscale to global models. Analysing surface-layer scaling for momentum, we test whether this assumption is indeed violated in such cases.</p><p>Momentum transport profiles in LES show that when deeper clouds with larger cloud cover are present, transport in the cloud layer is larger. In the cross-wind component of the profile, the four categories show different deceleration in the mixed layer, and different acceleration near the top of the mixed layer. Likely, the stronger inversion-jump in the cross-wind causes this momentum flux character.</p><p>With this study, we provide an overview of the effects that have been observed in different cloudiness and convective conditions and gained understanding of the important processes and implications of the cloud effects on momentum transport.</p>

Surface-layer scintillation measurements of daytime sensible heat and momentum fluxes

1994 ◽  
Vol 68 (4) ◽  
pp. 357-373 ◽  
Author(s):  
A. E. Green ◽  
K. J. McAneney ◽  
M. S. Astill
Keyword(s):  
Surface Layer ◽  
Sensible Heat ◽  
Momentum Fluxes

The oxidation of Inconel alloy MA754 at low oxidation potential

1983 ◽  
Vol 41 ◽  
pp. 218-219
Author(s):  
D. N. Braski ◽  
P. D. Goodell ◽  
J. V. Cathcart ◽  
R. H. Kane
Keyword(s):  
Surface Layer ◽  
Oxidation Potential ◽  
Metal Interface ◽  
Elevated Temperature Strength ◽  
Surface Conditions ◽  
Inconel Alloy ◽  
Inco Alloy ◽  
Resistance To Oxidation ◽  
Oxide Particles ◽  
Cold Worked

It has been known for some time that the addition of small oxide particles to an 80 Ni—20 Cr alloy not only increases its elevated-temperature strength, but also markedly improves its resistance to oxidation. The mechanism by which the oxide dispersoid enhances the oxidation resistance is being studied collaboratively by ORNL and INCO Alloy Products Company.Initial experiments were performed using INCONEL alloy MA754, which is nominally: 78 Ni, 20 Cr, 0.05 C, 0.3 Al, 0.5 Ti, 1.0 Fe, and 0.6 Y2O3 (wt %).Small disks (3 mm diam × 0.38 mm thick) were cut from MA754 plate stock and prepared with two different surface conditions. The first was prepared by mechanically polishing one side of a disk through 0.5 μm diamond on a syntron polisher while the second used an additional sulfuric acid-methanol electropolishing treatment to remove the cold-worked surface layer. Disks having both surface treatments were oxidized in a radiantly heated furnace for 30 s at 1000°C. Three different environments were investigated: hydrogen with nominal dew points of 0°C, —25°C, and —55°C. The oxide particles and films were examined in TEM by using extraction replicas (carbon) and by backpolishing to the oxide/metal interface. The particles were analyzed by EDS and SAD.

Structural analysis of the surface-layer protein of spirillum serpens by high-resolution electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 738-739
Author(s):  
W. H. Wu ◽  
R. M. Glaeser
Keyword(s):  
Electron Microscopy ◽  
Surface Layer ◽  
Structural Analysis ◽  
High Resolution ◽  
Low Dose ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Surface Layer Protein ◽  
Morphological Unit ◽  
Resolution Electron

Spirillum serpens possesses a surface layer protein which exhibits a regular hexagonal packing of the morphological subunits. A morphological model of the structure of the protein has been proposed at a resolution of about 25 Å, in which the morphological unit might be described as having the appearance of a flared-out, hollow cylinder with six ÅspokesÅ at the flared end. In order to understand the detailed association of the macromolecules, it is necessary to do a high resolution structural analysis. Large, single layered arrays of the surface layer protein have been obtained for this purpose by means of extensive heating in high CaCl2, a procedure derived from that of Buckmire and Murray. Low dose, low temperature electron microscopy has been applied to the large arrays.As a first step, the samples were negatively stained with neutralized phosphotungstic acid, and the specimens were imaged at 40,000 magnification by use of a high resolution cold stage on a JE0L 100B. Low dose images were recorded with exposures of 7-9 electrons/Å2. The micrographs obtained (Fig. 1) were examined by use of optical diffraction (Fig. 2) to tell what areas were especially well ordered.

Electron-Mirror Microscopic Aspects of Ferroelectric Domains of BaTiO3 And Ca2Sr (C2H5CO2)6

1970 ◽  
Vol 28 ◽  
pp. 478-479
Author(s):  
Teruo Someya ◽  
Jinzo Kobayashi
Keyword(s):  
Surface Layer ◽  
Electric Fields ◽  
Quantitative Study ◽  
Recent Progress ◽  
Ferroelectric Domain ◽  
Resolving Power ◽  
Surface Pattern ◽  
Crystal Surfaces ◽  
One Dimensional ◽  
Ferroelectric Domains

Recent progress in the electron-mirror microscopy (EMM), e.g., an improvement of its resolving power together with an increase of the magnification makes it useful for investigating the ferroelectric domain physics. English has recently observed the domain texture in the surface layer of BaTiO3. The present authors ) have developed a theory by which one can evaluate small one-dimensional electric fields and/or topographic step heights in the crystal surfaces from their EMM pictures. This theory was applied to a quantitative study of the surface pattern of BaTiO3).

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