Sample records for mixed layer response

  1. Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode

    NASA Astrophysics Data System (ADS)

    Sallée, J. B.; Speer, K. G.; Rintoul, S. R.

    2010-04-01

    Interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface. The depth of this layer is determined by wind forcing and heating from the atmosphere. Variations in mixed-layer depth affect the rate of exchange between the atmosphere and deeper ocean, the capacity of the ocean to store heat and carbon and the availability of light and nutrients to support the growth of phytoplankton. However, the response of the Southern Ocean mixed layer to changes in the atmosphere is not well known. Here we analyse temperature and salinity data from Argo profiling floats to show that the Southern Annular Mode (SAM), the dominant mode of atmospheric variability in the Southern Hemisphere, leads to large-scale anomalies in mixed-layer depth that are zonally asymmetric. From a simple heat budget of the mixed layer we conclude that meridional winds associated with departures of the SAM from zonal symmetry cause anomalies in heat flux that can, in turn, explain the observed changes of mixed-layer depth and sea surface temperature. Our results suggest that changes in the SAM, including recent and projected trends attributed to human activity, drive variations in Southern Ocean mixed-layer depth, with consequences for air-sea exchange, ocean sequestration of heat and carbon, and biological productivity.

  2. Laboratory simulations of the atmospheric mixed-layer in flow ...

    EPA Pesticide Factsheets

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundary layer can have a strong influence on the concentration of pollutants within this layer. Deflections of streamlines at the height of the interface are primarily a function of hill Froude number (Fr), the ratio of mixed-layer height (zi) to terrain height (h), and the crosswind dimension of the terrain. The magnitude of the deflections increases as Fr increases and zi / h decreases. For mixing-height streamlines that are initially below the terrain top, the response is linear with Fr; for those initially above the terrain feature the response to Fr is more complex. Once Fr exceeds about 2, the terrain related response of the mixed layer interface decreases somewhat with increasing Fr (toward more neutral flow). Deflections are also shown to increase as the crosswind dimensions of the terrain increases. Comparisons with numerical modeling, limited field data and other laboratory measurements reported in the literature are favorable. Additionally, visual observations of dye streamers suggests that the flow structure exhibited for our elevated inversions passing over three dimensional hills is similar to that reported in the literature for continuously stratified flow over two-dimensional h

  3. Receptivity to Unsteady Disturbances at the Trailing Edge in a Finite-Width Mixing Layer Flow.

    NASA Astrophysics Data System (ADS)

    Rabchuk, James Allen

    1995-01-01

    A theoretical study of the receptivity to harmonic disturbances at the trailing edge of a finite-width mixing layer has been carried out. The unsteady Kutta condition at the trailing edge has been reexamined at the vorticity scale of the steady mixing layer profile, and the underlying physical mechanism of this condition explained. The receptivity problem of harmonic forcing at the trailing edge is shown to reduce to an initial-value problem for the downstream mixing layer or wake. A linear coupling term for the response field amplitude is derived which is proportional to the square root of the Strouhal number and the difference in the gradient of the forcing pressure field tangential to the plate near the trailing edge. An initial-value problem is then solved for an inviscid, incompressible mixing layer with a piecewise linear velocity profile leaving the trailing edge of a flat plate, subject to harmonic forcing. The Wiener-Hopf technique is used to solve for the stream function of the response field over a range of forcing frequencies and mean flow velocities. The solutions are shown to agree with previous solutions for infinitesimally thin shear layers from Bechert, 1988 and Orszag and Crow, 1970, in the limit that the Strouhal number relative to the mixing layer thickness, S, is small. In addition, solutions are obtained for moderate values of S, for which the mixing layer is most unstable. It is shown that for increasing S, the initial amplitudes of the discrete modes of instability decrease like 1 over S and then level off, while the neutrally stable mode of response is increasingly amplified. It is also shown that the overall phase of the response is nearly independent of S, except at a cross-stream position where the phase shifts by 180 degrees and the amplitude of the response goes to zero, which moves from the low to the high speed flow as S increases.

  4. Upper Ocean Response to Hurricanes Katrina and Rita (2005) from Multi-sensor Satellites

    NASA Astrophysics Data System (ADS)

    Gierach, M. M.; Bulusu, S.

    2006-12-01

    Analysis of satellite observations and model simulations of the mixed layer provided an opportunity to assess the biological and physical effects of hurricanes Katrina and Rita (2005) in the Gulf of Mexico. Oceanic cyclonic circulation was intensified by the hurricanes' wind field, maximizing upwelling, surface cooling, and deepening the mixed layer. Two areas of maximum surface chlorophyll-a concentration and sea surface cooling were detected with peak intensities ranging from 2-3 mg m-3 and 4-6°C, along the tracks of Katrina and Rita. The temperature of the mixed layer cooled approximately 2°C and the depth of the mixed layer deepened by approximately 33-52 m. The forced deepening of the mixed layer injected nutrients into the euphotic zone, generating phytoplankton blooms 3-5 days after the passage of Katrina and Rita (2005).

  5. Tropical warm pool rainfall variability and impact on upper ocean variability throughout the Madden-Julian oscillation

    NASA Astrophysics Data System (ADS)

    Thompson, Elizabeth J.

    Heating and rain freshening often stabilize the upper tropical ocean, bringing the ocean mixed layer depth to the sea surface. Thin mixed layer depths concentrate subsequent fluxes of heat, momentum, and freshwater in a thin layer. Rapid heating and cooling of the tropical sea surface is important for controlling or triggering atmospheric convection. Ocean mixed layer depth and SST variability due to rainfall events have not been as comprehensively explored as the ocean's response to heating or momentum fluxes, but are very important to understand in the tropical warm pool where precipitation exceeds evaporation and many climate phenomena such as ENSO and the MJO (Madden Julian Oscillation) originate. The first part of the dissertation investigates tropical, oceanic convective and stratiform rainfall variability and determines how to most accurately estimate rainfall accumulation with radar from each rain type. The second, main part of the dissertation uses central Indian Ocean salinity and temperature microstructure measurements and surrounding radar-derived rainfall maps throughout two DYNAMO MJO events to determine the impact of precipitating systems on upper-ocean mixed layer depth and resulting SST variability. The ocean mixed layer was as shallow as 0-5 m during 528/1071 observation hours throughout 2 MJOs (54% of the data record). Out of 43 observation days, thirty-eight near-surface mixed layer depth events were attributed to freshwater stabilization, called rain-formed mixed layers (RFLs). Thirty other mixed layer stratification events were classified as diurnal warm layers (DWLs) due to stable temperature stratification by daytime heating. RFLs and DWLs were observed to interact in two ways: 1) RFLs fill preexisting DWLs and add to total near-surface mixed layer stratification, which occurred ten times; 2) RFLs last long enough to heat, creating a new DWL on top of the RFL, which happened nine times. These combination stratification events were responsible for the highest SST warming rates and some of the highest SSTs leading up to the most active precipitation and wind stage of the each MJO. DWLs without RFL interaction helped produce the highest SSTs in suppressed MJO conditions. As storm intensity, frequency, duration, and the ability of storms to maintain stratiform rain areas increased, RFLS became more common in the disturbed and active MJO phases. Along with the barrier layer, DWL and RFL stratification events helped suppress wind-mixing, cooling, and mixed layer deepening throughout the MJO. We hypothesize that both salinity and temperature stratification events, and their interactions, are important for controlling SST variability and therefore MJO initiation in the Indian Ocean. Most RFLs were caused by submesoscale and mesoscale convective systems with stratiform rain components and local rain accumulations above 10 mm but with winds mostly below 8 m s-1. We hypothesize that the stratiform rain components of storms helped stratify the ocean by providing weak but widespread, steady, long-lived freshwater fluxes. Although generally limited to rain rates ≤ 10 mm hr-1, it is demonstrated that stratiform rain can exert a strong buoyancy flux into the ocean, i.e. as high as maximum daytime solar heating. Storm morphology and the preexisting vertical structure of ocean stability were critical in determining ocean mixed layer depth variability in the presence of rain. Therefore, we suggest that high spatial and temporal resolution coupled ocean-atmosphere models that can parameterize or resolve storm morphology as well as ocean mixed layer and barrier layer evolution are needed to reproduce the diurnal and intraseasonal SST variability documented throughout the MJO.

  6. Southern Ocean Mixed-Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

    NASA Astrophysics Data System (ADS)

    Buongiorno Nardelli, B.; Guinehut, S.; Verbrugge, N.; Cotroneo, Y.; Zambianchi, E.; Iudicone, D.

    2017-12-01

    The depth of the upper ocean mixed layer provides fundamental information on the amount of seawater that directly interacts with the atmosphere. Its space-time variability modulates water mass formation and carbon sequestration processes related to both the physical and biological pumps. These processes are particularly relevant in the Southern Ocean, where surface mixed-layer depth estimates are generally obtained either as climatological fields derived from in situ observations or through numerical simulations. Here we demonstrate that weekly observation-based reconstructions can be used to describe the variations of the mixed-layer depth in the upper ocean over a range of space and time scales. We compare and validate four different products obtained by combining satellite measurements of the sea surface temperature, salinity, and dynamic topography and in situ Argo profiles. We also compute an ensemble mean and use the corresponding spread to estimate mixed-layer depth uncertainties and to identify the more reliable products. The analysis points out the advantage of synergistic approaches that include in input the sea surface salinity observations obtained through a multivariate optimal interpolation. Corresponding data allow to assess mixed-layer depth seasonal and interannual variability. Specifically, the maximum correlations between mixed-layer anomalies and the Southern Annular Mode are found at different time lags, related to distinct summer/winter responses in the Antarctic Intermediate Water and Sub-Antarctic Mode Waters main formation areas.

  7. The ocean mixed layer under Southern Ocean sea-ice: seasonal cycle and forcing.

    NASA Astrophysics Data System (ADS)

    Violaine, P.; Sallee, J. B.; Schmidtko, S.; Roquet, F.; Charrassin, J. B.

    2016-02-01

    The mixed-layer at the surface of the ocean is the gateway for all exchanges between air and sea. A vast area of the Southern Ocean is however seasonally capped by sea-ice, which alters this gateway and the characteristic the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass formation and circulation, carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the mixed layer, as well as the processes responsible for its evolution, are poorly understood due to the lack of in-situ observations and measurements. We urgently need to better understand the forcing and the characteristics of the ocean mixed-layer under sea-ice if we are to understand and predict the world's climate. In this study, we combine a range of distinct sources of observation to overcome this lack in our understanding of the Polar Regions. Working on Elephant Seal-derived data as well as ship-based observations and Argo float data, we describe the seasonal cycle of the characteristics and stability of the ocean mixed layer over the entire Southern Ocean (South of 40°S), and specifically under sea-ice. Mixed-layer budgets of heat and freshwater are used to investigate the main forcings of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary role.Our results suggest that changes in regional sea-ice distribution or sea-ice seasonal cycle duration, as currently observed, would widely affect the buoyancy budget of the underlying mixed-layer, and impacts large-scale water-mass formation and transformation.

  8. Functioning of microbial complexes in aerated layers of a highmoor peat bog

    NASA Astrophysics Data System (ADS)

    Golovchenko, A. V.; Bogdanova, O. Yu.; Stepanov, A. L.; Polyanskaya, L. M.; Zvyagintsev, D. G.

    2010-09-01

    Monitoring was carried out using the luminescent-microscopic method of the abundance parameters of different groups of microorganisms in a monolith and in the mixed layers of a highmoor peat bog (oligotrophic residual-eutrophic peat soil) in a year-long model experiment. The increase of the aeration as a result of mixing of the layers enhanced the activity of the soil fungi. This was attested to by the following changes: the increase of the fungal mycelium length by 6 times and of the fungal biomass by 4 times and the double decrease of the fraction of spores in the fungal complex. The response of the fungal complex to mixing was different in the different layers of the peat bog. The maximal effect was observed in the T1 layer and the minimal one in the T2 layer. The emission of CO2 in the mixed samples was 1.5-2 times higher than that from the undisturbed peat samples. In contrast with the fungi, the bacteria and actinomycetes were not affected by the aeration of the highmoor layers.

  9. A molecular dynamics study of the role of pressure on the response of reactive materials to thermal initiation

    NASA Astrophysics Data System (ADS)

    Weingarten, N. Scott; Mattson, William D.; Yau, Anthony D.; Weihs, Timothy P.; Rice, Betsy M.

    2010-05-01

    To elucidate the mechanisms of energy release in a reacting nickel/aluminum bilayer, we simulate the exothermic alloying reactions using both microcanonical and isoenthalpic-isobaric molecular dynamics simulations and an embedded-atom method type potential. The mechanism of the mixing consists of a sequence of steps in which mixing and reaction first occurs at the interface; the resulting heat generated from the mixing then melts the Al layer; subsequent mixing leads to further heat generation after which the Ni layer melts. The mixing continues until the alloying reactions are completed. The results indicate that pressure has a significant influence on the rates of atomic mixing and alloying reactions. Local pressures and temperatures within the individual layers at the time of melting are calculated, and these results are compared with the pressure-dependent melting curves determined for pure Al and pure Ni using this interaction potential.

  10. Rayleigh-Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. II

    NASA Astrophysics Data System (ADS)

    Zhou, Ye

    2017-12-01

    Rayleigh-Taylor (RT) and Richtmyer-Meshkov(RM) instabilities are well-known pathways towards turbulent mixing layers, in many cases characterized by significant mass and species exchange across the mixing layers (Zhou, 2017. Physics Reports, 720-722, 1-136). Mathematically, the pathway to turbulent mixing requires that the initial interface be multimodal, to permit cross-mode coupling leading to turbulence. Practically speaking, it is difficult to experimentally produce a non-multi-mode initial interface. Numerous methods and approaches have been developed to describe the late, multimodal, turbulent stages of RT and RM mixing layers. This paper first presents the initial condition dependence of RT mixing layers, and introduces parameters that are used to evaluate the level of "mixedness" and "mixed mass" within the layers, as well as the dependence on density differences, as well as the characteristic anisotropy of this acceleration-driven flow, emphasizing some of the key differences between the two-dimensional and three-dimensional RT mixing layers. Next, the RM mixing layers are discussed, and differences with the RT mixing layer are elucidated, including the RM mixing layers dependence on the Mach number of the initiating shock. Another key feature of the RM induced flows is its response to a reshock event, as frequently seen in shock-tube experiments as well as inertial confinement events. A number of approaches to modeling the evolution of these mixing layers are then described, in order of increasing complexity. These include simple buoyancy-drag models, Reynolds-averaged Navier-Stokes models of increased complexity, including K- ε, K-L, and K- L- a models, up to full Reynolds-stress models with more than one length-scale. Multifield models and multiphase models have also been implemented. Additional complexities to these flows are examined as well as modifications to the models to understand the effects of these complexities. These complexities include the presence of magnetic fields, compressibility, rotation, stratification and additional instabilities. The complications induced by the presence of converging geometries are also considered. Finally, the unique problems of astrophysical and high-energy-density applications, and efforts to model these are discussed.

  11. The role of feedbacks in Antarctic sea ice change

    NASA Astrophysics Data System (ADS)

    Feltham, D. L.; Frew, R. C.; Holland, P.

    2017-12-01

    The changes in Antarctic sea ice over the last thirty years have a strong seasonal dependence, and the way these changes grow in spring and decay in autumn suggests that feedbacks are strongly involved. The changes may ultimately be caused by atmospheric warming, the winds, snowfall changes, etc., but we cannot understand these forcings without first untangling the feedbacks. A highly simplified coupled sea ice -mixed layer model has been developed to investigate the importance of feedbacks on the evolution of sea ice in two contrasting regions in the Southern Ocean; the Amundsen Sea where sea ice extent has been decreasing, and the Weddell Sea where it has been expanding. The change in mixed layer depth in response to changes in the atmosphere to ocean energy flux is implicit in a strong negative feedback on ice cover changes in the Amundsen Sea, with atmospheric cooling leading to a deeper mixed layer resulting in greater entrainment of warm Circumpolar Deep Water, causing increased basal melting of sea ice. This strong negative feedback produces counter intuitive responses to changes in forcings in the Amundsen Sea. This feedback is absent in the Weddell due to the complete destratification and strong water column cooling that occurs each winter in simulations. The impact of other feedbacks, including the albedo feedback, changes in insulation due to ice thickness and changes in the freezing temperature of the mixed layer, were found to be of secondary importance compared to changes in the mixed layer depth.

  12. Response of mixed-phase boundary layer clouds with rapid and slow ice nucleation processes to cloud-top temperature trend

    NASA Astrophysics Data System (ADS)

    Fridlind, A. M.; Avramov, A.; Ackerman, A. S.; Alpert, P. A.; Knopf, D. A.; DeMott, P. J.; Brooks, S. D.; Glen, A.

    2015-12-01

    It has been argued on the basis of some laboratory data sets, observed mixed-phase cloud systems, and numerical modeling studies that weakly active or slowly consumed ice forming nuclei (IFN) may be important to natural cloud systems. It has also been argued on the basis of field measurements that ice nucleation under mixed-phase conditions appears to occur predominantly via a liquid-phase mechanism, requiring the presence of liquid droplets prior to substantial ice nucleation. Here we analyze the response of quasi-Lagrangian large-eddy simulations of mixed-phase cloud layers to IFN operating via a liquid-phase mode using assumptions that result in either slow or rapid depletion of IFN from the cloudy boundary layer. Using several generalized case studies that do not exhibit riming or drizzle, based loosely on field campaign data, we vary environmental conditions such that the cloud-top temperature trend varies. One objective of this work is to identify differing patterns in ice formation intensity that may be distinguishable from ground-based or satellite platforms.

  13. Sensitivity of the two-dimensional shearless mixing layer to the initial turbulent kinetic energy and integral length scale

    NASA Astrophysics Data System (ADS)

    Fathali, M.; Deshiri, M. Khoshnami

    2016-04-01

    The shearless mixing layer is generated from the interaction of two homogeneous isotropic turbulence (HIT) fields with different integral scales ℓ1 and ℓ2 and different turbulent kinetic energies E1 and E2. In this study, the sensitivity of temporal evolutions of two-dimensional, incompressible shearless mixing layers to the parametric variations of ℓ1/ℓ2 and E1/E2 is investigated. The sensitivity methodology is based on the nonintrusive approach; using direct numerical simulation and generalized polynomial chaos expansion. The analysis is carried out at Reℓ 1=90 for the high-energy HIT region and different integral length scale ratios 1 /4 ≤ℓ1/ℓ2≤4 and turbulent kinetic energy ratios 1 ≤E1/E2≤30 . It is found that the most influential parameter on the variability of the mixing layer evolution is the turbulent kinetic energy while variations of the integral length scale show a negligible influence on the flow field variability. A significant level of anisotropy and intermittency is observed in both large and small scales. In particular, it is found that large scales have higher levels of intermittency and sensitivity to the variations of ℓ1/ℓ2 and E1/E2 compared to the small scales. Reconstructed response surfaces of the flow field intermittency and the turbulent penetration depth show monotonic dependence on ℓ1/ℓ2 and E1/E2 . The mixing layer growth rate and the mixing efficiency both show sensitive dependence on the initial condition parameters. However, the probability density function of these quantities shows relatively small solution variations in response to the variations of the initial condition parameters.

  14. Surface boundary layer turbulence in the Southern ocean

    NASA Astrophysics Data System (ADS)

    Merrifield, Sophia; St. Laurent, Louis; Owens, Breck; Naveira Garabato, Alberto

    2015-04-01

    Due to the remote location and harsh conditions, few direct measurements of turbulence have been collected in the Southern Ocean. This region experiences some of the strongest wind forcing of the global ocean, leading to large inertial energy input. While mixed layers are known to have a strong seasonality and reach 500m depth, the depth structure of near-surface turbulent dissipation and diffusivity have not been examined using direct measurements. We present data collected during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) field program. In a range of wind conditions, the wave affected surface layer (WASL), where surface wave physics are actively forcing turbulence, is contained to the upper 15-20m. The lag-correlation between wind stress and turbulence shows a strong relationship up to 6 hours (˜1/2 inertial period), with the winds leading the oceanic turbulent response, in the depth range between 20-50m. We find the following characterize the data: i) Profiles that have a well-defined hydrographic mixed layer show that dissipation decays in the mixed layer inversely with depth, ii) WASLs are typically 15 meters deep and 30% of mixed layer depth, iii) Subject to strong winds, the value of dissipation as a function of depth is significantly lower than predicted by theory. Many dynamical processes are known to be missing from upper-ocean parameterizations of mixing in global models. These include surface-wave driven processes such as Langmuir turbulence, submesocale frontal processes, and nonlocal representations of mixing. Using velocity, hydrographic, and turbulence measurements, the existence of coherent structures in the boundary layer are investigated.

  15. A New Theory of Mix in Omega Capsule Implosions

    NASA Astrophysics Data System (ADS)

    Knoll, Dana; Chacon, Luis; Rauenzahn, Rick; Simakov, Andrei; Taitano, William; Welser-Sherrill, Leslie

    2014-10-01

    We put forth a new mix model that relies on the development of a charge-separation electrostatic double-layer at the fuel-pusher interface early in the implosion of an Omega plastic ablator capsule. The model predicts a sizable pusher mix (several atom %) into the fuel. The expected magnitude of the double-layer field is consistent with recent radial electric field measurements in Omega plastic ablator implosions. Our theory relies on two distinct physics mechanisms. First, and prior to shock breakout, the formation of a double layer at the fuel-pusher interface due to fast preheat-driven ionization. The double-layer electric field structure accelerates pusher ions fairly deep into the fuel. Second, after the double-layer mix has occurred, the inward-directed fuel velocity and temperature gradients behind the converging shock transports these pusher ions inward. We first discuss the foundations of this new mix theory. Next, we discuss our interpretation of the radial electric field measurements on Omega implosions. Then we discuss the second mechanism that is responsible for transporting the pusher material, already mixed via the double-layer deep into the fuel, on the shock convergence time scale. Finally we make a connection to recent mix motivated experimental data on. This work conducted under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory, managed by LANS, LLC under Contract DE-AC52-06NA25396.

  16. Ocean response to typhoons in the western North Pacific: Composite results from Argo data

    NASA Astrophysics Data System (ADS)

    Lin, Sheng; Zhang, Wen-Zhou; Shang, Shao-Ping; Hong, Hua-Sheng

    2017-05-01

    Composite structures of ocean temperature and salinity anomalies caused by tropical cyclones (TCs) or typhoons in the western North Pacific Ocean were obtained from Argo data. These structures were used to analyze ocean responses to typhoons and the dynamic mechanisms inherent in those responses with a particular focus on upwelling. TC-induced cooling is often strongly rightward-biased in the surface layer, and shifts toward the typhoon track at depths exceeding roughly 100 m. In the central water column within approximately 75 km of the typhoon track, subsurface warming predicted by vertical mixing is restrained and replaced by cooling due to upwelling. Upwelling contributes 15% on average to temperature cooling in the near surface layer (10-30 m), 84% in the subsurface layer (30-250 m) and 94% in the deep layer (250-600 m) during the period of 0.5-2.5 days after the typhoon's passage. It is suggested that the sea surface cooling effect of vertical mixing can be enhanced by the upwelling. The effect of upwelling is also prominent in the salinity response to typhoons. The composite results from the Argo data clearly reveal basic ocean responses to typhoons and indicate the important role of upwelling therein.

  17. High static stability in the mixing layer above the extratropical tropopause

    NASA Astrophysics Data System (ADS)

    Kunz, A.; Konopka, P.; Müller, R.; Pan, L. L.; Schiller, C.; Rohrer, F.

    2009-08-01

    The relationship between the static stability N2 and the mixing in the tropopause inversion layer (TIL) is investigated using in situ aircraft observations during SPURT (trace gas transport in the tropopause region). With a new simple measure of mixing degree based on O3-CO tracer correlations, high N2 related to an enhanced mixing in the extratropical mixing layer is found. This relation becomes even more pronounced if fresh mixing events are excluded, indicating that mixing within the TIL occurs on a larger than synoptic timescale. A temporal variance analysis of N2 suggests that processes responsible for the composition of the TIL take place on seasonal timescales. Using radiative transfer calculations, we simulate the influence of a change in O3 and H2O vertical gradients on the temperature gradient and thus on the static stability above the tropopause, which are contrasted in an idealized nonmixed atmosphere and in a reference mixed atmosphere. The results show that N2 increases with enhanced mixing degree near the tropopause. At the same time, the temperature above the tropopause decreases together with the development of an inversion and the TIL. In the idealized case of nonmixed profiles the TIL vanishes. Furthermore, the results suggest that H2O plays a major role in maintaining the temperature inversion and the TIL structure compared to O3. The results substantiate the link between the extratropical mixing layer and the TIL.

  18. Effect of integrating straw into agricultural soils on soil infiltration and evaporation.

    PubMed

    Cao, Jiansheng; Liu, Changming; Zhang, Wanjun; Guo, Yunlong

    2012-01-01

    Soil water movement is a critical consideration for crop yield in straw-integrated fields. This study used an indoor soil column experiment to determine soil infiltration and evaporation characteristics in three forms of direct straw-integrated soils (straw mulching, straw mixing and straw inter-layering). Straw mulching is covering the land surface with straw. Straw mixing is mixing straw with the top 10 cm surface soil. Then straw inter-layering is placing straw at the 20 cm soil depth. There are generally good correlations among the mulch integration methods at p < 0.05, and with average errors/biases <10%. Straw mixing exhibited the best effect in terms of soil infiltration, followed by straw mulching. Due to over-burden weight-compaction effect, straw inter-layering somehow retarded soil infiltration. In terms of soil water evaporation, straw mulching exhibited the best effect. This was followed by straw mixing and then straw inter-layering. Straw inter-layering could have a long-lasting positive effect on soil evaporation as it limited the evaporative consumption of deep soil water. The responses of the direct straw integration modes to soil infiltration and evaporation could lay the basis for developing efficient water-conservation strategies. This is especially useful for water-scarce agricultural regions such as the arid/semi-arid regions of China.

  19. Black carbon solar absorption suppresses turbulence in the atmospheric boundary layer.

    PubMed

    Wilcox, Eric M; Thomas, Rick M; Praveen, Puppala S; Pistone, Kristina; Bender, Frida A-M; Ramanathan, Veerabhadran

    2016-10-18

    The introduction of cloud condensation nuclei and radiative heating by sunlight-absorbing aerosols can modify the thickness and coverage of low clouds, yielding significant radiative forcing of climate. The magnitude and sign of changes in cloud coverage and depth in response to changing aerosols are impacted by turbulent dynamics of the cloudy atmosphere, but integrated measurements of aerosol solar absorption and turbulent fluxes have not been reported thus far. Here we report such integrated measurements made from unmanned aerial vehicles (UAVs) during the CARDEX (Cloud Aerosol Radiative Forcing and Dynamics Experiment) investigation conducted over the northern Indian Ocean. The UAV and surface data reveal a reduction in turbulent kinetic energy in the surface mixed layer at the base of the atmosphere concurrent with an increase in absorbing black carbon aerosols. Polluted conditions coincide with a warmer and shallower surface mixed layer because of aerosol radiative heating and reduced turbulence. The polluted surface mixed layer was also observed to be more humid with higher relative humidity. Greater humidity enhances cloud development, as evidenced by polluted clouds that penetrate higher above the top of the surface mixed layer. Reduced entrainment of dry air into the surface layer from above the inversion capping the surface mixed layer, due to weaker turbulence, may contribute to higher relative humidity in the surface layer during polluted conditions. Measurements of turbulence are important for studies of aerosol effects on clouds. Moreover, reduced turbulence can exacerbate both the human health impacts of high concentrations of fine particles and conditions favorable for low-visibility fog events.

  20. Black carbon solar absorption suppresses turbulence in the atmospheric boundary layer

    PubMed Central

    Wilcox, Eric M.; Thomas, Rick M.; Praveen, Puppala S.; Pistone, Kristina; Bender, Frida A.-M.; Ramanathan, Veerabhadran

    2016-01-01

    The introduction of cloud condensation nuclei and radiative heating by sunlight-absorbing aerosols can modify the thickness and coverage of low clouds, yielding significant radiative forcing of climate. The magnitude and sign of changes in cloud coverage and depth in response to changing aerosols are impacted by turbulent dynamics of the cloudy atmosphere, but integrated measurements of aerosol solar absorption and turbulent fluxes have not been reported thus far. Here we report such integrated measurements made from unmanned aerial vehicles (UAVs) during the CARDEX (Cloud Aerosol Radiative Forcing and Dynamics Experiment) investigation conducted over the northern Indian Ocean. The UAV and surface data reveal a reduction in turbulent kinetic energy in the surface mixed layer at the base of the atmosphere concurrent with an increase in absorbing black carbon aerosols. Polluted conditions coincide with a warmer and shallower surface mixed layer because of aerosol radiative heating and reduced turbulence. The polluted surface mixed layer was also observed to be more humid with higher relative humidity. Greater humidity enhances cloud development, as evidenced by polluted clouds that penetrate higher above the top of the surface mixed layer. Reduced entrainment of dry air into the surface layer from above the inversion capping the surface mixed layer, due to weaker turbulence, may contribute to higher relative humidity in the surface layer during polluted conditions. Measurements of turbulence are important for studies of aerosol effects on clouds. Moreover, reduced turbulence can exacerbate both the human health impacts of high concentrations of fine particles and conditions favorable for low-visibility fog events. PMID:27702889

  1. A Mixed Multi-Field Finite Element Formulation for Thermopiezoelectric Composite Shells

    NASA Technical Reports Server (NTRS)

    Lee, Ho-Jun; Saravanos, Dimitris A.

    1999-01-01

    Analytical formulations are presented which account for the coupled mechanical, electrical, and thermal response of piezoelectric composite shell structures. A new mixed multi-field laminate theory is developed which combines "single layer" assumptions for the displacements along with layerwise fields for the electric potential and temperature. This laminate theory is formulated using curvilinear coordinates and is based on the principles of linear thermopiezoelectricity. The mechanics have the inherent capability to explicitly model both the active and sensory responses of piezoelectric composite shells in thermal environment. Finite element equations are derived and implemented for an eight-noded shell element. Numerical studies are conducted to investigate both the sensory and active responses of piezoelectric composite shell structures subjected to thermal loads. Results for a cantilevered plate with an attached piezoelectric layer are com- pared with corresponding results from a commercial finite element code and a previously developed program. Additional studies are conducted on a cylindrical shell with an attached piezoelectric layer to demonstrate capabilities to achieve thermal shape control on curved piezoelectric structures.

  2. In-situ observation of switchable nanoscale topography for y-shaped binary brushes in fluids.

    PubMed

    Lin, Yen-Hsi; Teng, Jing; Zubarev, Eugene R; Shulha, Hennady; Tsukruk, Vladimir V

    2005-03-01

    Direct, in-fluid observation of the surface morphology and nanomechanical properties of the mixed brushes composed of Y-shaped binary molecules PS-PAA revealed nanoscale network-like surface topography formed by coexisting stretched soluble PAA arms and collapsed insoluble PS chains in water. Placement of Y-shaped brushes in different fluids resulted in dramatic reorganization ranging from soft repellent layer covered by swollen PS arms in toluene to an adhesive, mixed layer composed of coexisting swollen PAA and collapsed PS arms in water. These binary layers with the overall nanoscale thickness can serve as adaptive nanocoatings with stimuli-responsive properties.

  3. Impact of Langmuir Turbulence on Upper Ocean Response to Hurricane Edouard: Model and Observations

    NASA Astrophysics Data System (ADS)

    Blair, A.; Ginis, I.; Hara, T.; Ulhorn, E.

    2017-12-01

    Tropical cyclone intensity is strongly affected by the air-sea heat flux beneath the storm. When strong storm winds enhance upper ocean turbulent mixing and entrainment of colder water from below the thermocline, the resulting sea surface temperature cooling may reduce the heat flux to the storm and weaken the storm. Recent studies suggest that this upper ocean turbulence is strongly affected by different sea states (Langmuir turbulence), which are highly complex and variable in tropical cyclone conditions. In this study, the upper ocean response under Hurricane Edouard (2014) is investigated using a coupled ocean-wave model with and without an explicit sea state dependent Langmuir turbulence parameterization. The results are compared with in situ observations of sea surface temperature and mixed layer depth from AXBTs, as well as satellite sea surface temperature observations. Overall, the model results of mixed layer deepening and sea surface temperature cooling under and behind the storm are consistent with observations. The model results show that the effects of sea state dependent Langmuir turbulence can be significant, particularly on the mixed layer depth evolution. Although available observations are not sufficient to confirm such effects, some observed trends suggest that the sea state dependent parameterization might be more accurate than the traditional (sea state independent) parameterization.

  4. Formation of mixed organic layers by stepwise electrochemical reduction of diazonium compounds.

    PubMed

    Santos, Luis; Ghilane, Jalal; Lacroix, Jean Christophe

    2012-03-28

    This work describes the formation of a mixed organic layer covalently attached to a carbon electrode. The strategy adopted is based on two successive electrochemical reductions of diazonium salts. First, bithiophene phenyl (BTB) diazonium salt is reduced using host/guest complexation in a water/cyclodextrin (β-CD) solution. The resulting layer consists of grafted BTB oligomers and cyclodextrin that can be removed from the surface. The electrochemical response of several outer-sphere redox probes on such BTB/CD electrodes is close to that of a diode, thanks to the easily p-dopable oligo(BTB) moieties. When CD is removed from the surface, pinholes are created and this diode like behavior is lost. Following this, nitrophenyl (NP) diazonium is reduced to graft a second component. Electrochemical study shows that upon grafting NP insulating moieties, the diode-like behavior of the layer is restored which demonstrates that NP is grafted predominately in the empty spaces generated by β-CD desorption. As a result, a mixed BTB/NP organic layer covalently attached to a carbon electrode is obtained using a stepwise electrochemical reduction of two diazonium compounds.

  5. Mixing and non-equilibrium chemical reaction in a compressible mixing layer. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Steinberger, Craig J.

    1991-01-01

    The effects of compressibility, chemical reaction exothermicity, and non-equilibrium chemical modeling in a reacting plane mixing layer were investigated by means of two dimensional direct numerical simulations. The chemical reaction was irreversible and second order of the type A + B yields Products + Heat. The general governing fluid equations of a compressible reacting flow field were solved by means of high order finite difference methods. Physical effects were then determined by examining the response of the mixing layer to variation of the relevant non-dimensionalized parameters. The simulations show that increased compressibility generally results in a suppressed mixing, and consequently a reduced chemical reaction conversion rate. Reaction heat release was found to enhance mixing at the initial stages of the layer growth, but had a stabilizing effect at later times. The increased stability manifested itself in the suppression or delay of the formation of large coherent structures within the flow. Calculations were performed for a constant rate chemical kinetics model and an Arrhenius type kinetic prototype. The choice of the model was shown to have an effect on the development of the flow. The Arrhenius model caused a greater temperature increase due to reaction than the constant kinetic model. This had the same effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

  6. Oceanic response to Typhoon Nari (2007) in the East China Sea

    NASA Astrophysics Data System (ADS)

    Oh, Kyung-Hee; Lee, Seok; Kang, Sok-Kuh; Song, Kyu-Min

    2017-06-01

    The oceanic response to a typhoon in the East China Sea (ECS) was examined using thermal and current structures obtained from ocean surface drifters and a bottom-moored current profiler installed on the right side of the typhoon's track. Typhoon Nari (2007) had strong winds as it passed the central region of the ECS. The thermal structure in the ECS responded to Typhoon Nari (2007) very quickly: the seasonal thermocline abruptly collapsed and the sea surface temperature dropped immediately by about 4°C after the typhoon passed. The strong vertical mixing and surface cooling caused by the typhoon resulted in a change in the thermal structure. Strong near-inertial oscillation occurred immediately after the typhoon passed and lasted for at least 4-5 days, during which a strong vertical current existed in the lower layer. Characteristics of the near-inertial internal oscillation were observed in the middle layer. The clockwise component of the inertial frequency was enhanced in the surface layer and at 63 m depth after the typhoon passed, with these layers almost perfectly out of phase. The vertical shear current was intensified by the interaction of the wind-driven current in the upper layer and the background semi-diurnal tidal current during the arrival of the typhoon, and also by the near-inertial internal oscillation after the typhoon passage. The strong near-inertial internal oscillation persisted without significant interfacial structure after the mixing of the thermocline, which could enhance the vertical mixing over several days.

  7. Solar radiation, phytoplankton pigments and the radiant heating of the equatorial Pacific warm pool

    NASA Technical Reports Server (NTRS)

    Siegel, David A.; Ohlmann, J. Carter; Washburn, Libe; Bidigare, Robert R.; Nosse, Craig T.; Fields, Erik; Zhou, Yimei

    1995-01-01

    Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are approx. 23 W/sq m and are a large fraction of the climatological mean net air-sea heat flux (approx. 40 W/sq m). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W/sq m at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13 C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.

  8. Modelling the vertical distribution of Prochlorococcus and Synechococcus in the North Pacific Subtropical Ocean.

    PubMed

    Rabouille, Sophie; Edwards, Christopher A; Zehr, Jonathan P

    2007-10-01

    A simple model was developed to examine the vertical distribution of Prochlorococcus and Synechococcus ecotypes in the water column, based on their adaptation to light intensity. Model simulations were compared with a 14-year time series of Prochlorococcus and Synechococcus cell abundances at Station ALOHA in the North Pacific Subtropical Gyre. Data were analysed to examine spatial and temporal patterns in abundances and their ranges of variability in the euphotic zone, the surface mixed layer and the layer in the euphotic zone but below the base of the mixed layer. Model simulations show that the apparent occupation of the whole euphotic zone by a genus can be the result of a co-occurrence of different ecotypes that segregate vertically. The segregation of ecotypes can result simply from differences in light response. A sensitivity analysis of the model, performed on the parameter alpha (initial slope of the light-response curve) and the DIN concentration in the upper water column, demonstrates that the model successfully reproduces the observed range of vertical distributions. Results support the idea that intermittent mixing events may have important ecological and geochemical impacts on the phytoplankton community at Station ALOHA.

  9. Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

    NASA Technical Reports Server (NTRS)

    Luneva, M. V.; Clayson, C. A.; Dubovikov, Mikhail

    2015-01-01

    In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

  10. Mixed Layer Temperature Budget for the Northward Propagating Summer Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Girishkumar, M. S.; Joseph, J.; Thangaprakash, V. P.; Pottapinjara, V.; McPhaden, M. J.

    2017-11-01

    Composite analyses of mixed layer temperature (MLT) budget terms from near-surface meteorological and oceanic observations in the central Bay of Bengal are utilized to evaluate the modulation of air-sea interactions and MLT processes in response to the summer monsoon intraseasonal oscillation (MISO). For this purpose, we use moored buoy data at 15°N, 12°N, and 8°N along 90°E together with TropFlux meteorological parameters and the Ocean Surface Current Analyses Real-time (OSCAR) current product. Our analysis shows a strong cooling tendency in MLT with maximum amplitude in the central and northern BoB during the northward propagation of enhanced convective activity associated with the active phase of the MISO; conversely, warming occurs during the suppressed phase of the MISO. The surface mixed layer is generally heated during convectively inactive phases of the MISO primarily due to increased net surface heat flux into the ocean. During convectively active MISO phases, the surface mixed layer is cooled by the combined influence of net surface heat loss to the atmosphere and entrainment cooling at the base of mixed layer. The variability of net surface heat flux is primarily due to modulation of latent heat flux and shortwave radiation. Shortwave is mostly controlled by an enhancement or reduction of cloudiness during the active and inactive MISO phases and latent heat flux is mostly controlled by variations in air-sea humidity difference.

  11. Argo float observations of basin-scale deep convection in the Irminger Sea during winter 2011-2012

    NASA Astrophysics Data System (ADS)

    Thierry, V.; Piron, A.; Mercier, H.; Caniaux, G.

    2016-02-01

    An analysis of Argo data during the 2011-2012 winter revealed the presence of an exceptionally large number of profiles over the Irminger Basin with mixed layer depths (MLD) exceeding 700 m, which was deep enough to reach the pool of the intermediate Labrador Sea Water located in the Irminger Sea. Among them, 4 profiles exhibited an MLD of 1000 m, which was the maximum value observed this winter. Owing to the exceptional Argo sampling in the Irminger Sea during that winter the different phases of the mixed layer deepening down to 1000 m and their spatial extents were observed for the first time in the Irminger Sea. Two intense convective periods occurred in late January south of Cape Farewell and in late February-early March east of Greenland. A final deepening period was observed in mid-March during which the deepest mixed layers were observed. This long deepening period occurred in large regional areas and was followed by a rapid restratification phase. A mixed layer heat budget along the trajectories of the 4 floats that sampled the deepest mixed layers showed that heat loss at the air-sea interface was mainly responsible for heat content variations in the mixed layer. Greenland Tip Jets were of primary importance for the development of deep convection in the Irminger Sea in the 2011-2012 winter. They enhanced the winter heat loss and two long (more than 24 hours), intense and close in time late events boosted the mixed layer deepening down to 1000m. Net air-sea fluxes, the number of Greenland Tip Jets, the stratification of the water column, the NAO index and Ekman-induced heat flux are pertinent indicators to assess the favorable conditions for the development of deep convection in the Irminger Sea. When considering each of those indicators, we concluded that the 2011-2012 event was not significantly different compared to the three other documented occurrences of deep convection in the Irminger Sea.This work is a contribution to the NAOS project.

  12. Characterization of ion beam modified ceramic wear surfaces using Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Wei, W.; Lankford, J.

    1987-01-01

    An investigation of the surface chemistry and morphology of the wear surfaces of ceramic material surfaces modified by ion beam mixing has been conducted using Auger electron spectroscopy and secondary electron microscopy. Studies have been conducted on ceramic/ceramic friction and wear couples made up of TiC and NiMo-bonded TiC cermet pins run against Si3N4 and partially stabilized zirconia disc surfaces modified by the ion beam mixing of titanium and nickel, as well as ummodified ceramic/ceramic couples in order to determine the types of surface changes leading to the improved friction and wear behavior of the surface modified ceramics in simulated diesel environments. The results of the surface analyses indicate that the formation of a lubricating oxide layer of titanium and nickel, is responsible for the improvement in ceramic friction and wear behavior. The beneficial effect of this oxide layer depends on several factors, including the adherence of the surface modified layer or subsequently formed oxide layer to the disc substrate, the substrate materials, the conditions of ion beam mixing, and the environmental conditions.

  13. Spatial and temporal variability of total organic carbon along 140°W in the equatorial Pacific Ocean in 1992

    NASA Astrophysics Data System (ADS)

    Peltzer, Edward T.; Hayward, Nancy A.

    Total organic carbon (TOC) was analyzed on four transects along 140°W in 1992 using a high temperature combustion/discrete injection (HTC/DI) analyzer. For two of the transects, the analyses were conducted on-board ship. Mixed-layer concentrations of organic carbon varied from about 80 μM C at either end of the transect (12°N and 12°S) to about 60 μM C at the equator. Total organic carbon concentrations decreased rapidly below the mixed-layer to about 38-40 μM C at 1000 m across the transect. Little variation was observed below this depth; deep water concentrations below 2000m were virtually monotonic at about 36 μM C. Repeat measurements made on subsequent cruises consistently found the same concentrations at 1000 m or deeper, but substantial variations were observed in the mixed-layer and the upper water column above 400 m depth. Linear mixing models of total organic carbon versus σθ exhibited zones of organic carbon formation and consumption. TOC was found to be inversely correlated with apparent oxygen utilization (AOU) in the region between the mixed-layer and the oxygen minimum. In the mixed-layer, TOC concentrations varied seasonally. Part of the variations in TOC at the equator was driven by changes in the upwelling rate in response to variations in physical forcing related to an El Niño and to the passage of tropical instability waves. TOC export fluxes, calculated from simple box models, averaged 8±4 mmol C m -2day -1 at the equator and also varied seasonally. These export fluxes account for 50-75% of the total carbon deficit and are consistent with other estimates and model predictions.

  14. Quantifying the relationship between PM2.5 concentration, visibility and planetary boundary layer height for long-lasting haze and fog-haze mixed events in Beijing

    NASA Astrophysics Data System (ADS)

    Luan, Tian; Guo, Xueliang; Guo, Lijun; Zhang, Tianhang

    2018-01-01

    Air quality and visibility are strongly influenced by aerosol loading, which is driven by meteorological conditions. The quantification of their relationships is critical to understanding the physical and chemical processes and forecasting of the polluted events. We investigated and quantified the relationship between PM2.5 (particulate matter with aerodynamic diameter is 2.5 µm and less) mass concentration, visibility and planetary boundary layer (PBL) height in this study based on the data obtained from four long-lasting haze events and seven fog-haze mixed events from January 2014 to March 2015 in Beijing. The statistical results show that there was a negative exponential function between the visibility and the PM2.5 mass concentration for both haze and fog-haze mixed events (with the same R2 of 0.80). However, the fog-haze events caused a more obvious decrease of visibility than that for haze events due to the formation of fog droplets that could induce higher light extinction. The PM2.5 concentration had an inversely linear correlation with PBL height for haze events and a negative exponential correlation for fog-haze mixed events, indicating that the PM2.5 concentration is more sensitive to PBL height in fog-haze mixed events. The visibility had positively linear correlation with the PBL height with an R2 of 0.35 in haze events and positive exponential correlation with an R2 of 0.56 in fog-haze mixed events. We also investigated the physical mechanism responsible for these relationships between visibility, PM2.5 concentration and PBL height through typical haze and fog-haze mixed event and found that a double inversion layer formed in both typical events and played critical roles in maintaining and enhancing the long-lasting polluted events. The variations of the double inversion layers were closely associated with the processes of long-wave radiation cooling in the nighttime and short-wave solar radiation reduction in the daytime. The upper-level stable inversion layer was formed by the persistent warm and humid southwestern airflow, while the low-level inversion layer was initially produced by the surface long-wave radiation cooling in the nighttime and maintained by the reduction of surface solar radiation in the daytime. The obvious descending process of the upper-level inversion layer induced by the radiation process could be responsible for the enhancement of the low-level inversion layer and the lowering PBL height, as well as high aerosol loading for these polluted events. The reduction of surface solar radiation in the daytime could be around 35 % for the haze event and 94 % for the fog-haze mixed event. Therefore, the formation and subsequent descending processes of the upper-level inversion layer should be an important factor in maintaining and strengthening the long-lasting severe polluted events, which has not been revealed in previous publications. The interactions and feedbacks between PM2.5 concentration and PBL height linked by radiation process caused a more significant and long-lasting deterioration of air quality and visibility in fog-haze mixed events. The interactions and feedbacks of all processes were particularly strong when the PM2.5 mass concentration was larger than 150-200 µg m-3.

  15. Lagrangian mixed layer modeling of the western equatorial Pacific

    NASA Technical Reports Server (NTRS)

    Shinoda, Toshiaki; Lukas, Roger

    1995-01-01

    Processes that control the upper ocean thermohaline structure in the western equatorial Pacific are examined using a Lagrangian mixed layer model. The one-dimensional bulk mixed layer model of Garwood (1977) is integrated along the trajectories derived from a nonlinear 1 1/2 layer reduced gravity model forced with actual wind fields. The Global Precipitation Climatology Project (GPCP) data are used to estimate surface freshwater fluxes for the mixed layer model. The wind stress data which forced the 1 1/2 layer model are used for the mixed layer model. The model was run for the period 1987-1988. This simple model is able to simulate the isothermal layer below the mixed layer in the western Pacific warm pool and its variation. The subduction mechanism hypothesized by Lukas and Lindstrom (1991) is evident in the model results. During periods of strong South Equatorial Current, the warm and salty mixed layer waters in the central Pacific are subducted below the fresh shallow mixed layer in the western Pacific. However, this subduction mechanism is not evident when upwelling Rossby waves reach the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific due to episodes of strong wind and light precipitation associated with the El Nino-Southern Oscillation. Comparison of the results between the Lagrangian mixed layer model and a locally forced Eulerian mixed layer model indicated that horizontal advection of salty waters from the central Pacific strongly affects the upper ocean salinity variation in the western Pacific, and that this advection is necessary to maintain the upper ocean thermohaline structure in this region.

  16. Upper ocean response to the passage of two sequential typhoons

    NASA Astrophysics Data System (ADS)

    Wu, Renhao; Li, Chunyan

    2018-02-01

    Two sequential typhoons, separated by five days, Chan-hom and Nangka in the summer of 2015, provided a unique opportunity to study the oceanic response and cold wake evolution. The upper ocean response to the passage of these two typhoons was investigated using multi-satellite, Argo float data and HYCOM global model output. The sea surface cooling (SSC) induced by Chan-hom was gradually enhanced along its track when the storm was intensified while moving over the ocean with shallow mixed layer. The location of maximum cooling of sea surface was determined by the storm's translation speed as well as pre-typhoon oceanic conditions. As a fast-moving storm, Chan-hom induced significant SSC on the right side of its track. Localized maximum cooling patches are found over a cyclonic eddy (CE). An analysis of data from Argo floats near the track of Chan-hom demonstrated that the mixed layer temperature (MLT) and mixed layer depth (MLD) had more variabilities on the right side than those on the left side of Chan-hom's track, while mixed layer salinity (MLS) response was different from those of MLT and MLD with an increase in salinity to the right side and a decrease in salinity to the left side of the track. Subsequently, because of the remnant effect of Chan-hom, the strong upwelling induced by Typhoon Nangka, the pre-existing CE as well as a slow translation speed (<2 m s-1) of the storm, the most significant SSC ( 6 °C) was observed over the CE region in the wake of the storm. Further, Nangka experienced a rapid weakening suggesting immediate negative feedback from the intensified SSC occurred in the CE region. After these two typhoons, the CE was enhanced and the sea surface height of eddy core was depressed by 10 cm. It took more than one month for SSC to restore to its pre-typhoon conditions, with the anomalous geostrophic current advection playing an important role in the process. The enhancement of chlorophyll-a concentrations was also noticed at both the CE region and close to Chan-hom's track.

  17. Effects of Precipitation on Ocean Mixed-Layer Temperature and Salinity as Simulated in a 2-D Coupled Ocean-Cloud Resolving Atmosphere Model

    NASA Technical Reports Server (NTRS)

    Li, Xiaofan; Sui, C.-H.; Lau, K-M.; Adamec, D.

    1999-01-01

    A two-dimensional coupled ocean-cloud resolving atmosphere model is used to investigate possible roles of convective scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets. The model couples a cloud resolving model with an embedded mixed layer-ocean circulation model. Five experiment are performed under imposed large-scale atmospheric forcing in terms of vertical velocity derived from the TOGA COARE observations during a selected seven-day period. The dominant variability of mixed-layer temperature and salinity are simulated by the coupled model with imposed large-scale forcing. The mixed-layer temperatures in the coupled experiments with 1-D and 2-D ocean models show similar variations when salinity effects are not included. When salinity effects are included, however, differences in the domain-mean mixed-layer salinity and temperature between coupled experiments with 1-D and 2-D ocean models could be as large as 0.3 PSU and 0.4 C respectively. Without fresh water effects, the nocturnal heat loss over ocean surface causes deep mixed layers and weak cooling rates so that the nocturnal mixed-layer temperatures tend to be horizontally-uniform. The fresh water flux, however, causes shallow mixed layers over convective areas while the nocturnal heat loss causes deep mixed layer over convection-free areas so that the mixed-layer temperatures have large horizontal fluctuations. Furthermore, fresh water flux exhibits larger spatial fluctuations than surface heat flux because heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.

  18. Central Tropical Pacific Variability And ENSO Response To Changing Climate Boundary Conditions: Evidence From Individual Line Island Foraminifera

    NASA Astrophysics Data System (ADS)

    Rustic, G. T.; Polissar, P. J.; Ravelo, A. C.; White, S. M.

    2017-12-01

    The El Niño Southern Oscillation (ENSO) plays a dominant role in Earth's climate variability. Paleoceanographic evidence suggests that ENSO has changed in the past, and these changes have been linked to large-scale climatic shifts. While a close relationship between ENSO evolution and climate boundary conditions has been predicted, testing these predictions remains challenging. These climate boundary conditions, including insolation, the mean surface temperature gradient of the tropical Pacific, global ice volume, and tropical thermocline depth, often co-vary and may work together to suppress or enhance the ocean-atmosphere feedbacks that drive ENSO variability. Furthermore, suitable paleo-archives spanning multiple climate states are sparse. We have aimed to test ENSO response to changing climate boundary conditions by generating new reconstructions of mixed-layer variability from sedimentary archives spanning the last three glacial-interglacial cycles from the Central Tropical Pacific Line Islands, where El Niño is strongly expressed. We analyzed Mg/Ca ratios from individual foraminifera to reconstruct mixed-layer variability at discrete time intervals representing combinations of climatic boundary conditions from the middle Holocene to Marine Isotope Stage (MIS) 8. We observe changes in the mixed-layer temperature variability during MIS 5 and during the previous interglacial (MIS 7) showing significant reductions in ENSO amplitude. Differences in variability during glacial and interglacial intervals are also observed. Additionally, we reconstructed mixed-layer and thermocline conditions using multi-species Mg/Ca and stable isotope measurements to more fully characterize the state of the Central Tropical Pacific during these intervals. These reconstructions provide us with a unique view of Central Tropical Pacific variability and water-column structure at discrete intervals under varying boundary climate conditions with which to assess factors that shape ENSO variability.

  19. Typhoon Impacts

    DTIC Science & Technology

    2014-09-30

    and Rmax is the radius of maximum winds . Figure 1 compares two properties of the cold wake, its location and its strength , from 6 storms. The...dimensional response of the underlying ocean including strong surface currents, upwelling of the thermocline, intense mixing across the thermocline, the...mixing determining the rate and character of wake dissipation. The wake is also expected to modify the atmospheric boundary layer and the biology

  20. Prescribed fire effects on the herbaceous layer of mixed-oak forests

    Treesearch

    Todd F. Hutchinson; Ralph E.J. Boerner; Steve Sutherland; Elaine Kennedy Sutherland; Marilyn Ortt; Louis R. Iverson; Louis R. Iverson

    2005-01-01

    In 1994, a multidisciplinary project was established to study the effects of prescribed fire on oak forests in southern Ohio. Here we describe the herbaceous layer response to fires over a 5-year period. In four study sites, treatments imposed were unburned, periodic (1996 and 1999), and annual (1996-1999) fires. Sample plots (n = 108) were stratified by an integrated...

  1. Fire and fire surrogate treatments in mixed-oak forests: Effects on herbaceous layer vegetation

    Treesearch

    Ross Phillips; Todd Hutchinson; Lucy Brudnak; Thomas Waldrop

    2007-01-01

    Herbaceous layer vegetation responses to prescribed fire and fire surrogate treatments (thinning and understory removal) were examined. Results from 3 to 4 years following treatment are presented for the Ohio Hills Country and the Southern Appalachian Mountain sites of the National Fire and Fire Surrogate Study. At the Ohio Hills site, changes in forest structure were...

  2. Mixing enhancement strategies and their mechanisms in supersonic flows: A brief review

    NASA Astrophysics Data System (ADS)

    Huang, Wei

    2018-04-01

    Achieving efficient fuel-air mixing is a crucial issue in the design of the scramjet engine due to the compressibility effect on the mixing shear layer growth and the stringent flow residence time limitation induced by the high-speed crossflow, and the potential solution is to enhance mixing between air and fuel by introducing of streamwise vortices in the flow field. In this survey, some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years, as well as their mixing augmentation mechanisms, were reviewed in detail, namely the pulsed transverse injection scheme, the traditional transverse injection coupled with the vortex generator, and the dual transverse injection system with a front porthole and a rear air porthole arranged in tandem. The streamwise vortices, through the large-scale stirring motion that they introduce, are responsible for the extraction of large amounts of energy from the mean flow that can be converted into turbulence, ultimately leading to increased mixing effectiveness. The streamwise vortices may be obtained by taking advantage of the shear layer between a jet and the cross stream or by employing intrusive physical devices. Finally, a promising mixing enhancement strategy in supersonic flows was proposed, and some remarks were provided.

  3. Tensiometry and dilational rheology of mixed β-lactoglobulin/ionic surfactant adsorption layers at water/air and water/hexane interfaces.

    PubMed

    Dan, Abhijit; Gochev, Georgi; Miller, Reinhard

    2015-07-01

    Oscillating drop tensiometry was applied to study adsorbed interfacial layers at water/air and water/hexane interfaces formed from mixed solutions of β-lactoglobulin (BLG, 1 μM in 10 mM buffer, pH 7 - negative net charge) and the anionic surfactant SDS or the cationic DoTAB. The interfacial pressure Π and the dilational viscoelasticity modulus |E| of the mixed layers were measured for mixtures of varying surfactant concentrations. The double capillary technique was employed which enables exchange of the protein solution in the drop bulk by surfactant solution (sequential adsorption) or by pure buffer (washing out). The first protocol allows probing the influence of the surfactant on a pre-adsorbed protein layer thus studying the protein/surfactant interactions at the interface. The second protocol gives access to the residual values of Π and |E| measured after the washing out procedure thus bringing information about the process of protein desorption. The DoTAB/BLG complexes exhibit higher surface activity and higher resistance to desorption in comparison with those for the SDS/BLG complexes due to hydrophobization via electrostatic binding of surfactant molecules. The neutral DoTAB/BLG complexes achieve maximum elastic response of the mixed layer. Mixed BLG/surfactant layers at the water/oil interface are found to reach higher surface pressure and lower maximum dilational elasticity than those at the water/air surface. The sequential adsorption mode experiments and the desorption study reveal that binding of DoTAB to pre-adsorbed BLG globules is somehow restricted at the water/air surface in comparison with the case of complex formation in the solution bulk and subsequently adsorbed at the water/air surface. Maximum elasticity is achieved with washed out layers obtained after simultaneous adsorption, i.e. isolation of the most surface active DoTAB/BLG complex. These specific effects are much less pronounced at the W/H interface. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. Investigation on flow and mixing characteristics of supersonic mixing layer induced by forced vibration of cantilever

    NASA Astrophysics Data System (ADS)

    Zhang, Dongdong; Tan, Jianguo; Lv, Liang

    2015-12-01

    The mixing process has been an important issue for the design of supersonic combustion ramjet engine, and the mixing efficiency plays a crucial role in the improvement of the combustion efficiency. In the present study, nanoparticle-based planar laser scattering (NPLS), particle image velocimetry (PIV) and large eddy simulation (LES) are employed to investigate the flow and mixing characteristics of supersonic mixing layer under different forced vibration conditions. The indexes of fractal dimension, mixing layer thickness, momentum thickness and scalar mixing level are applied to describe the mixing process. Results show that different from the development and evolution of supersonic mixing layer without vibration, the flow under forced vibration is more likely to present the characteristics of three-dimensionality. The laminar flow region of mixing layer under forced vibration is greatly shortened and the scales of rolled up Kelvin-Helmholtz vortices become larger, which promote the mixing process remarkably. The fractal dimension distribution reveals that comparing with the flow without vibration, the turbulent fluctuation of supersonic mixing layer under forced vibration is more intense. Besides, the distribution of mixing layer thickness, momentum thickness and scalar mixing level are strongly influenced by forced vibration. Especially, when the forcing frequency is 4000 Hz, the mixing layer thickness and momentum thickness are 0.0391 m and 0.0222 m at the far field of 0.16 m, 83% and 131% higher than that without vibration at the same position, respectively.

  5. Analysis of Mixing Layer LES Data with Convective Mach Number 0.9 to 1.3

    NASA Astrophysics Data System (ADS)

    Helm, Clara M.; Martin, M. Pino

    2017-11-01

    The study of compressible mixing layers is essential to gaining a fundamental physical understanding of the global effects of compressibility on the development of turbulence in shear (Smits & Dussauge 2006). Research on compressible mixing layers is particularly difficult mainly because of the sensitivity of the mixing layer to initial conditions. A mixing layer occurs naturally in separated shock turbulent boundary layer interactions (STBLIs). We use our STBLI database to study the properties of mixing layers with convective Mach numbers of 0.9, 1.1, and 1.3. We report on the spreading rate, turbulence stress level, vortex shedding frequency, vortex convection velocity, and differences in the three-dimensional form of the vortices. The results are compared with mixing layer data available in literature and evaluated using the various scaling laws that have been proposed over the years. We discuss to what extent the mixing layer in the STBLI represents the canonical case and what additional insight into the is research area it provides. This work is supported by the Air Force Office of Scientific Research under Grant FA9550-17-1-0104.

  6. Evaluation of layered and mixed passive treatment systems for acid mine drainage.

    PubMed

    Jeen, Sung-Wook; Mattson, Bruce

    2016-11-01

    Laboratory column tests for passive treatment systems for mine drainage from a waste rock storage area were conducted to evaluate suitable reactive mixture, system configuration, effects of influent water chemistry, and required residence time. Five columns containing straw, chicken manure, mushroom compost, and limestone (LS), in either layered or mixed configurations, were set up to simulate the treatment system. The results showed that all of the five columns removed metals of concern (i.e. Al, Cd, Co, Cu, Fe, Ni, and Zn) with a residence time of 15 h and greater. Reaction mechanisms responsible for the removal of metals may include sulfate reduction and subsequent sulfide precipitation, precipitation of secondary carbonates and hydroxides, co-precipitation, and sorption on organic substrates and secondary precipitates. The results suggest that the mixed systems containing organic materials and LS perform better than the layered systems, sequentially treated by organic and LS layers, due to the enhanced pH adjustment, which is beneficial to bacterial activity and precipitation of secondary minerals. The column tests provide a basis for the design of a field-scale passive treatment system, such as a reducing and alkalinity producing system or a permeable reactive barrier.

  7. Shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern South China Sea

    NASA Astrophysics Data System (ADS)

    Yang, Bing; Hou, Yijun; Hu, Po; Liu, Ze; Liu, Yahao

    2015-05-01

    Based on observed temperature and velocity in 2005 in northwestern South China Sea, the shallow ocean responses to three tropical cyclones were examined. The oceanic response to Washi was similar to common observations with 2°C cooling of the ocean surface and slight warming of the thermocline resulted from vertical entrainment. Moreover, the wavefield was dominated by first mode near-inertial oscillations, which were red-shifted and trapped by negative background vorticity leading to an e-folding timescale of 12 days. The repeated reflections by the surface and bottom boundaries were thought to yield the successive emergence of higher modes. The oceanic responses to Vicente appeared to be insignificant with cooling of the ocean surface by only 0.5°C and near-inertial currents no larger than 0.10 m/s as a result of a deepened surface mixed layer. However, the oceanic responses to Typhoon Damrey were drastic with cooling of 4.5°C near the surface and successive barotropic-like near-inertial oscillations. During the forced stage, the upper ocean heat content decreased conspicuously by 11.65% and the stratification was thoroughly destroyed by vertical mixing. In the relaxation stage, the water particle had vertical displacement of 20-30 m generated by inertial pumping. The current response to Damrey was weaker than Washi due to the deepened mixed layer and the destroyed stratification. Our results suggested that the shallow water oceanic responses to tropical cyclones varied significantly with the intensity of tropical cyclones, and was affected by local stratification and background vorticity.

  8. Scalar entrainment in the mixing layer

    NASA Technical Reports Server (NTRS)

    Sandham, N. D.; Mungal, M. G.; Broadwell, J. E.; Reynolds, W. C.

    1988-01-01

    New definitions of entrainment and mixing based on the passive scalar field in the plane mixing layer are proposed. The definitions distinguish clearly between three fluid states: (1) unmixed fluid, (2) fluid engulfed in the mixing layer, trapped between two scalar contours, and (3) mixed fluid. The difference betwen (2) and (3) is the amount of fluid which has been engulfed during the pairing process, but has not yet mixed. Trends are identified from direct numerical simulations and extensions to high Reynolds number mixing layers are made in terms of the Broadwell-Breidenthal mixing model. In the limit of high Peclet number (Pe = ReSc) it is speculated that engulfed fluid rises in steps associated with pairings, introducing unmixed fluid into the large scale structures, where it is eventually mixed at the Kolmogorov scale. From this viewpoint, pairing is a prerequisite for mixing in the turbulent plane mixing layer.

  9. Direct numerical simulations of a reacting turbulent mixing layer by a pseudospectral-spectral element method

    NASA Technical Reports Server (NTRS)

    Mcmurtry, Patrick A.; Givi, Peyman

    1992-01-01

    An account is given of the implementation of the spectral-element technique for simulating a chemically reacting, spatially developing turbulent mixing layer. Attention is given to experimental and numerical studies that have investigated the development, evolution, and mixing characteristics of shear flows. A mathematical formulation is presented of the physical configuration of the spatially developing reacting mixing layer, in conjunction with a detailed representation of the spectral-element method's application to the numerical simulation of mixing layers. Results from 2D and 3D calculations of chemically reacting mixing layers are given.

  10. Comparison of the key mechanisms leading to rollovers in Liquefied Natural Gas using Computational Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Hubert, Antoine; Dadonau, Maksim; Dembele, Siaka; Denissenko, Petr; Wen, Jennifer

    2017-11-01

    Growing demand for the LNG fosters growth of the number of production sites with varying composition and density. Combining different sources of LNG may result in a stably stratified system, in which heat and mass transfer between the layers is limited. Heating of the LNG due to wall thermal conductivity leads to formation of convection cells confined within the layers. While the upper layer can release the extra energy via preferential methane boil-off, the bottom layer cannot and hence becomes superheated. Gradual density equilibration reduces stratification and may eventually lead to a sudden mixing event called ``rollover'', accompanied by violent evaporation of the superheated LNG. Three phenomena are potentially responsible for density equilibration. The first is the growing difference in thermal expansion of the layers due to the reduced ability of the bottom layer to reject heat. The second is the penetration of the heated near-wall boundary layer into the upper layer. The third is the ``entrainment mixing'' occurring at the contact surface between the two layers. The present study uses CFD to compare these mechanisms. Boussinesq approximation and an extended version of the k- ɛ model is used. The code is validated by comparison with a large-scale LNG rollover experiment.

  11. The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

    NASA Technical Reports Server (NTRS)

    Chen, Dake; Busalacchi, Antonio J.; Rothstein, Lewis M.

    1994-01-01

    The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat flux contributions.

  12. Influences of Ocean Thermohaline Stratification on Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Toole, J. M.; Timmermans, M.-L.; Perovich, D. K.; Krishfield, R. A.; Proshutinsky, A.; Richter-Menge, J. A.

    2009-04-01

    The Arctic Ocean's surface mixed layer constitutes the dynamical and thermodynamical link between the sea ice and the underlying waters. Wind stress, acting directly on the surface mixed layer or via wind-forced ice motion, produce surface currents that can in turn drive deep ocean flow. Mixed layer temperature is intimately related to basal sea ice growth and melting. Heat fluxes into or out of the surface mixed layer can occur at both its upper and lower interfaces: the former via air-sea exchange at leads and conduction through the ice, the latter via turbulent mixing and entrainment at the layer base. Variations in Arctic Ocean mixed layer properties are documented based on more than 16,000 temperature and salinity profiles acquired by Ice-Tethered Profilers since summer 2004 and analyzed in conjunction with sea ice observations from Ice Mass Balance Buoys and atmospheric heat flux estimates. Guidance interpreting the observations is provided by a one-dimensional ocean mixed layer model. The study focuses attention on the very strong density stratification about the mixed layer base in the Arctic that, in regions of sea ice melting, is increasing with time. The intense stratification greatly impedes mixed layer deepening by vertical convection and shear mixing, and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth/decay. Consistent with previous work, this study demonstrates that the Arctic sea ice is most sensitive to changes in ocean mixed layer heat resulting from fluxes across its upper (air-sea and/or ice-water) interface.

  13. High Operating Temperature Barrier Infrared Detector with Tailorable Cutoff Wavelength

    NASA Technical Reports Server (NTRS)

    Ting, David Z. (Inventor); Hill, Cory J. (Inventor); Seibel, Alexander (Inventor); Bandara, Sumith Y. (Inventor); Gunapala, Sarath D. (Inventor)

    2015-01-01

    A barrier infrared detector with absorber materials having selectable cutoff wavelengths and its method of manufacture is described. A GaInAsSb absorber layer may be grown on a GaSb substrate layer formed by mixing GaSb and InAsSb by an absorber mixing ratio. A GaAlAsSb barrier layer may then be grown on the barrier layer formed by mixing GaSb and AlSbAs by a barrier mixing ratio. The absorber mixing ratio may be selected to adjust a band gap of the absorber layer and thereby determine a cutoff wavelength for the barrier infrared detector. The absorber mixing ratio may vary along an absorber layer growth direction. Various contact layer architectures may be used. In addition, a top contact layer may be isolated into an array of elements electrically isolated as individual functional detectors that may be used in a detector array, imaging array, or focal plane array.

  14. Effect of a fast-moving tropical storm Washi on phytoplankton in the northwestern South China Sea

    NASA Astrophysics Data System (ADS)

    Zhao, Hui; Pan, Jiayi; Han, Guoqi; Devlin, Adam T.; Zhang, Shuwen; Hou, Yijun

    2017-04-01

    Tropical cyclones may augment nutrients in the ocean surface layer through mixing, entrainment, and upwelling, triggering phytoplankton blooms in oligotrophic waters such as the South China Sea (SCS). Previous studies focused mainly on responses of marine environments to strong or slow-moving typhoons in the SCS. In this study, we analyze variations of chlorophyll a (Chl a) and oceanic conditions in the continental shelf region east of Hainan Island during the fast-moving tropical storm Washi and investigate its influences on phytoplankton bloom and related dynamic mechanisms. Results indicate that there was significant variation of Chl a concentration in the continental shelf region, with low values (about 0.1 mg m-3) before the storm and a 30% increase after the storm. This increase was spatially variable, much larger nearshore than offshore. Power spectral analysis of Acoustic Doppler Current Profiler (ADCP) data at a shelf site near the study region reveals strong near-inertial oscillations (NIOs) in the upper layer, with a period of about 36 h, close to the local inertial period. The NIOs intensified mixing and modified the stratification of the upper layer, inducing uplift of nutrients and Chl a into the mixed layer from below, and leading to surface Chl a increase. The relatively shallow nutricline and thermocline in the continental shelf region before the storm were favorable for upwelling of nutrients and generation of NIOs. Advection of nutrients from enhanced runoff during and after the storm may be responsible for the larger increase of the Chl a nearshore.

  15. Transverse ageostrophic circulations associated with elevated mixed layers

    NASA Technical Reports Server (NTRS)

    Keyser, D.; Carlson, T. N.

    1984-01-01

    The nature of the frontogenetically forced transverse ageostrophic circulations connected with elevated mixed layer structure is investigated as a first step toward diagnosing the complex vertical circulation patterns occurring in the vicinity of elevated mixed layers within a severe storm environment. The Sawyer-Eliassen ageostrophic circulation equation is reviewed and applied to the elevated mixed layer detected in the SESAME IV data set at 2100 GMT of May 9, 1979. The results of the ageostrophic circulation diagnosis are confirmed and refined by considering an analytic specification for the elevated mixed layer structure.

  16. Ocean Mixed Layer Response to Gap Wind Scenarios

    DTIC Science & Technology

    2006-12-01

    Kostas Rados for helpful discussions and MATLAB codes. • LT. Robin Corey Cherrett USN for advice and discussions. Professor Qing Wang, thank you...and the flow can extent for hundreds of miles (Clarke 1988, Cherrett 2006). The magnitude of these winds usually depends on the pressure gradient...was studied by Cherrett (2006) with the emphases on the atmospheric boundary layer and surface characteristics of the gap outflow region. Since our

  17. Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

    DOE PAGES

    Flippo, K. A.; Doss, F. W.; Kline, J. L.; ...

    2016-11-23

    While using a large volume high-energy-density fluid shear experiment ( 8.5 cm 3 ) at the National Ignition Facility, we have demonstrated for the first time the ability to significantly alter the evolution of a supersonic sheared mixing layer by controlling the initial conditions of that layer. Furthermore, by altering the initial surface roughness of the tracer foil, we demonstrate the ability to transition the shear mixing layer from a highly ordered system of coherent structures to a randomly ordered system with a faster growing mix layer, indicative of strong mixing in the layer at a temperature of severalmore » tens of electron volts and at near solid density. Moreover, simulations using a turbulent-mix model show good agreement with the experimental results and poor agreement without turbulent mix.« less

  18. Biomimetic Deposition of Hydroxyapatite by Mixed Acid Treatment of Titanium Surfaces.

    PubMed

    Zhao, J M; Park, W U; Hwang, K H; Lee, J K; Yoon, S Y

    2015-03-01

    A simple chemical method was established for inducing bioactivity of Ti metal. In the present study, two kinds of mixed acid solutions were used to treat Ti specimens to induce Ca-P formation. Following a strong mixed acid activation process, Ca-P coatings successfully formed on the Ti surfaces in the simulated body fluid. Strong mixed acid etching was used to increase the roughness of the metal surface, because the porous and rough surfaces allow better adhesion between Ca-P coatings and substrate. Nano-scale modification of titanium surfaces can alter cellular and tissue responses, which may benefit osseointegration and dental implant therapy. Some specimens were treated with a 5 M NaOH aqueous solution, and then heat treated at 600 °C in order to form an amorphous sodium titanate layer on their surface. This treated titanium metal is believed to form a dense and uniform bone-like apatite layer on its surface in a simulated body fluid (SBF). This study proved that mixed acid treatment is not only important for surface passivation but is also another bioactive treatment for titanium surfaces, an alternative to alkali treatment. In addition, mixed acid treatment uses a lower temperature and shorter time period than alkali treatment.

  19. The ocean mixed layer under Southern Ocean sea-ice: Seasonal cycle and forcing

    NASA Astrophysics Data System (ADS)

    Pellichero, Violaine; Sallée, Jean-Baptiste; Schmidtko, Sunke; Roquet, Fabien; Charrassin, Jean-Benoît

    2017-02-01

    The oceanic mixed layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer, all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed layer. The interaction between the ocean mixed layer and sea-ice plays a key role for water mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed layer are poorly understood due to the sparseness of in situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the polar regions. Working with elephant seal-derived, ship-based, and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity, and vertical entrainment play only secondary roles. Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed layer, and impact large-scale water mass formation and transformation with far reaching consequences for ocean ventilation.

  20. Effect of shock interactions on mixing layer between co-flowing supersonic flows in a confined duct

    NASA Astrophysics Data System (ADS)

    Rao, S. M. V.; Asano, S.; Imani, I.; Saito, T.

    2018-03-01

    Experiments are conducted to observe the effect of shock interactions on a mixing layer generated between two supersonic streams of Mach number M _{1} = 1.76 and M _{2} = 1.36 in a confined duct. The development of this mixing layer within the duct is observed using high-speed schlieren and static pressure measurements. Two-dimensional, compressible Reynolds averaged Navier-Stokes equations are solved using the k-ω SST turbulence model in Fluent. Further, adverse pressure gradients are imposed by placing inserts of small (<7% of duct height) but finite (> boundary layer thickness) thickness on the walls of the test section. The unmatched pressures cause the mixing layer to bend and lead to the formation of shock structures that interact with the mixing layer. The mixing layer growth rate is found to increase after the shock interaction (nearly doubles). The strongest shock is observed when a wedge insert is placed in the M _{2} flow. This shock interacts with the mixing layer exciting flow modes that produce sinusoidal flapping structures which enhance the mixing layer growth rate to the maximum (by 1.75 times). Shock fluctuations are characterized, and it is observed that the maximum amplitude occurs when a wedge insert is placed in the M _{2} flow.

  1. Seasonal Mixed Layer Heat Budget in the Southeast Tropical Atlantic

    NASA Astrophysics Data System (ADS)

    Scannell, H. A.; McPhaden, M. J.

    2016-12-01

    We analyze a mixed layer heat budget at 6ºS, 8ºE from a moored buoy of the Prediction and Research Moored Array in the Atlantic (PIRATA) to better understand the causes of seasonal mixed layer temperature variability in the southeast tropical Atlantic. This region is of interest because it is susceptible to warm biases in coupled global climate models and has historically been poorly sampled. Previous work suggests that thermodynamic changes in both latent heat loss and absorbed solar radiation dominate mixed layer properties away from the equator in the tropical Atlantic, while advection and entrainment are more important near the equator. Changes in mixed layer salinity can also influence temperature through the formation of barrier layers and density gradients. Freshwater flux from the Congo River, migration of the Intertropical Convergence Zone and advection of water masses are considered important contributors to mixed layer salinity variability in our study region. We analyze ocean temperature, salinity and meteorological data beginning in 2013 using mooring, Argo, and satellite platforms to study how seasonal temperature variability in the mixed layer is influenced by air-sea interactions and ocean dynamics.

  2. Mechanisms Responsible for the Observed Thermodynamic Structure in a Convective Boundary Layer Over the Hudson Valley of New York State

    NASA Astrophysics Data System (ADS)

    Freedman, Jeffrey M.; Fitzjarrald, David R.

    2017-02-01

    We examine cases of a regional elevated mixed layer (EML) observed during the Hudson Valley Ambient Meteorology Study (HVAMS) conducted in New York State, USA in 2003. Previously observed EMLs referred to topographic domains on scales of 105 -106 km2 . Here, we present observational evidence of the mechanisms responsible for the development and maintenance of regional EMLs overlying a valley-based convective boundary layer (CBL) on much smaller spatial scales (<5000 km2) . Using observations from aircraft-based, balloon-based, and surface-based platforms deployed during the HVAMS, we show that cross-valley horizontal advection, along-valley channelling, and fog-induced cold-air pooling are responsible for the formation and maintenance of the EML and valley-CBL coupling over New York State's Hudson Valley. The upper layer stability of the overlying EML constrains growth of the valley CBL, and this has important implications for air dispersion, aviation interests, and fog forecasting.

  3. High Static Stability in the Mixed Layer Above the Extratropical Tropopause

    NASA Astrophysics Data System (ADS)

    Kunz, A.; Konopka, P.; Müller, R.; Pan, L. L.; Schiller, C.

    2009-04-01

    A strong relationship between the static stability N2 in the tropopause inversion layer (TIL) and the intensity of mixing is evident from in-situ observations during SPURT. With a new simple measure of mixing intensity based on O3/CO tracer correlations, a very high mixing intensity connected to a high N2 is found in the extratropical mixing layer. Using radiative transfer calculations we simulate the influence of trace gases such as O3 and H2O on the temperature gradient and thus on the static stability above the tropopause in an idealized (L-shaped) non-mixed and reference mixed atmosphere. N2 enhances due to an intensifying mixing in the LS. At the same time the temperature decreases together with a development of an inversion and the TIL. Hereby H2O plays the dominant role in maintenance the temperature inversion and the TIL structure. In case of non mixed profiles the TIL vanishes. The results motivate a link between the mixing layer and the TIL. The mixing layer contains on the one hand older air masses, with high values of N2 due to radiative adjustment. This part of the mixing layer is spatial identically to the TIL. On the other hand, there are younger air masses with somehow lower N2 values within the mixing layer, because of fast intrusion processes from the troposphere due to the permeability or so-called mid-latitude-breaks associated with the jet.

  4. The effects of mixed layer dynamics on ice growth in the central Arctic

    NASA Astrophysics Data System (ADS)

    Kitchen, Bruce R.

    1992-09-01

    The thermodynamic model of Thorndike (1992) is coupled to a one dimensional, two layer ocean entrainment model to study the effect of mixed layer dynamics on ice growth and the variation in the ocean heat flux into the ice due to mixed layer entrainment. Model simulations show the existence of a negative feedback between the ice growth and the mixed layer entrainment, and that the underlying ocean salinity has a greater effect on the ocean beat flux than does variations in the underlying ocean temperature. Model simulations for a variety of surface forcings and initial conditions demonstrate the need to include mixed layer dynamics for realistic ice prediction in the arctic.

  5. The new oxide paradigm for solid state ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Rogers, D. J.; Bove, P.; Arrateig, X.; Sandana, V. E.; Teherani, F. H.; Razeghi, M.; McClintock, R.; Frisch, E.; Harel, S.

    2018-03-01

    The bandgap of wurzite ZnO layers grown on 2 inch diameter c-Al2O3 substrates by pulsed laser deposition was engineered from 3.7 to 4.8 eV by alloying with Mg. Above this Mg content the layers transformed from single phase hcp to mixed hcp/fcc phase before becoming single phase fcc above a bandgap of about 5.5 eV. Metal-Semiconductor-Metal (MSM) photodetectors based on gold Inter-Digitated-Transducer structures were fabricated from the single phase hcp layers by single step negative photolithography and then packaged in TO5 cans. The devices gave over 6 orders of magnitude of separation between dark and light signal with solar rejection ratios (I270 : I350) of over 3 × 105 and dark signals of 300 pA (at a bias of -5V). Spectral responsivities were engineered to fit the "Deutscher Verein des Gas- und Wasserfaches" industry standard form and gave over two decade higher responsivities (14 A/W, peaked at 270 nm) than commercial SiC based devices. Homogeneous Ga2O3 layers were also grown on 2 inch diameter c-Al2O3 substrates by PLD. Optical transmission spectra were coherent with a bandgap that increased from 4.9 to 5.4 eV when film thickness was decreased from 825 to 145 nm. X-ray diffraction revealed that the films were of the β-Ga2O3 (monoclinic) polytype with strong (-201) orientation. β-Ga2O3 MSM photodetectors gave over 4 orders of magnitude of separation between dark and light signal (at -5V bias) with dark currents of 250 pA and spectral responsivities of up to 40 A/W (at -0.75V bias). It was found that the spectral responsivity peak position could be decreased from 250 to 230 nm by reducing film thickness from 825 to 145 nm. This shift in peak responsivity wavelength with film thickness (a) was coherent with the apparent bandgap shift that was observed in transmission spectroscopy for the same layers and (b) conveniently provides a coverage of the spectral region in which MgZnO layers show fcc/hcp phase mixing.

  6. Parameterization of large-scale turbulent diffusion in the presence of both well-mixed and weakly mixed patchy layers

    NASA Astrophysics Data System (ADS)

    Osman, M. K.; Hocking, W. K.; Tarasick, D. W.

    2016-06-01

    Vertical diffusion and mixing of tracers in the upper troposphere and lower stratosphere (UTLS) are not uniform, but primarily occur due to patches of turbulence that are intermittent in time and space. The effective diffusivity of regions of patchy turbulence is related to statistical parameters describing the morphology of turbulent events, such as lifetime, number, width, depth and local diffusivity (i.e., diffusivity within the turbulent patch) of the patches. While this has been recognized in the literature, the primary focus has been on well-mixed layers, with few exceptions. In such cases the local diffusivity is irrelevant, but this is not true for weakly and partially mixed layers. Here, we use both theory and numerical simulations to consider the impact of intermediate and weakly mixed layers, in addition to well-mixed layers. Previous approaches have considered only one dimension (vertical), and only a small number of layers (often one at each time step), and have examined mixing of constituents. We consider a two-dimensional case, with multiple layers (10 and more, up to hundreds and even thousands), having well-defined, non-infinite, lengths and depths. We then provide new formulas to describe cases involving well-mixed layers which supersede earlier expressions. In addition, we look in detail at layers that are not well mixed, and, as an interesting variation on previous models, our procedure is based on tracking the dispersion of individual particles, which is quite different to the earlier approaches which looked at mixing of constituents. We develop an expression which allows determination of the degree of mixing, and show that layers used in some previous models were in fact not well mixed and so produced erroneous results. We then develop a generalized model based on two dimensional random-walk theory employing Rayleigh distributions which allows us to develop a universal formula for diffusion rates for multiple two-dimensional layers with general degrees of mixing. We show that it is the largest, most vigorous and less common turbulent layers that make the major contribution to global diffusion. Finally, we make estimates of global-scale diffusion coefficients in the lower stratosphere and upper troposphere. For the lower stratosphere, κeff ≈ 2x10-2 m2 s-1, assuming no other processes contribute to large-scale diffusion.

  7. Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

    DOE PAGES

    Haines, Brian Michael; Grim, Gary P.; Fincke, James R.; ...

    2016-07-29

    Here, we present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employmore » any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

  8. Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Haines, Brian M., E-mail: bmhaines@lanl.gov; Fincke, James R.; Shah, Rahul C.

    We present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employ anymore » adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

  9. Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Haines, Brian Michael; Grim, Gary P.; Fincke, James R.

    Here, we present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employmore » any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

  10. Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

    NASA Astrophysics Data System (ADS)

    Haines, Brian M.; Grim, Gary P.; Fincke, James R.; Shah, Rahul C.; Forrest, Chad J.; Silverstein, Kevin; Marshall, Frederic J.; Boswell, Melissa; Fowler, Malcolm M.; Gore, Robert A.; Hayes-Sterbenz, Anna C.; Jungman, Gerard; Klein, Andreas; Rundberg, Robert S.; Steinkamp, Michael J.; Wilhelmy, Jerry B.

    2016-07-01

    We present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a "CD Mixcap," is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employ any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.

  11. Numerical Investigations of Wave-Induced Mixing in Upper Ocean Layer

    NASA Astrophysics Data System (ADS)

    Guan, Changlong

    2017-04-01

    The upper ocean layer is playing an important role in ocean-atmosphere interaction. The typical characteristics depicting the upper ocean layer are the sea surface temperature (SST) and the mixed layer depth (MLD). So far, the existing ocean models tend to over-estimate SST and to under-estimate MLD, due to the inadequate mixing in the mixing layer, which is owing to that several processes related mixing in physics are ignored in these ocean models. The mixing induced by surface gravity wave is expected to be able to enhance the mixing in the upper ocean layer, and therefore the over-estimation of SST and the under-estimate of MLD could be improved by including wave-induced mixing. The wave-induced mixing could be accomplished by the physical mechanisms, such as wave breaking (WB), wave-induced Reynolds stress (WR), and wave-turbulence interaction (WT). The General Ocean Turbulence Model (GOTM) is employed to investigate the effects of the three mechanisms concerning wave-induced mixing. The numerical investigation is carried out for three turbulence closure schemes, say, k-epsilon, k-omega and Mellor-Yamada (1982), with the observational data from OSC Papa station and wave data from ECMWF. The mixing enhancement by various waved-induced mixing mechanisms is investigated and verified.

  12. Fronts and eddies: Engines for biogeochemical variability of the Central Red Sea during winter-spring periods

    NASA Astrophysics Data System (ADS)

    Zarokanellos, Nikolaos; Jones, Burton

    2017-04-01

    The central Red Sea (CRS) has been shown to be characterized by significant eddy activity throughout the year. In winter, weakened stratification may lead to enhanced vertical exchange contributing to physical and biogeochemical processes. In winter 2014-2015 we began an extended glider time series to monitor a region in the northern CRS where eddy activity is significant. Remote sensing and glider observations that include CTD, oxygen, CDOM and chlorophyll fluorescence, and multi-wavelength optical backscatter, have been used to characterize the effects of winter mixing and eddy activity in this region. During winter, deep mixing driven by surface cooling and strong winds combined with eddy features, can supply nutrients into the upper layer dramatically modifies the environment from its typically stratified conditions. These mixing events disperse the phytoplankton from the deep chlorophyll maximum throughout the upper mixed layer, and increase the chlorophyll signature detected by ocean color imagery. In addition to the mixing, cyclonic eddies in the region can enhance the vertical displacement of deeper, nutrient containing water toward the euphotic zone contributing to increased chlorophyll concentration and biological productivity. Remote sensing analyses indicate that these eddies also contribute to significant horizontal dispersion including the exchange between the open sea and coastal coral reef ecosystems. During the winter mixing periods, diel fluctuations in phytoplankton biomass have been observed indicative of solar driven plankton dynamics. The biogeochemical response to the subsurface physical processes provides a sensitive indicator to the processes that result from the mixing and eddy dynamics - processes that are not necessarily detectable via remote sensing. In order to understand the seasonal responses, but also the interannual influences on these processes, sustained in situ autonomous platform measurements are essential.

  13. Picophytoplankton variability: Influence of winter convective mixing and advection in the northeastern Arabian Sea

    NASA Astrophysics Data System (ADS)

    Bemal, Suchandan; Anil, Arga Chandrashekar; Shankar, D.; Remya, R.; Roy, Rajdeep

    2018-04-01

    The deepening of mixed layer and ensuing changes in optical and physicochemical properties of euphotic zone can influence phytoplankton community dynamics in the northeastern Arabian Sea during winter monsoon. The response of picophytoplankton community to such changes during winter convective mixing is not well understood. Herein, we have compared variations in the picophytoplankton community structure during early (November-December 2012), peak (end-January 2014) and late (mid-February 2015) winter monsoon from three separate cruises in the southern northeastern Arabian Sea. The higher Synechococcus abundance owing to entrainment of nutrients in mixed layer was observed during peak winter monsoon, while the concomitant changes in nitrate concentration, light and oxygen environment restricted Prochlorococcus growth resulting in lower abundance during the same period. This highlights the diverse responses of picophytoplankton groups to physicochemical changes of water column during winter convective mixing. The divinyl chlorophyll b/a ratio (marker for Prochlorococcus ecotypes) indicated prevalence of one low-light adapted ecotype (sensitive to light shock) in sub-surface water, one high-light adapted ecotype in surface water during early winter monsoon and both disappeared during intense mixing period in peak winter monsoon. Subsequently, a distinct low-light adapted ecotype, capable to tolerate light shock, was noticed during late winter monsoon and we argue that this ecotype is introduced to southern northeastern Arabian Sea through advection from north by sub-surface circulation. The total picophytoplankton biomass available to microbial loop is restored during late winter monsoon, when stratification begins, with a higher abundance of Synechococcus and the re-occurrence of Prochlorococcus population in the region. These inferences indicate that variability in picophytoplankton community structure and their contribution to the microbial loop are driven by convective mixing and advection, which in turn influence ecosystem functioning and trophodynamics of the southern northeastern Arabian Sea.

  14. Variability of the Mixed-Layer Height Over Mexico City

    NASA Astrophysics Data System (ADS)

    García-Franco, J. L.; Stremme, W.; Bezanilla, A.; Ruiz-Angulo, A.; Grutter, M.

    2018-02-01

    The diurnal and seasonal variability of the mixed-layer height in urban areas has implications for ground-level air pollution and the meteorological conditions. Measurements of the backscatter of light pulses with a commercial lidar system were performed for a continuous period of almost six years between 2011 and 2016 in the southern part of Mexico City. The profiles were temporally and vertically smoothed, clouds were filtered out, and the mixed-layer height was determined with an ad hoc treatment of both the filtered and unfiltered profiles. The results are in agreement when compared with values of mixed-layer height reconstructed from, (i) radiosonde data, and (ii) surface and vertical column densities of a trace gas. The daily maxima of the mean mixed-layer height reach values > 3 km above ground level in the months of March-April, and are clearly lower (< 2.7 km ) during the colder months from September-December. Mean daily minima are typically observed at 0700 local time (UTC - 6h), and are lowest during the winter months with values on average below 500 m. The data presented here show an anti-correlation between high-pollution episodes and the height of the mixed layer. The growth rate of the convective mixed-layer height has a seasonal behaviour, which is characterized together with the mixed-layer-height anomalies. A clear residual layer is evident from the backscattered signals recorded in days with specific atmospheric conditions, but also from the cloud-filtered mean diurnal profiles. The occasional presence of a residual layer results in an overestimation of the reported mixed-layer height during the night and early morning hours.

  15. Problem of the thermodynamic status of the mixed-layer minerals

    USGS Publications Warehouse

    Zen, E.-A.

    1962-01-01

    Minerals that show mixed layering, particularly with the component layers in random sequence, pose problems because they may behave thermodynamically as single phases or as polyphase aggregates. Two operational criteria are proposed for their distinction. The first scheme requires two samples of mixed-layer material which differ only in the proportions of the layers. If each of these two samples are allowed to equilibrate with the same suitably chosen monitoring solution, then the intensive parameters of the solution will be invariant if the mixed-layer sample is a polyphase aggregate, but not otherwise. The second scheme makes use of the fact that portions of many titration curves of clay minerals show constancy of the chemical activities of the components in the equilibrating solutions, suggesting phase separation. If such phase separation occurs for a mixed-layer material, then, knowing the number of independent components in the system, it should be possible to decide on the number of phases the mixed-layer material represents. Knowledge of the phase status of mixed-layer material is essential to the study of the equilibrium relations of mineral assemblages involving such material, because a given mixed-layer mineral will be plotted and treated differently on a phase diagram, depending on whether it is a single phase or a polyphase aggregate. Extension of the titration technique to minerals other than the mixed-layer type is possible. In particular, this method may be used to determine if cryptoperthites and peristerites are polyphase aggregates. In general, for any high-order phase separation, the method may be used to decide just at what point in this continuous process the system must be regarded operationally as a polyphase aggregate. ?? 1962.

  16. Variability of the Mixed-Layer Height Over Mexico City

    NASA Astrophysics Data System (ADS)

    García-Franco, J. L.; Stremme, W.; Bezanilla, A.; Ruiz-Angulo, A.; Grutter, M.

    2018-06-01

    The diurnal and seasonal variability of the mixed-layer height in urban areas has implications for ground-level air pollution and the meteorological conditions. Measurements of the backscatter of light pulses with a commercial lidar system were performed for a continuous period of almost six years between 2011 and 2016 in the southern part of Mexico City. The profiles were temporally and vertically smoothed, clouds were filtered out, and the mixed-layer height was determined with an ad hoc treatment of both the filtered and unfiltered profiles. The results are in agreement when compared with values of mixed-layer height reconstructed from, (i) radiosonde data, and (ii) surface and vertical column densities of a trace gas. The daily maxima of the mean mixed-layer height reach values > 3 km above ground level in the months of March-April, and are clearly lower (< 2.7 km) during the colder months from September-December. Mean daily minima are typically observed at 0700 local time (UTC - 6h), and are lowest during the winter months with values on average below 500 m. The data presented here show an anti-correlation between high-pollution episodes and the height of the mixed layer. The growth rate of the convective mixed-layer height has a seasonal behaviour, which is characterized together with the mixed-layer-height anomalies. A clear residual layer is evident from the backscattered signals recorded in days with specific atmospheric conditions, but also from the cloud-filtered mean diurnal profiles. The occasional presence of a residual layer results in an overestimation of the reported mixed-layer height during the night and early morning hours.

  17. High-Sensitivity and Low-Hysteresis Porous MIM-Type Capacitive Humidity Sensor Using Functional Polymer Mixed with TiO2 Microparticles

    PubMed Central

    Liu, Ming-Qing; Wang, Cong; Kim, Nam-Young

    2017-01-01

    In this study, a high-sensitivity and low-hysteresis porous metal–insulator–metal-type capacitive humidity sensor is investigated using a functional polymer mixed with TiO2 microparticles. The humidity sensor consists of an optimally designed porous top electrode, a functional polymer humidity sensitive layer, a bottom electrode, and a glass substrate. The porous top electrode is designed to increase the contact area between the sensing layer and water vapor, leading to high sensitivity and quick response time. The functional polymer mixed with TiO2 microparticles shows excellent hysteresis under a wide humidity-sensing range with good long-term stability. The results show that as the relative humidity ranges from 10% RH to 90% RH, the proposed humidity sensor achieves a high sensitivity of 0.85 pF/% RH and a fast response time of less than 35 s. Furthermore, the sensor shows an ultra-low hysteresis of 0.95% RH at 60% RH, a good temperature dependence, and a stable capacitance value with a maximum of 0.17% RH drift during 120 h of continuous test. PMID:28157167

  18. Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

    EPA Science Inventory

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundar...

  19. DNSs of Multicomponent Gaseous and Drop-Laden Mixing Layers Achieving Transition to Turbulence

    NASA Technical Reports Server (NTRS)

    Bellan, Josette; Selle, Laurent

    2007-01-01

    A paper describes direct numerical simulations (DNSs) of three-dimensional mixing-layer flows undergoing transition to turbulence; the mixing layers may or may not be laden with evaporating liquid drops.

  20. Influence of Typhoon Matsa on Phytoplankton Chlorophyll-a off East China

    PubMed Central

    Shao, Jinchao; Han, Guoqi; Yang, Dezhou

    2015-01-01

    Typhoons can cause strong disturbance, mixing, and upwelling in the upper layer of the oceans. Rich nutrients from the subsurface layer can be brought to the euphotic layer, which will induce the phytoplankton to breed and grow rapidly. In this paper, we investigate the impact of an intense and fast moving tropical storm, Typhoon Matsa, on phytoplankton chlorophyll-a (Chl-a) concentration off East China. By using satellite remote sensing data, we analyze the changes of Chl-a concentration, Sea Surface Temperature (SST) and wind speed in the pre- and post-typhoon periods. We also give a preliminary discussion on the different responses of the Chl-a concentration between nearshore and offshore waters. In nearshore/coastal regions where nutrients are generally rich, the Chl-a maximum occurs usually at the surface or at the layer close to the surface. And, in offshore tropical oligotrophic oceans, the subsurface maxima of Chl-a exist usually in the stratified water column. In an offshore area east of Taiwan, the Chl-a concentration rose gradually in about two weeks after the typhoon. However, in a coastal area north of Taiwan high Chl-a concentration decreased sharply before landfall, rebounded quickly to some degree after landfall, and restored gradually to the pre-typhoon level in about two weeks. The Chl-a concentration presented a negative correlation with the wind speed in the nearshore area during the typhoon, which is opposite to the response in the offshore waters. The phenomena may be attributable to onshore advection of low Chl-a water, coastal downwelling and intensified mixing, which together bring pre-typhoon surface Chl-a downward in the coastal area. In the offshore area, the typhoon may trigger increase of Chl-a concentration through uptake of nutrients by typhoon-induced upwelling and entrainment mixing. PMID:26407324

  1. Planar ceramic membrane assembly and oxidation reactor system

    DOEpatents

    Carolan, Michael Francis; Dyer, legal representative, Kathryn Beverly; Wilson, Merrill Anderson; Ohm, Ted R.; Kneidel, Kurt E.; Peterson, David; Chen, Christopher M.; Rackers, Keith Gerard; Dyer, deceased, Paul Nigel

    2007-10-09

    Planar ceramic membrane assembly comprising a dense layer of mixed-conducting multi-component metal oxide material, wherein the dense layer has a first side and a second side, a porous layer of mixed-conducting multi-component metal oxide material in contact with the first side of the dense layer, and a ceramic channeled support layer in contact with the second side of the dense layer. The planar ceramic membrane assembly can be used in a ceramic wafer assembly comprising a planar ceramic channeled support layer having a first side and a second side; a first dense layer of mixed-conducting multi-component metal oxide material having an inner side and an outer side, wherein the inner side is in contact with the first side of the ceramic channeled support layer; a first outer support layer comprising porous mixed-conducting multi-component metal oxide material and having an inner side and an outer side, wherein the inner side is in contact with the outer side of the first dense layer; a second dense layer of mixed-conducting multi-component metal oxide material having an inner side and an outer side, wherein the inner side is in contact with the second side of the ceramic channeled layer; and a second outer support layer comprising porous mixed-conducting multi-component metal oxide material and having an inner side and an outer side, wherein the inner side is in contact with the outer side of the second dense layer.

  2. Planar ceramic membrane assembly and oxidation reactor system

    DOEpatents

    Carolan, Michael Francis; Dyer, legal representative, Kathryn Beverly; Wilson, Merrill Anderson; Ohrn, Ted R.; Kneidel, Kurt E.; Peterson, David; Chen, Christopher M.; Rackers, Keith Gerard; Dyer, Paul Nigel

    2009-04-07

    Planar ceramic membrane assembly comprising a dense layer of mixed-conducting multi-component metal oxide material, wherein the dense layer has a first side and a second side, a porous layer of mixed-conducting multi-component metal oxide material in contact with the first side of the dense layer, and a ceramic channeled support layer in contact with the second side of the dense layer. The planar ceramic membrane assembly can be used in a ceramic wafer assembly comprising a planar ceramic channeled support layer having a first side and a second side; a first dense layer of mixed-conducting multi-component metal oxide material having an inner side and an outer side, wherein the inner side is in contact with the first side of the ceramic channeled support layer; a first outer support layer comprising porous mixed-conducting multi-component metal oxide material and having an inner side and an outer side, wherein the inner side is in contact with the outer side of the first dense layer; a second dense layer of mixed-conducting multi-component metal oxide material having an inner side and an outer side, wherein the inner side is in contact with the second side of the ceramic channeled layer; and a second outer support layer comprising porous mixed-conducting multi-component metal oxide material and having an inner side and an outer side, wherein the inner side is in contact with the outer side of the second dense layer.

  3. Compressibility effects on turbulent mixing

    NASA Astrophysics Data System (ADS)

    Panickacheril John, John; Donzis, Diego

    2016-11-01

    We investigate the effect of compressibility on passive scalar mixing in isotropic turbulence with a focus on the fundamental mechanisms that are responsible for such effects using a large Direct Numerical Simulation (DNS) database. The database includes simulations with Taylor Reynolds number (Rλ) up to 100, turbulent Mach number (Mt) between 0.1 and 0.6 and Schmidt number (Sc) from 0.5 to 1.0. We present several measures of mixing efficiency on different canonical flows to robustly identify compressibility effects. We found that, like shear layers, mixing is reduced as Mach number increases. However, data also reveal a non-monotonic trend with Mt. To assess directly the effect of dilatational motions we also present results with both dilatational and soleniodal forcing. Analysis suggests that a small fraction of dilatational forcing decreases mixing time at higher Mt. Scalar spectra collapse when normalized by Batchelor variables which suggests that a compressive mechanism similar to Batchelor mixing in incompressible flows might be responsible for better mixing at high Mt and with dilatational forcing compared to pure solenoidal mixing. We also present results on scalar budgets, in particular on production and dissipation. Support from NSF is gratefully acknowledged.

  4. Numerical simulation of the non-Newtonian mixing layer

    NASA Technical Reports Server (NTRS)

    Azaiez, Jalel; Homsy, G. M.

    1993-01-01

    This work is a continuing effort to advance our understanding of the effects of polymer additives on the structures of the mixing layer. In anticipation of full nonlinear simulations of the non-Newtonian mixing layer, we examined in a first stage the linear stability of the non-Newtonian mixing layer. The results of this study show that, for a fluid described by the Oldroyd-B model, viscoelasticity reduces the instability of the inviscid mixing layer in a special limit where the ratio (We/Re) is of order 1 where We is the Weissenberg number, a measure of the elasticity of the flow, and Re is the Reynolds number. In the present study, we pursue this project with numerical simulations of the non-Newtonian mixing layer. Our primary objective is to determine the effects of viscoelasticity on the roll-up structure. We also examine the origin of the numerical instabilities usually encountered in the simulations of non-Newtonian fluids.

  5. Chemical Reactions in Turbulent Mixing Flows

    DTIC Science & Technology

    1989-10-15

    response, following the program control actuation. 3 in 2 vs. roughly the 8in2 required for the M1 = 1.5 (high speed stream Mach number) flow planned for...Papamoschou & Roshko (1988) as the compressibility-effect parameter, on the growth rate of the mixing layers was studied. In a finite thickness...attained is at present controversial; an issue that will have to be resolved both theoretically as well as with the planned for experiments. A sample plot

  6. The salinity effect in a mixed layer ocean model

    NASA Technical Reports Server (NTRS)

    Miller, J. R.

    1976-01-01

    A model of the thermally mixed layer in the upper ocean as developed by Kraus and Turner and extended by Denman is further extended to investigate the effects of salinity. In the tropical and subtropical Atlantic Ocean rapid increases in salinity occur at the bottom of a uniformly mixed surface layer. The most significant effects produced by the inclusion of salinity are the reduction of the deepening rate and the corresponding change in the heating characteristics of the mixed layer. If the net surface heating is positive, but small, salinity effects must be included to determine whether the mixed layer temperature will increase or decrease. Precipitation over tropical oceans leads to the development of a shallow stable layer accompanied by a decrease in the temperature and salinity at the sea surface.

  7. Ordered mixed-layer structures in the Mighei carbonaceous chondrite matrix

    NASA Technical Reports Server (NTRS)

    Mackinnon, I. D. R.

    1982-01-01

    High resolution transmission electron microscopy of the Mighei carbonaceous chondrite matrix has revealed the presence of a new mixed layer structure material. This mixed-layer material consists of an ordered arrangement of serpentine-type (S) and brucite-type (B) layers in the sequence SBBSBB. Electron diffraction and imaging techniques show that the basal periodicity is approximately 17 A. Discrete crystals of SBB-type material are typically curved, of small size (less than 1 micron) and show structural variations similar to the serpentine group minerals. Mixed-layer material also occurs in association with planar serpentine. Characteristics of SBB-type material are not consistent with known terrestrial mixed-layer clay minerals. Evidence for formation by a condensation event or by subsequent alteration of pre-existing material is not yet apparent.

  8. Near-inertial kinetic energy budget of the mixed layer and shear evolution in the transition layer in the Arabian Sea during the monsoons

    NASA Astrophysics Data System (ADS)

    Majumder, Sudip; Tandon, Amit; Rudnick, Daniel L.; Thomas Farrar, J.

    2015-09-01

    We present the horizontal kinetic energy (KE) balance of near-inertial currents in the mixed layer and explain shear evolution in the transition layer using observations from a mooring at 15.26° N in the Arabian Sea during the southwest monsoon. The highly sheared and stratified transition layer at the mixed-layer base varies between 5 m and 35 m and correlates negatively with the wind stress. Results from the mixed layer near-inertial KE (NIKE) balance suggest that wind energy at times can energize the transition layer and at other times is fully utilized within the mixed layer. A simple two layer model is utilized to study the shear evolution in the transition layer and shown to match well with observations. The shear production in this model arises from alignment of wind stress and shear. Although the winds are unidirectional during the monsoon, the shear in the transition layer is predominantly near-inertial. The near-inertial shear bursts in the observations show the same phasing and magnitude at near-inertial frequencies as the wind-shear alignment term.

  9. Estimation of the mixing layer height over a high altitude site in Central Himalayan region by using Doppler lidar

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shukla, K. K.; Phanikumar, D. V.; Newsom, Rob K.

    2014-03-01

    A Doppler lidar was installed at Manora Peak, Nainital (29.4 N; 79.2 E, 1958 amsl) to estimate mixing layer height for the first time by using vertical velocity variance as basic measurement parameter for the period September-November 2011. Mixing layer height is found to be located ~0.57 +/- 0.1and 0.45 +/- 0.05km AGL during day and nighttime, respectively. The estimation of mixing layer height shows good correlation (R>0.8) between different instruments and with different methods. Our results show that wavelet co-variance transform is a robust method for mixing layer height estimation.

  10. Effect of the Barrier Layer on the Upper Ocean Response to MJO Forcing

    NASA Astrophysics Data System (ADS)

    Bulusu, S.

    2014-12-01

    Recently, attention has been given to an upper ocean feature known as the Barrier Layer, which has been shown to impact meteorological phenomena from ENSO to tropical cyclones by suppressing vertical mixing, which reduces sea surface cooling and enhances surface heat fluxes. The calculation defines the Barrier Layer as the difference between the Isothermal Layer Depth (ILD) and Mixed Layer Depth (MLD). Proper representation of these features relies on precise observations of SSS to attain accurate measurements of the MLD and subsequently, the BLT. Compared to the many available in situ SSS measurements, the NASA Aquarius salinity mission currently obtains the closest observations to the true SSS. The role of subsurface features will be better understood through increased accuracy of SSS measurements. In this study BLT estimates are derived from satellite measurements using a multilinear regression model (MRM) in the Indian Ocean. The MRM relates BLT to satellite derived SSS, sea surface temperature (SST) and sea surface height anomalies (SSHA). Besides being a variable that responds passively to atmospheric conditions, SSS significantly controls upper ocean density and therefore the MLD. The formation of a Barrier Layer can lead to possible feedbacks that impact the atmospheric component of the Madden-Julian Oscillation (MJO), as stated as one of the three major hypotheses of the DYNAMO field campaign. This layer produces a stable stratification, reducing vertical mixing, which influences surface heat fluxes and thus could possibly impact atmospheric conditions during the MJO. Establishing the magnitude and extent of SSS variations during the MJO will be a useful tool for data assimilation into models to correctly represent both oceanic thermodynamic characteristics and atmospheric processes during intraseasonal variations.

  11. Hydrographic and fish larvae distribution during the "Godzilla El Niño 2015-2016" in the northern end of the shallow oxygen minimum zone of the Eastern Tropical Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Sánchez-Velasco, L.; Beier, E.; Godínez, V. M.; Barton, E. D.; Santamaría-del-Angel, E.; Jiménez-Rosemberg, S. P. A.; Marinone, S. G.

    2017-03-01

    Based on hydrographic data and vertical distributions of tropical species of fish larvae (Diogenichthys laternatus, Vinciguerria lucetia, Bregmaceros bathymaster, and Auxis spp.), effects of "Godzilla El Niño 2015-2016" in the shallow oxygen minimum zone off Mexico were analyzed. Zooplankton samples were collected during four cruises, before (February 2010 and April 2012) and during (June 2015 and March 2016) the warm event. Temporal series of sea surface temperature revealed that June 2015 was the warmest June of the last years. Conservative temperature was >2°C higher than normal in the surface mixed layer, and the suboxic layer (4.4 µmol/kg) reached as shallow as 100 m depth. Unexpected results were that larval abundances were relatively high during the warm event, unlike zooplankton volumes, which declined. Before the warm event, V. lucetia and Auxis spp. were more abundant in the surface mixed layer, while B. bathymaster and D. laternatus dominated in the thermocline and shallow hypoxic layer (44 µmol/kg). However, during the event in June 2015, all species were most abundant in the surface mixed layer, which implied that the species adapted to hypoxia had inverted their normal pattern of distribution, possibly as consequence of the rise of the suboxic layer; however, further observations are required to confirm this generality. Results showed no dramatic change in the total larval abundance during the warm event. Nevertheless, a differential response in their vertical distribution was evident in association with changes in the depth of the shallow hypoxic and suboxic layers. This might indicate adaptability of tropical species to prolonged periods of warming in the oceans.

  12. Simulating the Cyclone Induced Turbulent Mixing in the Bay of Bengal using COAWST Model

    NASA Astrophysics Data System (ADS)

    Prakash, K. R.; Nigam, T.; Pant, V.

    2017-12-01

    Mixing in the upper oceanic layers (up to a few tens of meters from surface) is an important process to understand the evolution of sea surface properties. Enhanced mixing due to strong wind forcing at surface leads to deepening of mixed layer that affects the air-sea exchange of heat and momentum fluxes and modulates sea surface temperature (SST). In the present study, we used Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model to demonstrate and quantify the enhanced cyclone induced turbulent mixing in case of a severe cyclonic storm. The COAWST model was configured over the Bay of Bengal (BoB) and used to simulate the atmospheric and oceanic conditions prevailing during the tropical cyclone (TC) Phailin that occurred over the BoB during 10-15 October 2013. The model simulated cyclone track was validated with IMD best-track and model SST validated with daily AVHRR SST data. Validation shows that model simulated track & intensity, SST and salinity were in good agreement with observations and the cyclone induced cooling of the sea surface was well captured by the model. Model simulations show a considerable deepening (by 10-15 m) of the mixed layer and shoaling of thermocline during TC Phailin. The power spectrum analysis was performed on the zonal and meridional baroclinic current components, which shows strongest energy at 14 m depth. Model results were analyzed to investigate the non-uniform energy distribution in the water column from surface up to the thermocline depth. The rotary spectra analysis highlights the downward direction of turbulent mixing during the TC Phailin period. Model simulations were used to quantify and interpret the near-inertial mixing, which were generated by cyclone induced strong wind stress and the near-inertial energy. These near-inertial oscillations are responsible for the enhancement of the mixing operative in the strong post-monsoon (October-November) stratification in the BoB.

  13. Upper oceanic response to tropical cyclone Phailin in the Bay of Bengal using a coupled atmosphere-ocean model

    NASA Astrophysics Data System (ADS)

    Prakash, Kumar Ravi; Pant, Vimlesh

    2017-01-01

    A numerical simulation of very severe cyclonic storm `Phailin', which originated in southeastern Bay of Bengal (BoB) and propagated northwestward during 10-15 October 2013, was carried out using a coupled atmosphere-ocean model. A Model Coupling Toolkit (MCT) was used to make exchanges of fluxes consistent between the atmospheric model `Weather Research and Forecasting' (WRF) and ocean circulation model `Regional Ocean Modelling System' (ROMS) components of the `Coupled Ocean-Atmosphere-Wave-Sediment Transport' (COAWST) modelling system. The track and intensity of tropical cyclone (TC) Phailin simulated by the WRF component of the coupled model agrees well with the best-track estimates reported by the India Meteorological Department (IMD). Ocean model component (ROMS) was configured over the BoB domain; it utilized the wind stress and net surface heat fluxes from the WRF model to investigate upper oceanic response to the passage of TC Phailin. The coupled model shows pronounced sea surface cooling (2-2.5 °C) and an increase in sea surface salinity (SSS) (2-3 psu) after 06 GMT on 12 October 2013 over the northwestern BoB. Signature of this surface cooling was also observed in satellite data and buoy measurements. The oceanic mixed layer heat budget analysis reveals relative roles of different oceanic processes in controlling the mixed layer temperature over the region of observed cooling. The heat budget highlighted major contributions from horizontal advection and vertical entrainment processes in governing the mixed layer cooling (up to -0.1 °C h-1) and, thereby, reduction in sea surface temperature (SST) in the northwestern BoB during 11-12 October 2013. During the post-cyclone period, the net heat flux at surface regained its diurnal variations with a noontime peak that provided a warming tendency up to 0.05 °C h-1 in the mixed layer. Clear signatures of TC-induced upwelling are seen in vertical velocity (about 2.5 × 10-3 m s-1), rise in isotherms and isohalines along 85-88° E longitudes in the northwestern BoB. The study demonstrates that a coupled atmosphere-ocean model (WRF + ROMS) serves as a useful tool to investigate oceanic response to the passage of cyclones.

  14. The Role of Late Summer Melt Pond Water Layers in the Ocean Mixed Layer on Enhancing Ice/Ocean Albedo Feedbacks in the Arctic

    NASA Astrophysics Data System (ADS)

    Stanton, T. P.; Shaw, W. J.

    2016-02-01

    Drainage of surface melt pond water into the top of the ocean mixed layer is seen widely in the Arctic ice pack in later summer (for example Gallaher et al 2015). Under calm conditions, this fresh water forms a thin, stratified layer immediately below the ice which is dynamically decoupled from the thicker, underlying seasonal mixed layer by the density difference between the two layers. The ephemeral surface layer is significantly warmer than the underlying ocean water owing to the higher freezing temperature of the fresh melt water. How the presence of this warm ephemeral layer enhances basal melt rate and speeds the destruction of the floes is investigated. High resolution timeseries measurements of T/S profiles in the 2m of the ocean immediately below the ice, and eddy-correlation fluxes of heat, salt and momentum 2.5m below the ice were made from an Autonomous Ocean Flux Buoy over a 2 month interval in later summer of 2015 as a component of the ONR Marginal Ice Zone project. The stratification and turbulent forcing observations are used with a 1 D turbulence closure model to understand how momentum and incoming radiative energy are stored and redistributed within the ephemeral layer. Under low wind forcing conditions both turbulent mixing energy and the water with high departure from freezing are trapped in the ephemeral layer by the strong density gradient at the base of the layer, resulting in rapid basal melting. This case is contrasted with model runs where the ephemeral layer heat is allowed to mix across the seasonal mixed layer, which results in slower basal melt rates. Consequently, the salinity-trapped warm ephemeral layer results in the formation of more open water earlier in the summer season, in turn resulting in increased cumulative heating of the ocean mixed layer, enhancing ice/ocean albedo feedbacks.

  15. Modeling the diurnal cycle of carbon monoxide: Sensitivity to physics, chemistry, biology, and optics

    NASA Astrophysics Data System (ADS)

    Gnanadesikan, Anand

    1996-05-01

    As carbon monoxide within the oceanic surface layer is produced by solar radiation, diluted by mixing, consumed by biota, and outgassed to the atmosphere, it exhibits a diurnal cycle. The effect of dilution and mixing on this cycle is examined using a simple model for production and consumption, coupled to three different mixed layer models. The magnitude and timing of the peak concentration, the magnitude of the average concentration, and the air-sea flux are considered. The models are run through a range of heating and wind stress and compared to experimental data reported by Kettle [1994]. The key to the dynamics is the relative size of four length scales; Dmix, the depth to which mixing occurs over the consumption time; L, the length scale over which production occurs; Lout, the depth to which the mixed layer is ventilated over the consumption time; and Lcomp, the depth to which the diurnal production can maintain a concentration in equilibrium with the atmosphere. If Dmix ≫ L, the actual model parameterization can be important. If the mixed layer is maintained by turbulent diffusion, Dmix can be substantially less than the mixed layer depth. If the mixed layer is parameterized as a homogeneous slab, Dmix is equivalent to the mixed layer depth. If Dmix > Lout, production is balanced by consumption rather than outgassing. The ratio between Dmix and Lcomp determines whether the ocean is a source or a sink for CO. The main thermocline depth H sets an upper limit for Dmix and hence Dmix/L, Dmix/Lout, and Dmix/Lcomp. The models are run to simulate a single day of observations. The mixing parameterization is shown to be very important, with a model which mixes using small-scale diffusion, producing markedly larger surface concentrations than models which homogenize the mixed layer completely and instantaneously.

  16. Observing the seasonal cycle of the upper ocean in the Ross Sea, Antarctica, with autonomous profiling floats

    NASA Astrophysics Data System (ADS)

    Porter, D. F.; Springer, S. R.; Padman, L.; Fricker, H. A.; Bell, R. E.

    2017-12-01

    The upper layers of the Southern Ocean where it meets the Antarctic ice sheet undergoes a large seasonal cycle controlled by surface radiation and by freshwater fluxes, both of which are strongly influenced by sea ice. In regions where seasonal sea ice and icebergs limit use of ice-tethered profilers and conventional moorings, autonomous profiling floats can sample the upper ocean. The deployment of seven Apex floats (by sea) and six ALAMO floats (by air) provides unique upper ocean hydrographic data in the Ross Sea close to the Ross Ice Shelf front. A novel choice of mission parameters - setting parking depth deeper than the seabed - limits their drift, allowing us to deploy the floats close to the ice shelf front, while sea ice avoidance algorithms allow the floats to to sample through winter under sea ice. Hydrographic profiles show the detailed development of the seasonal mixed layer close to the Ross front, and interannual variability of the seasonal mixed layer and deeper water masses on the central Ross Sea continental shelf. After the sea ice breakup in spring, a warm and fresh surface mixed layer develops, further warming and deepening throughout the summer. The mixed layer deepens, with maximum temperatures exceeding 0ºC in mid-February. By March, the surface energy budget becomes negative and sea ice begins to form, creating a cold, saline and dense surface layer. Once these processes overcome the stable summer stratification, convection erodes the surface mixed layer, mixing some heat downwards to deeper layers. There is considerable interannual variability in the evolution and strength of the surface mixed layer: summers with shorter ice-free periods result in a cooler and shallower surface mixed layer, which accumulates less heat than the summers with longer ice-free periods. Early ice breakup occurred in all floats in 2016/17 summer, enhancing the absorbed solar flux leading to a warmer surface mixed layer. Together, these unique measurements from autonomous profilers provide insight into the hydrographic state of the Ross Sea at the start of the spring period of sea-ice breakup, and how ocean mixing and sea ice interact to initiate the summer open-water season.

  17. Experiments on the enhancement of compressible mixing via streamwise vorticity. II - Vortex strength assessment and seed particle dynamics

    NASA Technical Reports Server (NTRS)

    Naughton, J. W.; Cattafesta, L. N.; Settles, G. S.

    1993-01-01

    The effect of streamwise vorticity on compressible axisymmetric mixing layers is examined using vortex strength assessment and seed particle dynamics analysis. Experimental results indicate that the particles faithfully represent the dynamics of the turbulent swirling flow. A comparison of the previously determined mixing layer growth rates with the present vortex strength data reveals that the increase of turbulent mixing up to 60 percent scales with the degree of swirl. The mixing enhancement appears to be independent of the compressibility level of the mixing layer.

  18. Assessment of Southern Ocean water mass circulation and characteristics in CMIP5 models: Historical bias and forcing response

    NASA Astrophysics Data System (ADS)

    Sallée, J.-B.; Shuckburgh, E.; Bruneau, N.; Meijers, A. J. S.; Bracegirdle, T. J.; Wang, Z.; Roy, T.

    2013-04-01

    The ability of the models contributing to the fifth Coupled Models Intercomparison Project (CMIP5) to represent the Southern Ocean hydrological properties and its overturning is investigated in a water mass framework. Models have a consistent warm and light bias spread over the entire water column. The greatest bias occurs in the ventilated layers, which are volumetrically dominated by mode and intermediate layers. The ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide. The mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias. Under increased radiative forcing, models simulate a warming and lightening of the entire water column, which is again greatest in the ventilated layers, highlighting the importance of these layers for propagating the climate signal into the deep ocean. While the intensity of the water mass overturning is relatively consistent between models, when compared to observation-based reconstructions, they exhibit a slightly larger rate of overturning at shallow to intermediate depths, and a slower rate of overturning deeper in the water column. Under increased radiative forcing, atmospheric fluxes increase the rate of simulated upper cell overturning, but this increase is counterbalanced by diapycnal fluxes, including mixed-layer horizontal mixing, and mostly vanishes.

  19. Prediction of Frequency for Simulation of Asphalt Mix Fatigue Tests Using MARS and ANN

    PubMed Central

    Fakhri, Mansour

    2014-01-01

    Fatigue life of asphalt mixes in laboratory tests is commonly determined by applying a sinusoidal or haversine waveform with specific frequency. The pavement structure and loading conditions affect the shape and the frequency of tensile response pulses at the bottom of asphalt layer. This paper introduces two methods for predicting the loading frequency in laboratory asphalt fatigue tests for better simulation of field conditions. Five thousand (5000) four-layered pavement sections were analyzed and stress and strain response pulses in both longitudinal and transverse directions was determined. After fitting the haversine function to the response pulses by the concept of equal-energy pulse, the effective length of the response pulses were determined. Two methods including Multivariate Adaptive Regression Splines (MARS) and Artificial Neural Network (ANN) methods were then employed to predict the effective length (i.e., frequency) of tensile stress and strain pulses in longitudinal and transverse directions based on haversine waveform. It is indicated that, under controlled stress and strain modes, both methods (MARS and ANN) are capable of predicting the frequency of loading in HMA fatigue tests with very good accuracy. The accuracy of ANN method is, however, more than MARS method. It is furthermore shown that the results of the present study can be generalized to sinusoidal waveform by a simple equation. PMID:24688400

  20. Prediction of frequency for simulation of asphalt mix fatigue tests using MARS and ANN.

    PubMed

    Ghanizadeh, Ali Reza; Fakhri, Mansour

    2014-01-01

    Fatigue life of asphalt mixes in laboratory tests is commonly determined by applying a sinusoidal or haversine waveform with specific frequency. The pavement structure and loading conditions affect the shape and the frequency of tensile response pulses at the bottom of asphalt layer. This paper introduces two methods for predicting the loading frequency in laboratory asphalt fatigue tests for better simulation of field conditions. Five thousand (5000) four-layered pavement sections were analyzed and stress and strain response pulses in both longitudinal and transverse directions was determined. After fitting the haversine function to the response pulses by the concept of equal-energy pulse, the effective length of the response pulses were determined. Two methods including Multivariate Adaptive Regression Splines (MARS) and Artificial Neural Network (ANN) methods were then employed to predict the effective length (i.e., frequency) of tensile stress and strain pulses in longitudinal and transverse directions based on haversine waveform. It is indicated that, under controlled stress and strain modes, both methods (MARS and ANN) are capable of predicting the frequency of loading in HMA fatigue tests with very good accuracy. The accuracy of ANN method is, however, more than MARS method. It is furthermore shown that the results of the present study can be generalized to sinusoidal waveform by a simple equation.

  1. Numerical study of terrain-induced mesoscale motions and hydrostatic form drag in a heated, growing mixed layer

    NASA Technical Reports Server (NTRS)

    Deardorff, J. W.; Ueyoshi, K.; Han, Y.-J.

    1984-01-01

    Han et al. (1982) have found in a previous numerical study of terrain-induced mesoscale motions that the orography caused a steady-state flow pattern to occur. The study was concerned with a simplified case in which no surface heating occurred. The present investigation considers an extension of this study to the more realistic case of a heated, growing daytime mixed layer containing horizontal variations of potential temperature as well as velocity. The model is also extended to include three layers above the mixed layer. It is found for a heated, growing mixed layer, that the mesoscale form drag is a thermal-anomaly or buoyancy effect associated with horizontal variations of potential temperature within the layer.

  2. Numerical Simulation of Atmospheric Response to Pacific Tropical Instability Waves(.

    NASA Astrophysics Data System (ADS)

    Small, R. Justin; Xie, Shang-Ping; Wang, Yuqing

    2003-11-01

    Tropical instability waves (TIWs) are 1000-km-long waves that appear along the sea surface temperature (SST) front of the equatorial cold tongue in the eastern Pacific. The study investigates the atmospheric planetary boundary layer (PBL) response to TIW-induced SST variations using a high-resolution regional climate model. An investigation is made of the importance of pressure gradients induced by changes in air temperature and moisture, and vertical mixing, which is parameterized in the model by a 1.5-level turbulence closure scheme. Significant turbulent flux anomalies of sensible and latent heat are caused by changes in the air sea temperature and moisture differences induced by the TIWs. Horizontal advection leads to the occurrence of the air temperature and moisture extrema downwind of the SST extrema. High and low hydrostatic surface pressures are then located downwind of the cold and warm SST patches, respectively. The maximum and minimum wind speeds occur in phase with SST, and a thermally direct circulation is created. The momentum budget indicates that pressure gradient, vertical mixing, and horizontal advection dominate. In the PBL the vertical mixing acts as a frictional drag on the pressure-gradient-driven winds. Over warm SST the mixed layer deepens relative to over cold SST. The model simulations of the phase and amplitude of wind velocity, wind convergence, and column-integrated water vapor perturbations due to TIWs are similar to those observed from satellite and in situ data.

  3. The Martian atmospheric planetary boundary layer stability, fluxes, spectra, and similarity

    NASA Technical Reports Server (NTRS)

    Tillman, James E.

    1994-01-01

    This is the first analysis of the high frequency data from the Viking lander and spectra of wind, in the Martian atmospheric surface layer, along with the diurnal variation of the height of the mixed surface layer, are calculated for the first time for Mars. Heat and momentum fluxes, stability, and z(sub O) are estimated for early spring, from a surface temperature model and from Viking Lander 2 temperatures and winds at 44 deg N, using Monin-Obukhov similarity theory. The afternoon maximum height of the mixed layer for these seasons and conditions is estimated to lie between 3.6 and 9.2 km. Estimations of this height is of primary importance to all models of the boundary layer and Martian General Circulation Models (GCM's). Model spectra for two measuring heights and three surface roughnesses are calculated using the depth of the mixed layer, and the surface layer parameters and flow distortion by the lander is also taken into account. These experiments indicate that z(sub O), probably lies between 1.0 and 3.0 cm, and most likely is closer to 1.0 cm. The spectra are adjusted to simulate aliasing and high frequency rolloff, the latter caused both by the sensor response and the large Kolmogorov length on Mars. Since the spectral models depend on the surface parameters, including the estimated surface temperature, their agreement with the calculated spectra indicates that the surface layer estimates are self consistent. This agreement is especially noteworthy in that the inertial subrange is virtually absent in the Martian atmosphere at this height, due to the large Kolmogorov length scale. These analyses extend the range of applicability of terrestrial results and demonstrate that it is possible to estimate the effects of severe aliasing of wind measurements, to produce a models which agree well with the measured spectra. The results show that similarity theory developed for Earth applies to Mars, and that the spectral models are universal.

  4. Anisotropy in Third-Order Nonlinear Optical Susceptibility of a Squarylium Dye in a Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Jin, Zhao-Hui; Li, Zhong-Yu; Kasatani, Kazuo; Okamoto, Hiroaki

    2006-03-01

    A squarylium dye is dissolved in 4-cyano-4'-pentylbiphenyl (5CB) and oriented by sandwiching mixtures between two pieces of rubbed glass plates. The optical absorption spectra of the oriented squarylium dye-5CB layers exhibit high anisotropy. The third-order nonlinear optical responses and susceptibilities χ(3)e of squarylium dye in 5CB are measured with light polarizations parallel and perpendicular to the orientational direction by the resonant femtosecond degenerate four-wave mixing (DFWM) technique. Temporal profiles of the DFWM signal of the oriented squarylium dye-5CB layers with light polarizations parallel and perpendicular to the orientational direction are measured with a time resolution of 0.3 ps (FWHM), and are found to consist of two components, i.e., the coherent instantaneous nonlinear response and slow response due to the formation of excited molecules. A high anisotropic ratio of χ(3)e, 10.8±1.2, is observed for the oriented layers.

  5. Soil nitrate accumulation dominates the nonlinear responses of soil CO2 and CH4 fluxes to multi-level nitrogen addition in a temperate needle-broadleaved mixed forest

    NASA Astrophysics Data System (ADS)

    Fang, Huajun

    2017-04-01

    The responses of soil-atmosphere carbon (C) exchange fluxes to increased atmospheric nitrogen (N) deposition are controversial, leading to great uncertainty in the evaluation on the C sink capacity of global forest ecosystems elicited by anthropogenic N inputs. To date, we hardly knew how much was the critical level of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO2 and CH4 fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha-1 yr-1) was conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO2 and CH4 fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0-10 cm depth) and dissolved N (NH4+-N, NO3-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0-10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥ 60 kg N ha-1 yr-1) significantly increased soil NO3-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH4+-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha-1 yr-1 significantly promoted soil CO2 emission and CH4 uptake, whereas high rate of N addition (140 kg N ha-1 yr-1) significantly inhibited them. Significant negative relationships were observed between changes in soil CO2 emission and CH4 uptake and changes in soil NO3-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO3-N accumulation could be important regulators of soil CO2 emission and CH4 uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical levels for the alteration of soil C fluxes should be considered in the ecological process models.

  6. An ocean large-eddy simulation of Langmuir circulations and convection in the surface mixed layer

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Skyllingstad, E.D.; Denbo, D.W.

    Numerical experiments were performed using a three-dimensional large-eddy simulation model of the ocean surface mixed layer that includes the Craik-Leibovich vortex force to parameterize the interaction of surface waves with mean currents. Results from the experiments show that the vortex force generates Langmuir circulations that can dominate vertical mixing. The simulated vertical velocity fields show linear, small-scale, coherent structures near the surface that extend downwind across the model domain. In the interior of the mixed layer, scales of motion increase to eddy sizes that are roughly equivalent to the mixed-layer depth. Cases with the vortex force have stronger circulations nearmore » the surface in contrast to cases with only heat flux and wind stress, particularly when the heat flux is positive. Calculations of the velocity variance and turbulence dissipation rates for cases with and without the vortex force, surface cooling, and wind stress indicate that wave-current interactions are a dominant mixing process in the upper mixed layer. Heat flux calculations show that the entrainment rate at the mixed-layer base can be up to two times greater when the vortex force is included. In a case with reduced wind stress, turbulence dissipation rates remained high near the surface because of the vortex force interaction with preexisting inertial currents. In deep mixed layers ({approximately}250 m) the simulations show that Langmuir circulations can vertically transport water 145 m during conditions of surface heating. Observations of turbulence dissipation rates and the vertical temperature structure support the model results. 42 refs., 20 figs., 21 tabs.« less

  7. Processes that generate and deplete liquid water and snow in thin midlevel mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Smith, Adam J.; Larson, Vincent E.; Niu, Jianguo; Kankiewicz, J. Adam; Carey, Lawrence D.

    2009-06-01

    This paper uses a numerical model to investigate microphysical, radiative, and dynamical processes in mixed-phase altostratocumulus clouds. Three cloud cases are chosen for study, each of which was observed by aircraft during the fifth or ninth Complex Layered Cloud Experiment (CLEX). These three clouds are numerically modeled using large-eddy simulation (LES). The observed and modeled clouds consist of a mixed-phase layer with a quasi-adiabatic profile of liquid, and a virga layer below that consists of snow. A budget of cloud (liquid) water mixing ratio is constructed from the simulations. It shows that large-scale ascent/descent, radiative cooling/heating, turbulent transport, and microphysical processes are all significant. Liquid is depleted indirectly via depositional growth of snow (the Bergeron-Findeisen process). This process is more influential than depletion of liquid via accretional growth of snow. Also constructed is a budget of snow mixing ratio, which turns out to be somewhat simpler. It shows that snow grows by deposition in and below the liquid (mixed-phase) layer, and sublimates in the remainder of the virga region below. The deposition and sublimation are balanced primarily by sedimentation, which transports the snow from the growth region to the sublimation region below. In our three clouds, the vertical extent of the virga layer is influenced more by the profile of saturation ratio below the liquid (mixed-phase) layer than by the mixing ratio of snow at the top of the virga layer.

  8. An experimental study of secondary vortex structure in mixing layers

    NASA Technical Reports Server (NTRS)

    Bell, J. H.; Mehta, Rabindra D.

    1990-01-01

    This report covers the first eight months of an experimental research project on the secondary vortex structure in plane mixing layers. The aim of the project is to obtain quantitative data on the behavior of the secondary structure in a turbulent mixing layer at reasonable reynolds numbers (Re(sub delta(sub w)) approx. 50,000). In particular, we hope to resolve the questions of how the scale of the secondary vortex structure changes with the scale of the mixing layer, and whether the structures are fixed in space, or whether they 'meander' in the spanwise direction.

  9. Analyses and simulations of the upper ocean's response to Hurricane Felix at the Bermuda Testbed Mooring site: 13-23 August 1995

    NASA Astrophysics Data System (ADS)

    Zedler, S. E.; Dickey, T. D.; Doney, S. C.; Price, J. F.; Yu, X.; Mellor, G. L.

    2002-12-01

    The center of Hurricane Felix passed 85 km to the southwest of the Bermuda Testbed Mooring (BTM; 31°44'N, 64°10'W) site on 15 August 1995. Data collected in the upper ocean from the BTM during this encounter provide a rare opportunity to investigate the physical processes that occur in a hurricane's wake. Data analyses indicate that the storm caused a large increase in kinetic energy at near-inertial frequencies, internal gravity waves in the thermocline, and inertial pumping, mixed layer deepening, and significant vertical redistribution of heat, with cooling of the upper 30 m and warming at depths of 30-70 m. The temperature evolution was simulated using four one-dimensional mixed layer models: Price-Weller-Pinkel (PWP), K Profile Parameterization (KPP), Mellor-Yamada 2.5 (MY), and a modified version of MY2.5 (MY2). The primary differences in the model results were in their simulations of temperature evolution. In particular, when forced using a drag coefficient that had a linear dependence on wind speed, the KPP model predicted sea surface cooling, mixed layer currents, and the maximum depth of cooling closer to the observations than any of the other models. This was shown to be partly because of a special parameterization for gradient Richardson number (RgKPP) shear instability mixing in response to resolved shear in the interior. The MY2 model predicted more sea surface cooling and greater depth penetration of kinetic energy than the MY model. In the MY2 model the dissipation rate of turbulent kinetic energy is parameterized as a function of a locally defined Richardson number (RgMY2) allowing for a reduction in dissipation rate for stable Richardson numbers (RgMY2) when internal gravity waves are likely to be present. Sensitivity simulations with the PWP model, which has specifically defined mixing procedures, show that most of the heat lost from the upper layer was due to entrainment (parameterized as a function of bulk Richardson number RbPWP), with the remainder due to local Richardson number (RgPWP) instabilities. With the exception of the MY model the models predicted reasonable estimates of the north and east current components during and after the hurricane passage at 25 and 45 m. Although the results emphasize differences between the modeled responses to a given wind stress, current controversy over the formulation of wind stress from wind speed measurements (including possible sea state and wave age and sheltering effects) cautions against using our results for assessing model skill. In particular, sensitivity studies show that MY2 simulations of the temperature evolution are excellent when the wind stress is increased, albeit with currents that are larger than observed. Sensitivity experiments also indicate that preexisting inertial motion modulated the amplitude of poststorm currents, but that there was probably not a significant resonant response because of clockwise wind rotation for our study site.

  10. Nonlinear Stability and Structure of Compressible Reacting Mixing Layers

    NASA Technical Reports Server (NTRS)

    Day, M. J.; Mansour, N. N.; Reynolds, W. C.

    2000-01-01

    The parabolized stability equations (PSE) are used to investigate issues of nonlinear flow development and mixing in compressible reacting shear layers. Particular interest is placed on investigating the change in flow structure that occurs when compressibility and heat release are added to the flow. These conditions allow the 'outer' instability modes- one associated with each of the fast and slow streams-to dominate over the 'central', Kelvin-Helmholtz mode that unaccompanied in incompressible nonreacting mixing layers. Analysis of scalar probability density functions in flows with dominant outer modes demonstrates the ineffective, one-sided nature of mixing that accompany these flow structures. Colayer conditions, where two modes have equal growth rate and the mixing layer is formed by two sets of vortices, offer some opportunity for mixing enhancement. Their extent, however, is found to be limited in the mixing layer's parameter space. Extensive validation of the PSE technique also provides a unique perspective on central- mode vortex pairing, further supporting the view that pairing is primarily governed perspective sheds insight on how linear stability theory is able to provide such an accurate prediction of experimentally-observed, fully nonlinear flow phenomenon.

  11. Upper Oceanic Energy Response to Tropical Cyclone Passage

    DTIC Science & Technology

    2013-04-15

    insolation, and the upper ocean stratification . The importance of the upper ocean energy content to TCs, particularly their intensification, has been...similar to those of Shay and Brewster (2010), who showed that the stable stratification of the east Pacific also makes the 100-m mixed layer depth a poor... The upper oceanic temporal response to tropical cyclone (TC) passage is investigated using a 6-yr daily record of data-driven analyses of two

  12. Coupling with ocean mixed layer leads to intraseasonal variability in tropical deep convection: Evidence from cloud-resolving simulations

    NASA Astrophysics Data System (ADS)

    Anber, Usama; Wang, Shuguang; Sobel, Adam

    2017-03-01

    The effect of coupling a slab ocean mixed layer to atmospheric convection is examined in cloud-resolving model (CRM) simulations in vertically sheared and unsheared environments without Coriolis force, with the large-scale circulation parameterized using the Weak Temperature Gradient (WTG) approximation. Surface fluxes of heat and moisture as well as radiative fluxes are fully interactive, and the vertical profile of domain-averaged horizontal wind is strongly relaxed toward specified profiles with vertical shear that varies from one simulation to the next. Vertical wind shear is found to play a critical role in the simulated behavior. There exists a threshold value of the shear strength above which the coupled system develops regular oscillations between deep convection and dry nonprecipitating states, similar to those found earlier in a much more idealized model which did not consider wind shear. The threshold value of the vertical shear found here varies with the depth of the ocean mixed layer. The time scale of the spontaneously generated oscillations also varies with mixed layer depth, from 10 days with a 1 m deep mixed layer to 50 days with a 10 m deep mixed layer. The results suggest the importance of the interplay between convection organized by vertical wind shear, radiative feedbacks, large-scale dynamics, and ocean mixed layer heat storage in real intraseasonal oscillations.

  13. The effect of under-ice melt ponds on their surroundings in the Arctic

    NASA Astrophysics Data System (ADS)

    Feltham, D. L.; Smith, N.; Flocco, D.

    2016-12-01

    In the summer months, melt water from the surface of the Arctic sea ice can percolate down through the ice and flow out of its base. This water is relatively warm and fresh compared to the ocean water beneath it, and so it floats between the ice and the oceanic mixed layer, forming pools of melt water called under-ice melt ponds. Sheets of ice, known as false bottoms, can subsequently form via double diffusion processes at the under-ice melt pond interface with the ocean, trapping the pond against the ice and completely isolating it from the ocean below. This has an insulating effect on the parent sea ice above the trapped pond, altering its rate of basal ablation. A one-dimensional, thermodynamic model of Arctic sea ice has been adapted to study the evolution of under-ice melt ponds and false bottoms over time. Comparing simulations of sea ice evolution with and without an under-ice melt pond provides a measure of how an under-ice melt pond affects the mass balance of the sea ice above it. Sensitivity studies testing the response of the model to a range of uncertain parameters have been performed, revealing some interesting implications of under-ice ponds during their life cycle. By changing the rate of basal ablation of the parent sea ice, and so the flux of fresh water and salt into the ocean, under-ice melt ponds affect the properties of the mixed layer beneath the sea ice. Our model of under-ice melt pond refreezing has been coupled to a simple oceanic mixed layer model to determine the effect on mixed layer depth, salinity and temperature.

  14. Material transport in a wind and buoyancy forced mixed layer

    NASA Astrophysics Data System (ADS)

    Mensa, J. A.; Özgökmen, T.; Poje, A. C.; Imberger, J.

    2016-02-01

    Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (|u10|=5ms-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(l), than those reported by Okubo (1970), while the wind- and buoyancy forced case shows a good agreement with Okubo's diffusivity amplitude, and scaling consistent with Richardson's 4/3rd law, kD(l) l4/3. The modelling results provide a framework for measuring material dispersion by mixed layer flow in future observational programs.

  15. Material transport in a convective surface mixed layer under weak wind forcing

    NASA Astrophysics Data System (ADS)

    Mensa, Jean A.; Özgökmen, Tamay M.; Poje, Andrew C.; Imberger, Jörg

    2015-12-01

    Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (| u10 | = 5m s-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(ℓ), than those reported by Okubo (1970), while the wind- and buoyancy-forced case shows a good agreement with Okubo's diffusivity amplitude, and the scaling is consistent with Richardson's 4/3rd law, kD ∼ ℓ4/3. These modeling results provide a framework for measuring material dispersion by mixed layer flows in future observational programs.

  16. Direct simulations of chemically reacting turbulent mixing layers, part 2

    NASA Technical Reports Server (NTRS)

    Metcalfe, Ralph W.; Mcmurtry, Patrick A.; Jou, Wen-Huei; Riley, James J.; Givi, Peyman

    1988-01-01

    The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques.

  17. Low-foot rugby hohlraum experiments on the NIF: Wall-gas mix and a connection with missing x-ray drive energy?

    NASA Astrophysics Data System (ADS)

    Amendt, Peter; Ross, J. Steven; Schneider, Marilyn; Jones, Oggie; Milovich, Jose; Moody, John

    2014-10-01

    Rugby-shaped hohlraums on the NIF have shown strong symmetry anomalies when simulated with the high-flux model. The wall-gas interface is Rayleigh-Taylor unstable and may lead to the formation of a late-time mix layer that impedes inner- cone propagation, resulting in a drive asymmetry on the capsule. Due to the rugby curvature near the laser entrance hole, the effect of mix may be more pronounced than in cylinders. At the same time a persistent pattern of 15--25% missing energy has been inferred in gas-filled hohlraums (ρ >= 0 . 96 mg/cc). A possible physical connection between formation of a mix layer and the plasma adiabatic lapse rate, where a temperature-gradient reversal is predicted to occur, is explored. Such a profile reversal, in turn, hinders electron conduction to the dense (ρ > 0 . 2 g/cc) Au region responsible for ~900 eV drive x-ray emission, leading to a hotter coronal plasma and reduced hohlraum efficiency. Remedial measures for recovering the loss in hohlraum efficiency through the use of higher-Z gas fills are explored. Prepared by LLNL under Contract DE-AC52-07NA27344.

  18. The urban moisture climate

    Treesearch

    Douglas L. Sisterson

    1977-01-01

    Data collected on 26 July 1974 as a part of project METROMEX in St. Louis show the three-dimensional structure of the urban moisture field. Mesoscale dry regions at the urban surface, corresponding to large residential and light industrial land-use characterization, were responsible for a reduction in specific humidity in the urban mixing layer. Anthropogenic sources...

  19. Upper Ocean Response to the Atmospheric Cold Pools Associated With the Madden-Julian Oscillation

    NASA Astrophysics Data System (ADS)

    Pei, Suyang; Shinoda, Toshiaki; Soloviev, Alexander; Lien, Ren-Chieh

    2018-05-01

    Atmospheric cold pools are frequently observed during the Madden-Julian Oscillation events and play an important role in the development and organization of large-scale convection. They are generally associated with heavy precipitation and strong winds, inducing large air-sea fluxes and significant sea surface temperature (SST) fluctuations. This study provides a first detailed investigation of the upper ocean response to the strong cold pools associated with the Madden-Julian Oscillation, based on the analysis of in situ data collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign and one-dimensional ocean model simulations validated by the data. During strong cold pools, SST drops rapidly due to the atmospheric cooling in a shoaled mixed layer caused by the enhanced near-surface salinity stratification generated by heavy precipitation. Significant contribution also comes from the component of surface heat flux produced by the cold rain temperature. After the period of heavy rain, while net surface cooling remains, SST gradually recovers due to the enhanced entrainment of warmer waters below the mixed layer.

  20. A robust multi-frequency mixing algorithm for suppression of rivet signal in GMR inspection of riveted structures

    NASA Astrophysics Data System (ADS)

    Safdernejad, Morteza S.; Karpenko, Oleksii; Ye, Chaofeng; Udpa, Lalita; Udpa, Satish

    2016-02-01

    The advent of Giant Magneto-Resistive (GMR) technology permits development of novel highly sensitive array probes for Eddy Current (EC) inspection of multi-layer riveted structures. Multi-frequency GMR measurements with different EC pene-tration depths show promise for detection of bottom layer notches at fastener sites. However, the distortion of the induced magnetic field due to flaws is dominated by the strong fastener signal, which makes defect detection and classification a challenging prob-lem. This issue is more pronounced for ferromagnetic fasteners that concentrate most of the magnetic flux. In the present work, a novel multi-frequency mixing algorithm is proposed to suppress rivet signal response and enhance defect detection capability of the GMR array probe. The algorithm is baseline-free and does not require any assumptions about the sample geometry being inspected. Fastener signal suppression is based upon the random sample consensus (RANSAC) method, which iteratively estimates parameters of a mathematical model from a set of observed data with outliers. Bottom layer defects at fastener site are simulated as EDM notches of different length. Performance of the proposed multi-frequency mixing approach is evaluated on finite element data and experimental GMR measurements obtained with unidirectional planar current excitation. Initial results are promising demonstrating the feasibility of the approach.

  1. Interannual variability of primary production and air-sea CO2 flux in the Atlantic and Indian sectors of the Southern Ocean.

    NASA Astrophysics Data System (ADS)

    Dufour, Carolina; Merlivat, Liliane; Le Sommer, Julien; Boutin, Jacqueline; Antoine, David

    2013-04-01

    As one of the major oceanic sinks of anthropogenic CO2, the Southern Ocean plays a critical role in the climate system. However, due to the scarcity of observations, little is known about physical and biological processes that control air-sea CO2 fluxes and how these processes might respond to climate change. It is well established that primary production is one of the major drivers of air-sea CO2 fluxes, consuming surface Dissolved Inorganic Carbon (DIC) during Summer. Southern Ocean primary production is though constrained by several limiting factors such as iron and light availability, which are both sensitive to mixed layer depth. Mixed layer depth is known to be affected by current changes in wind stress or freshwater fluxes over the Southern Ocean. But we still don't know how primary production may respond to anomalous mixed layer depth neither how physical processes may balance this response to set the seasonal cycle of air-sea CO2 fluxes. In this study, we investigate the impact of anomalous mixed layer depth on surface DIC in the Atlantic and Indian sectors of the Subantarctic zone of the Southern Ocean (60W-60E, 38S-55S) with a combination of in situ data, satellite data and model experiment. We use both a regional eddy permitting ocean biogeochemical model simulation based on NEMO-PISCES and data-based reconstruction of biogeochemical fields based on CARIOCA buoys and SeaWiFS data. A decomposition of the physical and biological processes driving the seasonal variability of surface DIC is performed with both the model data and observations. A good agreement is found between the model and the data for the amplitude of biological and air-sea flux contributions. The model data are further used to investigate the impact of winter and summer anomalies in mixed layer depth on surface DIC over the period 1990-2004. The relative changes of each physical and biological process contribution are quantified and discussed.

  2. [Characteristics of Winter Atmospheric Mixing Layer Height in Beijing-Tianjin-Hebei Region and Their Relationship with the Atmospheric Pollution].

    PubMed

    Li, Meng; Tang, Gui-qian; Huang, Jun; Liu, Zi-rui; An, Jun-lin; Wang, Yue-si

    2015-06-01

    Atmospheric mixing layer height (MLH) is one of the main factors affecting the atmospheric diffusion and plays an important role in air quality assessment and distribution of the pollutants. Based on the ceilometers data, this paper has made synchronous observation on MLH in Beijing-Tianjin-Hebei region (Beijing, Tianjin, Shijiazhuang and Qinhuangdao) in heavy polluted February 2014 and analyzed the respective overall change and its regional features. Results show that in February 2014,the average of mixing layer height in Qinhuangdao is the highest, up to 865 +/- 268 m, and in Shijiazhuang is the lowest (568 +/- 207 m), Beijing's and Tianjin's are in between, 818 +/- 319 m and 834 +/- 334 m respectively; Combined with the meteorological data, we find that radiation and wind speed are main factors of the mixing layer height; The relationship between the particle concentration and mixing layer height in four sites suggests that mixing layer is less than 800 m, concentration of fine particulate matter in four sites will exceed the national standard (GB 3095-2012, 75 microg x m(-3)). During the period of observation, the proportion of days that mixing layer is less than 800 m in Beijing, Tianjin, Shijiazhuang and Qinhuangdao are 50%, 43%, 80% and 50% respectively. Shijiazhuang though nearly formation contaminant concentration is high, within the atmospheric mixed layer pollutant load is not high. Unfavorable atmospheric diffusion conditions are the main causes of heavy pollution in Shijiazhuang for a long time. The results of the study are of great significance for cognitive Beijing-Tianjin-Hebei area pollution distribution, and can provide a scientific reference for reasonable distribution of regional pollution sources.

  3. The roll-up and merging of coherent structures in shallow mixing layers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lam, M. Y., E-mail: celmy@connect.ust.hk; Ghidaoui, M. S.; Kolyshkin, A. A.

    2016-09-15

    The current study seeks a fundamental explanation to the development of two-dimensional coherent structures (2DCSs) in shallow mixing layers. A nonlinear numerical model based on the depth-averaged shallow water equations is used to investigate the temporal evolution of shallow mixing layers, where the mapping from temporal to spatial results is made using the velocity at the center of the mixing layers. The flow is periodic in the streamwise direction. Transmissive boundary conditions are used in the cross-stream boundaries to prevent reflections. Numerical results are compared to linear stability analysis, mean-field theory, and secondary stability analysis. Results suggest that the onsetmore » and development of 2DCS in shallow mixing layers are the result of a sequence of instabilities governed by linear theory, mean-field theory, and secondary stability theory. The linear instability of the shearing velocity gradient gives the onset of 2DCS. When the perturbations reach a certain amplitude, the flow field of the perturbations changes from a wavy shape to a vortical (2DCS) structure because of nonlinearity. The development of the vertical 2DCS does not appear to follow weakly nonlinear theory; instead, it follows mean-field theory. After the formation of 2DCS, separate 2DCSs merge to form larger 2DCS. In this way, 2DCSs grow and shallow mixing layers develop and grow in scale. The merging of 2DCS in shallow mixing layers is shown to be caused by the secondary instability of the 2DCS. Eventually 2DCSs are dissipated by bed friction. The sequence of instabilities can cause the upscaling of the turbulent kinetic energy in shallow mixing layers.« less

  4. Cloud and boundary layer interactions over the Arctic sea-ice in late summer

    NASA Astrophysics Data System (ADS)

    Shupe, M. D.; Persson, P. O. G.; Brooks, I. M.; Tjernström, M.; Sedlar, J.; Mauritsen, T.; Sjogren, S.; Leck, C.

    2013-05-01

    Observations from the Arctic Summer Cloud Ocean Study (ASCOS), in the central Arctic sea-ice pack in late summer 2008, provide a detailed view of cloud-atmosphere-surface interactions and vertical mixing processes over the sea-ice environment. Measurements from a suite of ground-based remote sensors, near surface meteorological and aerosol instruments, and profiles from radiosondes and a helicopter are combined to characterize a week-long period dominated by low-level, mixed-phase, stratocumulus clouds. Detailed case studies and statistical analyses are used to develop a conceptual model for the cloud and atmosphere structure and their interactions in this environment. Clouds were persistent during the period of study, having qualities that suggest they were sustained through a combination of advective influences and in-cloud processes, with little contribution from the surface. Radiative cooling near cloud top produced buoyancy-driven, turbulent eddies that contributed to cloud formation and created a cloud-driven mixed layer. The depth of this mixed layer was related to the amount of turbulence and condensed cloud water. Coupling of this cloud-driven mixed layer to the surface boundary layer was primarily determined by proximity. For 75% of the period of study, the primary stratocumulus cloud-driven mixed layer was decoupled from the surface and typically at a warmer potential temperature. Since the near-surface temperature was constrained by the ocean-ice mixture, warm temperatures aloft suggest that these air masses had not significantly interacted with the sea-ice surface. Instead, back trajectory analyses suggest that these warm airmasses advected into the central Arctic Basin from lower latitudes. Moisture and aerosol particles likely accompanied these airmasses, providing necessary support for cloud formation. On the occasions when cloud-surface coupling did occur, back trajectories indicated that these air masses advected at low levels, while mixing processes kept the mixed layer in equilibrium with the near-surface environment. Rather than contributing buoyancy forcing for the mixed-layer dynamics, the surface instead simply appeared to respond to the mixed-layer processes aloft. Clouds in these cases often contained slightly higher condensed water amounts, potentially due to additional moisture sources from below.

  5. Cloud and boundary layer interactions over the Arctic sea ice in late summer

    NASA Astrophysics Data System (ADS)

    Shupe, M. D.; Persson, P. O. G.; Brooks, I. M.; Tjernström, M.; Sedlar, J.; Mauritsen, T.; Sjogren, S.; Leck, C.

    2013-09-01

    Observations from the Arctic Summer Cloud Ocean Study (ASCOS), in the central Arctic sea-ice pack in late summer 2008, provide a detailed view of cloud-atmosphere-surface interactions and vertical mixing processes over the sea-ice environment. Measurements from a suite of ground-based remote sensors, near-surface meteorological and aerosol instruments, and profiles from radiosondes and a helicopter are combined to characterize a week-long period dominated by low-level, mixed-phase, stratocumulus clouds. Detailed case studies and statistical analyses are used to develop a conceptual model for the cloud and atmosphere structure and their interactions in this environment. Clouds were persistent during the period of study, having qualities that suggest they were sustained through a combination of advective influences and in-cloud processes, with little contribution from the surface. Radiative cooling near cloud top produced buoyancy-driven, turbulent eddies that contributed to cloud formation and created a cloud-driven mixed layer. The depth of this mixed layer was related to the amount of turbulence and condensed cloud water. Coupling of this cloud-driven mixed layer to the surface boundary layer was primarily determined by proximity. For 75% of the period of study, the primary stratocumulus cloud-driven mixed layer was decoupled from the surface and typically at a warmer potential temperature. Since the near-surface temperature was constrained by the ocean-ice mixture, warm temperatures aloft suggest that these air masses had not significantly interacted with the sea-ice surface. Instead, back-trajectory analyses suggest that these warm air masses advected into the central Arctic Basin from lower latitudes. Moisture and aerosol particles likely accompanied these air masses, providing necessary support for cloud formation. On the occasions when cloud-surface coupling did occur, back trajectories indicated that these air masses advected at low levels, while mixing processes kept the mixed layer in equilibrium with the near-surface environment. Rather than contributing buoyancy forcing for the mixed-layer dynamics, the surface instead simply appeared to respond to the mixed-layer processes aloft. Clouds in these cases often contained slightly higher condensed water amounts, potentially due to additional moisture sources from below.

  6. Receptivity of the compressible mixing layer

    NASA Astrophysics Data System (ADS)

    Barone, Matthew F.; Lele, Sanjiva K.

    2005-09-01

    Receptivity of compressible mixing layers to general source distributions is examined by a combined theoretical/computational approach. The properties of solutions to the adjoint Navier Stokes equations are exploited to derive expressions for receptivity in terms of the local value of the adjoint solution. The result is a description of receptivity for arbitrary small-amplitude mass, momentum, and heat sources in the vicinity of a mixing-layer flow, including the edge-scattering effects due to the presence of a splitter plate of finite width. The adjoint solutions are examined in detail for a Mach 1.2 mixing-layer flow. The near field of the adjoint solution reveals regions of relatively high receptivity to direct forcing within the mixing layer, with receptivity to nearby acoustic sources depending on the source type and position. Receptivity ‘nodes’ are present at certain locations near the splitter plate edge where the flow is not sensitive to forcing. The presence of the nodes is explained by interpretation of the adjoint solution as the superposition of incident and scattered fields. The adjoint solution within the boundary layer upstream of the splitter-plate trailing edge reveals a mechanism for transfer of energy from boundary-layer stability modes to Kelvin Helmholtz modes. Extension of the adjoint solution to the far field using a Kirchhoff surface gives the receptivity of the mixing layer to incident sound from distant sources.

  7. Discrete element simulation of charging and mixed layer formation in the ironmaking blast furnace

    NASA Astrophysics Data System (ADS)

    Mitra, Tamoghna; Saxén, Henrik

    2016-11-01

    The burden distribution in the ironmaking blast furnace plays an important role for the operation as it affects the gas flow distribution, heat and mass transfer, and chemical reactions in the shaft. This work studies certain aspects of burden distribution by small-scale experiments and numerical simulation by the discrete element method (DEM). Particular attention is focused on the complex layer-formation process and the problems associated with estimating the burden layer distribution by burden profile measurements. The formation of mixed layers is studied, and a computational method for estimating the extent of the mixed layer, as well as its voidage, is proposed and applied on the results of the DEM simulations. In studying a charging program and its resulting burden distribution, the mixed layers of coke and pellets were found to show lower voidage than the individual burden layers. The dynamic evolution of the mixed layer during the charging process is also analyzed. The results of the study can be used to gain deeper insight into the complex charging process of the blast furnace, which is useful in the design of new charging programs and for mathematical models that do not consider the full behavior of the particles in the burden layers.

  8. Specific features of the inverse magnetoelectric effect in two-layered Tb0.12Dy0.2Fe0.68-PbZr0.53Ti0.47O3 composites

    NASA Astrophysics Data System (ADS)

    Kalgin, A. V.; Gridnev, S. A.; Gribe, Z. H.

    2014-07-01

    The two-layered Tb0.12Dy0.2Fe0.68-PbZr0.53Ti0.47O3 magnetoelectric composites have been prepared by the deposition of ferromagnetic layers of different thicknesses from a thoroughly mixed Tb0.12Dy0.2Fe0.68 ferromagnetic powder and an epoxy glue on preliminarily polarized PbZr0.53Ti0.47O3 piezoelectric layers. The dependences of the inverse magnetoelectric effect on the frequency and strength of an electric field, the strength of a constant magnetic field, the thickness of a ferromagnetic layer, the average size of Tb0.12Dy0.2Fe0.68 grains in the ferromagnetic layer, and the temperature have been determined. Conditions for the maximum magnetoelectric response have been established.

  9. A three-dimensional simulation of transition and early turbulence in a time-developing mixing layer

    NASA Technical Reports Server (NTRS)

    Cain, A. B.; Reynolds, W. C.; Ferziger, J. H.

    1981-01-01

    The physics of the transition and early turbulence regimes in the time developing mixing layer was investigated. The sensitivity of the mixing layer to the disturbance field of the initial condition is considered. The growth of the momentum thickness, the mean velocity profile, the turbulence kinetic energy, the Reynolds stresses, the anisotropy tensor, and particle track pictures of computations are all examined in an effort to better understand the physics of these regimes. The amplitude, spectrum shape, and random phases of the initial disturbance field were varied. A scheme of generating discrete orthogonal function expansions on some nonuniform grids was developed. All cases address the early or near field of the mixing layer. The most significant result shows that the secondary instability of the mixing layer is produced by spanwise variations in the straining field of the primary vortex structures.

  10. Method for fabricating solar cells having integrated collector grids

    NASA Technical Reports Server (NTRS)

    Evans, J. C., Jr. (Inventor)

    1979-01-01

    A heterojunction or Schottky barrier photovoltaic device comprising a conductive base metal layer compatible with and coating predominately the exposed surface of the p-type substrate of the device such that a back surface field region is formed at the interface between the device and the base metal layer, a transparent, conductive mixed metal oxide layer in integral contact with the n-type layer of the heterojunction or Schottky barrier device having a metal alloy grid network of the same metal elements of the oxide constituents of the mixed metal oxide layer embedded in the mixed metal oxide layer, an insulating layer which prevents electrical contact between the conductive metal base layer and the transparent, conductive metal oxide layer, and a metal contact means covering the insulating layer and in intimate contact with the metal grid network embedded in the transparent, conductive oxide layer for conducting electrons generated by the photovoltaic process from the device.

  11. High strain rate deformation of layered nanocomposites

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P.; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A.; Thomas, Edwin L.

    2012-11-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

  12. High strain rate deformation of layered nanocomposites.

    PubMed

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A; Thomas, Edwin L

    2012-01-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

  13. Multi-sensor quantification of aerosol-induced variability in warm clouds over eastern China

    NASA Astrophysics Data System (ADS)

    Wang, Fu; Guo, Jianping; Zhang, Jiahua; Huang, Jingfeng; Min, Min; Chen, Tianmeng; Liu, Huan; Deng, Minjun; Li, Xiaowen

    2015-07-01

    Aerosol-cloud (AC) interactions remain uncharacterized due to difficulties in obtaining accurate aerosol and cloud observations. In this study, we quantified the aerosol indirect effects (AIE) on warm clouds over Eastern China based on near-simultaneous retrievals from MODIS/AQUA, CALIOP/CALIPSO, and CPR/CLOUDSAT between June 2006 and December 2010. The seasonality of aerosols from ground-based PM10 (aerosol particles with diameter of 10 μm or less) significantly differed from that estimated using MODIS aerosol optical depth (AOD). This result was supported by the lower level frequency profile of aerosol occurrence from CALIOP, indicative of the significant role of CALIOP in the AC interaction. To focus on warm clouds, cloud layers with base (top) altitudes above 7 (10) km were excluded. The combination of CALIOP and CPR was applied to determine the exact position of warm clouds relative to aerosols out of the following six scenarios in terms of AC mixing states: 1) aerosol only (AO); 2) cloud only (CO); 3) single aerosol layer-single cloud layer (SASC); 4) single aerosol layer-double cloud layers (SADC); 5) double aerosol layers - single cloud layer (DASC); and 6) others. The cases with vertical distance between aerosol and cloud layer less (more) than 100 m (700 m) were marked mixed (separated), and the rest as uncertain. Results showed that only 8.95% (7.53%) belonged to the mixed (separated and uncertain) state among all of the collocated AC overlapping cases, including SASC, SADC, and DASC. Under mixed conditions, the cloud droplet effective radius (CDR) decreased with increasing AOD at moderate aerosol loading (AOD<0.4), and then became saturated at an AOD of around 0.5, followed by an increase in CDR with increasing AOD, known as boomerang shape. Under separated conditions, no apparent changes in CDR with AOD were observed. We categorized the AC dataset into summer- and winter-season subsets to determine how the boomerang shape varied with season. The response of CDR to AOD in summer exhibited similar but much more deepened boomerang shape, as compared with the all year round case. In contrast, CDR in winter did not follow the boomerang shape for its continued decreasing with increasing AOD, even after the saturation zone (AOD around 0.5) of a cloud droplet.

  14. Lagrangian pathways of upwelling in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Viglione, Giuliana A.; Thompson, Andrew F.

    2016-08-01

    The spatial and temporal variability of upwelling into the mixed layer in the Southern Ocean is studied using a 1/10° ocean general circulation model. Virtual drifters are released in a regularly spaced pattern across the Southern Ocean at depths of 250, 500, and 1000 m during both summer and winter months. The drifters are advected along isopycnals for a period of 4 years, unless they outcrop into the mixed layer, where lateral advection and a parameterization of vertical mixing are applied. The focus of this study is on the discrete exchange between the model mixed layer and the interior. Localization of interior-mixed layer exchange occurs downstream of major topographic features across the Indian and Pacific basins, creating "hotspots" of outcropping. Minimal outcropping occurs in the Atlantic basin, while 59% of drifters outcrop in the Pacific sector and in Drake Passage (the region from 140° W to 40° W), a disproportionately large amount even when considering the relative basin sizes. Due to spatial and temporal variations in mixed layer depth, the Lagrangian trajectories provide a statistical measure of mixed layer residence times. For each exchange into the mixed layer, the residence time has a Rayleigh distribution with a mean of 30 days; the cumulative residence time of the drifters is 261 ± 194 days, over a period of 4 years. These results suggest that certain oceanic gas concentrations, such as CO2 and 14C, will likely not reach equilibrium with the atmosphere before being resubducted.

  15. Hydrogen trapping under the effect of W-C mixed layers

    NASA Astrophysics Data System (ADS)

    Liu, N.; Huang, J.; Sato, K.; Xu, Q.; Shi, L. Q.; Wang, Y. X.

    2014-03-01

    The retention of hydrogen (H) isotope in plasma-facing materials (PFMs) is an important issue for next step fusion device. We used density functional theory (DFT) to study the chemical bonds of H in tungsten-carbon (W-C) mixed layers of tungsten surface, aiming to explore the retention behaviour of H in PFMs. The solubility of C in W was first calculated for revealing the phase components in W-C mixed layers. It was found that C has low solubility in W, which prefers to be segregated on the W surface. Vacancies can enhance the solution of C in W. This makes C appear somewhat carbide feature. Thus, W-C mixed layers should contain multiple phase components. H retention strongly depends on the phase components in the W-C mixed layers. The solution of C will suppress the retention of H in W no matter whether neighbouring vacancies are present, or not. Hydrocarbon precursors, which were observed in desorption experiments, prefer to form by means of H binding to C atoms in C amorphous, or in precipitators in the W-C mixed layers, while not in tungsten carbide phase or in W bulk. Our investigation reasonably explains the experimental results.

  16. High Static Stability in the Mixed Layer Above the Extratropical Tropopause

    NASA Astrophysics Data System (ADS)

    Kunz, A.; Konopka, P.; Müller, R.; Schiller, C.

    2008-12-01

    A strong relationship between the static stability N2 and the strength of mixing in the mixed layer above the extratropical tropopause is evident from in-situ data observed during the SPURT aircraft campaigns. We present a method for quantifying the strength of mixing from O3/CO tracer correlations and we find that N2 is positively correlated with the strength of mixing. Age of air simulations with the CLaMS model reveal two different types of mixed regions. One type consisting of older airmasses with higher values of N2 which are created by radiative adjustment after a mixing event. These airmasses are within the TIL (Tropopause Inversion Layer), considering the TIL as part of the mixing layer. The second type comprises younger airmasses with somehow lower stratospheric N2 values within the mixing layer, because of recent intrusion processes due to the permeability or so-called mid-latitude-breaks associated with the jet stream. With the help of radiative transfer calculations we simulate the influence of trace gases such as O3 and H2O on the temperature gradient and thus on the static stability above the tropopause in the idealized case of non-mixing (L-shape) O3 and H2O profiles and in the reference case of mixed profiles. Within the altitude range of the SPURT campaigns the mean vertical SPURT profiles are used as reference, which are fitted to the HALOE climatological profiles above the UT/LS.

  17. Temperature Versus Salinity Gradients Below the Ocean Mixed Layer

    DTIC Science & Technology

    2012-05-03

    where salinity controls the depth of the mixed layer are understood to have “barrier” layers [Lukas and Lindstrom , 1991], where the depth of vertically...the horizontal. For example, Rudnick and Martin [2002] have shown that the ocean mixed layer at sub-mesoscales is horizontally well density compensated...Res., 102, 23,063–23,078, doi:10.1029/97JC01443. Barron, C. N., A. B. Kara, P. J. Martin , R. C. Rhodes, and L. F. Smedstad (2006), Formulation

  18. Development of a Hybrid RANS/LES Method for Compressible Mixing Layer Simulations

    NASA Technical Reports Server (NTRS)

    Georgiadis, Nicholas J.; Alexander, J. Iwan D.; Reshotko, Eli

    2001-01-01

    A hybrid method has been developed for simulations of compressible turbulent mixing layers. Such mixing layers dominate the flows in exhaust systems of modem day aircraft and also those of hypersonic vehicles currently under development. The hybrid method uses a Reynolds-averaged Navier-Stokes (RANS) procedure to calculate wall bounded regions entering a mixing section, and a Large Eddy Simulation (LES) procedure to calculate the mixing dominated regions. A numerical technique was developed to enable the use of the hybrid RANS/LES method on stretched, non-Cartesian grids. The hybrid RANS/LES method is applied to a benchmark compressible mixing layer experiment. Preliminary two-dimensional calculations are used to investigate the effects of axial grid density and boundary conditions. Actual LES calculations, performed in three spatial directions, indicated an initial vortex shedding followed by rapid transition to turbulence, which is in agreement with experimental observations.

  19. Investigation of mixed-host organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Yeh Yee, Kee

    One of the limiting factors to the OLED stability or lifetime is the charge buildup at the bilayer heterojunction (HJ) between the hole transport layer (HTL) and electron transport layer (ETL). In recent years, this abrupt interface has been moderated by mixing HTL and ETL to form a single mixed-host, light emitting layer. For uniformly mixed-host (UM) OLED, the device lifetime and also the efficiency were improved due to the spatial broadening of the recombination zone. Similar device architectures, such as the step-wise graded mixed-host (SGM-OLED) and the continuously graded mixed-host (CGM-OLED) have also been implemented by a number of researchers. In this work, a premix of hole transport material (HTM) and electron transport material (ETM), namely TPD and Alq, is prepared for one-step thermal evaporation of the mixed-host light emitting layer (EML). Depending on the evaporation rate, the CGM-OLEDs with different concentration profiles of HTM and ETM in the EML are obtained, which are inversely proportional to each other.

  20. Lidar observation of marine mixed layer

    NASA Technical Reports Server (NTRS)

    Yamagishi, Susumu; Yamanouchi, Hiroshi; Tsuchiya, Masayuki

    1992-01-01

    Marine mixed layer is known to play an important role in the transportation of pollution exiting ship funnels. The application of a diffusion model is critically dependent upon a reliable estimate of a lid. However, the processes that form lids are not well understood, though considerable progress toward marine boundary layer has been achieved. This report describes observations of the marine mixed layer from the course Ise-wan to Nii-jima with the intention of gaining a better understanding of their structure by a shipboard lidar. These observations were made in the summer of 1991. One interesting feature of the observations was that the multiple layers of aerosols, which is rarely numerically modeled, was encountered. No attempt is yet made to present a systematic analysis of all the data collected. Instead we focus on observations that seem to be directly relevant to the structure of the mixed layer.

  1. Development of a nonlocal convective mixing scheme with varying upward mixing rates for use in air quality and chemical transport models.

    PubMed

    Mihailović, Dragutin T; Alapaty, Kiran; Sakradzija, Mirjana

    2008-06-01

    Asymmetrical convective non-local scheme (CON) with varying upward mixing rates is developed for simulation of vertical turbulent mixing in the convective boundary layer in air quality and chemical transport models. The upward mixing rate form the surface layer is parameterized using the sensible heat flux and the friction and convective velocities. Upward mixing rates varying with height are scaled with an amount of turbulent kinetic energy in layer, while the downward mixing rates are derived from mass conservation. This scheme provides a less rapid mass transport out of surface layer into other layers than other asymmetrical convective mixing schemes. In this paper, we studied the performance of a nonlocal convective mixing scheme with varying upward mixing in the atmospheric boundary layer and its impact on the concentration of pollutants calculated with chemical and air-quality models. This scheme was additionally compared versus a local eddy-diffusivity scheme (KSC). Simulated concentrations of NO(2) and the nitrate wet deposition by the CON scheme are closer to the observations when compared to those obtained from using the KSC scheme. Concentrations calculated with the CON scheme are in general higher and closer to the observations than those obtained by the KSC scheme (of the order of 15-20%). Nitrate wet deposition calculated with the CON scheme are in general higher and closer to the observations than those obtained by the KSC scheme. To examine the performance of the scheme, simulated and measured concentrations of a pollutant (NO(2)) and nitrate wet deposition was compared for the year 2002. The comparison was made for the whole domain used in simulations performed by the chemical European Monitoring and Evaluation Programme Unified model (version UNI-ACID, rv2.0) where schemes were incorporated.

  2. Quasi-Geostrophic Diagnosis of Mixed-Layer Dynamics Embedded in a Mesoscale Turbulent Field

    NASA Astrophysics Data System (ADS)

    Chavanne, C. P.; Klein, P.

    2016-02-01

    A new quasi-geostrophic model has been developed to diagnose the three-dimensional circulation, including the vertical velocity, in the upper ocean from high-resolution observations of sea surface height and buoyancy. The formulation for the adiabatic component departs from the classical surface quasi-geostrophic framework considered before since it takes into account the stratification within the surface mixed-layer that is usually much weaker than that in the ocean interior. To achieve this, the model approximates the ocean with two constant-stratification layers : a finite-thickness surface layer (or the mixed-layer) and an infinitely-deep interior layer. It is shown that the leading-order adiabatic circulation is entirely determined if both the surface streamfunction and buoyancy anomalies are considered. The surface layer further includes a diabatic dynamical contribution. Parameterization of diabatic vertical velocities is based on their restoring impacts of the thermal-wind balance that is perturbed by turbulent vertical mixing of momentum and buoyancy. The model skill in reproducing the three-dimensional circulation in the upper ocean from surface data is checked against the output of a high-resolution primitive-equation numerical simulation. Correlation between simulated and diagnosed vertical velocities are significantly improved in the mixed-layer for the new model compared to the classical surface quasi-geostrophic model, reaching 0.9 near the surface.

  3. Mixed mosaic membranes prepared by layer-by-layer assembly for ionic separations.

    PubMed

    Rajesh, Sahadevan; Yan, Yu; Chang, Hsueh-Chia; Gao, Haifeng; Phillip, William A

    2014-12-23

    Charge mosaic membranes, which possess distinct cationic and anionic domains that traverse the membrane thickness, are capable of selectively separating dissolved salts from similarly sized neutral solutes. Here, the generation of charge mosaic membranes using facile layer-by-layer assembly methodologies is reported. Polymeric nanotubes with pore walls lined by positively charged polyethylenimine moieties or negatively charged poly(styrenesulfonate) moieties were prepared via layer-by-layer assembly using track-etched membranes as sacrificial templates. Subsequently, both types of nanotubes were deposited on a porous support in order to produce mixed mosaic membranes. Scanning electron microscopy demonstrates that the facile deposition techniques implemented result in nanotubes that are vertically aligned without overlap between adjacent elements. Furthermore, the nanotubes span the thickness of the mixed mosaic membranes. The effects of this unique nanostructure are reflected in the transport characteristics of the mixed mosaic membranes. The hydraulic permeability of the mixed mosaic membranes in piezodialysis operations was 8 L m(-2) h(-1) bar(-1). Importantly, solute rejection experiments demonstrate that the mixed mosaic membranes are more permeable to ionic solutes than similarly sized neutral molecules. In particular, negative rejection of sodium chloride is observed (i.e., the concentration of NaCl in the solution that permeates through a mixed mosaic membrane is higher than in the initial feed solution). These properties illustrate the ability of mixed mosaic membranes to permeate dissolved ions selectively without violating electroneutrality and suggest their utility in ionic separations.

  4. Modeling the interplay between sea ice formation and the oceanic mixed layer: Limitations of simple brine rejection parameterizations

    NASA Astrophysics Data System (ADS)

    Barthélemy, Antoine; Fichefet, Thierry; Goosse, Hugues; Madec, Gurvan

    2015-02-01

    The subtle interplay between sea ice formation and ocean vertical mixing is hardly represented in current large-scale models designed for climate studies. Convective mixing caused by the brine release when ice forms is likely to prevail in leads and thin ice areas, while it occurs in models at the much larger horizontal grid cell scale. Subgrid-scale parameterizations have hence been developed to mimic the effects of small-scale convection using a vertical distribution of the salt rejected by sea ice within the mixed layer, instead of releasing it in the top ocean layer. Such a brine rejection parameterization is included in the global ocean-sea ice model NEMO-LIM3. Impacts on the simulated mixed layers and ocean temperature and salinity profiles, along with feedbacks on the sea ice cover, are then investigated in both hemispheres. The changes are overall relatively weak, except for mixed layer depths, which are in general excessively reduced compared to observation-based estimates. While potential model biases prevent a definitive attribution of this vertical mixing underestimation to the brine rejection parameterization, it is unlikely that the latter can be applied in all conditions. In that case, salt rejections do not play any role in mixed layer deepening, which is unrealistic. Applying the parameterization only for low ice-ocean relative velocities improves model results, but introduces additional parameters that are not well constrained by observations.

  5. Modelling the interplay between sea ice formation and the oceanic mixed layer: limitations of simple brine rejection parameterizations

    NASA Astrophysics Data System (ADS)

    Barthélemy, Antoine; Fichefet, Thierry; Goosse, Hugues; Madec, Gurvan

    2015-04-01

    The subtle interplay between sea ice formation and ocean vertical mixing is hardly represented in current large-scale models designed for climate studies. Convective mixing caused by the brine release when ice forms is likely to prevail in leads and thin ice areas, while it occurs in models at the much larger horizontal grid cell scale. Subgrid-scale parameterizations have hence been developed to mimic the effects of small-scale convection using a vertical distribution of the salt rejected by sea ice within the mixed layer, instead of releasing it in the top ocean layer. Such a brine rejection parameterization is included in the global ocean--sea ice model NEMO-LIM3. Impacts on the simulated mixed layers and ocean temperature and salinity profiles, along with feedbacks on the sea ice cover, are then investigated in both hemispheres. The changes are overall relatively weak, except for mixed layer depths, which are in general excessively reduced compared to observation-based estimates. While potential model biases prevent a definitive attribution of this vertical mixing underestimation to the brine rejection parameterization, it is unlikely that the latter can be applied in all conditions. In that case, salt rejections do not play any role in mixed layer deepening, which is unrealistic. Applying the parameterization only for low ice--ocean relative velocities improves model results, but introduces additional parameters that are not well constrained by observations.

  6. Prediction of dynamic and mixing characteristics of drop-laden mixing layers using DNS and LES

    NASA Technical Reports Server (NTRS)

    Okong'o, N.; Leboissetier, A.; Bellan, J.

    2004-01-01

    Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) have been conducted of a temporal mixing layer laden with evaporating drops, in order to assess the ability of LES to reproduce dynamic and mixing aspects of the DNS which affect combustion, independently of combustion models.

  7. The three-dimensional evolution of a plane mixing layer. Part 2: Pairing and transition to turbulence

    NASA Technical Reports Server (NTRS)

    Moser, Robert D.; Rogers, Michael M.

    1992-01-01

    The evolution of three-dimensional temporally evolving plane mixing layers through as many as three pairings was simulated numerically. Initial conditions for all simulations consisted of a few low-wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity. Three-dimensional perturbations were used with amplitudes ranging from infinitesimal to large enough to trigger a rapid transition to turbulence. Pairing is found both to inhibit the growth of infinitesimal three-dimensional disturbances and to trigger the transition to turbulence in highly three dimensional flows. The mechanisms responsible for the growth of three-dimensionality as well as the initial phases of the transition to turbulence are described. The transition to turbulence is accompanied by the formation of thin sheets of span wise vorticity, which undergo a secondary roll up. Transition also produces an increase in the degree of scalar mixing, in agreement with experimental observations of mixing transition. Simulations were also conducted to investigate changes in span wise length scale that may occur in response to the change in stream wise length scale during a pairing. The linear mechanism for this process was found to be very slow, requiring roughly three pairings to complete a doubling of the span wise scale. Stronger three-dimensionality can produce more rapid scale changes but is also likely to trigger transition to turbulence. No evidence was found for a change from an organized array of rib vortices at one span wise scale to a similar array at a larger span wise scale.

  8. The seasonal cycle of the mixing layer height and its impact on black carbon concentrations in the Kathmandu Valley (Nepal)

    NASA Astrophysics Data System (ADS)

    Mues, Andrea; Rupakheti, Maheswar; Hoor, Peter; Bozem, Heiko; Münkel, Christoph; Lauer, Axel; Butler, Tim

    2016-04-01

    The properties and the vertical structure of the mixing layer as part of the planetary boundary layer are of key importance for local air quality. They have a substantial impact on the vertical dispersion of pollutants in the lower atmosphere and thus on their concentrations near the surface. In this study, ceilometer measurements taken within the framework of the SusKat project (Sustainable Atmosphere for the Kathmandu Valley) are used to investigate the mixing layer height in the Kathmandu Valley, Nepal. The applied method is based on the assumption that the aerosol concentration is nearly constant in the vertical and distinctly higher within the mixing layer than in the air above. Thus, the height with the steepest gradient within the ceilometer backscatter profile marks the top of the mixing layer. Ceilometer and black carbon (BC) measurements conducted from March 2013 through February 2014 provide a unique and important dataset for the analysis of the meteorological and air quality conditions in the Kathmandu Valley. In this study the mean diurnal cycle of the mixing layer height in the Kathmandu Valley for each season (pre-monsoon, monsoon, post-monsoon and winter season) and its dependency on the meteorological situation is investigated. In addition, the impact of the mixing layer height on the BC concentration is analyzed and compared to the relevance of other important processes such as emissions, horizontal advection and deposition. In all seasons the diurnal cycle is typically characterized by low mixing heights during the night, gradually increasing after sun rise reaching to maximum values in the afternoon before decreasing again. Seasonal differences can be seen particularly in the height of the mixing layer, e.g. from on average 153/1200 m (pre-monsoon) to 241/755 m (monsoon season) during the night/day, and the duration of enhanced mixing layer heights during daytime (around 12 hours (pre-monsoon season) to 8 hours (winter)). During the monsoon season, the observed diurnal cycle typically shows the lowest amplitude and the lowest mixing height during the day and the highest in the night and morning hours of all seasons. These characteristics can mainly be explained with frequently present clouds and the associated lack of incoming solar radiation and outgoing longwave radiation. In general there is a clear anti-correlation of the BC concentration and the mixing layer height although this relation is less pronounced in the monsoon season. The shape and magnitude of the BC diurnal cycle differs between the seasons (e.g., daily maximum concentration from around 6 to 50 μg/m3 depending on the season). This is partly due to the different meteorological conditions including the mixing layer height but also caused by the different (seasonal and diurnal) time profiles of the main emission sources. From late December to April, for instance, brick kilns are major emitters of black carbon. The brick kilns emit continuously throughout the day whereas in the other months sources with more pronounced diurnal cycles, such as traffic and cooking activities, are dominating the total emissions.

  9. Effects of inter-fullerene π-band mixings in the photoexcitation of hybrid plasmons in the C60@C240 molecule

    NASA Astrophysics Data System (ADS)

    de, Rume; Madjet, Mohamed; Chakraborty, Himadri

    2013-05-01

    We perform a detailed study of the ground state electronic structure of a two-layer fullerene onion molecule C60@C240. Calculations are carried out in a quantum mechanical framework of local density approximation (LDA) where the onion's ion-core of sixty C4+ ions from C60 and two hundred and forty of those from C240 is smeared into a classical jellium distribution. Significant inter-fullerene mixing between the bands of single-node radial symmetry, the π-bands, is found. We then compute the photoionization from all the levels of the system using a time-dependent version of LDA at photon energies where the ionization is dominated by the inter-layer hybridization of collective plasmon resonances. It is determined, by comparing the isolated fullerene cross sections with the cross section of the onion system for both π and σ (having nodeless radial waves) symmetry, that the π-band mixing is predominantly responsible for the production of plasmon hybrids. Supported by NSF and DOE.

  10. Mid-depth temperature maximum in an estuarine lake

    NASA Astrophysics Data System (ADS)

    Stepanenko, V. M.; Repina, I. A.; Artamonov, A. Yu; Gorin, S. L.; Lykossov, V. N.; Kulyamin, D. V.

    2018-03-01

    The mid-depth temperature maximum (TeM) was measured in an estuarine Bol’shoi Vilyui Lake (Kamchatka peninsula, Russia) in summer 2015. We applied 1D k-ɛ model LAKE to the case, and found it successfully simulating the phenomenon. We argue that the main prerequisite for mid-depth TeM development is a salinity increase below the freshwater mixed layer, sharp enough in order to increase the temperature with depth not to cause convective mixing and double diffusion there. Given that this condition is satisfied, the TeM magnitude is controlled by physical factors which we identified as: radiation absorption below the mixed layer, mixed-layer temperature dynamics, vertical heat conduction and water-sediments heat exchange. In addition to these, we formulate the mechanism of temperature maximum ‘pumping’, resulting from the phase shift between diurnal cycles of mixed-layer depth and temperature maximum magnitude. Based on the LAKE model results we quantify the contribution of the above listed mechanisms and find their individual significance highly sensitive to water turbidity. Relying on physical mechanisms identified we define environmental conditions favouring the summertime TeM development in salinity-stratified lakes as: small-mixed layer depth (roughly, ~< 2 m), transparent water, daytime maximum of wind and cloudless weather. We exemplify the effect of mixed-layer depth on TeM by a set of selected lakes.

  11. Corrosion of low alloy steel containing 0.5% chromium in supercritical CO2-saturated brine and water-saturated supercritical CO2 environments

    NASA Astrophysics Data System (ADS)

    Wei, Liang; Gao, Kewei; Li, Qian

    2018-05-01

    The corrosion behavior of P110 low-Cr alloy steel in supercritical CO2-saturated brine (aqueous phase) and water-saturated supercritical CO2 (SC CO2 phase) was investigated. The results show that P110 steel primarily suffered general corrosion in the aqueous phase, while severe localized corrosion occurred in the SC CO2 phase. The formation of corrosion product scale on P110 steel in the aqueous phase divided into three stages: formation of the initial corrosion layer containing amorphous Cr(OH)3, FeCO3 and a small amount of Fe3C; transformation of initial corrosion layer to mixed layer, which consisted of FeCO3 and a small amount of Cr(OH)3 and Fe3C; growth and dissolution of the mixed layer. Finally, only a single mixed layer covered on the steel in the aqueous phase. However, the scale formed in SC CO2 phase consisted of two layers: the inner mixed layer and the dense outer FeCO3 crystalline layer.

  12. Anomalies of the upper water column in the Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Rivetti, Irene; Boero, Ferdinando; Fraschetti, Simonetta; Zambianchi, Enrico; Lionello, Piero

    2017-04-01

    The evolution of the upper water column in the Mediterranean Sea during more than 60 years is reconstructed in terms of few parameters describing the mixed layer and the seasonal thermocline. The analysis covers the period 1945-2011 using data from three public sources: MEDAR-MEDATLAS, World Ocean Database, MFS-VOS program. Five procedures for estimating the mixed layer depth are described, discussed and compared using the 20-year long time series of temperature profiles of the DYFAMED station in the Ligurian Sea. On this basis the so-called three segments profile model (which approximates the upper water column with three segments representing mixed layer, thermocline and deep layer) has been selected for a systematic analysis at Mediterranean scale. A widespread increase of the thickness and temperature of the mixed layer, increase of the depth and decrease of the temperature of the thermocline base have been observed in summer and autumn during the recent decades. It is shown that positive temperature extremes of the mixed layer and of its thickness are potential drivers of the mass mortalities of benthic invertebrates documented since 1983. Hotspots of mixed layer anomalies have been also identified. These results refine previous analyses showing that ongoing and future warming of upper Mediterranean is likely to increase mass mortalities by producing environmental conditions beyond the limit of tolerance of some benthic species.

  13. CGILS Phase 2 LES intercomparison of response of subtropical marine low cloud regimes to CO 2 quadrupling and a CMIP3 composite forcing change: Large eddy simulation of cloud feedbacks

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Blossey, Peter N.; Bretherton, Christopher S.; Cheng, Anning

    We extended Phase 1 of the CGILS large-eddy simulation (LES) intercomparison in order to understand if subtropical marine boundary-layer clouds respond to idealized climate perturbations consistently in six LES models. Here the responses to quadrupled carbon dioxide (“fast adjustment”) and to a composite climate perturbation representative of CMIP3 multimodel mean 2×CO 2 near-equilibrium conditions are analyzed. As in Phase 1, the LES is run to equilibrium using specified steady summertime forcings representative of three locations in the Northeast Pacific Ocean in shallow well-mixed stratocumulus, decoupled stratocumulus, and shallow cumulus cloud regimes. Our results are generally consistent with a single-LES studymore » of Bretherton et al. (2013) on which this intercomparison was based. Both quadrupled CO 2 and the composite climate perturbation result in less cloud and a shallower boundary layer for all models in well-mixed stratocumulus and for all but a single LES in decoupled stratocumulus and shallow cumulus, corroborating similar findings from global climate models (GCMs). For both perturbations, the amount of cloud reduction varies across the models, but there is less intermodel scatter than in GCMs. Furthermore, the cloud radiative effect changes are much larger in the stratocumulus-capped regimes than in the shallow cumulus regime, for which precipitation buffering may damp the cloud response. In the decoupled stratocumulus and cumulus regimes, both the CO 2 increase and CMIP3 perturbations reduce boundary-layer decoupling, due to the shallowing of inversion height.« less

  14. CGILS Phase 2 LES intercomparison of response of subtropical marine low cloud regimes to CO 2 quadrupling and a CMIP3 composite forcing change: Large eddy simulation of cloud feedbacks

    DOE PAGES

    Blossey, Peter N.; Bretherton, Christopher S.; Cheng, Anning; ...

    2016-10-27

    We extended Phase 1 of the CGILS large-eddy simulation (LES) intercomparison in order to understand if subtropical marine boundary-layer clouds respond to idealized climate perturbations consistently in six LES models. Here the responses to quadrupled carbon dioxide (“fast adjustment”) and to a composite climate perturbation representative of CMIP3 multimodel mean 2×CO 2 near-equilibrium conditions are analyzed. As in Phase 1, the LES is run to equilibrium using specified steady summertime forcings representative of three locations in the Northeast Pacific Ocean in shallow well-mixed stratocumulus, decoupled stratocumulus, and shallow cumulus cloud regimes. Our results are generally consistent with a single-LES studymore » of Bretherton et al. (2013) on which this intercomparison was based. Both quadrupled CO 2 and the composite climate perturbation result in less cloud and a shallower boundary layer for all models in well-mixed stratocumulus and for all but a single LES in decoupled stratocumulus and shallow cumulus, corroborating similar findings from global climate models (GCMs). For both perturbations, the amount of cloud reduction varies across the models, but there is less intermodel scatter than in GCMs. Furthermore, the cloud radiative effect changes are much larger in the stratocumulus-capped regimes than in the shallow cumulus regime, for which precipitation buffering may damp the cloud response. In the decoupled stratocumulus and cumulus regimes, both the CO 2 increase and CMIP3 perturbations reduce boundary-layer decoupling, due to the shallowing of inversion height.« less

  15. A Water Model Study on Mixing Behavior of the Two-Layered Bath in Bottom Blown Copper Smelting Furnace

    NASA Astrophysics Data System (ADS)

    Shui, Lang; Cui, Zhixiang; Ma, Xiaodong; Jiang, Xu; Chen, Mao; Xiang, Yong; Zhao, Baojun

    2018-05-01

    The bottom-blown copper smelting furnace is a novel copper smelter developed in recent years. Many advantages of this furnace have been found, related to bath mixing behavior under its specific gas injection scheme. This study aims to use an oil-water double-phased laboratory-scale model to investigate the impact of industry-adjustable variables on bath mixing time, including lower layer thickness, gas flow rate, upper layer thickness and upper layer viscosity. Based on experimental results, an overall empirical relationship of mixing time in terms of these variables has been correlated, which provides the methodology for industry to optimize mass transfer in the furnace.

  16. Development of a personal dosimetry system based on optically stimulated luminescence of alpha-Al2O3:C for mixed radiation fields.

    PubMed

    Lee, S Y; Lee, K J

    2001-04-01

    To develop a personal optically stimulated luminescence (OSL) dosimetry system for mixed radiation fields using alpha-Al2O3:C, a discriminating badge filter system was designed by taking advantage of its optically stimulable properties and energy dependencies. This was done by designing a multi-element badge system for powder layered alpha-Al2O3:C material and an optical reader system based on high-intensity blue light-emitting diode (LED). The design of the multielement OSL dosimeter badge system developed allows the measurement of a personal dose equivalent value Hp(d) in mixed radiation fields of beta and gamma. Dosimetric properties of the personal OSL dosimeter badge system investigated here were the dose response, energy response and multi-readability. Based on the computational simulations and experiments of the proposed dosimeter design, it was demonstrated that a multi-element dosimeter system with an OSL technology based on alpha-Al2O3:C is suitable to obtain personal dose equivalent information in mixed radiation fields.

  17. Frontolysis by surface heat flux in the Agulhas Return Current region with a focus on mixed layer processes: observation and a high-resolution CGCM

    NASA Astrophysics Data System (ADS)

    Ohishi, Shun; Tozuka, Tomoki; Komori, Nobumasa

    2016-12-01

    Detailed mechanisms for frontogenesis/frontolysis of the Agulhas Return Current (ARC) Front, defined as the maximum of the meridional sea surface temperature (SST) gradient at each longitude within the ARC region (40°-50°E, 55°-35°S), are investigated using observational datasets. Due to larger (smaller) latent heat release to the atmosphere on the northern (southern) side of the front, the meridional gradient of surface net heat flux (NHF) is found throughout the year. In austral summer, surface warming is weaker (stronger) on the northern (southern) side, and thus the NHF tends to relax the SST front. The weaker (stronger) surface warming, at the same time, leads to the deeper (shallower) mixed layer on the northern (southern) side. This enhances the frontolysis, because deeper (shallower) mixed layer is less (more) sensitive to surface warming. In austral winter, stronger (weaker) surface cooling on the northern (southern) side contributes to the frontolysis. However, deeper (shallower) mixed layer is induced by stronger (weaker) surface cooling on the northern (southern) side and suppresses the frontolysis, because the deeper (shallower) mixed layer is less (more) sensitive to surface cooling. Therefore, the frontolysis by the NHF becomes stronger (weaker) through the mixed layer processes in austral summer (winter). The cause of the meridional gradient of mixed layer depth is estimated using diagnostic entrainment velocity and the Monin-Obukhov depth. Furthermore, the above mechanisms obtained from the observation are confirmed using outputs from a high-resolution coupled general circulation model. Causes of model biases are also discussed.

  18. Arctic Ocean Model Intercomparison Using Sound Speed

    NASA Astrophysics Data System (ADS)

    Dukhovskoy, D. S.; Johnson, M. A.

    2002-05-01

    The monthly and annual means from three Arctic ocean - sea ice climate model simulations are compared for the period 1979-1997. Sound speed is used to integrate model outputs of temperature and salinity along a section between Barrow and Franz Josef Land. A statistical approach is used to test for differences among the three models for two basic data subsets. We integrated and then analyzed an upper layer between 2 m - 50 m, and also a deep layer from 500 m to the bottom. The deep layer is characterized by low time-variability. No high-frequency signals appear in the deep layer having been filtered out in the upper layer. There is no seasonal signal in the deep layer and the monthly means insignificantly oscillate about the long-period mean. For the deep ocean the long-period mean can be considered quasi-constant, at least within the 19 year period of our analysis. Thus we assumed that the deep ocean would be the best choice for comparing the means of the model outputs. The upper (mixed) layer was chosen to contrast the deep layer dynamics. There are distinct seasonal and interannual signals in the sound speed time series in this layer. The mixed layer is a major link in the ocean - air interaction mechanism. Thus, different mean states of the upper layer in the models might cause different responses in other components of the Arctic climate system. The upper layer also strongly reflects any differences in atmosphere forcing. To compare data from the three models we have used a one-way t-test for the population mean, the Wilcoxon one-sample signed-rank test (when the requirement of normality of tested data is violated), and one-way ANOVA method and F-test to verify our hypothesis that the model outputs have the same mean sound speed. The different statistical approaches have shown that all models have different mean characteristics of the deep and upper layers of the Arctic Ocean.

  19. Nucleation and convection effects in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz (Principal Investigator)

    1996-01-01

    The following activities are reported on: repartitioning of NaCl and protein impurities in lysozyme crystallization; dependence of lysozyme growth kinetics on step sources and impurities; facet morphology response to nonuniformities in nutrient and impurity supply; interactions in undersaturated and supersaturated lysozyme solutions; heterogeneity determination and purification of commercial hen egg white lysozyme; nonlinear response of layer growth dynamics in the mixed kinetics-bulk transport regime; development of a simultaneous multiangle light scattering technique; and x-ray topography of tetragonal lysozyme grown by the temperature-control technique.

  20. The Climatological Seasonal Response of the Ocean Mixed Layer in the Equatorial and Tropical Pacific Ocean

    DTIC Science & Technology

    1988-03-01

    response of the ocean and the seasonal changes in atmospheric forcing. The pattern of 20 DiSTPIBUTION/ AVAILABILIT Y OF aRS7RACT 21 ABSTRACT SECURITY...Speed with M LD .............................. 50 3.20 Time Rate of Change of Heat in the Water Column at 155 oE Contour Interval is 35W m 2...52 3.21 Dilerence of Net Surface Heating ad Heat .* the Water Column at 155 oE

  1. Synoptic-to-planetary scale wind variability enhances phytoplankton biomass at ocean fronts

    NASA Astrophysics Data System (ADS)

    Whitt, D. B.; Taylor, J. R.; Lévy, M.

    2017-06-01

    In nutrient-limited conditions, phytoplankton growth at fronts is enhanced by winds, which drive upward nutrient fluxes via enhanced turbulent mixing and upwelling. Hence, depth-integrated phytoplankton biomass can be 10 times greater at isolated fronts. Using theory and two-dimensional simulations with a coupled physical-biogeochemical ocean model, this paper builds conceptual understanding of the physical processes driving upward nutrient fluxes at fronts forced by unsteady winds with timescales of 4-16 days. The largest vertical nutrient fluxes occur when the surface mixing layer penetrates the nutricline, which fuels phytoplankton in the mixed layer. At a front, mixed layer deepening depends on the magnitude and direction of the wind stress, cross-front variations in buoyancy and velocity at the surface, and potential vorticity at the base of the mixed layer, which itself depends on past wind events. Consequently, mixing layers are deeper and more intermittent in time at fronts than outside fronts. Moreover, mixing can decouple in time from the wind stress, even without other sources of physical variability. Wind-driven upwelling also enhances depth-integrated phytoplankton biomass at fronts; when the mixed layer remains shallower than the nutricline, this results in enhanced subsurface phytoplankton. Oscillatory along-front winds induce both oscillatory and mean upwelling. The mean effect of oscillatory vertical motion is to transiently increase subsurface phytoplankton over days to weeks, whereas slower mean upwelling sustains this increase over weeks to months. Taken together, these results emphasize that wind-driven phytoplankton growth is both spatially and temporally intermittent and depends on a diverse combination of physical processes.

  2. Observations of the Evolution of Turbulent Dissipation within the Ocean Surface Boundary Layer: an OSMOSIS study

    NASA Astrophysics Data System (ADS)

    Lucas, N. S.; Allen, J.; Belcher, S. E.; Boyd, T.; Brannigan, L.; Inall, M.; Palmer, M.; Polton, J.; Rippeth, T. P.

    2016-02-01

    This study presents a new 9.5 day dataset showing the evolution of the Ocean Surface Boundary Layer (OSBL) and dissipation of turbulence kinetic energy (TKE), carried out as part of OSMOSIS[i], at a location in the North East Atlantic Ocean in September 2012. The TKE dissipation measurements were made using three methods; (i) repeated profiling between 100m and the surface by an Ocean Microstructure glider, (ii) three series of profiles made using a loosely tethered velocity microstructure glider and (iii) a moored pulse-pulse coherent high frequency ADCP. Supporting measurements show the evolution of the water column structure, including surface wave measurements from a TRIAXYS wave buoy. This data shows two distinct regimes; the first, spanning 4 days with relatively low winds, displays a distinct diurnal cycle with the deepening of the active mixing layer during the night which shoaled during the day. The second spanned a significant storm, (with maximum winds speeds reaching 20 m s-1 and significant wave heights reaching 6 m), during which, rather than a deepening of the mixed layer as predicted by classical theory, the primary effect was a broadening of the transition layer, similar to that found by Dohan and Davies (2011). During the storm, significant dissipation was observed throughout the surface mixed layer and into the transition layer, driving fluxes of heat downwards through the base of the surface mixed layer. [i] Ocean Surface Mixing and Submesoscale Interaction Study Dohan, K. & Davis, R.E., 2011. Mixing in the Transition Layer during Two Storm Events. Journal of Physical Oceanography. 41 (1). pp. 42-66.

  3. Mixed layers of sodium caseinate + dextran sulfate: influence of order of addition to oil-water interface.

    PubMed

    Jourdain, Laureline S; Schmitt, Christophe; Leser, Martin E; Murray, Brent S; Dickinson, Eric

    2009-09-01

    We report on the interfacial properties of electrostatic complexes of protein (sodium caseinate) with a highly sulfated polysaccharide (dextran sulfate). Two routes were investigated for preparation of adsorbed layers at the n-tetradecane-water interface at pH = 6. Bilayers were made by the layer-by-layer deposition technique whereby polysaccharide was added to a previously established protein-stabilized interface. Mixed layers were made by the conventional one-step method in which soluble protein-polysaccharide complexes were adsorbed directly at the interface. Protein + polysaccharide systems gave a slower decay of interfacial tension and stronger dilatational viscoelastic properties than the protein alone, but there was no significant difference in dilatational properties between mixed layers and bilayers. Conversely, shear rheology experiments exhibited significant differences between the two kinds of interfacial layers, with the mixed system giving much stronger interfacial films than the bilayer system, i.e., shear viscosities and moduli at least an order of magnitude higher. The film shear viscoelasticity was further enhanced by acidification of the biopolymer mixture to pH = 2 prior to interface formation. Taken together, these measurements provide insight into the origin of previously reported differences in stability properties of oil-in-water emulsions made by the bilayer and mixed layer approaches. Addition of a proteolytic enzyme (trypsin) to both types of interfaces led to a significant increase in the elastic modulus of the film, suggesting that the enzyme was adsorbed at the interface via complexation with dextran sulfate. Overall, this study has confirmed the potential of shear rheology as a highly sensitive probe of associative electrostatic interactions and interfacial structure in mixed biopolymer layers.

  4. Coupling between lower-tropospheric convective mixing and low-level clouds: Physical mechanisms and dependence on convection scheme.

    PubMed

    Vial, Jessica; Bony, Sandrine; Dufresne, Jean-Louis; Roehrig, Romain

    2016-12-01

    Several studies have pointed out the dependence of low-cloud feedbacks on the strength of the lower-tropospheric convective mixing. By analyzing a series of single-column model experiments run by a climate model using two different convective parametrizations, this study elucidates the physical mechanisms through which marine boundary-layer clouds depend on this mixing in the present-day climate and under surface warming. An increased lower-tropospheric convective mixing leads to a reduction of low-cloud fraction. However, the rate of decrease strongly depends on how the surface latent heat flux couples to the convective mixing and to boundary-layer cloud radiative effects: (i) on the one hand, the latent heat flux is enhanced by the lower-tropospheric drying induced by the convective mixing, which damps the reduction of the low-cloud fraction, (ii) on the other hand, the latent heat flux is reduced as the lower troposphere stabilizes under the effect of reduced low-cloud radiative cooling, which enhances the reduction of the low-cloud fraction. The relative importance of these two different processes depends on the closure of the convective parameterization. The convective scheme that favors the coupling between latent heat flux and low-cloud radiative cooling exhibits a stronger sensitivity of low-clouds to convective mixing in the present-day climate, and a stronger low-cloud feedback in response to surface warming. In this model, the low-cloud feedback is stronger when the present-day convective mixing is weaker and when present-day clouds are shallower and more radiatively active. The implications of these insights for constraining the strength of low-cloud feedbacks observationally is discussed.

  5. Coupling between lower‐tropospheric convective mixing and low‐level clouds: Physical mechanisms and dependence on convection scheme

    PubMed Central

    Bony, Sandrine; Dufresne, Jean‐Louis; Roehrig, Romain

    2016-01-01

    Abstract Several studies have pointed out the dependence of low‐cloud feedbacks on the strength of the lower‐tropospheric convective mixing. By analyzing a series of single‐column model experiments run by a climate model using two different convective parametrizations, this study elucidates the physical mechanisms through which marine boundary‐layer clouds depend on this mixing in the present‐day climate and under surface warming. An increased lower‐tropospheric convective mixing leads to a reduction of low‐cloud fraction. However, the rate of decrease strongly depends on how the surface latent heat flux couples to the convective mixing and to boundary‐layer cloud radiative effects: (i) on the one hand, the latent heat flux is enhanced by the lower‐tropospheric drying induced by the convective mixing, which damps the reduction of the low‐cloud fraction, (ii) on the other hand, the latent heat flux is reduced as the lower troposphere stabilizes under the effect of reduced low‐cloud radiative cooling, which enhances the reduction of the low‐cloud fraction. The relative importance of these two different processes depends on the closure of the convective parameterization. The convective scheme that favors the coupling between latent heat flux and low‐cloud radiative cooling exhibits a stronger sensitivity of low‐clouds to convective mixing in the present‐day climate, and a stronger low‐cloud feedback in response to surface warming. In this model, the low‐cloud feedback is stronger when the present‐day convective mixing is weaker and when present‐day clouds are shallower and more radiatively active. The implications of these insights for constraining the strength of low‐cloud feedbacks observationally is discussed. PMID:28239438

  6. Computation of turbulent high speed mixing layers using a two-equation turbulence model

    NASA Technical Reports Server (NTRS)

    Narayan, J. R.; Sekar, B.

    1991-01-01

    A two-equation turbulence model was extended to be applicable for compressible flows. A compressibility correction based on modelling the dilational terms in the Reynolds stress equations were included in the model. The model is used in conjunction with the SPARK code for the computation of high speed mixing layers. The observed trend of decreasing growth rate with increasing convective Mach number in compressible mixing layers is well predicted by the model. The predictions agree well with the experimental data and the results from a compressible Reynolds stress model. The present model appears to be well suited for the study of compressible free shear flows. Preliminary results obtained for the reacting mixing layers are included.

  7. Forced free-shear layer measurements

    NASA Technical Reports Server (NTRS)

    Leboeuf, Richard L.

    1994-01-01

    Detailed three-dimensional three-component phase averaged measurements of the spanwise and streamwise vorticity formation and evolution in acoustically forced plane free-shear flows have been obtained. For the first time, phase-averaged measurements of all three velocity components have been obtained in both a mixing layer and a wake on three-dimensional grids, yielding the spanwise and streamwise vorticity distributions without invoking Taylor's hypothesis. Initially, two-frequency forcing was used to phase-lock the roll-up and first pairing of the spanwise vortical structures in a plane mixing layer. The objective of this study was to measure the near-field vortical structure morphology in a mixing layer with 'natural' laminar initial boundary layers. For the second experiment the second and third subharmonics of the fundamental roll-up frequency were added to the previous two-frequency forcing in order to phase-lock the roll-up and first three pairings of the spanwise rollers in the mixing layer. The objective of this study was to determine the details of spanwise scale changes observed in previous time-averaged measurements and flow visualization of unforced mixing layers. For the final experiment, single-frequency forcing was used to phase-lock the Karman vortex street in a plane wake developing from nominally two-dimensional laminar initial boundary layers. The objective of this study was to compare measurements of the three-dimensional structure in a wake developing from 'natural' initial boundary layers to existing models of wake vortical structure.

  8. Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms

    NASA Astrophysics Data System (ADS)

    Sednev, I.; Menon, S.; McFarquhar, G.

    2008-06-01

    The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM) scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE) campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP) on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9th-10th October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity) against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process of ice phase initiation due to freezing of supercooled water in both saturated and undersaturated (w.r.t. water) environments is as important as primary ice crystal origination from water vapor. We also find that the BFP is a process mainly responsible for the rates of glaciation of simulated clouds. These glaciation rates cannot be adequately represented by a water-ice saturation adjustment scheme that only depends on temperature and liquid and solid hydrometeors' contents as is widely used in bulk microphysics schemes and are better represented by processes that also account for supersaturation changes as the hydrometeors grow.

  9. Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms

    NASA Astrophysics Data System (ADS)

    Sednev, I.; Menon, S.; McFarquhar, G.

    2009-07-01

    The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM) scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE) campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP) on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9-10 October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity) against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process of ice phase initiation due to freezing of supercooled water in both saturated and subsaturated (w.r.t. water) environments is as important as primary ice crystal origination from water vapor. We also find that the BFP is a process mainly responsible for the rates of glaciation of simulated clouds. These glaciation rates cannot be adequately represented by a water-ice saturation adjustment scheme that only depends on temperature and liquid and solid hydrometeors' contents as is widely used in bulk microphysics schemes and are better represented by processes that also account for supersaturation changes as the hydrometeors grow.

  10. Seasonal cycle of oceanic mixed layer and upper-ocean heat fluxes in the Mediterranean Sea from in-situ observations.

    NASA Astrophysics Data System (ADS)

    Houpert, Loïc; Testor, Pierre; Durrieu de Madron, Xavier; Estournel, Claude; D'Ortenzio, Fabrizio

    2013-04-01

    Heat fluxes across the ocean-atmosphere interface play a crucial role in the upper turbulent mixing. The depth reached by this turbulent mixing is indicated by an homogenization of seawater properties in the surface layer, and is defined as the Mixed Layer Depth (MLD). The thickness of the mixed layer determines also the heat content of the layer that directly interacts with the atmosphere. The seasonal variability of these air-sea fluxes is crucial in the calculation of heat budget. An improvement in the estimate of these fluxes is needed for a better understanding of the Mediterranean ocean circulation and climate, in particular in Regional Climate Models. There are few estimations of surface heat fluxes based on oceanic observations in the Mediterranean, and none of them are based on mixed layer observations. So, we proposed here new estimations of these upper-ocean heat fluxes based on mixed layer. We present high resolution Mediterranean climatology (0.5°) of the mean MLD based on a comprehensive collection of temperature profiles of last 43 years (1969-2012). The database includes more than 150,000 profiles, merging CTD, XBT, ARGO Profiling floats, and gliders observations. This dataset is first used to describe the seasonal cycle of the mixed layer depth on the whole Mediterranean on a monthly climatological basis. Our analysis discriminates several regions with coherent behaviors, in particular the deep water formation sites, characterized by significant differences in the winter mixing intensity. Heat storage rates (HSR) were calculated as the time rate of change of the heat content integrated from the surface down to a specific depth that is defined as the MLD plus an integration constant. Monthly climatology of net heat flux (NHF) from ERA-Interim reanalysis was balanced by the 1°x1° resolution heat storage rate climatology. Local heat budget balance and seasonal variability in the horizontal heat flux are then discussed by taking into account uncertainties, due to errors in monthly value estimation and to intra-annual and inter-annual variability.

  11. Mixed layer warming-deepening in the Mediterranean Sea and its effect on the marine environment

    NASA Astrophysics Data System (ADS)

    Rivetti, Irene; Boero, Ferdinando; Fraschetti, Simonetta; Zambianchi, Enrico; Lionello, Piero

    2015-04-01

    This work aims at investigating the evolution of the ocean mixed layer in the Mediterranean Sea and linking it to the occurrence of mass mortalities of benthic invertebrates. The temporal evolution of selected parameters describing the mixed layer and the seasonal thermocline is provided for the whole Mediterranean Sea for spring, summer and autumn and for the period 1945-2011. For this analysis all temperature profiles collected in the basin with bottles, Mechanical Bathy-Thermographs (MBT), eXpendable Bathy-Thermographs (XBT), and Conductivity-Temperature-Depth (CTD) have been used (166,990). These data have been extracted from three public sources: the MEDAR-MEDATLAS, the World Ocean Database 2013 and the MFS-VOS program. Five different methods for estimating the mixed layer depth are compared using temperature profiles collected at the DYFAMED station in the Ligurian Sea and one method, the so-called three-segment method, has been selected for a systematic analysis of the evolution of the uppermost part of the whole Mediterranean Sea. This method approximates the upper water column with three segments representing mixed layer, thermocline and deep layer and has shown to be the most suitable method for capturing the mixed layer depth for most shapes of temperature profiles. Mass mortalities events of benthic invertebrates have been identified by an extensive search of all data bases in ISI Web of Knowledge considering studies published from 1945 to 2011. Studies reporting the geographical coordinates, the timing of the events, the species involved and the depth at which signs of stress occurred have been considered. Results show a general increase of thickness and temperature of the mixed layer, deepening and cooling of the thermocline base in summer and autumn. Possible impacts of these changes are mass mortalities events of benthic invertebrates that have been documented since 1983 mainly in summer and autumn. It is also shown that most mass mortalities occurred in months with anomalously high mixed layer depth temperature leading to the conclusion that warming of upper Mediterranean Sea has allowed interannual temperature variability to reach environmental conditions beyond the thermal tolerance of some species.

  12. Response of the Atmospheric Boundary Layer and Soil Layer to a High Altitude, Dense Aerosol Cover.

    NASA Astrophysics Data System (ADS)

    Garratt, J. R.; Pittock, A. B.; Walsh, K.

    1990-01-01

    The response of the atmospheric boundary layer to the appearance of a high-altitude smoke layer has been investigated in a mesoscale numerical model of the atmosphere. Emphasis is placed on the changes in mean boundary-layer structure and near-surface temperatures when smoke of absorption optical depth (AOD) in the, range 0 to 1 is introduced. Calculations have been made at 30°S, for different soil thermal properties and degrees of surface wetness, over a time period of several days during which major smoke-induced cooling occurs. The presence of smoke reduces the daytime mixed-layer depth and, for large enough values of AOD, results in a daytime surface inversion with large cooling confined to heights of less than a few hundred meters. Smoke-induced reductions in daytime soil and air temperatures of several degrees are typical, dependent critically upon soil wetness and smoke AOD. Locations near the coast experience reduced cooling whenever there is a significant onshore flow related to a sea breeze (this would also be the case with a large-scale onshore flow). The sea breeze itself disappears for large enough smoke AOD and, over sloping coastal terrain, a smoke-induced, offshore drainage flow may exist throughout the diurnal cycle.

  13. Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

    NASA Astrophysics Data System (ADS)

    Cronin, M. F.; Pelland, N.; Emerson, S. R.; Crawford, W. R.

    2015-12-01

    Data from two National Oceanographic and Atmospheric Administration (NOAA) surface moorings in the North Pacific, in combination with data from satellite, Argo floats and glider (when available), are used to evaluate the residual diffusive flux of heat across the base of the mixed layer from the surface mixed layer heat budget. The diffusion coefficient (i.e., diffusivity) is then computed by dividing the diffusive flux by the temperature gradient in the 20-m transition layer just below the base of the mixed layer. At Station Papa in the NE Pacific subpolar gyre, this diffusivity is 1×10-4 m2/s during summer, increasing to ~3×10-4 m2/s during fall. During late winter and early spring, diffusivity has large errors. At other times, diffusivity computed from the mixed layer salt budget at Papa correlate with those from the heat budget, giving confidence that the results are robust for all seasons except late winter-early spring and can be used for other tracers. In comparison, at the Kuroshio Extension Observatory (KEO) in the NW Pacific subtropical recirculation gyre, somewhat larger diffusivity are found based upon the mixed layer heat budget: ~ 3×10-4 m2/s during the warm season and more than an order of magnitude larger during the winter, although again, wintertime errors are large. These larger values at KEO appear to be due to the increased turbulence associated with the summertime typhoons, and weaker wintertime stratification.

  14. Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

    NASA Astrophysics Data System (ADS)

    Cronin, Meghan F.; Pelland, Noel A.; Emerson, Steven R.; Crawford, William R.

    2015-11-01

    Data from two National Oceanographic and Atmospheric Administration (NOAA) surface moorings in the North Pacific, in combination with data from satellite, Argo floats and glider (when available), are used to evaluate the residual diffusive flux of heat across the base of the mixed layer from the surface mixed layer heat budget. The diffusion coefficient (i.e., diffusivity) is then computed by dividing the diffusive flux by the temperature gradient in the 20 m transition layer just below the base of the mixed layer. At Station Papa in the NE Pacific subpolar gyre, this diffusivity is 1 × 10-4 m2/s during summer, increasing to ˜3 × 10-4 m2/s during fall. During late winter and early spring, diffusivity has large errors. At other times, diffusivity computed from the mixed layer salt budget at Papa correlate with those from the heat budget, giving confidence that the results are robust for all seasons except late winter-early spring and can be used for other tracers. In comparison, at the Kuroshio Extension Observatory (KEO) in the NW Pacific subtropical recirculation gyre, somewhat larger diffusivities are found based upon the mixed layer heat budget: ˜ 3 × 10-4 m2/s during the warm season and more than an order of magnitude larger during the winter, although again, wintertime errors are large. These larger values at KEO appear to be due to the increased turbulence associated with the summertime typhoons, and weaker wintertime stratification.

  15. Impact and Ballistic Response of Hybridized Thermoplastic Laminates

    DTIC Science & Technology

    2011-02-01

    hybrid panels exhibit the lowest dynamic and residual deflection through all samples. Kevlar and [0/90] HB25 layup are similar in performance...HB25 + 2 Layer K705 Phenolic 1422.00 15.646 15.1638 Shot on Aramid Face 60/40 Mix HB25/LF1 1424.06 15.646 16.256 Shot on HB25 Face Dyneema HB80...Carbon 1420.46 16.764 16.3576 Shot on Carbon Face HB25 + 3-ply LF1 1427.38 16.866 18.4404 Shot on LF1 Face HB25 + 2 Layer K745 Phenolic 1418.00

  16. A Two-Timescale Response to Ozone Depletion: Importance of the Background State

    NASA Astrophysics Data System (ADS)

    Seviour, W.; Waugh, D.; Gnanadesikan, A.

    2015-12-01

    It has been recently suggested that the response of Southern Ocean sea-ice extent to stratospheric ozone depletion is time-dependent; that the ocean surface initially cools due to enhanced northward Ekman drift caused by a poleward shift in the eddy-driven jet, and then warms after some time due to upwelling of warm waters from below the mixed layer. It is therefore possible that ozone depletion could act to favor a short-term increase in sea-ice extent. However, many uncertainties remain in understanding this mechanism, with different models showing widely differing time-scales and magnitudes of the response. Here, we analyze an ensemble of coupled model simulations with a step-function ozone perturbation. The two-timescale response is present with an approximately 30 year initial cooling period. The response is further shown to be highly dependent upon the background ocean temperature and salinity stratification, which is influenced by both natural internal variability and the isopycnal eddy mixing parameterization. It is suggested that the majority of inter-model differences in the Southern Ocean response to ozone depletion is caused by differences in stratification.

  17. Boundary layer ozone - An airborne survey above the Amazon Basin

    NASA Technical Reports Server (NTRS)

    Gregory, Gerald L.; Browell, Edward V.; Warren, Linda S.

    1988-01-01

    Ozone data obtained over the forest canopy of the Amazon Basin during July and August 1985 in the course of NASA's Amazon Boundary Layer Experiment 2A are discussed, and ozone profiles obtained during flights from Belem to Tabatinga, Brazil, are analyzed to determine any cross-basin effects. The analyses of ozone data indicate that the mixed layer of the Amazon Basin, for the conditions of undisturbed meteorology and in the absence of biomass burning, is a significant sink for tropospheric ozone. As the coast is approached, marine influences are noted at about 300 km inland, and a transition from a forest-controlled mixed layer to a marine-controlled mixed layer is noted.

  18. Upper Ocean Inertial Currents Forced by a Strong Storm. I: Mixed Layer. II: Propagation into the Thermocline

    DTIC Science & Technology

    1993-12-20

    inertial waves during OCEAN STORMS. (this volume) Sanford, T. B., P. G. Black, J. R. Haustein , J. W. Feeney, G. Z. Forristall, and J. F. Price, 1987...J. R. Haustein , J. W. Feeney, G.Z. Forristall, J. F. Price, 1987: Ocean response to a hurricane, Part I: Observations. J. Phys. Oceanogr., 17, 2065

  19. Using a hybrid model to predict solute transfer from initially saturated soil into surface runoff with controlled drainage water.

    PubMed

    Tong, Juxiu; Hu, Bill X; Yang, Jinzhong; Zhu, Yan

    2016-06-01

    The mixing layer theory is not suitable for predicting solute transfer from initially saturated soil to surface runoff water under controlled drainage conditions. By coupling the mixing layer theory model with the numerical model Hydrus-1D, a hybrid solute transfer model has been proposed to predict soil solute transfer from an initially saturated soil into surface water, under controlled drainage water conditions. The model can also consider the increasing ponding water conditions on soil surface before surface runoff. The data of solute concentration in surface runoff and drainage water from a sand experiment is used as the reference experiment. The parameters for the water flow and solute transfer model and mixing layer depth under controlled drainage water condition are identified. Based on these identified parameters, the model is applied to another initially saturated sand experiment with constant and time-increasing mixing layer depth after surface runoff, under the controlled drainage water condition with lower drainage height at the bottom. The simulation results agree well with the observed data. Study results suggest that the hybrid model can accurately simulate the solute transfer from initially saturated soil into surface runoff under controlled drainage water condition. And it has been found that the prediction with increasing mixing layer depth is better than that with the constant one in the experiment with lower drainage condition. Since lower drainage condition and deeper ponded water depth result in later runoff start time, more solute sources in the mixing layer are needed for the surface water, and larger change rate results in the increasing mixing layer depth.

  20. Medium-Index Mixed-Oxide Layers for Use in AR-Coatings

    NASA Astrophysics Data System (ADS)

    Ganner, Peter

    1986-10-01

    Ttedesign philosophy of MC-AR-Coatings can be divided into two categories: a) Restriction to two film materials, namely one high-index and one low-index material and b) Use of medium-index layers in addition to high- and low-index layers. Both philosophies have advan-tages and drawbacks. In case a) the total number of layers necessary to obtain a required reflectance curve has to be higher. Thus in case of production errors it can be a problem to find out which layer was responsible for a deviation of the measured reflectance from the nominal one. In case b) using more than two materials reduces the total number of layers and consequently, pinpointing the cause of even small production errors is made simpler. Unfortunately there are not many materials commercially available which can be used to make hard, durable and robust films in the medium-index range namely between n=1.65 and n=2.00. In this paper the results of homogeneous mixtures of Alumina (Al203) and Tantala (Ta205) used for EB-gun evaporated medium-index films in AR-coatings is presented. It is shown that by proper adjustment of the weight percentages of the oxide mixture one can get homogeneous films in this index range. A number of design examples show the favourable application of such layers in AR-coatings. Among the most important ones is the well known QHQ-design for BBAR-coatings as well as AR-designs of the multiple half wave type with extended bandwidth. Further applications of the mixed-oxide layers are AR-coatings for cemented optical elements and beam splitters.

  1. LIF measurements of scalar mixing in turbulent shear layers

    NASA Technical Reports Server (NTRS)

    Karasso, Paris S.; Mungal, M. G.

    1993-01-01

    The structure of shear layer flows at high Reynolds numbers remains a very interesting problem. Straight mixing layers have been studied and yielded information on the probability density function (pdf) of a passive scalar across the layer. Konrad and Koochesfahani & Dimotakis measured the pdf of the mixture fraction for mixing layers of moderate Reynolds numbers, each about 25,000 (Re based on velocity difference and visual thickness). Their measurements showed a 'non-marching' pdf (central hump which is invariant from edge to edge across the layer), a result which is linked to the visualizations of the spanwise Kelvin-Helmholtz (K-H) instability mode, which is the primary instability for plane shear layer flows. A secondary instability mode, the Taylor-Gortler (T-G) instability, which is associated with streamwise vortical structures, has also been observed in shear layers. Image reconstruction by Jimenez et al. and volume renderings by Karasso & Mungal at low Re numbers have demonstrated that the K-H and the T-G instability modes occur simultaneously in a non-mutually destructive way, evidence that supports the quasi two-dimensional aspect of these flows and the non-marching character of the pdf at low Reynolds numbers. At higher Re numbers though, the interaction of these two instability modes is still unclear and may affect the mixing process. In this study, we perform measurements of the concentration pdf of plane mixing layers for different operating conditions. At a speed ratio of r = U(sub 1)/U(sub 2) = 4:1, we examine three Reynolds number cases: Re = 14,000, Re = 31,000, and Re = 62,000. Some other Re number cases' results, not presented in detail, are invoked to explain the behavior of the pdf of the concentration field. A case of r = 2.6:1 at Re = 20,000 is also considered. The planar laser-induced fluorescence technique is used to yield quantitative measurements. The different Re are obtained by changing the velocity magnitudes of the two streams. The question of resolution of these measurements is addressed. In order to investigate the effects of the initial conditions on the development and the structure of the mixing layer, the boundary layer on the high-speed side of the splitter plate is tripped. The average concentration and the average mixed fluid concentration are also calculated to further understand the changes in the shear layer for the different cases examined.

  2. Lidar Characterization of Boundary Layer Transport and Mixing for Estimating Urban-Scale Greenhouse Gas Emissions

    NASA Astrophysics Data System (ADS)

    Hardesty, R. Michael; Brewer, W. Alan; Sandberg, Scott P.; Weickmann, Ann M.; Shepson, Paul B.; Cambaliza, Maria; Heimburger, Alexie; Davis, Kenneth J.; Lauvaux, Thomas; Miles, Natasha L.; Sarmiento, Daniel P.; Deng, A. J.; Gaudet, Brian; Karion, Anna; Sweeney, Colm; Whetstone, James

    2016-06-01

    A compact commercial Doppler lidar has been deployed in Indianapolis for two years to measure wind profiles and mixing layer properties as part of project to improve greenhouse measurements from large area sources. The lidar uses vertical velocity variance and aerosol structure to measure mixing layer depth. Comparisons with aircraft and the NOAA HRDL lidar generally indicate good performance, although sensitivity might be an issue under low aerosol conditions.

  3. Characteristics of the nocturnal boundary layer inferred from ozone measurements onboard a Zeppelin airship

    NASA Astrophysics Data System (ADS)

    Rohrer, Franz; Li, Xin; Hofzumahaus, Andreas; Ehlers, Christian; Holland, Frank; Klemp, Dieter; Lu, Keding; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas

    2014-05-01

    The nocturnal boundary layer (NBL) is a sublayer within the planetary boundary layer (PBL) which evolves above solid land each day in the late afternoon due to radiation cooling of the surface. It is a region of several hundred meters thickness which inhibits vertical mixing. A residual and a surface layer remain above and below the NBL. Inside the surface layer, almost all direct emissions of atmospheric constituents take place during this time. This stratification lasts until the next morning after sunrise. Then, the heating of the surface generates a new convectionally mixed layer which successively eats up the NBL from below. This process lasts until shortly before noon when the NBL disappears completely and the PBL is mixed convectionally. Ozone measurements onboard a Zeppelin airship in The Netherlands, in Italy, and in Finland are used to analyse this behaviour with respect to atmospheric constituents and consequences for the diurnal cycles observed in the surface layer, the nocturnal boundary layer, and the residual layer are discussed.

  4. TEM and STEM Studies on the Cross-sectional Morphologies of Dual-/Tri-layer Broadband SiO2 Antireflective Films

    NASA Astrophysics Data System (ADS)

    Wang, Shuangyue; Yan, Hongwei; Li, Dengji; Qiao, Liang; Han, Shaobo; Yuan, Xiaodong; Liu, Wei; Xiang, Xia; Zu, Xiaotao

    2018-02-01

    Dual-layer and tri-layer broadband antireflective (AR) films with excellent transmittance were successfully fabricated using base-/acid-catalyzed mixed sols and propylene oxide (PO) modified silica sols. The sols and films were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), transmission electron microscope (TEM), and scanning transmission electron microscope (STEM). FTIR and TEM results suggest that the PO molecules were covalently bonded to the silica particles and the bridge structure existing in PO modified silica sol is responsible for the low density of the top layer. The density ratio between different layers was measured by cross-sectional STEM, and the results are 1.69:1 and 2.1:1.7:1 from bottom-layer to top-layer for dual-layer and tri-layer films, respectively. The dual-layer film demonstrates good stability with 99.8% at the central wavelength of 351 nm and nearly 99.5% at the central wavelength of 1053 nm in laser system, and for the tri-layer AR film, the maximum transmittance reached nearly 100% at both the central wavelengths of 527 and 1053 nm.

  5. Turbulent mixing layers in the interstellar medium of galaxies

    NASA Technical Reports Server (NTRS)

    Slavin, J. D.; Shull, J. M.; Begelman, M. C.

    1993-01-01

    We propose that turbulent mixing layers are common in the interstellar medium (ISM). Injection of kinetic energy into the ISM by supernovae and stellar winds, in combination with density and temperature inhomogeneities, results in shear flows. Such flows will become turbulent due to the high Reynolds number (low viscosity) of the ISM plasma. These turbulent boundary layers will be particularly interesting where the shear flow occurs at boundaries of hot (approximately 10(exp 6) K) and cold or warm (10(exp 2) - 10(exp 4) K) gas. Mixing will occur in such layers producing intermediate-temperature gas at T is approximately equal to 10(exp 5.0) - 10(exp 5.5) that radiates strongly in the optical, ultraviolet, and EUV. We have modeled these layers under the assumptions of rapid mixing down to the atomic level and steady flow. By including the effects of non-equilibrium ionization and self-photoionization of the gas as it cools after mixing, we predict the intensities of numerous optical, infrared, and ultraviolet emission lines, as well as absorption column densities of C 4, N 5, Si 4, and O 6.

  6. The use of Argo for validation and tuning of mixed layer models

    NASA Astrophysics Data System (ADS)

    Acreman, D. M.; Jeffery, C. D.

    We present results from validation and tuning of 1-D ocean mixed layer models using data from Argo floats and data from Ocean Weather Station Papa (145°W, 50°N). Model tests at Ocean Weather Station Papa showed that a bulk model could perform well provided it was tuned correctly. The Large et al. [Large, W.G., McWilliams, J.C., Doney, S.C., 1994. Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterisation. Rev. Geophys. 32 (Novermber), 363-403] K-profile parameterisation (KPP) model also gave a good representation of mixed layer depth provided the vertical resolution was sufficiently high. Model tests using data from a single Argo float indicated a tendency for the KPP model to deepen insufficiently over an annual cycle, whereas the tuned bulk model and general ocean turbulence model (GOTM) gave a better representation of mixed layer depth. The bulk model was then tuned using data from a sample of Argo floats and a set of optimum parameters was found; these optimum parameters were consistent with the tuning at OWS Papa.

  7. Simulating and understanding the gap outflow and oceanic response over the Gulf of Tehuantepec during GOTEX

    NASA Astrophysics Data System (ADS)

    Hong, Xiaodong; Peng, Melinda; Wang, Shouping; Wang, Qing

    2018-06-01

    Tehuantepecer is a strong mountain gap wind traveling through Chivela Pass into eastern Pacific coast in southern Mexico, most commonly between October and February and brings huge impacts on local and surrounding meteorology and oceanography. Gulf of Tehuantepec EXperiment (GOTEX) was conducted in February 2004 to enhance the understanding of the strong offshore gap wind, ocean cooling, vertical circulations and interactions among them. The gap wind event during GOTEX was simulated using the U.S. Navy Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®). The simulations are compared and validated with the observations retrieved from several satellites (GOES 10-12, MODIS/Aqua/Terra, TMI, and QuikSCAT) and Airborne EXpendable BathyThermograph (AXBT). The study shows that the gap wind outflow has a fanlike pattern expending from the coast and with a strong diurnal variability. The surface wind stress and cooling along the axis of the gap wind outflow caused intense upwelling and vertical mixing in the upper ocean; both contributed to the cooling of the ocean mixed layer under the gap wind. The cooling pattern of sea surface temperature (SST) also reflects temperature advection by the nearby ocean eddies to have a crescent shape. Two sensitivity experiments were conducted to understand the relative roles of the wind stress and heat flux on the ocean cooling. The control has more cooling right under the gap flow region than either the wind-stress-only or the heat-flux-only experiment. Overall, the wind stress has a slightly larger effect in bringing down the ocean temperature near the surface and plays a more important role in local ocean circulations beneath the mixed layer. The impact of surface heat flux on the ocean is more limited to the top 30 m within the mixed layer and is symmetric to the gap flow region by cooling the ocean under the gap flow region and reducing the warming on both sides. The effect of surface wind stress is to induce more cooling in the mixed layer under the gap wind through upwelling associated with Ekman divergence at the surface. Its effect deeper down is antisymmetric related to the nearby thermocline dome by inducing more upwelling to the east side of the gap flow region and more downwelling on the west side. Diagnostics from the mixed layer heat budget for the control and sensitivity experiments confirm that the surface heat flux has more influence on the broader area and the wind stress has more influence in a deeper region.

  8. Tropical Cyclone Induced Air-Sea Interactions Over Oceanic Fronts

    NASA Astrophysics Data System (ADS)

    Shay, L. K.

    2012-12-01

    Recent severe tropical cyclones underscore the inherent importance of warm background ocean fronts and their interactions with the atmospheric boundary layer. Central to the question of heat and moisture fluxes, the amount of heat available to the tropical cyclone is predicated by the initial mixed layer depth and strength of the stratification that essentially set the level of entrainment mixing at the base of the mixed layer. In oceanic regimes where the ocean mixed layers are thin, shear-induced mixing tends to cool the upper ocean to form cold wakes which reduces the air-sea fluxes. This is an example of negative feedback. By contrast, in regimes where the ocean mixed layers are deep (usually along the western part of the gyres), warm water advection by the nearly steady currents reduces the levels of turbulent mixing by shear instabilities. As these strong near-inertial shears are arrested, more heat and moisture transfers are available through the enthalpy fluxes (typically 1 to 1.5 kW m-2) into the hurricane boundary layer. When tropical cyclones move into favorable or neutral atmospheric conditions, tropical cyclones have a tendency to rapidly intensify as observed over the Gulf of Mexico during Isidore and Lili in 2002, Katrina, Rita and Wilma in 2005, Dean and Felix in 2007 in the Caribbean Sea, and Earl in 2010 just north of the Caribbean Islands. To predict these tropical cyclone deepening (as well as weakening) cycles, coupled models must have ocean models with realistic ocean conditions and accurate air-sea and vertical mixing parameterizations. Thus, to constrain these models, having complete 3-D ocean profiles juxtaposed with atmospheric profiler measurements prior, during and subsequent to passage is an absolute necessity framed within regional scale satellite derived fields.

  9. Investigating land-atmosphere coupling and convective triggering associated with the moistening of the northern North American Great Plains

    NASA Astrophysics Data System (ADS)

    Gerken, Tobias; Bromley, Gabriel; Stoy, Paul

    2017-04-01

    Parts of the North American northern Great Plains have undergone a 6 W m-2 decrease in summertime radiative forcing. At the same time agricultural practices have shifted from keeping fields fallow during the summer ("summer fallow") towards no-till cropping systems that increase summertime evapotranspiration and decrease soil carbon loss. MERRA (Modern-Era Retrospective analysis for Research and Applications) for the area near Fort Peck, Montana, (a FLUXNET site established in 2000) shows a decrease of summertime (June-August) sensible heat fluxes ranging from -3.6 to -8.5 W m-2 decade-1, which is associated with an increase of latent heat fluxes of similar magnitude (5.2-9.1 W m-2 decade-1). While net radiation changed little, increasing downward longwave radiation (2.2-4.6 W m-2 decade-1) due to greater cloud cover, was mostly compensated by reduced solar irradiance. The result was a strong decrease of summer Bowen ratios from 1.5-2 in 1980 to approximately 1-1.25 in 2015. At the same time, atmospheric soundings have shown significant increases in both convective available convective energy (CAPE) and convective inhibition (CIN) for the same time span. Overall, these findings are consistent with the effects on increased summertime evapotranspiration due to reduction in summer fallow that should lead to smaller Bowen ratios and a larger build-up of moist static energy as expressed in higher values of CAPE. In order to further investigate the impact of the surface energy balance and flux partitioning on convective development and local land-atmosphere coupling in the North American prairies, a 1-dimensional mixed-layer model is used to compare the evolution of mixed-layer heights to the lifted condensation level, a necessary but not sufficient condition for the occurrence of convective precipitation. Using summertime eddy covariance data from Fort Peck and atmospheric soundings from the nearby Glasgow airport, we establish that the mixed-layer model adequately captures mixed-layer heights and timing of locally triggered convection at the site. The model is then used to quantify the sensitivity of mixing-layer height, CAPE and convective triggering potential, in response to changes in surface flux partitioning between latent and sensible heat due to changes in soil moisture and agricultural management. Results are used to establish the exact nature or land-atmosphere coupling associated with moistening of the atmospheric boundary-layer and increases in convective triggering and will contribute to disentangling local and regional effects on trends in observed precipitation in the northern Great Plains.

  10. Importance of deep mixing and silicic acid in regulating phytoplankton biomass and community in the iron-limited Antarctic Polar Front region in summer

    NASA Astrophysics Data System (ADS)

    Cheah, Wee; Soppa, Mariana A.; Wiegmann, Sonja; Ossebaar, Sharyn; Laglera, Luis M.; Strass, Volker H.; Santos-Echeandía, Juan; Hoppema, Mario; Wolf-Gladrow, Dieter; Bracher, Astrid

    2017-04-01

    Phytoplankton community structure and their physiological response in the vicinity of the Antarctic Polar Front (APF; 44°S to 53°S, centred at 10°E) were investigated as part of the ANT-XXVIII/3 Eddy-Pump cruise conducted in austral summer 2012. Our results show that under iron-limited (< 0.3 μmolm-3) conditions, high total chlorophyll-a (TChl-a) concentrations (> 0.6 mgm-3) can be observed at stations with deep mixed layer (> 60 m) across the APF. In contrast, light was excessive at stations with shallower mixed layer and phytoplankton were producing higher amounts of photoprotective pigments, diadinoxanthin (DD) and diatoxanthin (DT), at the expense of TChl-a, resulting in higher ratios of (DD+DT)/TChl-a. North of the APF, significantly lower silicic acid (Si(OH)4) concentrations (< 2 mmolm-3) lead to the domination of nanophytoplankton consisting mostly of haptophytes, which produced higher ratios of (DD+DT)/TChl-a under relatively low irradiance conditions. The Si(OH)4 replete (> 5 mmolm-3) region south of the APF, on the contrary, was dominated by microphytoplankton (diatoms and dinoflagellates) with lower ratios of (DD+DT)/TChl-a, despite having been exposed to higher levels of irradiance. The significant correlation between nanophytoplankton and (DD+DT)/TChl-a indicates that differences in taxon-specific response to light are also influencing TChl-a concentration in the APF during summer. Our results reveal that provided mixing is deep and Si(OH)4 is replete, TChl-a concentrations higher than 0.6 mgm-3 are achievable in the iron-limited APF waters during summer.

  11. Curtailing effect of awakening on visual responses of cortical neurons by cholinergic activation of inhibitory circuits.

    PubMed

    Kimura, Rui; Safari, Mir-Shahram; Mirnajafi-Zadeh, Javad; Kimura, Rie; Ebina, Teppei; Yanagawa, Yuchio; Sohya, Kazuhiro; Tsumoto, Tadaharu

    2014-07-23

    Visual responsiveness of cortical neurons changes depending on the brain state. Neural circuit mechanism underlying this change is unclear. By applying the method of in vivo two-photon functional calcium imaging to transgenic rats in which GABAergic neurons express fluorescent protein, we analyzed changes in visual response properties of cortical neurons when animals became awakened from anesthesia. In the awake state, the magnitude and reliability of visual responses of GABAergic neurons increased whereas the decay of responses of excitatory neurons became faster. To test whether the basal forebrain (BF) cholinergic projection is involved in these changes, we analyzed effects of electrical and optogenetic activation of BF on visual responses of mouse cortical neurons with in vivo imaging and whole-cell recordings. Electrical BF stimulation in anesthetized animals induced the same direction of changes in visual responses of both groups of neurons as awakening. Optogenetic activation increased the frequency of visually evoked action potentials in GABAergic neurons but induced the delayed hyperpolarization that ceased the late generation of action potentials in excitatory neurons. Pharmacological analysis in slice preparations revealed that photoactivation-induced depolarization of layer 1 GABAergic neurons was blocked by a nicotinic receptor antagonist, whereas non-fast-spiking layer 2/3 GABAergic neurons was blocked only by the application of both nicotinic and muscarinic receptor antagonists. These results suggest that the effect of awakening is mediated mainly through nicotinic activation of layer 1 GABAergic neurons and mixed nicotinic/muscarinic activation of layer 2/3 non-fast-spiking GABAergic neurons, which together curtails the visual responses of excitatory neurons. Copyright © 2014 the authors 0270-6474/14/3410122-12$15.00/0.

  12. Airborne lidar observations of long-range transport in the free troposphere

    NASA Technical Reports Server (NTRS)

    Shipley, S. T.; Browell, E. V.; Mcdougal, D. S.; Orndorff, B. L.; Haagenson, P.

    1984-01-01

    Airborne lidar measurements of ozone and aerosols in the lower troposphere show the presence of pollutant layers above the mixed layer. Two case studies are analyzed to identify probable source regions and mechanisms for material injection into the free troposphere above local mixed layers. An elevated haze/oxidant layer observed over South Carolina on Aug. 2, 1980, was found to originate in cumulus convection over Georgia on Aug. 1, 1980. An extensive haze/oxidant layer observed over southeastern Virginia on July 31, 1981, is shown to have been in contact with the New England mixed layer on July 30, 1981. This transported air mass is estimated to contribute approximately 30 percent of the ozone maximum measured at the surface in the Norfolk, VA, area on July 31, 1981. Such elevated 'reservoir' layers are transported over long ranges and are not detected by sensors which are confined to the surface.

  13. Comparing Production and Placement of Warm-Mix Asphalt to Traditional Hot-Mix Asphalt for Constructing Airfield Pavements

    DTIC Science & Technology

    2013-08-01

    Sasobit® STA 0+35 cross-section layer thicknesses as constructed............................... 36  Figure 50. Evotherm ™ center-line layer thicknesses...as constructed. ................................................ 37  Figure 51. Evotherm ™ STA 0+15 cross-section layer thicknesses as constructed...37  Figure 52. Evotherm ™ STA 0+25 cross-section layer thicknesses as constructed. .......................... 38  Figure 53

  14. Mixing-induced fluid destratification and ullage condensation

    NASA Technical Reports Server (NTRS)

    Meserole, Jere S.; Jones, Ogden S.; Fortini, Anthony F.

    1987-01-01

    In many applications, on-orbit storage and transfer of cryogens will require forced mixing to control tank pressure without direct venting to space. During a no-vent transfer or during operation of a thermodynamic vent system in a cryogen storage tank, pressure control is achieved by circulating cool liquid to the liquid-vapor interface to condense some of the ullage vapor. To measure the pressure and temperature response rates in mixing-induced condensation, an experiment has been developed using Freon 11 to simulate the two-phase behavior of a cryogen. A thin layer at the liquid surface is heated to raise the tank pressure, and then a jet mixer is turned on to circulate the liquid, cool the surface, and reduce the pressure. Many nozzle configurations and flow rates are used. Tank pressure and the temperature profiles in the ullage and the liquid are measured. Initial data from this ground test are shown correlated with normal-gravity and drop-tower dye-mixing data. Pressure collapse times are comparable to the dye-mixing times, whereas the times needed for complete thermal mixing are much longer than the dye-mixing times.

  15. A numerical study of mixing enhancement in supersonic reacting flow fields. [in scramjets

    NASA Technical Reports Server (NTRS)

    Drummond, J. Philip; Mukunda, H. S.

    1988-01-01

    NASA Langley has intensively investigated the components of ramjet and scramjet systems for endoatmospheric, airbreathing hypersonic propulsion; attention is presently given to the optimization of scramjet combustor fuel-air mixing and reaction characteristics. A supersonic, spatially developing and reacting mixing layer has been found to serve as an excellent physical model for the mixing and reaction process. Attention is presently given to techniques that have been applied to the enhancement of the mixing processes and the overall combustion efficiency of the mixing layer. A fuel injector configuration has been computationally designed which significantly increases mixing and reaction rates.

  16. Nutrient Dynamics in the Northern South China Sea Shelf-sea (NoSoCS)

    NASA Astrophysics Data System (ADS)

    Wong, G. T.; Guo, X.

    2011-12-01

    The Northern South China Sea Shelf-sea (NoSoCS) is situated in the sub-tropics along the southern Chinese coast between the southern end of the Taiwan Strait and the Hainan Island. Samples were collected in four cross-shelf transects in summer, 2010 and two cross-shelf transects in winter, 2011 in this Shelf-sea. The shelf may be sub-divided into the inner shelf (<40 m, low water temperature, high chlorophyll concentration), the middle shelf (50-80 m), and the outer shelf (90-120 m, high water temperature, low nutrient and chlorophyll concentrations). The mixed layer depth and the top of the nutricline depth (at ~30 m in the summer and ~70 m in the winter) were shallower than the shelf break depth (~120 m) in both seasons. The relatively nutrient-rich upper nutricline water (>1 μM in NO3- and >0.1 μM in soluble reactive phosphate) stretched across the shelf at least to the middle shelf. Thus, vertical mixing, even to relatively shallow depths, on the shelf may supply nutrients to and play a critical role in determining the primary production in the mixed layer. At least three such processes were observed. Through the year, internal waves of various strengths generated at the Luzon Strait propagated westward along the bottom of the mixed layer and dissipated along the middle and outer shelf. The effects of these waves were especially conspicuous north of the Dongsha Atoll and their action enhances vertical mixing. In the summer, upwelling occurred in the inner/middle shelf off Dongshan in response to the along shore southwest monsoon and the topographic forcing by the ridge extending offshore from Dongshan to the Taiwan Bank. In the winter, surface cooling and the strong northeast monsoon led to complete overturn in the shelf. The maximum density, reaching 24.6, in the surface waters was found offshore in the inner and middle shelf. This density was equivalent to the density of the water at >100 m offshore. As a result, this dense water also appeared as a layer of bottom water that extended across the shelf to the shelf edge.

  17. Remote sensing observations of phytoplankton increases triggered by successive typhoons

    NASA Astrophysics Data System (ADS)

    Huang, Lei; Zhao, Hui; Pan, Jiayi; Devlin, Adam

    2017-12-01

    Phytoplankton blooms in the Western North Pacific, triggered by two successive typhoons with different intensities and translation speeds under different pre-existing oceanic conditions, were observed and analyzed using remotely sensed chlorophyll-a (Chl-a), sea surface temperature (SST), and sea surface height anomaly (SSHA) data, as well as typhoon parameters and CTD (conductivity, temperature, and depth) profiles. Typhoon Sinlaku, with relatively weaker intensity and slower translation speed, induced a stronger phytoplankton bloom than Jangmi with stronger intensity and faster translation speed (Chl-a>0.18 mg·m‒3 versus Chl-a<0.15 mg·m‒3) east of Taiwan Island. Translation speed may be one of the important mechanisms that affect phytoplankton blooms in the study area. Pre-existing cyclonic circulations provided a relatively unstable thermodynamic structure for Sinlaku, and therefore cold water with rich nutrients could be brought up easily. The mixed-layer deepening caused by Typhoon Sinlaku, which occurred first, could have triggered an unfavorable condition for the phytoplankton bloom induced by Typhoon Jangmi which followed afterwards. The sea surface temperature cooling by Jangmi was suppressed due to the presence of the thick upper-ocean mixed-layer, which prevented the deeper cold water from being entrained into the upper-ocean mixed layer, leading to a weaker phytoplankton augment. The present study suggests that both wind (including typhoon translation speed and intensity) and pre-existing conditions (e.g., mixed-layer depths, eddies, and nutrients) play important roles in the strong phytoplankton bloom, and are responsible for the stronger phytoplankton bloom after Sinlaku's passage than that after Jangmi's passage. A new typhoon-influencing parameter is introduced that combines the effects of the typhoon forcing (including the typhoon intensity and translation speed) and the oceanic pre-condition. This parameter shows that the forcing effect of Sinlaku was stronger than that of Jangmi.

  18. Large Eddy Simulation of Heat Entrainment Under Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Ramudu, Eshwan; Gelderloos, Renske; Yang, Di; Meneveau, Charles; Gnanadesikan, Anand

    2018-01-01

    Arctic sea ice has declined rapidly in recent decades. The faster than projected retreat suggests that free-running large-scale climate models may not be accurately representing some key processes. The small-scale turbulent entrainment of heat from the mixed layer could be one such process. To better understand this mechanism, we model the Arctic Ocean's Canada Basin, which is characterized by a perennial anomalously warm Pacific Summer Water (PSW) layer residing at the base of the mixed layer and a summertime Near-Surface Temperature Maximum (NSTM) within the mixed layer trapping heat from solar radiation. We use large eddy simulation (LES) to investigate heat entrainment for different ice-drift velocities and different initial temperature profiles. The value of LES is that the resolved turbulent fluxes are greater than the subgrid-scale fluxes for most of our parameter space. The results show that the presence of the NSTM enhances heat entrainment from the mixed layer. Additionally there is no PSW heat entrained under the parameter space considered. We propose a scaling law for the ocean-to-ice heat flux which depends on the initial temperature anomaly in the NSTM layer and the ice-drift velocity. A case study of "The Great Arctic Cyclone of 2012" gives a turbulent heat flux from the mixed layer that is approximately 70% of the total ocean-to-ice heat flux estimated from the PIOMAS model often used for short-term predictions. Present results highlight the need for large-scale climate models to account for the NSTM layer.

  19. Mixing Layer Formation near the Tropopause Due to Gravity Wave Critical Level Interactions in a Cloud-Resolving Model.

    NASA Astrophysics Data System (ADS)

    Moustaoui, Mohamed; Joseph, Binson; Teitelbaum, Hector

    2004-12-01

    A plausible mechanism for the formation of mixing layers in the lower stratosphere above regions of tropical convection is demonstrated numerically using high-resolution, two-dimensional (2D), anelastic, nonlinear, cloud-resolving simulations. One noteworthy point is that the mixing layer simulated in this study is free of anvil clouds and well above the cloud anvil top located in the upper troposphere. Hence, the present mechanism is complementary to the well-known process by which overshooting cloud turrets causes mixing within stratospheric anvil clouds. The paper is organized as a case study verifying the proposed mechanism using atmospheric soundings obtained during the Central Equatorial Pacific Experiment (CEPEX), when several such mixing layers, devoid of anvil clouds, had been observed. The basic dynamical ingredient of the present mechanism is (quasi stationary) gravity wave critical level interactions, occurring in association with a reversal of stratospheric westerlies to easterlies below the tropopause region. The robustness of the results is shown through simulations at different resolutions. The insensitivity of the qualitative results to the details of the subgrid scheme is also evinced through further simulations with and without subgrid mixing terms. From Lagrangian reconstruction of (passive) ozone fields, it is shown that the mixing layer is formed kinematically through advection by the resolved-scale (nonlinear) velocity field.

  20. The role of ice nuclei recycling in the maintenance of cloud ice in Arctic mixed-phase stratocumulus

    DOE PAGES

    Solomon, Amy; Feingold, G.; Shupe, M. D.

    2015-09-25

    This study investigates the maintenance of cloud ice production in Arctic mixed-phase stratocumulus in large eddy simulations that include a prognostic ice nuclei (IN) formulation and a diurnal cycle. Balances derived from a mixed-layer model and phase analyses are used to provide insight into buffering mechanisms that maintain ice in these cloud systems. We find that, for the case under investigation, IN recycling through subcloud sublimation considerably prolongs ice production over a multi-day integration. This effective source of IN to the cloud dominates over mixing sources from above or below the cloud-driven mixed layer. Competing feedbacks between dynamical mixing andmore » recycling are found to slow the rate of ice lost from the mixed layer when a diurnal cycle is simulated. Furthermore, the results of this study have important implications for maintaining phase partitioning of cloud ice and liquid that determine the radiative forcing of Arctic mixed-phase clouds.« less

  1. The role of ice nuclei recycling in the maintenance of cloud ice in Arctic mixed-phase stratocumulus

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Solomon, Amy; Feingold, G.; Shupe, M. D.

    This study investigates the maintenance of cloud ice production in Arctic mixed-phase stratocumulus in large eddy simulations that include a prognostic ice nuclei (IN) formulation and a diurnal cycle. Balances derived from a mixed-layer model and phase analyses are used to provide insight into buffering mechanisms that maintain ice in these cloud systems. We find that, for the case under investigation, IN recycling through subcloud sublimation considerably prolongs ice production over a multi-day integration. This effective source of IN to the cloud dominates over mixing sources from above or below the cloud-driven mixed layer. Competing feedbacks between dynamical mixing andmore » recycling are found to slow the rate of ice lost from the mixed layer when a diurnal cycle is simulated. Furthermore, the results of this study have important implications for maintaining phase partitioning of cloud ice and liquid that determine the radiative forcing of Arctic mixed-phase clouds.« less

  2. A new method for estimating the turbulent heat flux at the bottom of the daily mixed layer

    NASA Technical Reports Server (NTRS)

    Imawaki, Shiro; Niiler, Pearn P.; Gautier, Catherine H.; Knox, Robert A.; Halpern, David

    1988-01-01

    Temperature data in the mixed layer and net solar irradiance data at the sea surface are used to estimate the vertical turbulent heat flux at the bottom of the daily mixed layer. The method is applied to data obtained in the eastern tropical Pacific, where the daily cycle in the temperature field is confined to the upper 10-25 m. Equatorial turbulence measurements indicate that the turbulent heat flux is much greater during nighttime than daytime.

  3. The turblent mixing layer - Geometry of large vortices

    NASA Astrophysics Data System (ADS)

    Browand, F. K.; Troutt, T. R.

    1985-09-01

    Large spanwide vortices in a mixing layer have been studied in numerous investigations. The present study represents an attempt to define the geometry of the large vortices. In the conducted experiments, the flow develops from a laminar boundary layer, or from an intentionally tripped turbulent boundary layer. However, no other forcing is provided. It is pointed out that in both cases the downstream structure becomes indistinguishable. The experimental apparatus and the employed techniques are discussed, taking into account details regarding the wind tunnel, the detection of the structure, and aspects of digitization. Attention is given to the mean growth of the mixing layer, the mean vortex spacing, the spanwise correlation of vortex structure, velocity-field visualizations, the transition criterion, and the permanence of structure.

  4. Radon Measurements of Atmospheric Mixing (RAMIX) 2006–2014 Final Campaign Summary

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fischer, ML; Biraud, SC

    2015-05-01

    Uncertainty in vertical mixing between the surface layer, boundary layer, and free troposphere leads to large uncertainty in “top-down” estimates of regional land-atmosphere carbon exchange (i.e., estimates based on measurements of atmospheric CO2 mixing ratios. Radon-222 (222Rn) is a valuable tracer for measuring atmospheric mixing because it is emitted from the land surface and has a short enough half-life (3.8 days) to allow characterization of mixing processes based on vertical profile measurements.

  5. Radon Measurements of Atmospheric Mixing (RAMIX) 2006–2014 Final Campaign Summary

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fischer, ML; Biraud, SC; Hirsch, A

    2015-05-01

    Uncertainty in vertical mixing between the surface layer, boundary layer, and free troposphere leads to large uncertainty in “top-down” estimates of regional land-atmosphere carbon exchange (i.e., estimates based on measurements of atmospheric CO 2 mixing ratios). The radioisotope radon-222 ( 222Rn) is a valuable tracer for measuring atmospheric mixing because it is emitted from the land surface and has a short enough half-life (3.8 days) to allow characterization of mixing processes based on vertical profile measurements.

  6. A perspective view of the plane mixing layer

    NASA Technical Reports Server (NTRS)

    Jimenez, J.; Cogollos, M.; Bernal, L. P.

    1984-01-01

    A three-dimensional model of the plane mixing layer is constructed by applying digital image processing and computer graphic techniques to laser fluorescent motion pictures of its transversal sections. A system of streamwise vortex pairs is shown to exist on top of the classical spanwise eddies. Its influence on mixing is examined.

  7. Temperature-Dependent Helium Ion-Beam Mixing in an Amorphous SiOC/Crystalline Fe Composite

    DOE PAGES

    Su, Qing; Price, Lloyd; Shao, Lin; ...

    2016-10-31

    Temperature dependent He-irradiation-induced ion-beam mixing between amorphous silicon oxycarbide (SiOC) and crystalline Fe was examined with a transmission electron microscope (TEM) and via Rutherford backscattering spectrometry (RBS). The Fe marker layer (7.2 ± 0.8 nm) was placed in between two amorphous SiOC layers (200 nm). The amount of ion-beam mixing after 298, 473, 673, 873, and 1073 K irradiation was investigated. Both TEM and RBS results showed no ion-beam mixing between Fe and SiOC after 473 and 673 K irradiation and a very trivial amount of ion-beam mixing (~2 nm) after 298 K irradiation. At irradiation temperatures higher than 873more » K, the Fe marker layer broke down and RBS could no longer be used to quantitatively examine the amount of ion mixing. The results indicate that the Fe/SiOC nanocomposite is thermally stable and tends to demix in the temperature range from 473 to 673 K. For application of this composite structure at temperatures of 873 K or higher, layer stability is a key consideration.« less

  8. Turbulence and Mixing in a Shallow Shelf Sea From Underwater Gliders

    NASA Astrophysics Data System (ADS)

    Schultze, Larissa K. P.; Merckelbach, Lucas M.; Carpenter, Jeffrey R.

    2017-11-01

    The seasonal thermocline in shallow shelf seas acts as a natural barrier for boundary-generated turbulence, damping scalar transport to the upper regions of the water column and controlling primary production to a certain extent. To better understand turbulence and mixing conditions within the thermocline, two unique 12 and 17 day data sets with continuous measurements of the dissipation rate of turbulent kinetic energy (ɛ) collected by autonomous underwater gliders under stratified to well-mixed conditions are presented. A highly intermittent ɛ signal was observed in the stratified thermocline region, which was mainly characterized by quiescent flow (turbulent activity index below 7). The rate of diapycnal mixing remained relatively constant for the majority of the time with peaks of higher fluxes that were responsible for much of the increase in bottom mixed layer temperature. The water column stayed predominantly strongly stratified, with a bulk Richardson number across the thermocline well above 2. A positive relationship between the intensity of turbulence, shear, and stratification was found. The trend between turbulence levels and the bulk Richardson number was relatively weak but suggests that ɛ increases as the bulk Richardson number approaches 1. The results also highlight the interpretation difficulties in both quantifying turbulent thermocline fluxes as well as the responsible mechanisms.

  9. Rain Impact Model Assessment of Near-Surface Salinity Stratification Following Rainfall

    NASA Astrophysics Data System (ADS)

    Drushka, K.; Jones, L.; Jacob, M. M.; Asher, W.; Santos-Garcia, A.

    2016-12-01

    Rainfall over oceans produces a layer of fresher surface water, which can have a significant effect on the exchanges between the surface and the bulk mixed layer and also on satellite/in-situ comparisons. For satellite sea surface salinity (SSS) measurements, the standard is the Hybrid Coordinate Ocean Model (HYCOM), but there is a significant difference between the remote sensing sampling depth of 0.01 m and the typical range of 5-10 m of in-situ instruments. Under normal conditions the upper layer of the ocean is well mixed and there is uniform salinity; however, under rainy conditions, there is a dilution of the near-surface salinity that mixes downward by diffusion and by mechanical mixing (gravity waves/wind speed). This significantly modifies the salinity gradient in the upper 1-2 m of the ocean, but these transient salinity stratifications dissipate in a few hours, and the upper layer becomes well mixed at a slightly fresher salinity. Based upon research conducted within the NASA/CONAE Aquarius/SAC-D mission, a rain impact model (RIM) was developed to estimate the change in SSS due to rainfall near the time of the satellite observation, with the objective to identify the probability of salinity stratification. RIM uses HYCOM (which does not include the short-term rain effects) and a NOAA global rainfall product CMORPH to model changes in the near-surface salinity profile in 0.5 h increments. Based upon SPURS-2 experimental near-surface salinity measurements with rain, this paper introduces a term in the RIM model that accounts for the effect of wind speed in the mechanical mixing, which translates into a dynamic vertical diffusivity; whereby a Generalized Ocean Turbulence Model (GOTM) is used to investigate the response to rain events of the upper few meters of the ocean. The objective is to determine how rain and wind forcing control the thickness, stratification strength, and lifetime of fresh lenses and to quantify the impacts of rain-formed fresh lenses on the fresh bias in satellite retrievals of salinity. Results will be presented of comparisons of RIM measurements at depth of a few meters with measurements from in-situ salinity instruments. Also, analytical results will be shown, which assess the accuracy of RIM salinity profiles under a variety of rain rate, wind/wave conditions.

  10. Numerical Investigation of a Cavitating Mixing Layer of Liquefied Natural Gas (LNG) Behind a Flat Plate Splitter

    NASA Astrophysics Data System (ADS)

    Rahbarimanesh, Saeed; Brinkerhoff, Joshua

    2017-11-01

    The mutual interaction of shear layer instabilities and phase change in a two-dimensional cryogenic cavitating mixing layer is investigated using a numerical model. The developed model employs the homogeneous equilibrium mixture (HEM) approach in a density-based framework to compute the temperature-dependent cavitation field for liquefied natural gas (LNG). Thermal and baroclinic effects are captured via iterative coupled solution of the governing equations with dynamic thermophysical models that accurately capture the properties of LNG. The mixing layer is simulated for vorticity-thickness Reynolds numbers of 44 to 215 and cavitation numbers of 0.1 to 1.1. Attached cavity structures develop on the splitter plate followed by roll-up of the separated shear layer via the well-known Kelvin-Helmholtz mode, leading to streamwise accumulation of vorticity and eventual shedding of discrete vortices. Cavitation occurs as vapor cavities nucleate and grow from the low-pressure cores in the rolled-up vortices. Thermal effects and baroclinic vorticity production are found to have significant impacts on the mixing layer instability and cavitation processes.

  11. The effects of the laminar/turbulent boundary layer states on the development of a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Foss, J. F.

    1977-01-01

    The effect of the laminar/turbulent boundary layer state on the mean and rms velocities of a developing plane mixing layer was investigated. The use of commonly accepted nondimensional representations of the data confirm (at least) an approximately self-preserving condition. It is suggested that the effects of the laminar/turbulent initial condition persist in the self-preserving region.

  12. Tradeoffs in Chemical and Thermal Variations in the Post-perovskite Phase Transition: Mixed Phase Regions in the Deep Lower Mantle?

    NASA Astrophysics Data System (ADS)

    Giles, G. F.; Spera, F. J.; Yuen, D. A.

    2005-12-01

    The recent discovery of a phase-transition in Mg-rich perovskite (Pv) to a post-perovskite (pPv) phase at lower mantle depths and its relationship to D", lower mantle heterogeneity and iron content prompted an investigation of the relative importance of lower mantle (LM) compositional and temperature fluctuations in creating topographic undulations on mixed phase regions. Above the transition, Mg-rich Pv makes up ~70 percent by mass of the LM. Using results from experimental phase equilibria, first-principles computations and thermodynamic relations for Fe2+-Mg mixing in silicates, a preliminary thermodynamic model for the perovskite to post-perovskite phase transition in the divariant system MgSiO3-FeSiO3 is developed. Complexities associated with components Fe2O3 and Al2O3 and other phases (Ca-Pv, magnesiowustite) are neglected. The model predicts phase transition pressures are sensitive to the FeSiO3 content of perovskite (~-1.5 GPa per one mole percent FeSiO3). This leads to considerable topography along the top boundary of the mixed phase region. The Clapeyron slope for the Pv to pPv transition at XFeSiO3=0.1 is +11 MPa/K about 20% higher than for pure Mg-Pv. Increasing bulk concentration of iron elevates the mixed (two-phase) layer above the core-mantle boundary (CMB); increasing temperature acts to push the mixed layer deeper into the LM into the D" thermal boundary layer resting upon the (CMB). For various LM geotherms and CMB temperatures, a single mixed layer of thickness ~300 km lies within the bottom 40% of the lower mantle. For low iron contents (XFeSiO3 ~5 mole percent or less), two perched layers are found. This is the divariant analog to the univariant double-crosser. The hotter the mantle, the deeper the mixed phase layer; the more iron-rich the LM, the higher the mixed phase layer. In a hotter Hadean Earth with interior temperatures everywhere 200-500 K warmer pPv is not stable unless the LM bulk composition is Fe-enriched compared to the present upper mantle.

  13. Modulating surface rheology by electrostatic protein/polysaccharide interactions.

    PubMed

    Ganzevles, Renate A; Zinoviadou, Kyriaki; van Vliet, Ton; Cohen, Martien A; de Jongh, Harmen H

    2006-11-21

    There is a large interest in mixed protein/polysaccharide layers at air-water and oil-water interfaces because of their ability to stabilize foams and emulsions. Mixed protein/polysaccharide adsorbed layers at air-water interfaces can be prepared either by adsorption of soluble protein/polysaccharide complexes or by sequential adsorption of complexes or polysaccharides to a previously formed protein layer. Even though the final protein and polysaccharide bulk concentrations are the same, the behavior of the adsorbed layers can be very different, depending on the method of preparation. The surface shear modulus of a sequentially formed beta-lactoglobulin/pectin layer can be up to a factor of 6 higher than that of a layer made by simultaneous adsorption. Furthermore, the surface dilatational modulus and surface shear modulus strongly (up to factors of 2 and 7, respectively) depend on the bulk -lactoglobulin/pectin mixing ratio. On the basis of the surface rheological behavior, a mechanistic understanding of how the structure of the adsorbed layers depends on the protein/polysaccharide interaction in bulk solution, mixing ratio, ionic strength, and order of adsorption to the interface (simultaneous or sequential) is derived. Insight into the effect of protein/polysaccharide interactions on the properties of adsorbed layers provides a solid basis to modulate surface rheological behavior.

  14. Linear stability analysis of particle-laden hypopycnal plumes

    NASA Astrophysics Data System (ADS)

    Farenzena, Bruno Avila; Silvestrini, Jorge Hugo

    2017-12-01

    Gravity-driven riverine outflows are responsible for carrying sediments to the coastal waters. The turbulent mixing in these flows is associated with shear and gravitational instabilities such as Kelvin-Helmholtz, Holmboe, and Rayleigh-Taylor. Results from temporal linear stability analysis of a two-layer stratified flow are presented, investigating the behavior of settling particles and mixing region thickness on the flow stability in the presence of ambient shear. The particles are considered suspended in the transport fluid, and its sedimentation is modeled with a constant valued settling velocity. Three scenarios, regarding the mixing region thickness, were identified: the poorly mixed environment, the strong mixed environment, and intermediate scenario. It was observed that Kelvin-Helmholtz and settling convection modes are the two fastest growing modes depending on the particles settling velocity and the total Richardson number. The second scenario presents a modified Rayleigh-Taylor instability, which is the dominant mode. The third case can have Kelvin-Helmholtz, settling convection, and modified Rayleigh-Taylor modes as the fastest growing mode depending on the combination of parameters.

  15. The Vertical Dust Profile over Gale Crater

    NASA Astrophysics Data System (ADS)

    Guzewich, S.; Newman, C. E.; Smith, M. D.; Moores, J.; Smith, C. L.; Moore, C.; Richardson, M. I.; Kass, D. M.; Kleinboehl, A.; Martin-Torres, F. J.; Zorzano, M. P.; Battalio, J. M.

    2017-12-01

    Regular joint observations of the atmosphere over Gale Crater from the orbiting Mars Reconnaissance Orbiter/Mars Climate Sounder (MCS) and Mars Science Laboratory (MSL) Curiosity rover allow us to create a coarse, but complete, vertical profile of dust mixing ratio from the surface to the upper atmosphere. We split the atmospheric column into three regions: the planetary boundary layer (PBL) within Gale Crater that is directly sampled by MSL (typically extending from the surface to 2-6 km in height), the region of atmosphere sampled by MCS profiles (typically 25-80 km above the surface), and the region of atmosphere between these two layers. Using atmospheric optical depth measurements from the Rover Environmental Monitoring System (REMS) ultraviolet photodiodes (in conjunction with MSL Mast Camera solar imaging), line-of-sight opacity measurements with the MSL Navigation Cameras (NavCam), and an estimate of the PBL depth from the MarsWRF general circulation model, we can directly calculate the dust mixing ratio within the Gale Crater PBL and then solve for the dust mixing ratio in the middle layer above Gale Crater but below the atmosphere sampled by MCS. Each atmospheric layer has a unique seasonal cycle of dust opacity, with Gale Crater's PBL reaching a maximum in dust mixing ratio near Ls = 270° and a minimum near Ls = 90°. The layer above Gale Crater, however, has a seasonal cycle that closely follows the global opacity cycle and reaches a maximum near Ls = 240° and exhibits a local minimum (associated with the "solsticial pauses") near Ls = 270°. Knowing the complete vertical profile also allows us to determine the frequency of high-altitude dust layers above Gale, and whether such layers truly exhibit the maximum dust mixing ratio within the entire vertical column. We find that 20% of MCS profiles contain an "absolute" high-altitude dust layer, i.e., one in which the dust mixing ratio within the high-altitude dust layer is the maximum dust mixing ratio in the vertical column of atmosphere over Gale Crater.

  16. Method of making bonded or sintered permanent magnets

    DOEpatents

    McCallum, R.W.; Dennis, K.W.; Lograsso, B.K.; Anderson, I.E.

    1993-08-31

    An isotropic permanent magnet is made by mixing a thermally responsive, low viscosity binder and atomized rare earth-transition metal (e.g., iron) alloy powder having a carbon-bearing (e.g., graphite) layer thereon that facilitates wetting and bonding of the powder particles by the binder. Prior to mixing with the binder, the atomized alloy powder may be sized or classified to provide a particular particle size fraction having a grain size within a given relatively narrow range. A selected particle size fraction is mixed with the binder and the mixture is molded to a desired complex magnet shape. A molded isotropic permanent magnet is thereby formed. A sintered isotropic permanent magnet can be formed by removing the binder from the molded mixture and thereafter sintering to full density.

  17. Method of making bonded or sintered permanent magnets

    DOEpatents

    McCallum, R.W.; Dennis, K.W.; Lograsso, B.K.; Anderson, I.E.

    1995-11-28

    An isotropic permanent magnet is made by mixing a thermally responsive, low viscosity binder and atomized rare earth-transition metal (e.g., iron) alloy powder having a carbon-bearing (e.g., graphite) layer thereon that facilitates wetting and bonding of the powder particles by the binder. Prior to mixing with the binder, the atomized alloy powder may be sized or classified to provide a particular particle size fraction having a grain size within a given relatively narrow range. A selected particle size fraction is mixed with the binder and the mixture is molded to a desired complex magnet shape. A molded isotropic permanent magnet is thereby formed. A sintered isotropic permanent magnet can be formed by removing the binder from the molded mixture and thereafter sintering to full density. 14 figs.

  18. Method of making bonded or sintered permanent magnets

    DOEpatents

    McCallum, R. William; Dennis, Kevin W.; Lograsso, Barbara K.; Anderson, Iver E.

    1995-11-28

    An isotropic permanent magnet is made by mixing a thermally responsive, low viscosity binder and atomized rare earth-transition metal (e.g., iron) alloy powder having a carbon-bearing (e.g., graphite) layer thereon that facilitates wetting and bonding of the powder particles by the binder. Prior to mixing with the binder, the atomized alloy powder may be sized or classified to provide a particular particle size fraction having a grain size within a given relatively narrow range. A selected particle size fraction is mixed with the binder and the mixture is molded to a desired complex magnet shape. A molded isotropic permanent magnet is thereby formed. A sintered isotropic permanent magnet can be formed by removing the binder from the molded mixture and thereafter sintering to full density.

  19. A random distribution reacting mixing layer model

    NASA Technical Reports Server (NTRS)

    Jones, Richard A.; Marek, C. John; Myrabo, Leik N.; Nagamatsu, Henry T.

    1994-01-01

    A methodology for simulation of molecular mixing, and the resulting velocity and temperature fields has been developed. The ideas are applied to the flow conditions present in the NASA Lewis Research Center Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data. A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow. Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature. Velocities are determined through summation of momentum contributions. The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3. The success of the model is attributed to the simulation of large-scale transport of fluid. The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and nonreacting shear layer present in the facility given basic assumptions about turbulence properties.

  20. Implementation of a diffusion convection surface evolution model in WallDYN

    NASA Astrophysics Data System (ADS)

    Schmid, K.

    2013-07-01

    In thermonuclear fusion experiments with multiple plasma facing materials the formation of mixed materials is inevitable. The formation of these mixed material layers is a dynamic process driven the tight interaction between transport in the plasma scrape off layer and erosion/(re-) deposition at the surface. To track this global material erosion/deposition balance and the resulting formation of mixed material layers the WallDYN code has been developed which couples surface processes and plasma transport. The current surface model in WallDYN cannot fully handle the growth of layers nor does it include diffusion. However at elevated temperatures diffusion is a key process in the formation of mixed materials. To remedy this shortcoming a new surface model has been developed which, for the first time, describes both layer growth/recession and diffusion in a single continuous diffusion/convection equation. The paper will detail the derivation of the new surface model and compare it to TRIDYN calculations.

  1. Seasonal cycle of the mixed layer depth, of the seasonal thermocline and of the upper-ocean heat rate in the Mediterranean Sea: an observational approach

    NASA Astrophysics Data System (ADS)

    Houpert, Loïc; Testor, Pierre; Durrieu de Madron, Xavier; Somot, Samuel; D'Ortenzio, Fabrizio; Estournel, Claude; Lavigne, Héloïse

    2014-05-01

    We present a relatively high resolution Mediterranean climatology (0.5°x0.5°x12 months) of the seasonal thermocline based on a comprehensive collection of temperature profiles of the last 44 years (1969-2012). The database includes more than 190,000 profiles, merging CTD, XBT, profiling floats, and gliders observations. This data set is first used to describe the seasonal cycle of the mixed layer depth and of the seasonal thermocline and on the whole Mediterranean on a monthly climatological basis. Our analysis discriminates several regions with coherent behaviors, in particular the deep water formation sites, characterized by significant differences in the winter mixing intensity. Heat Storage Rate (HSR) is calculated as the time rate of change of the heat content due to variations in the temperature integrated from the surface down to the base of the seasonal thermocline. Heat Entrainment Rate (HER) is calculated as the time rate of change of the heat content due to the deepening of thermocline base. We propose a new independent estimate of the seasonal cycle of the Net surface Heat Flux, calculated on average over the Mediterranean Sea for the 1979-2011 period, based only on in-situ observations. We used our new climatologies of HSR and of HER, combined to existing climatology of the horizontal heat flux at Gibraltar Strait. Although there is a good agreement between our estimation of NHF, from observations, with modeled NHF, some differences may be noticed during specific periods. A part of these differences may be explained by the high temporal and spatial variability of the Mixed Layer Depth and of the seasonal thermocline, responsible for very localized heat transfer in the ocean.

  2. Comparison between the land surface response of the ECMWF model and the FIFE-1987 data

    NASA Technical Reports Server (NTRS)

    Betts, Alan K.; Ball, John H.; Beljaars, Anton C. M.

    1993-01-01

    An averaged time series for the surface data for the 15 x 15 km FIFE site was prepared for the summer of 1987. Comparisons with 48-hr forecasts from the ECMWF model for extended periods in July, August, and October 1987 identified model errors in the incoming SW radiation in clear skies, the ground heat flux, the formulation of surface evaporation, the soil-moisture model, and the entrainment at boundary-layer top. The model clear-sky SW flux is too high at the surface by 5-10 percent. The ground heat flux is too large by a factor of 2 to 3 because of the large thermal capacity of the first soil layer (which is 7 cm thick), and a time truncation error. The surface evaporation was near zero in October 1987, rather than of order 70 W/sq m at noon. The surface evaporation falls too rapidly after rainfall, with a time-scale of a few days rather than the 7-10 d (or more) of the observations. On time-scales of more than a few days the specified 'climate layer' soil moisture, rather than the storage of precipitation, has a large control on the evapotranspiration. The boundary-layer-top entrainment is too low. This results in a moist bias in the boundary-layer mixing ratio of order 2 g/Kg in forecasts from an experimental analysis with nearly realistic surface fluxes; this because there is insufficient downward mixing of dry air.

  3. Simulation of the planetary boundary layer with the UCLA general circulation model

    NASA Technical Reports Server (NTRS)

    Suarez, M. J.; Arakawa, A.; Randall, D. A.

    1981-01-01

    A planetary boundary layer (PBL) model is presented which employs a mixed layer entrainment formulation to describe the mass exchange between the mixed layer with the upper, laminar atmosphere. A modified coordinate system couples the mixed layer model with large scale and sub-grid scale processes of a general circulation model. The vertical coordinate is configured as a sigma coordinate with the lower boundary, the top of the PBL, and the prescribed pressure level near the tropopause expressed as coordinate surfaces. The entrainment mass flux is parameterized by assuming the dissipation rate of turbulent kinetic energy to be proportional to the positive part of the generation by convection or mechanical production. The results of a simulation of July are presented for the entire globe.

  4. Decay of deep water convection in CMIP5 GCMs in the North Atlantic and Southern Ocean in the 21st century

    NASA Astrophysics Data System (ADS)

    Molodtsov, S.; Anis, A.; Marinov, I.; Cabre, A.

    2016-12-01

    Contemporary changes in the climate system due to anthropogenic activity have already resulted in unprecedented melting rates of the polar ice caps. This in turn may have a significant impact on the thermohaline circulation in the future. The freshening of the surface waters increases stable stratification in regions of deep water formation, eventually triggering a weakening and, ultimately, may bring to a cessation of deep convection in these regions. Here we present comparatively an analysis of the response of deep convective processes in the North Atlantic (NA) and Southern Ocean (SO) to anthropogenic forcing using output from the latest generation of Earth System Models (ESM), part of the CMIP5 intercomparison. Our findings indicate an attenuation of deep convection by the end of the 21st century from ESM simulations under representative concentration pathways (RCP) 8.5 scenario when compared to the years under historical scenario in both NA and SO. The average depth of the mixed layer in the regions studied during March/September, the months with maximum mixed layer depths in the NA/SO, respectively, was found to decrease dramatically by the end of the 21st century. Furthermore, the increase in stratification and decrease in mixed layer depths, resulting in the decay of deep convection, leads to accumulation of excess heat, previously released during the convection events, in the ocean interior in both regions.

  5. Warmer, deeper, and greener mixed layers in the North Atlantic subpolar gyre over the last 50 years.

    PubMed

    Martinez, Elodie; Raitsos, Dionysios E; Antoine, David

    2016-02-01

    Shifts in global climate resonate in plankton dynamics, biogeochemical cycles, and marine food webs. We studied these linkages in the North Atlantic subpolar gyre (NASG), which hosts extensive phytoplankton blooms. We show that phytoplankton abundance increased since the 1960s in parallel to a deepening of the mixed layer and a strengthening of winds and heat losses from the ocean, as driven by the low frequency of the North Atlantic Oscillation (NAO). In parallel to these bottom-up processes, the top-down control of phytoplankton by copepods decreased over the same time period in the western NASG, following sea surface temperature changes typical of the Atlantic Multi-decadal Oscillation (AMO). While previous studies have hypothesized that climate-driven warming would facilitate seasonal stratification of surface waters and long-term phytoplankton increase in subpolar regions, here we show that deeper mixed layers in the NASG can be warmer and host a higher phytoplankton biomass. These results emphasize that different modes of climate variability regulate bottom-up (NAO control) and top-down (AMO control) forcing on phytoplankton at decadal timescales. As a consequence, different relationships between phytoplankton, zooplankton, and their physical environment appear subject to the disparate temporal scale of the observations (seasonal, interannual, or decadal). The prediction of phytoplankton response to climate change should be built upon what is learnt from observations at the longest timescales. © 2015 John Wiley & Sons Ltd.

  6. Helicity in supercritical temporal mixing layers

    NASA Technical Reports Server (NTRS)

    Bellan, J.; Okong'o, N.

    2003-01-01

    Databases of transitional states obtained from Direct Numerical Simulations (DNS) of temporal, supercritical mixing layers for two species systems, 02/H2 and C7Hle/N2, are analyzed to elucidate species-specific turbulence aspects.

  7. Heat and salt budgets over the Gulf Stream North Wall during LatMix survey in winter 2012.

    NASA Astrophysics Data System (ADS)

    Sanchez-Rios, A.; Shearman, R. K.; D'Asaro, E. A.; Lee, C.; Gula, J.; Klymak, J. M.

    2016-02-01

    As part of the ONR-sponsored LatMix Experiment, ship-based and glider-based observations following a Lagrangian float are used to examine the evolution of temperature, salinity and density along the Gulf Stream north wall in wintertime. Satellite observations during the survey and the in-situ measurements showed the presence of submesoscale (<10 km) features along the front. Models have successfully reproduced similar features, but observations are lacking, particularly at the small scales needed to understand their role in the transport of heat and salt across the front and out of the mixed layer. Calculating the trend in time at each depth and cross-front location we found an increase of heat and salinity in regions where the strongest cross-front gradients of velocity were observed at the mixed layer and around 150m depth, these changes are density compensated and suggest isopycnal mixing and a connection between the mixed layer and subsurface layers. The large Rossby number (Ro>1) calculated for this regions corroborates the possibility of submesoscale dynamics. Using a heat and salinity budget, we show that surface forcing, entrainment from below and advection by the mean flow velocities are not sufficient to explain the observed rate of change of heat and salinity in the mixed layer. Although confidence estimates prevent an accurate flux divergence calculation, Reynold flux estimates are consistent with a cross-frontal exchange that can reproduce the observed temporal trends.

  8. Mixing and phytoplankton dynamics in a submarine canyon in the West Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Carvalho, Filipa; Kohut, Josh; Oliver, Matthew J.; Sherrell, Robert M.; Schofield, Oscar

    2016-07-01

    Bathymetric depressions (canyons) exist along the West Antarctic Peninsula shelf and have been linked with increased phytoplankton biomass and sustained penguin colonies. However, the physical mechanisms driving this enhanced biomass are not well understood. Using a Slocum glider data set with over 25,000 water column profiles, we evaluate the relationship between mixed layer depth (MLD, estimated using the depth of maximum buoyancy frequency) and phytoplankton vertical distribution. We use the glider deployments in the Palmer Deep region to examine seasonal and across canyon variability. Throughout the season, the ML becomes warmer and saltier, as a result of vertical mixing and advection. Shallow ML and increased stratification due to sea ice melt are linked to higher chlorophyll concentrations. Deeper mixed layers, resulting from increased wind forcing, show decreased chlorophyll, suggesting the importance of light in regulating phytoplankton productivity. Spatial variations were found in the canyon head region where local physical water column properties were associated with different biological responses, reinforcing the importance of local canyon circulation in regulating phytoplankton distribution in the region. While the mechanism initially hypothesized to produce the observed increases in phytoplankton over the canyons was the intrusion of warm, nutrient enriched modified Upper Circumpolar Deep Water (mUCDW), our analysis suggests that ML dynamics are key to increased primary production over submarine canyons in the WAP.

  9. A novel formulation for unsteady counterflow flames using a thermal-conductivity-weighted coordinate

    NASA Astrophysics Data System (ADS)

    Weiss, Adam D.; Vera, Marcos; Liñán, Amable; Sánchez, Antonio L.; Williams, Forman A.

    2018-01-01

    A general formulation is given for the description of reacting mixing layers in stagnation-type flows subject to both time-varying strain and pressure. The salient feature of the formulation is the introduction of a thermal-conductivity-weighted transverse coordinate that leads to a compact transport operator that facilitates numerical integration and theoretical analysis. For steady counterflow mixing layers, the associated transverse mass flux is shown to be effectively linear in terms of the new coordinate, so that the conservation equations for energy and chemical species uncouple from the mass and momentum conservation equations, thereby greatly simplifying the solution. Comparisons are shown with computations of diffusion flames with infinitely fast reaction using both the classic Howarth-Dorodnitzyn density-weighted coordinate and the new thermal-conductivity-weighted coordinate, illustrating the advantages of the latter. Also, as an illustrative application of the formulation to the computation of unsteady counterflows, the flame response to harmonically varying strain is examined in the linear limit.

  10. Wolf-Rayet stars of type WN/WC and mixing processes during core helium burning of massive stars

    NASA Technical Reports Server (NTRS)

    Langer, N.

    1991-01-01

    Consequences of the recent finding that most WN/WC spectra probably originate from individual Wolf-Rayet stars for the internal structure of massive stars are discussed. Numerical models including the effect of slow-down or prevention of convective mixing due to molecular weight gradients are presented, in which a transition layer with a composition mixture of H- and He-burning ashes is formed above the convective He-burning core. These models are able to qualitatively account for the observed WN/WC frequency and agree quantitatively with the only WN/WC-composition determination so far. It is argued that the same transition layer may be responsible for the final blue loop which the SN 1987 A progenitor performed some 10,000 yr before explosion. These results indicate that composition barriers may be efficient in restricting convection during central helium burning, in contrast to computations relying on the Schwarzschild criterion for convection, with or without overshooting.

  11. Observational study of upper ocean cooling due to Phet super cyclone in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Muni Krishna, K.

    2016-05-01

    Phet super cyclone (31 May-7 June 2010) was the most intense and also the rarest of the rare track in Arabian Sea as per the recorded history during 1877-2009. The present study focuses on the ocean physical responses to Phet cyclone using satellite and Argo observations. The sea surface temperature is decreased to 6 °C with an approximately 350 km long and 100 km width area in the Arabian Sea after the cyclone passage. The translation speed of cyclone is 3.86 m/s, the mixed layer is 79 m, and thermocline displacement is 13 m at the cooling area. With the relationship of wind stress curl and Ekman pumping velocity (EPV), the author found that the speed of EPV was increased after the passage of cyclone. So the extent of the SST drop was probably due to the moving speed of cyclone and the depth of the mixed layer.

  12. Use of weathered and fresh bottom ash mix layers as a subbase in road constructions: environmental behavior enhancement by means of a retaining barrier.

    PubMed

    Del Valle-Zermeño, R; Chimenos, J M; Giró-Paloma, J; Formosa, J

    2014-12-01

    The presence of neoformed cement-like phases during the weathering of non-stabilized freshly quenched bottom ash favors the development of a bound pavement material with improved mechanical properties. Use of weathered and freshly quenched bottom ash mix layers placed one over the other allowed the retention of leached heavy metals and metalloids by means of a reactive percolation barrier. The addition of 50% of weathered bottom ash to the total subbase content diminished the release of toxic species to below environmental regulatory limits. The mechanisms of retention and the different processes and factors responsible of leaching strongly depended on the contaminant under concern as well as on the chemical and physical factors. Thus, the immediate reuse of freshly quenched bottom ash as a subbase material in road constructions is possible, as both the mechanical properties and long-term leachability are enhanced. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. Seasonality of eddy kinetic energy in an eddy permitting global climate model

    NASA Astrophysics Data System (ADS)

    Uchida, Takaya; Abernathey, Ryan; Smith, Shafer

    2017-10-01

    We examine the seasonal cycle of upper-ocean mesoscale turbulence in a high resolution CESM climate simulation. The ocean model component (POP) has 0.1° resolution, mesoscale resolving at low and middle latitudes. Seasonally and regionally resolved wavenumber power spectra are calculated for sea-surface eddy kinetic energy (EKE). Although the interpretation of the spectral slopes in terms of turbulence theory is complicated by the strong presence of dissipation and the narrow inertial range, the EKE spectra consistently show higher power at small scales during winter throughout the ocean. Potential hypotheses for this seasonality are investigated. Diagnostics of baroclinc energy conversion rates and evidence from linear quasigeostrophic stability analysis indicate that seasonally varying mixed-layer instability is responsible for the seasonality in EKE. The ability of this climate model, which is not considered submesoscale resolving, to produce mixed layer instability although damped by dissipation, demonstrates the ubiquity and robustness of this process for modulating upper ocean EKE.

  14. The lagRST Model: A Turbulence Model for Non-Equilibrium Flows

    NASA Technical Reports Server (NTRS)

    Lillard, Randolph P.; Oliver, A. Brandon; Olsen, Michael E.; Blaisdell, Gregory A.; Lyrintzis, Anastasios S.

    2011-01-01

    This study presents a new class of turbulence model designed for wall bounded, high Reynolds number flows with separation. The model addresses deficiencies seen in the modeling of nonequilibrium turbulent flows. These flows generally have variable adverse pressure gradients which cause the turbulent quantities to react at a finite rate to changes in the mean flow quantities. This "lag" in the response of the turbulent quantities can t be modeled by most standard turbulence models, which are designed to model equilibrium turbulent boundary layers. The model presented uses a standard 2-equation model as the baseline for turbulent equilibrium calculations, but adds transport equations to account directly for non-equilibrium effects in the Reynolds Stress Tensor (RST) that are seen in large pressure gradients involving shock waves and separation. Comparisons are made to several standard turbulence modeling validation cases, including an incompressible boundary layer (both neutral and adverse pressure gradients), an incompressible mixing layer and a transonic bump flow. In addition, a hypersonic Shock Wave Turbulent Boundary Layer Interaction with separation is assessed along with a transonic capsule flow. Results show a substantial improvement over the baseline models for transonic separated flows. The results are mixed for the SWTBLI flows assessed. Separation predictions are not as good as the baseline models, but the over prediction of the peak heat flux downstream of the reattachment shock that plagues many models is reduced.

  15. Tests of Parameterized Langmuir Circulation Mixing in the Oceans Surface Mixed Layer II

    DTIC Science & Technology

    2017-08-11

    inertial oscillations in the ocean are governed by three-dimensional processes that are not accounted for in a one-dimensional simulation , and it was...Unlimited 52 Paul Martin (228) 688-5447 Recent large-eddy simulations (LES) of Langmuir circulation (LC) within the surface mixed layer (SML) of...used in the Navy Coastal Ocean Model (NCOM) and tested for (a) a simple wind-mixing case, (b) simulations of the upper ocean thermal structure at Ocean

  16. Development of the CD symcap platform to study gas-shell mix in implosions at the National Ignition Facility

    DOE PAGES

    Casey, D. T.; Smalyuk, V. A.; Tipton, R. E.; ...

    2014-09-09

    Surrogate implosions play an important role at the National Ignition Facility (NIF) for isolating aspects of the complex physical processes associated with fully integrated ignition experiments. The newly developed CD Symcap platform has been designed to study gas-shell mix in indirectly driven, pure T₂-gas filled CH-shell implosions equipped with 4 μm thick CD layers. This configuration provides a direct nuclear signature of mix as the DT yield (above a characterized D contamination background) is produced by D from the CD layer in the shell, mixing into the T-gas core. The CD layer can be placed at different locations within themore » CH shell to probe the depth and extent of mix. CD layers placed flush with the gas-shell interface and recessed up to 8 μm have shown that most of the mix occurs at the inner-shell surface. In addition, time-gated x-ray images of the hotspot show large brightly-radiating objects traversing through the hotspot around bang-time, which are likely chunks of CH/CD plastic. This platform is a powerful new capability at the NIF for understanding mix, one of the key performance issues for ignition experiments.« less

  17. Use of screenings to produce HMA mixtures

    DOT National Transportation Integrated Search

    2002-10-01

    Thin-lift hot mix asphalt (HMA) layers are utilized in almost every maintenance and rehabilitation application. These mix types require smaller maximum particle sizes than most conventional HMA surface layers. Although the primary functions of thin-l...

  18. Defect-induced mix experiment for NIF

    NASA Astrophysics Data System (ADS)

    Schmitt, M. J.; Bradley, P. A.; Cobble, J. A.; Hsu, S. C.; Krasheninnikova, N. S.; Kyrala, G. A.; Magelssen, G. R.; Murphy, T. J.; Obrey, K. A.; Tregillis, I. L.; Wysocki, F. J.; Finnegan, S. M.

    2013-11-01

    The Defect Induced Mix Experiment (DIME-II) will measure the implosion and mix characteristics of CH capsules filled with 5 atmospheres of DT by incorporating mid-Z dopant layers of Ge and Ga. This polar direct drive (PDD) experiment also will demonstrate the filling of a CH capsule at target chamber center using a fill tube. Diagnostics for these experiments include areal x-ray backlighting to obtain early time images of the implosion trajectory and a multiple-monochromatic imager (MMI) to collect spectrally-resolved images of the capsule dopant line emission near bangtime. The inclusion of two (or more) thin dopant layers at separate depths within the capsule shell facilitates spatial correlation of mix between the layers and the hot gas core on a single shot. The dopant layers are typically 2 μm thick and contain dopant concentrations of 1.5%. Three dimensional Hydra simulations have been performed to assess the effects of PDD asymmetry on capsule performance.

  19. Closing the Seasonal Ocean Surface Temperature Balance in the Eastern Tropical Oceans from Remote Sensing and Model Reanalyses

    NASA Technical Reports Server (NTRS)

    Roberts, J. Brent; Clayson, C. A.

    2012-01-01

    Residual forcing necessary to close the MLTB on seasonal time scales are largest in regions of strongest surface heat flux forcing. Identifying the dominant source of error - surface heat flux error, mixed layer depth estimation, ocean dynamical forcing - remains a challenge in the eastern tropical oceans where ocean processes are very active. Improved sub-surface observations are necessary to better constrain errors. 1. Mixed layer depth evolution is critical to the seasonal evolution of mixed layer temperatures. It determines the inertia of the mixed layer, and scales the sensitivity of the MLTB to errors in surface heat flux and ocean dynamical forcing. This role produces timing impacts for errors in SST prediction. 2. Errors in the MLTB are larger than the historical 10Wm-2 target accuracy. In some regions, a larger accuracy can be tolerated if the goal is to resolve the seasonal SST cycle.

  20. LANL C10.2 Projects in FY13

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Batha, Steven H.; Fincke, James R.; Schmitt, Mark J.

    2012-06-07

    LANL has two projects in C10.2: Defect-Induced Mix Experiment (DIME) (ongoing, several runs at Omega; NIF shots this summer); and Shock/Shear (tested at Omega for two years; NIF shots in second half of FY13). Each project is jointly funded by C10.2, other C10 MTEs, and Science Campaigns. DIME is investigating 4{pi} and feature-induced mix in spherically convergent ICF implosions by using imaging of the mix layer. DIME prepared for NIF by demonstrating its PDD mix platform on Omega including imaging mid-Z doped layers and defects. DIME in FY13 will focus on PDD symmetry-dependent mix and moving burn into the mixmore » region for validation of mix/burn models. Re-Shock and Shear are two laser-driven experiments designed to study the turbulent mixing of materials. In FY-2012 43 shear and re-shock experimental shots were executed on the OMEGA laser and a complete time history obtained for both. The FY-2013 goal is to transition the experiment to NIF where the larger scale will provide a longer time period for mix layer growth.« less

  1. A Two-Timescale Response of the Southern Ocean to Ozone Depletion: Importance of the Background State

    NASA Astrophysics Data System (ADS)

    Seviour, W.; Waugh, D.; Gnanadesikan, A.

    2016-02-01

    It has been recently suggested that the response of Southern Ocean sea-ice extent to stratospheric ozone depletion is time-dependent; that the ocean surface initially cools due to enhanced northward Ekman drift caused by a poleward shift in the eddy-driven jet, and then warms after some time due to upwelling of warm waters from below the mixed layer. It is therefore possible that ozone depletion could act to favor a short-term increase in sea-ice extent. However, many uncertainties remain in understanding this mechanism, with different models showing widely differing time-scales and magnitudes of the response. Here, we analyze an ensemble of coupled model simulations with a step-function ozone perturbation. The two-timescale response is present with an approximately 30 year initial cooling period. The response is further shown to be highly dependent upon the background ocean temperature and salinity stratification, which is influenced by both natural internal variability and the isopycnal eddy mixing parameterization. It is suggested that the majority of inter-model differences in the Southern Ocean response to ozone depletion are caused by differences in stratification.

  2. The mean and turbulent flow structure of a weak hydraulic jump

    NASA Astrophysics Data System (ADS)

    Misra, S. K.; Kirby, J. T.; Brocchini, M.; Veron, F.; Thomas, M.; Kambhamettu, C.

    2008-03-01

    The turbulent air-water interface and flow structure of a weak, turbulent hydraulic jump are analyzed in detail using particle image velocimetry measurements. The study is motivated by the need to understand the detailed dynamics of turbulence generated in steady spilling breakers and the relative importance of the reverse-flow and breaker shear layer regions with attention to their topology, mean flow, and turbulence structure. The intermittency factor derived from turbulent fluctuations of the air-water interface in the breaker region is found to fit theoretical distributions of turbulent interfaces well. A conditional averaging technique is used to calculate ensemble-averaged properties of the flow. The computed mean velocity field accurately satisfies mass conservation. A thin, curved shear layer oriented parallel to the surface is responsible for most of the turbulence production with the turbulence intensity decaying rapidly away from the toe of the breaker (location of largest surface curvature) with both increasing depth and downstream distance. The reverse-flow region, localized about the ensemble-averaged free surface, is characterized by a weak downslope mean flow and entrainment of water from below. The Reynolds shear stress is negative in the breaker shear layer, which shows that momentum diffuses upward into the shear layer from the flow underneath, and it is positive just below the mean surface indicating a downward flux of momentum from the reverse-flow region into the shear layer. The turbulence structure of the breaker shear layer resembles that of a mixing layer originating from the toe of the breaker, and the streamwise variations of the length scale and growth rate are found to be in good agreement with observed values in typical mixing layers. All evidence suggests that breaking is driven by a surface-parallel adverse pressure gradient and a streamwise flow deceleration at the toe of the breaker. Both effects force the shear layer to thicken rapidly, thereby inducing a sharp free surface curvature change at the toe.

  3. Similarity scaling of turbulence in small temperate lake: implication for gas flux: implication for gas flux

    NASA Astrophysics Data System (ADS)

    Tedford, E. W.; MacIntyre, S.; Miller, S. D.; Czikowsky, M. J.

    2013-12-01

    The actively mixing layer, or surface layer, is the region of the upper mixed layer of lakes, oceans and the atmosphere directly influenced by wind, heating and cooling. Turbulence within the surface mixing layer has a direct impact on important ecological processes. The Monin-Obukhov length scale (LMO) is a critical length scale used in predicting and understanding turbulence in the actively mixed layer. On the water side of the air-water interface, LMO is defined as: LMO=-u*^3/(0.4 JB0) where u*, the shear velocity, is defined as (τ/rho)^0.5 where τ is the shear stress and rho is the density of water and JBO is the buoyancy flux at the surface. Above the depth equal to the absolute value of the Monin-Obukhov length scale (zMO), wind shear is assumed to dominate the production of turbulent kinetic energy (TKE). Below zMO, the turbulence is assumed to be suppressed when JB0 is stabilizing (warming surface waters) and enhanced when the buoyancy flux is destabilizing (cooling surface waters). Our observed dissipations were well represented using the canonical similarity scaling equations. The Monin-Obukhov length scale was generally effective in separating the surface-mixing layer into two regions: an upper region, dominated by wind shear; and a lower region, dominated by buoyancy flux. During both heating and cooling and above a depth equal to |LMO|, turbulence was dominated by wind shear and dissipation followed law of the wall scaling although was slightly augmented by buoyancy flux during both heating and cooling. Below a depth equal to |LMO| during cooling, dissipation was nearly uniform with depth. Although distinguishing between an upper region of the actively mixing layer dominated by wind stress and a lower portion dominated by buoyancy flux is typically accurate the most accurate estimates of dissipation include the effects of both wind stress and buoyancy flux throughout the actively mixed layer. We demonstrate and discuss the impact of neglecting the non-dominant forcing (buoyancy flux above zMO and wind stress below zMO) above and below zMO.

  4. Upper Ocean Mixing Processes and Circulation in the Arabian Sea during Monsoons using Remote Sensing, Hydrographic Observations and HYCOM Simulations

    DTIC Science & Technology

    2015-09-30

    effecting the salinity of the upper layer and the formation of the barrier layer (BL) within the isothermal layer. The BL in turn controls vertical mixing...daily values over a month with a 1° horizontal resolution [Reynolds et al., 2002]. Daily data (from Coriolis project) and Monthly gridded Argo

  5. Spatiotemporal Variability in Observations of Urban Mixed-Layer Heights from Surface-based Lidar Systems during DISCOVER-AQ 2011

    NASA Astrophysics Data System (ADS)

    Lewis, J. R.; Banks, R. F.; Berkoff, T.; Welton, E. J.; Joseph, E.; Thompson, A. M.; Decola, P.; Hegarty, J. D.

    2015-12-01

    Accurate characterization of the planetary boundary layer height is crucial for numerical weather prediction, estimating pollution emissions and modeling air quality. More so, given the increasing trend in global urban populations, there is a growing need to improve our understanding of the urban boundary layer structure and development. The Deriving Information on Surface conditions from COlumn and VERtically resolved observations relevant to Air Quality (DISCOVER-AQ) 2011 field campaign, which took place in the Baltimore-Washington DC region, offered a unique opportunity to study boundary layer processes in an urban area using a geographically dense collection of surface-based lidar systems (see figure). Lidars use aerosols as tracers for atmospheric boundary layer dynamics with high vertical and temporal resolutions. In this study, we use data from two permanent Micropulse Lidar Network (MPLNET) sites and five field deployed Micropulse lidar (MPL) systems in order to observe spatiotemporal variations in the daytime mixed layer height. We present and compare lidar-derived retrievals of the mixed layer height using two different methods. The first method uses the wavelet covariance transform and a "fuzzy logic" attribution scheme in order to determine the mixed layer height. The second method uses an objective approach utilizing a time-adaptive extended Kalman filter. Independent measurements of the boundary layer height are obtained using profiles from ozonesonde launches at the Beltsville and Edgewood sites for comparison with lidar observations.

  6. Control of Evaporation Behavior of an Inkjet-Printed Dielectric Layer Using a Mixed-Solvent System

    NASA Astrophysics Data System (ADS)

    Yang, Hak Soon; Kang, Byung Ju; Oh, Je Hoon

    2016-01-01

    In this study, the evaporation behavior and the resulting morphology of inkjet-printed dielectric layers were controlled using a mixed-solvent system to fabricate uniform poly-4-vinylphenol (PVP) dielectric layers without any pinholes. The mixed-solvent system consisted of two different organic solvents: 1-hexanol and ethanol. The effects of inkjet-printing variables such as overlap condition, substrate temperature, and different printing sequences (continuous and interlacing printing methods) on the inkjet-printed dielectric layer were also investigated. Increasing volume fraction of ethanol (VFE) is likely to reduce the evaporation rate gradient and the drying time of the inkjet-printed dielectric layer; this diminishes the coffee stain effect and thereby improves the uniformity of the inkjet-printed dielectric layer. However, the coffee stain effect becomes more severe with an increase in the substrate temperature due to the enhanced outward convective flow. The overlap condition has little effect on the evaporation behavior of the printed dielectric layer. In addition, the interlacing printing method results in either a stronger coffee stain effect or wavy structures of the dielectric layers depending on the VFE of the PVP solution. All-inkjet-printed capacitors without electrical short circuiting can be successfully fabricated using the optimized PVP solution (VFE = 0.6); this indicates that the mixed-solvent system is expected to play an important role in the fabrication of high-quality inkjet-printed dielectric layers in various printed electronics applications.

  7. Area production in supercritical, transitional mixing layers for reactive flow applications

    NASA Technical Reports Server (NTRS)

    Bellan, J.; Okong'o, N.

    2002-01-01

    An investigation of surface area production is conducted for supercritical mixing layers; the results are relevant to flame area evolution and fluid disintegration. In this study, the surface is chosen perpendicular to the mass fraction gradient.

  8. Detailed characteristics of drop-laden mixing layers: LES predictions compared to DNS

    NASA Technical Reports Server (NTRS)

    Okong'o, N.; Leboissetier, A.; Bellan, J.

    2004-01-01

    Results have been compared from Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) of a temporal mixing layer laden with evaporating drops, to assess the ability of LES to reproduce detailed characteristics of DNS.

  9. A Hybrid Numerical Method for Turbulent Mixing Layers. Degree awarded by Case Western Reserve Univ.

    NASA Technical Reports Server (NTRS)

    Georgiadis, Nicholas J.

    2001-01-01

    A hybrid method has been developed for simulations of compressible turbulent mixing layers. Such mixing layers dominate the flows in exhaust systems of modern day aircraft and also those of hypersonic vehicles currently under development. The method configurations in which a dominant structural feature provides an unsteady mechanism to drive the turbulent development in the mixing layer. The hybrid method uses a Reynolds-averaged Navier-Stokes (RANS) procedure to calculate wall bounded regions entering a mixing section, and a Large Eddy Simulation (LES) procedure to calculate the mixing dominated regions. A numerical technique was developed to enable the use of the hybrid RANS-LES method on stretched, non-Cartesian grids. Closure for the RANS equations was obtained using the Cebeci-Smith algebraic turbulence model in conjunction with the wall-function approach of Ota and Goldberg. The wall-function approach enabled a continuous computational grid from the RANS regions to the LES region. The LES equations were closed using the Smagorinsky subgrid scale model. The hybrid RANS-LES method is applied to a benchmark compressible mixing layer experiment. Preliminary two dimensional calculations are used to investigate the effects of axial grid density and boundary conditions. Vortex shedding from the base region of a splitter plate separating the upstream flows was observed to eventually transition to turbulence. The location of the transition, however, was much further downstream than indicated by experiments. Actual LES calculations, performed in three spatial directions, also indicated vortex shedding, but the transition to turbulence was found to occur much closer to the beginning of the mixing section. which is in agreement with experimental observations. These calculations demonstrated that LES simulations must be performed in three dimensions. Comparisons of time-averaged axial velocities and turbulence intensities indicated reasonable agreement with experimental data.

  10. Validation of an ocean shelf model for the prediction of mixed-layer properties in the Mediterranean Sea west of Sardinia

    NASA Astrophysics Data System (ADS)

    Onken, Reiner

    2017-04-01

    The Regional Ocean Modeling System (ROMS) has been employed to explore the sensitivity of the forecast skill of mixed-layer properties to initial conditions, boundary conditions, and vertical mixing parameterisations. The initial and lateral boundary conditions were provided by the Mediterranean Forecasting System (MFS) or by the MERCATOR global ocean circulation model via one-way nesting; the initial conditions were additionally updated through the assimilation of observations. Nowcasts and forecasts from the weather forecast models COSMO-ME and COSMO-IT, partly melded with observations, served as surface boundary conditions. The vertical mixing was parameterised by the GLS (generic length scale) scheme Umlauf and Burchard (2003) in four different set-ups. All ROMS forecasts were validated against the observations which were taken during the REP14-MED survey to the west of Sardinia. Nesting ROMS in MERCATOR and updating the initial conditions through data assimilation provided the best agreement of the predicted mixed-layer properties with the time series from a moored thermistor chain. Further improvement was obtained by the usage of COSMO-ME atmospheric forcing, which was melded with real observations, and by the application of the k-ω vertical mixing scheme with increased vertical eddy diffusivity. The predicted temporal variability of the mixed-layer temperature was reasonably well correlated with the observed variability, while the modelled variability of the mixed-layer depth exhibited only agreement with the observations near the diurnal frequency peak. For the forecasted horizontal variability, reasonable agreement was found with observations from a ScanFish section, but only for the mesoscale wave number band; the observed sub-mesoscale variability was not reproduced by ROMS.

  11. Mixed layer depths via Doppler lidar during low-level jet events

    NASA Astrophysics Data System (ADS)

    Carroll, Brian; Demoz, Belay; Bonin, Timothy; Delgado, Ruben

    2018-04-01

    A low-level jet (LLJ) is a prominent wind speed peak in the lower troposphere. Nocturnal LLJs have been shown to transport and mix atmospheric constituents from the residual layer down to the surface, breaching quiescent nocturnal conditions due to high wind shear. A new fuzzy logic algorithm combining turbulence and aerosol information from Doppler lidar scans can resolve the strength and depth of this mixing below the jet. Conclusions will be drawn about LLJ relations to turbulence and mixing.

  12. Pretreated Butterfly Wings for Tuning the Selective Vapor Sensing.

    PubMed

    Piszter, Gábor; Kertész, Krisztián; Bálint, Zsolt; Biró, László Péter

    2016-09-07

    Photonic nanoarchitectures occurring in the scales of Blue butterflies are responsible for their vivid blue wing coloration. These nanoarchitectures are quasi-ordered nanocomposites which are constituted from a chitin matrix with embedded air holes. Therefore, they can act as chemically selective sensors due to their color changes when mixing volatile vapors in the surrounding atmosphere which condensate into the nanoarchitecture through capillary condensation. Using a home-built vapor-mixing setup, the spectral changes caused by the different air + vapor mixtures were efficiently characterized. It was found that the spectral shift is vapor-specific and proportional with the vapor concentration. We showed that the conformal modification of the scale surface by atomic layer deposition and by ethanol pretreatment can significantly alter the optical response and chemical selectivity, which points the way to the efficient production of sensor arrays based on the knowledge obtained through the investigation of modified butterfly wings.

  13. Pretreated Butterfly Wings for Tuning the Selective Vapor Sensing

    PubMed Central

    Piszter, Gábor; Kertész, Krisztián; Bálint, Zsolt; Biró, László Péter

    2016-01-01

    Photonic nanoarchitectures occurring in the scales of Blue butterflies are responsible for their vivid blue wing coloration. These nanoarchitectures are quasi-ordered nanocomposites which are constituted from a chitin matrix with embedded air holes. Therefore, they can act as chemically selective sensors due to their color changes when mixing volatile vapors in the surrounding atmosphere which condensate into the nanoarchitecture through capillary condensation. Using a home-built vapor-mixing setup, the spectral changes caused by the different air + vapor mixtures were efficiently characterized. It was found that the spectral shift is vapor-specific and proportional with the vapor concentration. We showed that the conformal modification of the scale surface by atomic layer deposition and by ethanol pretreatment can significantly alter the optical response and chemical selectivity, which points the way to the efficient production of sensor arrays based on the knowledge obtained through the investigation of modified butterfly wings. PMID:27618045

  14. Solid-state membrane module

    DOEpatents

    Gordon, John Howard [Salt Lake City, UT; Taylor, Dale M [Murray, UT

    2011-06-07

    Solid-state membrane modules comprising at least one membrane unit, where the membrane unit has a dense mixed conducting oxide layer, and at least one conduit or manifold wherein the conduit or manifold comprises a dense layer and at least one of a porous layer and a slotted layer contiguous with the dense layer. The solid-state membrane modules may be used to carry out a variety of processes including the separating of any ionizable component from a feedstream wherein such ionizable component is capable of being transported through a dense mixed conducting oxide layer of the membrane units making up the membrane modules. For ease of construction, the membrane units may be planar.

  15. Relationship Between the Sonic Layer Depth and Mixed Layer Depth Identified from U.S. Navy Sea Glider Data

    DTIC Science & Technology

    2014-09-01

    LAYER DEPTH AND MIXED LAYER DEPTH IDENTIFIED FROM U.S. NAVY SEA GLIDER DATA Vance A. Villarreal September 2014 Thesis Advisor: Peter C. Chu Second...searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments...DEPTH IDENTIFIED FROM U.S. NAVY SEA GLIDER DATA 5. FUNDING NUMBERS 6. AUTHOR(S) Vance A. Villarreal 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES

  16. Biological Behavior of Osteoblast Cell and Apatite Forming Ability of the Surface Modified Ti Alloys.

    PubMed

    Zhao, Jingming; Hwang, K H; Choi, W S; Shin, S J; Lee, J K

    2016-02-01

    Titanium as one kind of biomaterials comes in direct contact with the body, making evaluation of biocompatibility an important aspect to biomaterials development. Surface chemistry of titanium plays an important role in osseointegration. Different surface modification alters the surface chemistry and result in different biological response. In this study, three kinds of mixed acid solutions were used to treat Ti specimens to induce Ca-P formation. Following a strong mixed acid activation process, Ca-P coating successfully formed on the Ti surfaces in simulated body fluid. Strong mixed acid increased the roughness of the metal surface, because the porous and rough surface allows better adhesion between Ca-P coatings and substrates. After modification of titanium surface by mixed acidic solution and subsequently H2O2/HCL treatment evaluation of biocompatibility was conducted from hydroxyapatite formation by biomimetic process and cell viability on modified titanium surface. Nano-scale modification of titanium surfaces can alter cellular and tissue responses, which may benefit osseointegration and dental implant therapy. Results from this study indicated that surface treatment methods affect the surface morphology, type of TiO2 layer formed and subsequent apatite deposition and biological responses. The thermo scientific alamarblue cell viability assay reagent is used to quantitatively measure the viability of mammalian cell lines, bacteria and fungi by incorporating a rapid, sensitive and reliable fluorometric/colorimetric growth indicator, without any toxic and side effect to cell line. In addition, mixed acid treatment uses a lower temperature and shorter time period than widely used alkali treatment.

  17. Numerical simulations of compressible mixing layers

    NASA Technical Reports Server (NTRS)

    Normand, Xavier

    1990-01-01

    Direct numerical simulations of two-dimensional temporally growing compressible mixing layers are presented. The Kelvin-Helmholtz instability is initially excited by a white-noise perturbation superimposed onto a hyperbolic tangent meanflow profile. The linear regime is studied at low resolution in the case of two flows of equal temperatures, for convective Mach numbers from 0.1 to 1 and for different values of the Reynolds number. At higher resolution, the complete evolution of a two-eddy mixing layer between two flows of different temperatures is simulated at moderate Reynolds number. Similarities and differences between flows of equal convective Mach numbers are discussed.

  18. Photoionized Mixing Layer Models of the Diffuse Ionized Gas

    NASA Astrophysics Data System (ADS)

    Binette, Luc; Flores-Fajardo, Nahiely; Raga, Alejandro C.; Drissen, Laurent; Morisset, Christophe

    2009-04-01

    It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer (TML) models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated, and mixed. The emission spectrum of such layers is compared with observations of Rand of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S II]/Hα, [O I]/Hα, [N II]/[S II], and [O III]/Hβ reasonably well. In one sequence of models, the hot wind velocity increases, while in the other, the ionization parameter and layer opacity increase. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.

  19. Combustion Diagnostics and Flow Visualization of Hypergolic Combustion and Gelled Mixing Behavior

    DTIC Science & Technology

    1997-12-19

    difference. Also, Exciplex Flourescence imaging has been implented to visualize diffusion layers which form at the contact interface of mixing...have been implemented and developed as a result of this effort. Among these techniques the most noteworthy involves a unique application of Exciplex ...fluorescence for visualization of diffusion layers formed between mixing liquids. Time resolved images of Exciplex fluorescence have been obtained

  20. Investigating Summer Thermal Stratification in Lake Ontario

    NASA Astrophysics Data System (ADS)

    James, S. C.; Arifin, R. R.; Craig, P. M.; Hamlet, A. F.

    2017-12-01

    Seasonal temperature variations establish strong vertical density gradients (thermoclines) between the epilimnion and hypolimnion. Accurate simulation of vertical mixing and seasonal stratification of large lakes is a crucial element of the thermodynamic coupling between lakes and the atmosphere in integrated models. Time-varying thermal stratification patterns can be accurately simulated with the versatile Environmental Fluid Dynamics Code (EFDC). Lake Ontario bathymetry was interpolated onto a 2-km-resolution curvilinear grid with vertical layering using a new approach in EFDC+, the so-called "sigma-zed" coordinate system which allows the number of vertical layers to be varied based on water depth. Inflow from the Niagara River and outflow to the St. Lawrence River in conjunction with hourly meteorological data from seven local weather stations plus three-hourly data from the North American Regional Reanalysis govern the hydrodynamic and thermodynamic responses of the Lake. EFDC+'s evaporation algorithm was updated to more accurately simulate net surface heat fluxes. A new vertical mixing scheme from Vinçon-Leite that implements different eddy diffusivity formulations above and below the thermocline was compared to results from the original Mellor-Yamada vertical mixing scheme. The model was calibrated by adjusting solar-radiation absorption coefficients in addition to background horizontal and vertical mixing parameters. Model skill was evaluated by comparing measured and simulated vertical temperature profiles at shallow (20 m) and deep (180 m) locations on the Lake. These model improvements, especially the new sigma-zed vertical discretization, accurately capture thermal-stratification patterns with low root-mean-squared errors when using the Vinçon-Leite vertical mixing scheme.

  1. Effect of initial conditions on constant pressure mixing between two turbulent streams

    NASA Astrophysics Data System (ADS)

    Kangovi, S.

    1983-02-01

    It is pointed out that a study of the process of mixing between two dissimilar streams has varied applications in different fields. The applications include the design of an after burner in a high by-pass ratio aircraft engine and the disposal of effluents in a stream. The mixing process determines important quantities related to the energy transfer from main stream to the secondary stream, the temperature and velocity profiles, and the local kinematic and dissipative structure within the mixing region, and the growth of the mixing layer. Hill and Page (1968) have proposed the employment of an 'assumed epsilon' method in which the eddy viscosity model of Goertler (1942) is modified to account for the initial boundary layer. The present investigation is concerned with the application of the assumed epsilon technique to the study of the effect of initial conditions on the development of the turbulent mixing layer between two compressible, nonisoenergetic streams at constant pressure.

  2. Photomixing of chlamydomonas rheinhardtii suspensions

    NASA Astrophysics Data System (ADS)

    Dervaux, Julien; Capellazzi Resta, Marina; Abou, Bérengère; Brunet, Philippe

    2014-11-01

    Chlamydomonas rheinhardtii is a fast swimming unicellular alga able to bias its swimming direction in gradients of light intensity, an ability know as phototaxis. We have investigated experimentally both the swimming behavior of individual cells and the macroscopic response of shallow suspensions of these micro-organisms in response to a localized light source. At low light intensity, algae exhibit positive phototaxis and accumulate beneath the excitation light. In weakly concentrated thin layers, the balance between phototaxis and cell motility results in steady symmetrical patterns compatible with a purely diffusive model using effective diffusion coefficients extracted from the analysis of individual cell trajectories. However, at higher cell density and layer depth, collective effects induce convective flows around the light source. These flows disturb the cell concentration patterns which spread and may then becomes unstable. Using large passive tracer particles, we have characterized the velocity fields associated with this forced bioconvection and their dependence on the cell density and layer depth. By tuning the light distribution, this mechanism of photo-bioconvection allows a fine control over the local fluid flows, and thus the mixing efficiency, in algal suspensions.

  3. Numerical Study of the Response of an Atmospheric Surface Layer to a Spatially Nonuniform Plant Canopy

    NASA Astrophysics Data System (ADS)

    Qiu, J.; Gu, Z. L.; Wang, Z. S.

    2008-05-01

    High-accuracy large-eddy simulations of neutral atmospheric surface-layer flow over a gapped plant canopy strip have been performed. Subgrid-scale (SGS) motions are parameterized by the Sagaut mixed length SGS model, with a modification to compute the SGS characteristic length self-adaptively. Shaw’s plant canopy model, taking the vertical variation of leaf area density into account, is applied to study the response of the atmospheric surface layer to the gapped dense forest strip. Differences in the region far away from the gap and in the middle of the gap are investigated, according to the instantaneous velocity magnitude, the zero-plane displacement, the potential temperature and the streamlines. The large-scale vortex structure, in the form of a roll vortex, is revealed in the region far away from the gap. The nonuniform spatial distribution of plants appears to cause the formation of the coherent structure. The roll vortex starts in the wake of the canopy, and results in strong fluctuations throughout the entire canopy region. Wind sweeps and ejections in the plant canopy are also attributed to the large vortex structure.

  4. Mixing Acid Salts and Layered Double Hydroxides in Nanoscale under Solid Condition

    PubMed Central

    Nakayama, Hirokazu; Hayashi, Aki

    2014-01-01

    The immobilization of potassium sorbate, potassium aspartate and sorbic acid in layered double hydroxide under solid condition was examined. By simply mixing two solids, immobilization of sorbate and aspartate in the interlayer space of nitrate-type layered double hydroxide, so called intercalation reaction, was achieved, and the uptakes, that is, the amount of immobilized salts and the interlayer distances of intercalation compounds were almost the same as those obtained in aqueous solution. However, no intercalation was achieved for sorbic acid. Although intercalation of sorbate and aspartate into chloride-type layered double hydroxide was possible, the uptakes for these intercalation compounds were lower than those obtained using nitrate-type layered double hydroxide. The intercalation under solid condition could be achieved to the same extent as for ion-exchange reaction in aqueous solution, and the reactivity was similar to that observed in aqueous solution. This method will enable the encapsulation of acidic drug in layered double hydroxide as nano level simply by mixing both solids. PMID:25080007

  5. Mixing Acid Salts and Layered Double Hydroxides in Nanoscale under Solid Condition.

    PubMed

    Nakayama, Hirokazu; Hayashi, Aki

    2014-07-30

    The immobilization of potassium sorbate, potassium aspartate and sorbic acid in layered double hydroxide under solid condition was examined. By simply mixing two solids, immobilization of sorbate and aspartate in the interlayer space of nitrate-type layered double hydroxide, so called intercalation reaction, was achieved, and the uptakes, that is, the amount of immobilized salts and the interlayer distances of intercalation compounds were almost the same as those obtained in aqueous solution. However, no intercalation was achieved for sorbic acid. Although intercalation of sorbate and aspartate into chloride-type layered double hydroxide was possible, the uptakes for these intercalation compounds were lower than those obtained using nitrate-type layered double hydroxide. The intercalation under solid condition could be achieved to the same extent as for ion-exchange reaction in aqueous solution, and the reactivity was similar to that observed in aqueous solution. This method will enable the encapsulation of acidic drug in layered double hydroxide as nano level simply by mixing both solids.

  6. Secondary growth mechanism of SiGe islands deposited on a mixed-phase microcrystalline Si by ion beam co-sputtering.

    PubMed

    Ke, S Y; Yang, J; Qiu, F; Wang, Z Q; Wang, C; Yang, Y

    2015-11-06

    We discuss the SiGe island co-sputtering deposition on a microcrystalline silicon (μc-Si) buffer layer and the secondary island growth based on this pre-SiGe island layer. The growth phenomenon of SiGe islands on crystalline silicon (c-Si) is also investigated for comparison. The pre-SiGe layer grown on μc-Si exhibits a mixed-phase structure, including SiGe islands and amorphous SiGe (a-SiGe) alloy, while the layer deposited on c-Si shows a single-phase island structure. The preferential growth and Ostwald ripening growth are shown to be the secondary growth mechanism of SiGe islands on μc-Si and c-Si, respectively. This difference may result from the effect of amorphous phase Si (AP-Si) in μc-Si on the island growth. In addition, the Si-Ge intermixing behavior of the secondary-grown islands on μc-Si is interpreted by constructing the model of lateral atomic migration, while this behavior on c-Si is ascribed to traditional uphill atomic diffusion. It is found that the aspect ratios of the preferential-grown super islands are higher than those of the Ostwald-ripening ones. The lower lateral growth rate of super islands due to the lower surface energy of AP-Si on the μc-Si buffer layer for the non-wetting of Ge at 700 °C and the stronger Si-Ge intermixing effect at 730 °C may be responsible for this aspect ratio difference.

  7. Aspects of Supercritical Turbulence: Direct Numerical Simulation of O2/H2 and C7H16/N2 Temporal Mixing Layers

    NASA Technical Reports Server (NTRS)

    Bellan, J.; Okongo, N. A.; Harstad, K. G.; Hutt, John (Technical Monitor)

    2002-01-01

    Results from Direct Numerical Simulations of temporal, supercritical mixing layers for two species systems are analyzed to elucidate species-specific turbulence aspects. The two species systems, O2/H2 and C7HG16/N2, have different thermodynamic characteristics; thus, although the simulations are performed at similar reduced pressure (ratio of the pressure to the critical pressure), the former system is dose to mixture ideality and has a relatively high solubility with respect to the latter, which exhibits strong departures from mixture ideality Due to the specified, smaller initial density stratification, the C7H16/N2 layers display higher growth and increased global molecular mixing as well as larger turbulence levels. However, smaller density gradients at the transitional state for the O2/H2 system indicate that on a local basis, the layer exhibits an enhanced mixing, this being attributed to the increased solubility and to mixture ideality. These thermodynamic features are shown to affect the irreversible entropy production (i.e. the dissipation), which is larger for the O2/H2 layer and is primarily concentrated in high density-gradient magnitude regions that are distortions of the initial density stratification boundary. In contrast, the regions of largest dissipation in the C7H16/N2 layer are located in high density-gradient magnitude regions resulting from the mixing of the two fluids.

  8. The Vertical Dust Profile Over Gale Crater, Mars

    NASA Astrophysics Data System (ADS)

    Guzewich, Scott D.; Newman, C. E.; Smith, M. D.; Moores, J. E.; Smith, C. L.; Moore, C.; Richardson, M. I.; Kass, D.; Kleinböhl, A.; Mischna, M.; Martín-Torres, F. J.; Zorzano-Mier, M.-P.; Battalio, M.

    2017-12-01

    We create a vertically coarse, but complete, profile of dust mixing ratio from the surface to the upper atmosphere over Gale Crater, Mars, using the frequent joint atmospheric observations of the orbiting Mars Climate Sounder (MCS) and the Mars Science Laboratory Curiosity rover. Using these data and an estimate of planetary boundary layer (PBL) depth from the MarsWRF general circulation model, we divide the vertical column into three regions. The first region is the Gale Crater PBL, the second is the MCS-sampled region, and the third is between these first two. We solve for a well-mixed dust mixing ratio within this third (middle) layer of atmosphere to complete the profile. We identify a unique seasonal cycle of dust within each atmospheric layer. Within the Gale PBL, dust mixing ratio maximizes near southern hemisphere summer solstice (Ls = 270°) and minimizes near winter solstice (Ls = 90-100°) with a smooth sinusoidal transition between them. However, the layer above Gale Crater and below the MCS-sampled region more closely follows the global opacity cycle and has a maximum in opacity near Ls = 240° and exhibits a local minimum (associated with the "solsticial pause" in dust storm activity) near Ls = 270°. With knowledge of the complete vertical dust profile, we can also assess the frequency of high-altitude dust layers over Gale. We determine that 36% of MCS profiles near Gale Crater contain an "absolute" high-altitude dust layer wherein the dust mixing ratio is the maximum in the entire vertical column.

  9. Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere-ocean-wave model

    NASA Astrophysics Data System (ADS)

    Prakash, Kumar Ravi; Nigam, Tanuja; Pant, Vimlesh

    2018-04-01

    A coupled atmosphere-ocean-wave model was used to examine mixing in the upper-oceanic layers under the influence of a very severe cyclonic storm Phailin over the Bay of Bengal (BoB) during 10-14 October 2013. The coupled model was found to improve the sea surface temperature over the uncoupled model. Model simulations highlight the prominent role of cyclone-induced near-inertial oscillations in subsurface mixing up to the thermocline depth. The inertial mixing introduced by the cyclone played a central role in the deepening of the thermocline and mixed layer depth by 40 and 15 m, respectively. For the first time over the BoB, a detailed analysis of inertial oscillation kinetic energy generation, propagation, and dissipation was carried out using an atmosphere-ocean-wave coupled model during a cyclone. A quantitative estimate of kinetic energy in the oceanic water column, its propagation, and its dissipation mechanisms were explained using the coupled atmosphere-ocean-wave model. The large shear generated by the inertial oscillations was found to overcome the stratification and initiate mixing at the base of the mixed layer. Greater mixing was found at the depths where the eddy kinetic diffusivity was large. The baroclinic current, holding a larger fraction of kinetic energy than the barotropic current, weakened rapidly after the passage of the cyclone. The shear induced by inertial oscillations was found to decrease rapidly with increasing depth below the thermocline. The dampening of the mixing process below the thermocline was explained through the enhanced dissipation rate of turbulent kinetic energy upon approaching the thermocline layer. The wave-current interaction and nonlinear wave-wave interaction were found to affect the process of downward mixing and cause the dissipation of inertial oscillations.

  10. Zirconia-based mixed potential sensor with Pt electrode prepared by spin-coating of polymeric precursor

    NASA Astrophysics Data System (ADS)

    Chrzan, A.; Woźniak, Ł.; Szymczewska, D.; Jasiński, P.

    2016-11-01

    Many types of yttria-stabilized zirconia (YSZ) based gas sensors have been explored extensively in recent years. Great attention have been directed to mixed-potential-type gas sensors. It is due to growing concerns with environmental issues. Not without a significance is the fact of very attractive performance of this type of sensor allowing to detect low concentration of pollutant gases. In this paper two types of YSZ based mixed-potential planar sensors were investigated, with platinum electrode painted using commercial paste and with spin coated platinum layer. Both types had second electrode in the form of porous gold. Measurements were performed at 400 °C in synthetic air and different concentrations of SO2. Gas flow was set to 100 cm3min-1 and the concentration of 50 ppm SO2 was tested. During this measurements the sensor was sintered in-situ at increasing temperatures. Sensor with 100 nm spin-coated platinum layer sintered at 700 °C was shown to exhibit two times smaller response than sensor with 5 μm porous electrode, while consisting of over 20 times smaller amount of Pt. The influence of sintering temperature on electrical conductivity of platinum films was also examined. Moreover, the platinum microstructure was investigated using SEM microscopy.

  11. The PRISM (Pliocene Palaeoclimate) reconstruction: Time for a paradigm shift

    USGS Publications Warehouse

    Dowsett, Harry J.; Robinson, Marci M.; Stoll, Danielle K.; Foley, Kevin M.; Johnson, Andrew L. A.; Williams, Mark; Riesselman, Christina

    2013-01-01

    Global palaeoclimate reconstructions have been invaluable to our understanding of the causes and effects of climate change, but single-temperature representations of the oceanic mixed layer for data–model comparisons are outdated, and the time for a paradigm shift in marine palaeoclimate reconstruction is overdue. The new paradigm in marine palaeoclimate reconstruction stems the loss of valuable climate information and instead presents a holistic and nuanced interpretation of multi-dimensional oceanographic processes and responses. A wealth of environmental information is hidden within the US Geological Survey's Pliocene Research,Interpretation and Synoptic Mapping (PRISM) marine palaeoclimate reconstruction, and we introduce here a plan to incorporate all valuable climate data into the next generation of PRISM products. Beyond the global approach and focus, we plan to incorporate regional climate dynamics with emphasis on processes, integrating multiple environmental proxies wherever available in order to better characterize the mixed layer, and developing a finer time slice within the Mid-Piacenzian Age of the Pliocene, complemented by underused proxies that offer snapshots into environmental conditions. The result will be a proxy-rich, temporally nested, process-oriented approach in a digital format - a relational database with geographic information system capabilities comprising a three-dimensional grid representing the surface layer, with a plethora of data in each cell.

  12. Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators

    NASA Astrophysics Data System (ADS)

    Singh, Ashish; Little, Jesse

    2016-11-01

    A low speed turbulent mixing layer (Reθo =1282, U1 /U2 = 0 . 28 and U2 = 11 . 8 m / s) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number (St) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. Air Force Office of Scientific Research (FA9550-12-1-0044).

  13. Disintegration of fluids under supercritical conditions from mixing layer studies

    NASA Technical Reports Server (NTRS)

    Okong'o, N.; Bellan, J.

    2003-01-01

    Databases of transitional states obtained from Direct Numerical simulations (DNS) of temporal, supercritical mixing layers for two species systems, O2/H2 and C7H16/N2, are analyzed to elucidate species-specific turbulence aspects and features of fluid disintegration.

  14. Determination of the in-place hot-mix asphalt layer modulus for rehabilitation projects using a mechanistic-empirical procedure.

    DOT National Transportation Integrated Search

    2006-01-01

    This project evaluated the procedures proposed by the Mechanistic-Empirical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. Thirty-three cores were extracted from nine sites in Virginia...

  15. Assessment of mixed-layer height estimation from single-wavelength ceilometer profiles

    EPA Science Inventory

    Differing boundary/mixed-layer height measurement methods were assessed in moderately polluted and clean environments, with a focus on the Vaisala CL51 ceilometer. This intercomparison was performed as part of ongoing measurements at the Chemistry And Physics of the Atmospheric B...

  16. Land-atmosphere-ocean interactions in the southeastern Atlantic: interannual variability

    NASA Astrophysics Data System (ADS)

    Sun, Xiaoming; Vizy, Edward K.; Cook, Kerry H.

    2018-02-01

    Land-atmosphere-ocean interactions in the southeastern South Atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate-level ocean model. In austral summer, zonal displacements of the South Atlantic subtropical high (SASH) can induce variations of mixed-layer currents in the Benguela upwelling region through surface wind stress curl anomalies near the Namibian coast, and an eastward shifted SASH is related to the first Pacific-South American mode. When the SASH is meridionally displaced, mixed layer vertically-integrated Ekman transport anomalies are mainly a response to the change of alongshore surface wind stress. The latitudinal shift of the SASH tends to dampen the anomalous alongshore wind by modulating the land-sea thermal contrast, while opposed by oceanic diffusion. Although the position of the SASH is closely linked to the phase of El Niño-Southern Oscillation (ENSO) and the southern annular mode (SAM) in austral summer, an overall relationship between Benguela upwelling strength and ENSO or SAM is absent. During austral winter, variations of the mixed layer Ekman transport in the Benguela upwelling region are connected to the strength of the SASH through its impact on both coastal wind stress curl and alongshore surface wind stress. Compared with austral summer, low-level cloud cover change plays a more important role. Although wintertime sea surface temperature fluctuations in the equatorial Atlantic are strong and may act to influence variability over the northern Benguela area, the surface heat budget analysis suggests that local air-sea interactions dominate.

  17. The influence of extratropical cloud phase and amount feedbacks on climate sensitivity

    NASA Astrophysics Data System (ADS)

    Frey, William R.; Kay, Jennifer E.

    2018-04-01

    Global coupled climate models have large long-standing cloud and radiation biases, calling into question their ability to simulate climate and climate change. This study assesses the impact of reducing shortwave radiation biases on climate sensitivity within the Community Earth System Model (CESM). The model is modified by increasing supercooled cloud liquid to better match absorbed shortwave radiation observations over the Southern Ocean while tuning to reduce a compensating tropical shortwave bias. With a thermodynamic mixed-layer ocean, equilibrium warming in response to doubled CO2 increases from 4.1 K in the control to 5.6 K in the modified model. This 1.5 K increase in equilibrium climate sensitivity is caused by changes in two extratropical shortwave cloud feedbacks. First, reduced conversion of cloud ice to liquid at high southern latitudes decreases the magnitude of a negative cloud phase feedback. Second, warming is amplified in the mid-latitudes by a larger positive shortwave cloud feedback. The positive cloud feedback, usually associated with the subtropics, arises when sea surface warming increases the moisture gradient between the boundary layer and free troposphere. The increased moisture gradient enhances the effectiveness of mixing to dry the boundary layer, which decreases cloud amount and optical depth. When a full-depth ocean with dynamics and thermodynamics is included, ocean heat uptake preferentially cools the mid-latitude Southern Ocean, partially inhibiting the positive cloud feedback and slowing warming. Overall, the results highlight strong connections between Southern Ocean mixed-phase cloud partitioning, cloud feedbacks, and ocean heat uptake in a climate forced by greenhouse gas changes.

  18. Approach for estimating the dynamic physical thresholds of phytoplankton production and biomass in the tropical-subtropical Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Gómez-Ocampo, E.; Gaxiola-Castro, G.; Durazo, Reginaldo

    2017-06-01

    Threshold is defined as the point where small changes in an environmental driver produce large responses in the ecosystem. Generalized additive models (GAMs) were used to estimate the thresholds and contribution of key dynamic physical variables in terms of phytoplankton production and variations in biomass in the tropical-subtropical Pacific Ocean off Mexico. The statistical approach used here showed that thresholds were shallower for primary production than for phytoplankton biomass (pycnocline < 68 m and mixed layer < 30 m versus pycnocline < 45 m and mixed layer < 80 m) but were similar for absolute dynamic topography and Ekman pumping (ADT < 59 cm and EkP > 0 cm d-1 versus ADT < 60 cm and EkP > 4 cm d-1). The relatively high productivity on seasonal (spring) and interannual (La Niña 2008) scales was linked to low ADT (45-60 cm) and shallow pycnocline depth (9-68 m) and mixed layer (8-40 m). Statistical estimations from satellite data indicated that the contributions of ocean circulation to phytoplankton variability were 18% (for phytoplankton biomass) and 46% (for phytoplankton production). Although the statistical contribution of models constructed with in situ integrated chlorophyll a and primary production data was lower than the one obtained with satellite data (11%), the fits were better for the former, based on the residual distribution. The results reported here suggest that estimated thresholds may reliably explain the spatial-temporal variations of phytoplankton in the tropical-subtropical Pacific Ocean off the coast of Mexico.

  19. Stability of mixing layers

    NASA Technical Reports Server (NTRS)

    Tam, Christopher; Krothapalli, A

    1993-01-01

    The research program for the first year of this project (see the original research proposal) consists of developing an explicit marching scheme for solving the parabolized stability equations (PSE). Performing mathematical analysis of the computational algorithm including numerical stability analysis and the determination of the proper boundary conditions needed at the boundary of the computation domain are implicit in the task. Before one can solve the parabolized stability equations for high-speed mixing layers, the mean flow must first be found. In the past, instability analysis of high-speed mixing layer has mostly been performed on mean flow profiles calculated by the boundary layer equations. In carrying out this project, it is believed that the boundary layer equations might not give an accurate enough nonparallel, nonlinear mean flow needed for parabolized stability analysis. A more accurate mean flow can, however, be found by solving the parabolized Navier-Stokes equations. The advantage of the parabolized Navier-Stokes equations is that its accuracy is consistent with the PSE method. Furthermore, the method of solution is similar. Hence, the major part of the effort of the work of this year has been devoted to the development of an explicit numerical marching scheme for the solution of the Parabolized Navier-Stokes equation as applied to the high-seed mixing layer problem.

  20. Update on Area Production in Mixing of Supercritical Fluids

    NASA Technical Reports Server (NTRS)

    Okongo, Nora; Bellan, Josette

    2003-01-01

    The focus of this research is on supercritical C7H16/N2 and O2/H2 mixing layers undergoing transitions to turbulence. The C7H16/N2 system serves as a simplified model of hydrocarbon/air systems in gas-turbine and diesel engines; the O2/H2 system is representative of liquid rocket engines. One goal of this research is to identify ways of controlling area production to increase disintegration of fluids and enhance combustion in such engines. As used in this research, "area production" signifies the fractional rate of change of surface area oriented perpendicular to the mass-fraction gradient of a mixing layer. In the study, a database of transitional states obtained from direct numerical simulations of the aforementioned mixing layers was analyzed to investigate global layer characteristics, phenomena in regions of high density-gradient magnitude (HDGM), irreversible entropy production and its relationship to the HDGM regions, and mechanisms leading to area production.

  1. Magnetic studies on Layered solid solution Lix(Ni0.4Mn0.6)2-xO2

    NASA Astrophysics Data System (ADS)

    Nakao, K.; Nakamura, T.; Yamada, Y.; Koshiba, N.

    2011-05-01

    Lix(Ni0.4Mn0.6)2-xO2 (1.09<=x<=1.23) were prepared by the solid-state reaction using LiOH and coprecipitated mixed hydroxide as raw materials. All the compounds have a layered rock-salt structure, and the cation mixing degree (Ni2+ occupancy in the Li-layer) decreases with an increase in x. From the low-temperature magnetic measurement, they all have negative Weiss temperature and spontaneous magnetization, that is, they are ferromagnetic materials. Both the Curie temperature and the spontaneous magnetization at 4.2K decrease with an increase in x. These magnetic variations are attributed to the lowering of the cation mixing degree: the magnetic interaction network turns to two-dimensional one with the loss of the inert-layer coupling. These situations may be considered semi-quantitatively using the ferromagnetic cluster model. Additionally, the cation mixing degree has an influence on their electrochemical properties such as cycle fading and rate capability.

  2. Turbulent entrainment in a strongly stratified barrier layer

    NASA Astrophysics Data System (ADS)

    Pham, H. T.; Sarkar, S.

    2017-06-01

    Large-eddy simulation (LES) is used to investigate how turbulence in the wind-driven ocean mixed layer erodes the stratification of barrier layers. The model consists of a stratified Ekman layer that is driven by a surface wind. Simulations at a wide range of N0/f are performed to quantify the effect of turbulence and stratification on the entrainment rate. Here, N0 is the buoyancy frequency in the barrier layer and f is the Coriolis parameter. The evolution of the mixed layer follows two stages: a rapid initial deepening and a late-time growth at a considerably slower rate. During the first stage, the mixed layer thickens to the depth that is proportional to u∗/fN0 where u∗ is the frictional velocity. During the second stage, the turbulence in the mixed layer continues to deepen further into the barrier layer, and the turbulent length scale is shown to scale with u∗/N0, independent of f. The late-time entrainment rate E follows the law of E=0.035Ri∗-1/2 where Ri∗ is the Richardson number. The exponent of -1/2 is identical but the coefficient of 0.035 is much smaller relative to the value of 2-3/2 for the nonrotating boundary layer. Simulations using the KPP model (version applicable to this simple case without additional effects of Langmuir turbulence or surface buoyancy flux) also yield the entrainment scaling of E∝Ri∗-1/2; however, the proportionality coefficient varies with the stratification. The structure of the Ekman current is examined to illustrate the strong effect of stratification in the limit of large N0/f.

  3. Structural properties and diffusion processes of the Cu 3Au (0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Wang, Fang; Zhang, Jian-Min; Zhang, Yan; Ji, Vincent

    2010-09-01

    The surface relaxation and surface energy of both the mixed AuCu and pure Cu terminated Cu 3Au (0 0 1) surfaces are simulated and calculated by using the modified analytical embedded-atom method. We find that the mixed AuCu termination is energetically preferred over the pure Cu termination thereby the mono-vacancy diffusion is also investigated in the topmost few layers of the mixed AuCu terminated Cu 3Au (0 0 1) surface. In the mixed AuCu terminated surface the relaxed Au atoms are raised above Cu atoms for 0.13 Å in the topmost layer. All the surface atoms displace outwards, this effect occurs in the first three layers and changes the first two inter-layer spacing. For mono-vacancy migration in the first layer, the migration energies of Au and Cu mono-vacancy via two-type in-plane displace: the nearest neighbor jump (NNJ) and the second nearest neighbor jump (2NNJ), are calculated and the results show that the NNJ requires a much lower energy than 2NNJ. For the evolution of the energy requirements for successive nearest neighbor jumps (SNNJ) along three different paths: circularity, zigzag and beeline, we find that the circularity path is preferred over the other two paths due to its minimum energy barriers and final energies. In the second layer, the NN jumps in intra- and inter-layer of the Cu mono-vacancy are investigated. The calculated energy barriers and final energies show that the vacancy prefer jump up to a proximate Cu site. This replacement between the Cu vacancy in the second layer and Cu atom in the first layer is remunerative for the Au atoms enrichment in the topmost layer.

  4. Relating large-scale subsidence to convection development in Arctic mixed-phase marine stratocumulus

    NASA Astrophysics Data System (ADS)

    Young, Gillian; Connolly, Paul J.; Dearden, Christopher; Choularton, Thomas W.

    2018-02-01

    Large-scale subsidence, associated with high-pressure systems, is often imposed in large-eddy simulation (LES) models to maintain the height of boundary layer (BL) clouds. Previous studies have considered the influence of subsidence on warm liquid clouds in subtropical regions; however, the relationship between subsidence and mixed-phase cloud microphysics has not specifically been studied. For the first time, we investigate how widespread subsidence associated with synoptic-scale meteorological features can affect the microphysics of Arctic mixed-phase marine stratocumulus (Sc) clouds. Modelled with LES, four idealised scenarios - a stable Sc, varied droplet (Ndrop) or ice (Nice) number concentrations, and a warming surface (representing motion southwards) - were subjected to different levels of subsidence to investigate the cloud microphysical response. We find strong sensitivities to large-scale subsidence, indicating that high-pressure systems in the ocean-exposed Arctic regions have the potential to generate turbulence and changes in cloud microphysics in any resident BL mixed-phase clouds.Increased cloud convection is modelled with increased subsidence, driven by longwave radiative cooling at cloud top and rain evaporative cooling and latent heating from snow growth below cloud. Subsidence strengthens the BL temperature inversion, thus reducing entrainment and allowing the liquid- and ice-water paths (LWPs, IWPs) to increase. Through increased cloud-top radiative cooling and subsequent convective overturning, precipitation production is enhanced: rain particle number concentrations (Nrain), in-cloud rain mass production rates, and below-cloud evaporation rates increase with increased subsidence.Ice number concentrations (Nice) play an important role, as greater concentrations suppress the liquid phase; therefore, Nice acts to mediate the strength of turbulent overturning promoted by increased subsidence. With a warming surface, a lack of - or low - subsidence allows for rapid BL turbulent kinetic energy (TKE) coupling, leading to a heterogeneous cloud layer, cloud-top ascent, and cumuli formation below the Sc cloud. In these scenarios, higher levels of subsidence act to stabilise the Sc layer, where the combination of these two forcings counteract one another to produce a stable, yet dynamic, cloud layer.

  5. Multi-layered zinc oxide-graphene composite thin films for selective nitrogen dioxide sensing

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; Bhowmick, T.; Majumder, S. B.

    2018-02-01

    In the present work, selective nitrogen dioxide (NO2) sensing characteristics of multi-layered graphene-zinc oxide (G-ZnO) thin films have been demonstrated at 150 °C. The response% of 5 ppm NO2 was measured to be 894% with response and recovery times estimated to be 150 s and 315 s, respectively. In these composite films, the interaction between graphene and zinc oxide is established through X-ray photoelectron spectroscopy in conjunction with the analyses of photoluminescence spectra. Superior NO2 sensing of these films is due to simultaneous chemiadsorption of molecular oxygen and NO2 gases onto graphene and ZnO surfaces, resulting in an appreciable increase in the depletion layer width and thereby the sensor resistance. The sensor responses for other reducing gases (viz., CO, H2, and i-C4H10) are postulated to be due to their catalytic oxidation on the sensor surface, resulting in a decrease in the sensor resistance upon gas exposure. At lower operating temperature, due to the molecular nature of the chemiadsorbed oxygen, poor catalytic oxidation leads to a far lower sensor response for reducing gases as compared to NO2. For mixed NO2 and reducing gas sensing, we have reported that fast Fourier transformation of the resistance transients of all these gases in conjunction with principal component analyses forms a reasonably distinct cluster and, therefore, could easily be differentiated.

  6. Observations of open-ocean deep convection in the northwestern Mediterranean Sea: Seasonal and interannual variability of mixing and deep water masses for the 2007-2013 Period

    NASA Astrophysics Data System (ADS)

    Houpert, L.; Durrieu de Madron, X.; Testor, P.; Bosse, A.; D'Ortenzio, F.; Bouin, M. N.; Dausse, D.; Le Goff, H.; Kunesch, S.; Labaste, M.; Coppola, L.; Mortier, L.; Raimbault, P.

    2016-11-01

    We present here a unique oceanographic and meteorological data set focus on the deep convection processes. Our results are essentially based on in situ data (mooring, research vessel, glider, and profiling float) collected from a multiplatform and integrated monitoring system (MOOSE: Mediterranean Ocean Observing System on Environment), which monitored continuously the northwestern Mediterranean Sea since 2007, and in particular high-frequency potential temperature, salinity, and current measurements from the mooring LION located within the convection region. From 2009 to 2013, the mixed layer depth reaches the seabed, at a depth of 2330m, in February. Then, the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly formed deep water. Each deep convection winter formed a new warmer and saltier "vintage" of deep water. These sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity (3.3 ± 0.2 × 10-3/yr) and potential temperature (3.2 ± 0.5 × 10-3 C/yr) observed from 2009 to 2013 for the 600-2300 m layer. For the first time, the overlapping of the three "phases" of deep convection can be observed, with secondary vertical mixing events (2-4 days) after the beginning of the restratification phase, and the restratification/spreading phase still active at the beginning of the following deep convection event.

  7. [Carbon storage of forest vegetation and allocation for main forest types in the east of Da-xing'an Mountains based on additive biomass model].

    PubMed

    Peng, Wei; Dong, Li Hu; Li, Feng Ri

    2016-12-01

    Based on the biomass investigation data of main forest types in the east of Daxing'an Mountains, the additive biomass models of 3 main tree species were developed and the changes of carbon storage and allocation of forest community of tree layer, shrub layer, herb layer and litter layer from different forest types were discussed. The results showed that the carbon storage of tree layer, shrub layer, herb layer and litter layer for Rhododendron dauricum-Larix gmelinii forest was 71.00, 0.34, 0.05 and 11.97 t·hm -2 , respectively. Similarly, the carbon storage of the four layers of Ledum palustre-L. gmelinii forest was 47.82, 0.88, 0, 5.04 t·hm -2 , 56.56, 0.44, 0.04, 8.72 t·hm -2 for R. dauricum-mixed forest of L. gmelinii-Betula platyphylla, 46.21, 0.66, 0.07, 6.16 t·hm -2 for L. palustre-mixed forest of L. gmelinii-B. platyphylla, 40.90, 1.37, 0.04, 3.67 t·hm -2 for R. dauricum-B. platyphylla forest, 36.28, 1.12, 0.18, 4.35 t·hm -2 for L. palustre-B. platyphylla forest. The carbon storage of forest community for the understory vegetation of R. dauricum was higher than that of the forest with L. palustre. In the condition of similar circumstances for the understory, the order of carbon storage for forest community was L. gmelinii forest > the mixed forest of L. gmelinii-B. platyphylla > B. platyphylla forest. The carbon storage of different forest types was different with the order of R. dauricum-L. gmelinii forest (83.36 t·hm -2 )> R. dauricum-mixed forest of L. gmelinii-B. platyphylla (65.76 t·hm -2 ) > L. palustre-L. gmelinii forest (53.74 t·hm -2 )> L. palustre-mixed forest of L. gmelinii-B. platyphylla (53.10 t·hm -2 )> R. dauricum-B. platyphylla forest (45.98 t·hm -2 ) > L. palustre-B. platyphylla forest (41.93 t·hm -2 ). The order of carbon storage for the vertical distribution in forest communities with diffe-rent forest types was the tree layer (85.2%-89.0%) > litter layer (8.0%-14.4%) > shrub layer (0.4%-2.7%) > herb layer (0-0.4%).

  8. Frictionless Contact of Multilayered Composite Half Planes Containing Layers With Complex Eigenvalues

    NASA Technical Reports Server (NTRS)

    Zhang, Wang; Binienda, Wieslaw K.; Pindera, Marek-Jerzy

    1997-01-01

    A previously developed local-global stiffness matrix methodology for the response of a composite half plane, arbitrarily layered with isotropic, orthotropic or monoclinic plies, to indentation by a rigid parabolic punch is further extended to accommodate the presence of layers with complex eigenvalues (e.g., honeycomb or piezoelectric layers). First, a generalized plane deformation solution for the displacement field in an orthotropic layer or half plane characterized by complex eigenvalues is obtained using Fourier transforms. A local stiffness matrix in the transform domain is subsequently constructed for this class of layers and half planes, which is then assembled into a global stiffness matrix for the entire multilayered half plane by enforcing continuity conditions along the interfaces. Application of the mixed boundary condition on the top surface of the half plane indented by a rigid punch results in an integral equation for the unknown pressure in the contact region. The integral possesses a divergent kernel which is decomposed into Cauchy-type and regular parts using the asymptotic properties of the local stiffness matrix and a relationship between Fourier and finite Hilbert transform of the contact pressure. The solution of the resulting singular integral equation is obtained using a collocation technique based on the properties of orthogonal polynomials developed by Erdogan and Gupta. Examples are presented that illustrate the important influence of low transverse properties of layers with complex eigenvalues, such as those exhibited by honeycomb, on the load versus contact length response and contact pressure distributions for half planes containing typical composite materials.

  9. Estimation of evaporation from equilibrium diurnal boundary layer humidity

    NASA Astrophysics Data System (ADS)

    Salvucci, G.; Rigden, A. J.; Li, D.; Gentine, P.

    2017-12-01

    Simplified conceptual models of the convective boundary layer as a well mixed profile of potential temperature (theta) and specific humidity (q) impinging on an initially stably stratified linear potential temperature profile have a long history in atmospheric sciences. These one dimensional representations of complex mixing are useful for gaining insights into land-atmosphere interactions and for prediction when state of the art LES approaches are infeasible. As previously shown (e.g. Betts), if one neglects the role of q in bouyancy, the framework yields a unique relation between mixed layer Theta, mixed layer height (h), and cumulative sensible heat flux (SH) throughout the day. Similarly assuming an initially q profile yields a simple relation between q, h, and cumulative latent heat flux (LH). The diurnal dynamics of theta and q are strongly dependent on SH and the initial lapse rates of theta (gamma_thet) and q (gamma q). In the estimation method proposed here, we further constrain these relations with two more assumptions: 1) The specific humidity is the same at the start of the period of boundary layer growth and at the collapse; and 2) Once the mixed layer reaches the LCL, further drying occurs proportionally to the deardorff convective velocity scale (omega) multiplied by q. Assumption (1) is based on the idea that below the cloud layer, there are no sinks of moisture within the mixed layer (neglecting lateral humidity divergence). Thus the net mixing of dry air aloft with evaporation from the surface must balance. Inclusion of the simple model of moisture loss above the LCL into the bulk-CBL model allows definition of an equilibrium humidity (q) condition at which the diurnal cycle of q repeats (i.e. additions of q from surface balance entrainment of dry air from above). Surprisingly, this framework allows estimation of LH from q, theta, and estimated net radiation by solving for the value of Evaporative Fraction (EF) for which the diurnal cycle of q repeats. Three parameters need specification: cloud area fraction, entrainment factor, and morning lapse rate. Surprisingly, a single set of values for these parameters are adequate to estimate EF at over 70 tested Ameriflux sites to within about 20%, though improvements are gained using a single regression model for gamma_thet that has been fitted to radiosonde data.

  10. Fixed versus mixed RSA: Explaining visual representations by fixed and mixed feature sets from shallow and deep computational models.

    PubMed

    Khaligh-Razavi, Seyed-Mahdi; Henriksson, Linda; Kay, Kendrick; Kriegeskorte, Nikolaus

    2017-02-01

    Studies of the primate visual system have begun to test a wide range of complex computational object-vision models. Realistic models have many parameters, which in practice cannot be fitted using the limited amounts of brain-activity data typically available. Task performance optimization (e.g. using backpropagation to train neural networks) provides major constraints for fitting parameters and discovering nonlinear representational features appropriate for the task (e.g. object classification). Model representations can be compared to brain representations in terms of the representational dissimilarities they predict for an image set. This method, called representational similarity analysis (RSA), enables us to test the representational feature space as is (fixed RSA) or to fit a linear transformation that mixes the nonlinear model features so as to best explain a cortical area's representational space (mixed RSA). Like voxel/population-receptive-field modelling, mixed RSA uses a training set (different stimuli) to fit one weight per model feature and response channel (voxels here), so as to best predict the response profile across images for each response channel. We analysed response patterns elicited by natural images, which were measured with functional magnetic resonance imaging (fMRI). We found that early visual areas were best accounted for by shallow models, such as a Gabor wavelet pyramid (GWP). The GWP model performed similarly with and without mixing, suggesting that the original features already approximated the representational space, obviating the need for mixing. However, a higher ventral-stream visual representation (lateral occipital region) was best explained by the higher layers of a deep convolutional network and mixing of its feature set was essential for this model to explain the representation. We suspect that mixing was essential because the convolutional network had been trained to discriminate a set of 1000 categories, whose frequencies in the training set did not match their frequencies in natural experience or their behavioural importance. The latter factors might determine the representational prominence of semantic dimensions in higher-level ventral-stream areas. Our results demonstrate the benefits of testing both the specific representational hypothesis expressed by a model's original feature space and the hypothesis space generated by linear transformations of that feature space.

  11. Numerical experiments with a wind- and buoyancy-driven two-and-a-half-layer upper ocean model

    NASA Astrophysics Data System (ADS)

    Cherniawsky, J. Y.; Yuen, C. W.; Lin, C. A.; Mysak, L. A.

    1990-09-01

    We describe numerical experiments with a limited domain (15°-67°N, 65° west to east) coarse-resolution two-and-a-half-layer upper ocean model. The model consists of two active variable density layers: a Niiler and Kraus (1977) type mixed layer and a pycnocline layer, which overlays a semipassive deep ocean. The mixed layer is forced with a cosine wind stress and Haney type heat and precipitation-evaporation fluxes, which were derived from zonally averaged climatological (Levitus, 1982) surface temperatures and salinities for the North Atlantic. The second layer is forced from below with (1) Newtonian cooling to climatological temperatures and salinities at the lower boundary, (2) convective adjustment, which occurs whenever the density of the second layer is unstable with respect to climatology, and (3) mass entrainment in areas of strong upwelling, when the deep ocean ventilates through the bottom surface. The sensitivity of this model to changes in its internal (mixed layer) and external (e.g., a Newtonian coupling coefficient) parameters is investigated and compared to the results from a control experiment. We find that the model is not overly sensitive to changes in most of the parameters that were tested, albeit these results may depend to some extent on the choice of the control experiment.

  12. Fabrication of selective-area growth InGaN LED by mixed-source hydride vapor-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Bae, Sung Geun; Jeon, Injun; Jeon, Hunsoo; Kim, Kyoung Hwa; Yang, Min; Yi, Sam Nyung; Lee, Jae Hak; Ahn, Hyung Soo; Yu, Young Moon; Sawaki, Nobuhiko; Kim, Suck-Whan

    2018-01-01

    We prepared InGaN light-emitting diodes (LEDs) with the active layers grown from a mixed source of Ga-In-N materials on an n-type GaN substrate by a selective-area growth method and three fabrication steps: photolithography, epitaxial layer growth, and metallization. The preparation followed a previously developed experimental process using apparatus for mixed-source hydride vapor-phase epitaxy (HVPE), which consisted of a multi-graphite boat, for insulating against the high temperature and to control the growth rate of epilayers, filled with the mixed source on the inside and a radio-frequency (RF) heating coil for heating to a high temperature (T > 900 °C) and for easy control of temperature outside the source zone. Two types of LEDs were prepared, with In compositions of 11.0 and 6.0% in the InGaN active layer, and room-temperature electroluminescence measurements exhibited a main peak corresponding to the In composition at either 420 or 390 nm. The consecutive growth of InGaN LEDs by the mixed-source HVPE method provides a technique for the production of LEDs with a wide range of In compositions in the active layer.

  13. Gravity Wave Dynamics in a Mesospheric Inversion Layer: 2. Instabilities, Turbulence, Fluxes, and Mixing

    NASA Astrophysics Data System (ADS)

    Fritts, David C.; Wang, Ling; Laughman, Brian; Lund, Thomas S.; Collins, Richard L.

    2018-01-01

    A companion paper by Fritts, Laughman, et al. (2017) employed an anelastic numerical model to explore the dynamics of gravity waves (GWs) encountering a mesospheric inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. That study revealed that MIL responses, including GW transmission, reflection, and instabilities, are sensitive functions of GW parameters. This paper expands on two of the Fritts, Laughman, et al. (2017) simulations to examine GW instability dynamics and turbulence in the MIL; forcing of the mean wind and stability environments by GW, instability, and turbulence fluxes; and associated heat and momentum transports. These direct numerical simulations resolve turbulence inertial-range scales and yield the following results: GW breaking and turbulence in the MIL occur below where they would otherwise, due to enhancements of GW amplitudes and shears in the MIL. 2-D GW and instability heat and momentum fluxes are 20-30 times larger than 3-D instability and turbulence fluxes. Mean fields are driven largely by 2-D GW and instability dynamics rather than 3-D instabilities and turbulence. 2-D and 3-D heat fluxes in regions of strong turbulence yield small departures from initial T(z) and N2(z) profiles, hence do not yield nearly adiabatic "mixed" layers. Our MIL results are consistent with the relation between the turbulent vertical velocity variance and energy dissipation rate proposed by Weinstock (1981) for the limited intervals evaluated.

  14. Numerical simulation of a plane turbulent mixing layer, with applications to isothermal, rapid reactions

    NASA Technical Reports Server (NTRS)

    Lin, P.; Pratt, D. T.

    1987-01-01

    A hybrid method has been developed for the numerical prediction of turbulent mixing in a spatially-developing, free shear layer. Most significantly, the computation incorporates the effects of large-scale structures, Schmidt number and Reynolds number on mixing, which have been overlooked in the past. In flow field prediction, large-eddy simulation was conducted by a modified 2-D vortex method with subgrid-scale modeling. The predicted mean velocities, shear layer growth rates, Reynolds stresses, and the RMS of longitudinal velocity fluctuations were found to be in good agreement with experiments, although the lateral velocity fluctuations were overpredicted. In scalar transport, the Monte Carlo method was extended to the simulation of the time-dependent pdf transport equation. For the first time, the mixing frequency in Curl's coalescence/dispersion model was estimated by using Broadwell and Breidenthal's theory of micromixing, which involves Schmidt number, Reynolds number and the local vorticity. Numerical tests were performed for a gaseous case and an aqueous case. Evidence that pure freestream fluids are entrained into the layer by large-scale motions was found in the predicted pdf. Mean concentration profiles were found to be insensitive to Schmidt number, while the unmixedness was higher for higher Schmidt number. Applications were made to mixing layers with isothermal, fast reactions. The predicted difference in product thickness of the two cases was in reasonable quantitative agreement with experimental measurements.

  15. Effectiveness of Three Different Irrigants - 17% Ethylenediaminetetraacetic Acid, Q-MIX, and Phytic Acid in Smear Layer Removal: A Comparative Scanning Electron Microscope Study.

    PubMed

    Jagzap, Janhavi Balasaheb; Patil, Sanjay S; Gade, Vandana Jaykumar; Chandhok, Deepika J; Upagade, Madhura A; Thakur, Deepa A

    2017-01-01

    Removal of smear layer from the root canal walls is important for long-standing endodontic success. The aim of this study is to evaluate and compare smear layer removing ability among 17% ethylenediaminetetraacetic acid (EDTA), Q-MIX, and phytic acid by scanning electron microscopy (SEM). This in-vitro experimental study assessed smear layer removal using three different irrigants. Thirty single-rooted freshly extracted human permanent premolars were collected, disinfected, and decoronated to a standardized root length of 13 mm. Root canals were cleaned and shaped till F2 universal rotary protaper at working length 1 mm short of the apex. They were randomly divided into three groups, and final irrigation was done accordingly. Group 1 ( n = 10): with 1 ml of 17% EDTA, Group 2 ( n = 10): with 1 ml of Q-MIX, Group 3 ( n = 10): with 1 ml of phytic acid. Samples were then longitudinally sectioned and evaluated under SEM at coronal, middle, and apical levels. Two-way analysis of variance and Tukey's post hoc test were performed. The level of significance was set at 0.05. Smear layer removing ability among irrigants and sections in descending order: 17 EDTA > Q-MIX > phytic acid; coronal > middle > apical. 17% EDTA showed better and promising results followed by Q-MIX and then phytic acid.

  16. Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump

    PubMed Central

    Dall’Olmo, Giorgio; Dingle, James; Polimene, Luca; Brewin, Robert J.W.; Claustre, Hervé

    2016-01-01

    The “mesopelagic” is the region of the ocean between about 100 and 1000 m that harbours one of the largest ecosystems and fish stocks on the planet1,2. This vastly unexplored ecosystem is believed to be mostly sustained by chemical energy, in the form of fast-sinking particulate organic carbon, supplied by the biological carbon pump3. Yet, this supply appears insufficient to match mesopelagic metabolic demands4–6. The mixed-layer pump is a physically-driven biogeochemical process7–11 that could further contribute to meet these energetic requirements. However, little is known about the magnitude and spatial distribution of this process at the global scale. Here we show that the mixed-layer pump supplies an important seasonal flux of organic carbon to the mesopelagic. By combining mixed-layer depths from Argo floats with satellite retrievals of particulate organic carbon, we estimate that this pump exports a global flux of about 0.3 Pg C yr−1 (range 0.1 – 0.5 Pg C yr−1). In high-latitude regions where mixed-layers are deep, this flux is on average 23%, but can be greater than 100% of the carbon supplied by fast sinking particles. Our results imply that a relatively large flux of organic carbon is missing from current energy budgets of the mesopelagic. PMID:27857779

  17. Self-similarity of a Rayleigh–Taylor mixing layer at low Atwood number with a multimode initial perturbation

    DOE PAGES

    Morgan, B. E.; Olson, B. J.; White, J. E.; ...

    2017-06-29

    High-fidelity large eddy simulation (LES) of a low-Atwood number (A = 0.05) Rayleigh-Taylor mixing layer is performed using the tenth-order compact difference code Miranda. An initial multimode perturbation spectrum is specified in Fourier space as a function of mesh resolution such that a database of results is obtained in which each successive level of increased grid resolution corresponds approximately to one additional doubling of the mixing layer width, or generation. The database is then analyzed to determine approximate requirements for self-similarity, and a new metric is proposed to quantify how far a given simulation is from the limit of self-similarity.more » It is determined that mixing layer growth reaches a high degree of self-similarity after approximately 4.5 generations. Statistical convergence errors and boundary effects at late time, however, make it impossible to draw similar conclusions regarding the self-similar growth of more sensitive turbulence parameters. Finally, self-similar turbulence profiles from the LES database are compared with one-dimensional simulations using the k-L-a and BHR-2 Reynolds-averaged Navier-Stokes (RANS) models. The k-L-a model, which is calibrated to reproduce a quadratic turbulence kinetic energy profile for a self-similar mixing layer, is found to be in better agreement with the LES than BHR-2 results.« less

  18. Density-ratio effects on buoyancy-driven variable-density turbulent mixing

    NASA Astrophysics Data System (ADS)

    Aslangil, Denis; Livescu, Daniel; Banerjee, Arindam

    2017-11-01

    Density-ratio effects on the turbulent mixing of two incompressible, miscible fluids with different densities subject to constant acceleration are studied by means of high-resolution Direct Numerical Simulations. In a triply periodic domain, turbulence is generated by stirring in response to the differential buoyancy forces within the flow. Later, as the fluids become molecularly mixed, dissipation starts to overcome turbulence generation by bouyancy. Thus, the flow evolution includes both turbulence growth and decay, and it displays features present in the core region of the mixing layer of the Rayleigh-Taylor as well as Richtmyer-Meshkov instabilities. We extend the previous studies by investigating a broad range of density-ratio, from 1-14.4:1, corresponding to Atwood numbers of 0.05-0.87. Here, we focus on the Atwood number dependence of mixing-efficiency, that is defined based on the energy-conversion ratios from potential energy to total and turbulent kinetic energies, the decay characteristics of buoyancy-assisted variable-density homogeneous turbulence, and the effects of high density-ratios on the turbulence structure and mixing process. Authors acknowledge financial support from DOE-SSAA (DE-NA0003195) and NSF CAREER (#1453056) awards.

  19. Did Irving Langmuir Observe Langmuir Circulations?

    NASA Astrophysics Data System (ADS)

    D'Asaro, E. A.; Harcourt, R. R.; Shcherbina, A.; Thomson, J. M.; Fox-Kemper, B.

    2012-12-01

    Although surface waves are known to play an important role in mixing the upper ocean, the current generation of upper ocean boundary layer parameterizations does not include the explicit effects of surface waves. Detailed simulations using LES models which include the Craik-Leibovich wave-current interactions, now provide quantitative predictions of the enhancement of boundary layer mixing by waves. Here, using parallel experiments in Lake Washington and at Ocean Station Papa, we show a clear enhancement of vertical kinetic energy across the entire upper ocean boundary layer which can be attributed to surface wave effects. The magnitude of this effect is close to that predicted by LES models, but is not large, less than a factor of 2 on average, and increased by large Stokes drift and shallow mixed layers. Global estimates show the largest wave enhancements occur on the equatorial side of the westerlies in late Spring, due to the combination of large waves, shallow mixed layers and weak winds. In Lakes, however, the waves and the Craik-Leibovich interactions are weak, making it likely that the counter-rotating vortices famously observed by Irving Langmuir in Lake George were not driven by wave-current interactions.

  20. Convection and the seeding of the North Atlantic bloom

    NASA Astrophysics Data System (ADS)

    D'Asaro, Eric A.

    Observations of vertical velocities in deep wintertime mixed layers using neutrally buoyant floats show that the convectively driven vertical velocities, roughly 1000 m per day, greatly exceed the sinking velocities of phytoplankton, 10 m or less per day. These velocities mix plankton effectively and uniformly across the convective layer and are therefore capable of returning those that have sunk to depth back into the euphotic zone. This mechanism cycles cells through the surface layer during the winter and provides a seed population for the spring bloom. A simple model of this mechanism applied to immortal phytoplankton in the subpolar Labrador Sea predicts that the seed population in early spring will be a few percent of the fall concentration if the plankton sink more slowly than the mean rate at which the surface well-mixed layer grows over the winter. Plankton that sink faster than this will mostly sink into the abyss with only a minute fraction remaining by spring. The shallower mixed layers of mid-latitudes are predicted to be much less effective at maintaining a seed population over the winter, limiting the ability of rapidly sinking cells to survive the winter.

  1. Reagentless biosensor based on layer-by-layer assembly of functional multiwall carbon nanotubes and enzyme-mediator biocomposite.

    PubMed

    Zhou, Xing-Hua; Xi, Feng-Na; Zhang, Yi-Ming; Lin, Xian-Fu

    2011-06-01

    A simple and controllable layer-by-layer (LBL) assembly method was proposed for the construction of reagentless biosensors based on electrostatic interaction between functional multiwall carbon nanotubes (MWNTs) and enzyme-mediator biocomposites. The carboxylated MWNTs were wrapped with polycations poly(allylamine hydrochloride) (PAH) and the resulting PAH-MWNTs were well dispersed and positively charged. As a water-soluble dye methylene blue (MB) could mix well with horseradish peroxidase (HRP) to form a biocompatible and negatively-charged HRP-MB biocomposite. A (PAH-MWNTs/HRP-MB)(n) bionanomultilayer was then prepared by electrostatic LBL assembly of PAH-MWNTs and HRP-MB on a polyelectrolyte precursor film-modified Au electrode. Due to the excellent biocompatibility of HRP-MB biocomposite and the uniform LBL assembly, the immobilized HRP could retain its natural bioactivity and MB could efficiently shuttle electrons between HRP and the electrode. The incorporation of MWNTs in the bionanomultilayer enhanced the surface coverage concentration of the electroactive enzyme and increased the catalytic current response of the electrode. The proposed biosensor displayed a fast response (2 s) to hydrogen peroxide with a low detection limit of 2.0×10⁻⁷ mol/L (S/N=3). This work provided a versatile platform in the further development of reagentless biosensors.

  2. The influence of oxalate-promoted growth of saponite and talc crystals

    USGS Publications Warehouse

    Schumann, Dirk; Hartman, Hyman; Eberl, Dennis D.; Sears, S. Kelly; Hesse, Reinhard; Vali, Hojatollah

    2013-01-01

    The intercalating growth of new silicate layers or metal hydroxide layers in the interlayer space of other clay minerals is known from various mixed-layer clay minerals such as illite-smectite (I-S), chlorite-vermiculite, and mica-vermiculite. In a recent study, the present authors proposed that smectite-group minerals can be synthesized from solution as new 2:1 silicate layers within the low-charge interlayers of rectorite. That study showed how oxalate catalyzes the crystallization of saponite from a silicate gel at low temperatures (60ºC) and ambient pressure. As an extension of this work the aim of the present study was to test the claim that new 2:1 silicate layers can be synthesized as new intercalating layers in the low-charge interlayers of rectorite and whether oxalate could promote such an intercalation synthesis. Two experiments were conducted at 60ºC and atmospheric pressure. First, disodium oxalate solution was added to a suspension of rectorite in order to investigate the effects that oxalate anions have on the structure of rectorite. In a second experiment, silicate gel of saponitic composition (calculated interlayer charge −0.33 eq/O10(OH)2) was mixed with a suspension of rectorite and incubated in disodium oxalate solution. The synthesis products were extracted after 3 months and analyzed by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The treatment of ultrathin sections with octadecylammonium (nC = 18) cations revealed the presence of 2:1 layer silicates with different interlayer charges that grew from the silicate gel. The oxalate-promoted nucleation of saponite and talc crystallites on the rectorite led to the alteration and ultimately to the destruction of the rectorite structure. The change was documented in HRTEM lattice-fringe images. The crystallization of new 2:1 layer silicates also occurred within the expandable interlayers of rectorite but not as new 2:1 silicate layers parallel to the previous 2:1 silicate layers. Instead, they grew independently of any orientation predetermined by the rectorite crystal substrate and their crystallization was responsible for the destruction of the rectorite structure.

  3. Spin-coated thin films of different metal phthalocyanines and porphyrin-phthalocyanine blend for optochemical sensors of volatile organic compounds

    NASA Astrophysics Data System (ADS)

    Rella, Roberto; Capone, Simona; Siciliano, Pietro; Spadavecchia, J.; Ciccarella, G.

    2004-06-01

    Spin-coated layers of ZnPc and CuP have been used as chemically interacting materials for the detection of alcohols, amines, ketones, alkanes and pyridine for applications in food quality control. The UV-VIS variations obtained by the exposure of the sensing layers to the mentioned analytes in controlled atmosphere have been analyzed and compared with those deriving by a single thin film obtained by mixing the two metal complexes in an appropriate ratio. A multichannel monitoring of the main bands of the sensing layer due to the interaction with the analyte vapors became the basis to construct a set of independent sensors located on a single sensing element. The effects in the variation of the absorption bands of the blend system are compared with the variations in absorbance observed with the two sensing layers fabricated separately with each single compound. The interaction between the VOCs species and the heterogeneous sensing layer shows a different behavior in the responses respect to the results obtained with each single compound.

  4. Release from or through a wax matrix system. IV. Generalized expression of the release process for a reservoir device tablet.

    PubMed

    Yonezawa, Yorinobu; Ishida, Sumio; Suzuki, Shinobu; Sunada, Hisakazu

    2002-09-01

    Generalization of the release process through the wax matrix layer was examined by use of a reservoir device tablet. The wax matrix layer of the reservoir device tablet was prepared from a physical mixture of lactose and hydrogenated castor oil to simplify the release properties. Release through the wax matrix layer showed zero-order kinetics in a steady state after a given lag time, and could be divided into two stages. The first stage was the formation process of water channel by dissolving the soluble component in the wax matrix layer. The lag time obtained by applying the square root law equation was well connected with the amount of the matrix layer and mixed weight ratio of components in this layer. The second stage was the zero-order release process of drug in the reservoir through the wax matrix layer, because the effective surface area was fixed. The release rate constants were connected with thickness of the matrix layer and permeability coefficient, and the permeability coefficients were connected with the diffusion coefficient of drug and porosity. Hence the release rate constant could be connected with the amount of matrix layer and the mixed weight ratio of components in the matrix layer. It was therefore suggested that the release process could be generalized using the amount of matrix layer and the mixed weight ratio of components in the matrix layer.

  5. Revealing the Location of the Mixing Layer in a Hot Bubble

    NASA Astrophysics Data System (ADS)

    Guerrero, M. A.; Fang, X.; Chu, Y.-H.; Toalá, J. A.; Gruendl, R. A.

    2017-10-01

    The fast stellar winds can blow bubbles in the circumstellar material ejected from previous phases of stellar evolution. These are found at different scales, from planetary nebulae (PNe) around stars evolving to the white dwarf stage, to Wolf-Rayet (WR) bubbles and up to large-scale bubbles around massive star clusters. In all cases, the fast stellar wind is shock-heated and a hot bubble is produced. Processes of mass evaporation and mixing of nebular material and heat conduction occurring at the mixing layer between the hot bubble and the optical nebula are key to determine the thermal structure of these bubbles and their evolution. In this contribution we review our current understanding of the X-ray observations of hot bubbles in PNe and present the first spatially-resolved study of a mixing layer in a PN.

  6. HST STIS Observations of the Mixing Layer in the Cat’s Eye Nebula

    NASA Astrophysics Data System (ADS)

    Fang, Xuan; Guerrero, Martín A.; Toalá, Jesús A.; Chu, You-Hua; Gruendl, Robert A.

    2016-05-01

    Planetary nebulae (PNe) are expected to have a ˜105 K interface layer between the ≥slant 106 K inner hot bubble and the ˜104 K optical nebular shell. The PN structure and evolution, and the X-ray emission, depend critically on the efficiency of the mixing of material at this interface layer. However, neither its location nor its spatial extent have ever been determined. Using high-spatial resolution HST STIS spectroscopic observations of the N v λ λ 1239,1243 lines in the Cat’s Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N v λ1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5× {10}16 cm and an electron density of ˜200 cm-3 for the mixing layer. With a thermal pressure of ˜2 × 10-8 dyn cm-2, the mixing layer is in pressure equilibrium with the hot bubble and ionized nebular rim of NGC 6543. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The observations are associated with program #12509.

  7. Impact of the Loess Plateau on the atmospheric boundary layer structure and air quality in the North China Plain: a case study.

    PubMed

    Hu, Xiao-Ming; Ma, ZhiQiang; Lin, Weili; Zhang, Hongliang; Hu, Jianlin; Wang, Ying; Xu, Xiaobin; Fuentes, Jose D; Xue, Ming

    2014-11-15

    The North China Plain (NCP), to the east of the Loess Plateau, experiences severe regional air pollution. During the daytime in the summer, the Loess Plateau acts as an elevated heat source. The impacts of such a thermal effect on meteorological phenomena (e.g., waves, precipitation) in this region have been discussed. However, its impacts on the atmospheric boundary layer structure and air quality have not been reported. It is hypothesized that the thermal effect of the Plateau likely modulates the boundary layer structure and ambient concentrations of pollutants over the NCP under certain meteorological conditions. Thus, this study investigates such effect and its impacts using measurements and three-dimensional model simulations. It is found that in the presence of daytime westerly wind in the lower troposphere (~1 km above the NCP), warmer air above the Loess Plateau was transported over the NCP and imposed a thermal inversion above the mixed boundary layer, which acted as a lid and suppressed the mixed layer growth. As a result, pollutants accumulated in the shallow mixed layer and ozone was efficiently produced. The downward branch of the thermally-induced Mountain-Plains Solenoid circulation over the NCP contributed to enhancing the capping inversion and exacerbating air pollution. Previous studies have reported that low mixed layer, a factor for elevated pollution in the NCP, may be caused by aerosol scattering and absorption of solar radiation, frontal inversion, and large scale subsidence. The present study revealed a different mechanism (i.e., westerly warm advection) for the suppression of the mixed layer in summer NCP, which caused severe O3 pollution. This study has important implications for understanding the essential meteorological factors for pollution episodes in this region and forecasting these severe events. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Response of the Land-Atmosphere System Over North-Central Oklahoma During the 2017 Eclipse

    NASA Astrophysics Data System (ADS)

    Turner, D. D.; Wulfmeyer, V.; Behrendt, A.; Bonin, T. A.; Choukulkar, A.; Newsom, R. K.; Brewer, W. A.; Cook, D. R.

    2018-02-01

    On 21 August 2017, a solar eclipse occurred over the continental United States resulting in a rapid reduction and subsequent increase of solar radiation over a large region of the country. The eclipse's effect on the land-atmosphere system is documented in unprecedented detail using a unique array of sensors deployed at three sites in north-central Oklahoma. The observations showed that turbulent fluxes of heat and momentum at the surface responded quickly to the change in solar radiation. The decrease in the sensible heat flux resulted in a decrease in the air temperature below 200 m, and a large decrease in turbulent motions throughout the boundary layer. Furthermore, the turbulent mixing in the boundary layer lagged behind the change in the surface fluxes, and this lag depended on the height above the surface. The turbulent motions increased and the convective boundary layer was reestablished as the sensible heat flux recovered.

  9. Mixed-layer kaolinite-montmorillonite from the Yucatan Peninsula, Mexico

    USGS Publications Warehouse

    Schultz, L.G.; Shepard, A.O.; Blackmon, P.D.; Starkey, H.C.

    1971-01-01

    Clay beds 1–2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite. Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers. The montmorillonite structural formulas average K0·2Na0·2Ca0·2Mg0·2(Al2·5Fe1·03+Mg0·5)(Al0·75Si7.25)O20+(OH)4−, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers. Nonexchangeable K+ indicates that a few layers are mica-like. Crystals are mostly round plates 1/10 to 1/20 µ across. The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 Å after heating at 300°C. The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins.

  10. Fusion yield rate recovery by escaping hot-spot fast ions in the neighboring fuel layer

    NASA Astrophysics Data System (ADS)

    Tang, Xian-Zhu; McDevitt, C. J.; Guo, Zehua; Berk, H. L.

    2014-02-01

    Free-streaming loss by fast ions can deplete the tail population in the hot spot of an inertial confinement fusion (ICF) target. Escaping fast ions in the neighboring fuel layer of a cryogenic target can produce a surplus of fast ions locally. In contrast to the Knudsen layer effect that reduces hot-spot fusion reactivity due to tail ion depletion, the inverse Knudsen layer effect increases fusion reactivity in the neighboring fuel layer. In the case of a burning ICF target in the presence of significant hydrodynamic mix which aggravates the Knudsen layer effect, the yield recovery largely compensates for the yield reduction. For mix-dominated sub-ignition targets, the yield reduction is the dominant process.

  11. MOFwich: Sandwiched Metal-Organic Framework-Containing Mixed Matrix Composites for Chemical Warfare Agent Removal.

    PubMed

    Peterson, Gregory W; Lu, Annie X; Hall, Morgan G; Browe, Matthew A; Tovar, Trenton; Epps, Thomas H

    2018-02-28

    This work describes a new strategy for fabricating mixed matrix composites containing layered metal-organic framework (MOF)/polymer films as functional barriers for chemical warfare agent protection. Through the use of mechanically robust polymers as the top and bottom encasing layers, a high-MOF-loading, high-performance-core layer can be sandwiched within. We term this multifunctional composite "MOFwich". We found that the use of elastomeric encasing layers enabled core layer reformation after breakage, an important feature for composites and membranes alike. The incorporation of MOFs into the core layer led to enhanced removal of chemical warfare agents while simultaneously promoting moisture vapor transport through the composite, showcasing the promise of these composites for protection applications.

  12. A mixed formulation for interlaminar stresses in dropped-ply laminates

    NASA Technical Reports Server (NTRS)

    Harrison, Peter N.; Johnson, Eric R.

    1993-01-01

    A structural model is developed for the linear elastic response of structures consisting of multiple layers of varying thickness such as laminated composites containing internal ply drop-offs. The assumption of generalized plane deformation is used to reduce the solution domain to two dimensions while still allowing some out-of-plane deformation. The Hellinger-Reissner variational principle is applied to a layerwise assumed stress distribution with the resulting governing equations solved using finite differences.

  13. A Non-Fickian Mixing Model for Stratified Turbulent Flows

    DTIC Science & Technology

    2013-09-30

    lateral gradients in the mixed layer, indicative of surface fronts, and with the magnitude of mixed layer depth MLD. Direct testing with our results shows...both are induced by atmospheric forcing. In our case, atmospheric fluxes and wind forcing are still the cause of SM occurrence, but mostly through their...California upwelling simulations, where MLD did not change significantly between HR and LR simulations. As suggested by Capet et al. (2008b), this is likely

  14. Eulerian and Lagrangian Parameterization of the Oceanic Mixed Layer using Large Eddy Simulation and MPAS-Ocean

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Van Roekel, Luke

    We have conducted a suite of Large Eddy Simulation (LES) to form the basis of a multi-model comparison (left). The results have led to proposed model improvements. We have verified that Eulerian-Lagrangian effective diffusivity estimates of mesoscale mixing are consistent with traditional particle statistics metrics (right). LES and Lagrangian particles will be utilized to better represent the movement of water into and out of the mixed layer.

  15. The Dynamics of Turbulent Scalar Mixing near the Edge of a Shear Layer

    NASA Astrophysics Data System (ADS)

    Taveira, R. M. R.; da Silva, C. B.; Pereira, J. C. F.

    2011-12-01

    In free shear flows a sharp and convoluted turbulent/nonturbulent (T/NT) interface separates the outer fluid region, where the flow is essentially irrotational, from the shear layer turbulent region. It was found recently that the entrainment mechanism is mainly caused by small scale ("nibbling") motions (Westerweel et al. (2005)). The dynamics of this interface is crucial to understand important exchanges of enstrophy and scalars that can be conceived as a three-stage process of entrainment, dispersion and diffusion (Dimotakis (2005)). A thorough understanding of scalar mixing and transport is of indisputable relevance to control turbulent combustion, propulsion and contaminant dispersion (Stanley et al. (2002)). The present work uses several DNS of turbulent jets at Reynolds number ranging from Reλ = 120 to Reλ = 160 (da Silva & Taveira (2010)) and a Schmidt number Sc = 0.7 to analyze the "scalar interface" and turbulent mixing of a passive scalar. Specifically, we employ conditional statistics, denoted by langlerangleI, in order to eliminate the intermittency that affects statistics close to the jet edge. The physical mechanisms behind scalar mixing near the T/NT interfaces, their scales and topology are investigated detail. Analysis of the instantaneous fields showed intense scalar gradient sheet-like structures along regions of persistent strain, in particular at the T/NT interface. The scalar gradient transport equation, at the jet edge, showed that almost all mixing mechanisms are taking place in a confined region, beyond which they become reduced to an almost in perfect balance between production and dissipation of scalar variance. At the T/NT interface transport mechanisms are the ones responsible for the growth in the scalar fluctuations to the entrained fluid, where convection plays a dominant role, smoothing scalar gradients inside the interface and boosting them as far as

  16. Lower tropospheric distributions of O3 and aerosol over Raoyang, a rural site in the North China Plain

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Xu, Xiaobin; Jia, Shihui; Ma, Ruisheng; Ran, Liang; Deng, Zhaoze; Lin, Weili; Wang, Ying; Ma, Zhiqiang

    2017-03-01

    The North China Plain (NCP) has become one of the most polluted regions in China, with the rapidly increasing economic growth in the past decades. High concentrations of ambient O3 and aerosol have been observed at urban as well as rural sites in the NCP. Most of the in situ observations of air pollutants have been conducted near the ground so that current knowledge about the vertical distributions of tropospheric O3 and aerosol over the NCP region is still limited. In this study, vertical profiles of O3 and size-resolved aerosol concentrations below 2.5 km were measured in summer 2014 over a rural site in the NCP, using an unmanned aerial vehicle (UAV) equipped with miniature analyzers. In addition, vertical profiles of aerosol scattering property in the lower troposphere and vertical profiles of O3 below 1 km were also observed at the site using a lidar and tethered balloon, respectively. The depths of the mixed layer and residual layer were determined according to the vertical gradients of lidar particle extinction and aerosol number concentration. Average O3 and size-resolved aerosol number concentration in both the mixed and residual layer were obtained from the data observed in seven UAV flights. The results show that during most of the flights the O3 levels above the top of mixed layer were higher than those below. Such a positive gradient in the vertical distribution of O3 makes the residual layer an important source of O3 in the mixed layer, particularly during the morning when the top of mixed layer is rapidly elevated. In contrast to O3, aerosol number concentration was normally higher in the mixed layer than in the residual layer, particularly in the early morning. Aerosol particles were overwhelmingly distributed in the size range < 1 µm, showing slight differences between the mixed and residual layers. Our measurements confirm that the lower troposphere over the rural area of the NCP is largely impacted by anthropogenic pollutants locally emitted or transported from urban areas. Compared with the historic O3 vertical profiles over Beijing from the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC), a strong increase in O3 can be found at all heights below 2.5 km in the decade from 2004 to 2014, with the largest enhancement of about 41.6 ppb. This indicates that the lower troposphere over the northern part of the NCP has experienced rapidly worsening photochemical pollution. This worsening trend in photochemical pollution deserves more attention in the future.

  17. Tethered balloon-based black carbon profiles within the lower troposphere of Shanghai in the 2013 East China smog

    NASA Astrophysics Data System (ADS)

    Li, Juan; Fu, Qingyan; Huo, Juntao; Wang, Dongfang; Yang, Wen; Bian, Qinggen; Duan, Yusen; Zhang, Yihua; Pan, Jun; Lin, Yanfen; Huang, Kan; Bai, Zhipeng; Wang, Sheng-Hsiang; Fu, Joshua S.; Louie, Peter K. K.

    2015-12-01

    A Tethered balloon-based field campaign was launched for the vertical observation of air pollutants within the lower troposphere of 1000 m for the first time over a Chinese megacity, Shanghai in December of 2013. A custom-designed instrumentation platform for tethered balloon observation and ground-based observation synchronously operated for the measurement of same meteorological parameters and typical air pollutants. One episodic event (December 13) was selected with specific focus on particulate black carbon, a short-lived climate forcer with strong warming effect. Diurnal variation of the mixing layer height showed very shallow boundary of less than 300 m in early morning and night due to nocturnal inversion while extended boundary of more than 1000 m from noon to afternoon. Wind profiles showed relatively stagnant synoptic condition in the morning, frequent shifts between upward and downward motion at noon and in the afternoon, and dominant downward motion with sea breeze in the evening. Characteristics of black carbon vertical profiles during four different periods of a day were analyzed and compared. In the morning, surface BC concentration averaged as high as 20 μg/m3 due to intense traffic emissions from the morning rush hours and unfavorable meteorological conditions. A strong gradient of BC concentrations with altitude was observed from the ground to the top of boundary layer at around 250-370 m. BC gradients turned much smaller above the boundary layer. BC profiles measured during noon and afternoon were the least dependent on heights. The largely extended boundary layer with strong vertical convection was responsible for a well mixing of BC particles in the whole measured column. BC profiles were similar between the early-evening and late-evening phases. The lower troposphere was divided into two stratified air layers with contrasted BC vertical distributions. Profiles at night showed strong gradients from the relatively high surface concentrations to low concentrations near the top of the boundary layer around 200 m. Above the boundary layer, BC increased with altitudes and reached a maximum at the top of 1000 m. Prevailing sea breeze within the boundary layer was mainly responsible for the quick cleanup of BC in the lower altitudes. In contrast, continental outflow via regional transport was the major cause of the enhanced BC aloft. This study provides a first insight of the black carbon vertical profiles over Eastern China, which will have significant implications for narrowing the gaps between the source emissions and observations as well as improving estimations of BC radiative forcing and regional climate.

  18. Testing cloud microphysics parameterizations in NCAR CAM5 with ISDAC and M-PACE observations

    NASA Astrophysics Data System (ADS)

    Liu, Xiaohong; Xie, Shaocheng; Boyle, James; Klein, Stephen A.; Shi, Xiangjun; Wang, Zhien; Lin, Wuyin; Ghan, Steven J.; Earle, Michael; Liu, Peter S. K.; Zelenyuk, Alla

    2011-01-01

    Arctic clouds simulated by the National Center for Atmospheric Research (NCAR) Community Atmospheric Model version 5 (CAM5) are evaluated with observations from the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Indirect and Semi-Direct Aerosol Campaign (ISDAC) and Mixed-Phase Arctic Cloud Experiment (M-PACE), which were conducted at its North Slope of Alaska site in April 2008 and October 2004, respectively. Model forecasts for the Arctic spring and fall seasons performed under the Cloud-Associated Parameterizations Testbed framework generally reproduce the spatial distributions of cloud fraction for single-layer boundary-layer mixed-phase stratocumulus and multilayer or deep frontal clouds. However, for low-level stratocumulus, the model significantly underestimates the observed cloud liquid water content in both seasons. As a result, CAM5 significantly underestimates the surface downward longwave radiative fluxes by 20-40 W m-2. Introducing a new ice nucleation parameterization slightly improves the model performance for low-level mixed-phase clouds by increasing cloud liquid water content through the reduction of the conversion rate from cloud liquid to ice by the Wegener-Bergeron-Findeisen process. The CAM5 single-column model testing shows that changing the instantaneous freezing temperature of rain to form snow from -5°C to -40°C causes a large increase in modeled cloud liquid water content through the slowing down of cloud liquid and rain-related processes (e.g., autoconversion of cloud liquid to rain). The underestimation of aerosol concentrations in CAM5 in the Arctic also plays an important role in the low bias of cloud liquid water in the single-layer mixed-phase clouds. In addition, numerical issues related to the coupling of model physics and time stepping in CAM5 are responsible for the model biases and will be explored in future studies.

  19. Interaction of Vascular Smooth Muscle Cells Under Low Shear Stress

    NASA Technical Reports Server (NTRS)

    Seidel, Charles L.

    1998-01-01

    The blood vessel wall consists of three cellular layers, an outer adventitial, a middle medial and an inner intimal layer. When the blood vessel forms in the embryo it begins as a tube composed of a single cell type called endothelial cells. Over time, other cells are recruited from the surrounding tissue to form additional layers on the outer surface of the endothelial tube. The cells that are recruited are called mesenchymal cells. Mesenchymal cells are responsible for the production of connective tissue that holds the blood vessel together and for developing into vascular smooth muscle cells that are responsible for regulating the diameter of the vessel (1) and therefore, blood flow. In a fully developed blood vessel, the endothelial cells make- up the majority of cells in the intimal layer while the mesenchymal cells make-up the majority of cells in the medial and adventitial layers. Within the medial layer of a mature vessel, cells are organized into multiple circular layers of alternating bands of connective tissue and cells. The cell layer is composed of a mixture of mesenchymal cells that have not developed into smooth muscle cells and fully developed smooth muscle cells (2). The assembly and organization of complex tissues is directed in part by a signaling system composed of proteins on the cell surface called adhesion molecules. Adhesion molecules enable cells to recognize each other as well as the composition of the connective tissue in which they reside (3). It was hypothesized that the different cell types that compose the vascular wall possess different adhesion molecules that enable them to recognize each other and through this recognition system, form the complex layered organization of the vascular wall. In other words, the layered organization is an intrinsic property of the cells. If this hypothesis is correct then the different cells that make up the vessel wall, when mixed together, should organize themselves into a layered structure resembling an intact blood vessel. Experiments described below were designed to test this hypothesis.

  20. Mixed-layered bismuth-oxygen-iodine materials for capture and waste disposal of radioactive iodine

    DOEpatents

    Krumhansl, James L; Nenoff, Tina M

    2013-02-26

    Materials and methods of synthesizing mixed-layered bismuth oxy-iodine materials, which can be synthesized in the presence of aqueous radioactive iodine species found in caustic solutions (e.g. NaOH or KOH). This technology provides a one-step process for both iodine sequestration and storage from nuclear fuel cycles. It results in materials that will be durable for repository conditions much like those found in Waste Isolation Pilot Plant (WIPP) and estimated for Yucca Mountain (YMP). By controlled reactant concentrations, optimized compositions of these mixed-layered bismuth oxy-iodine inorganic materials are produced that have both a high iodine weight percentage and a low solubility in groundwater environments.

  1. Asymptotic solution of the turbulent mixing layer for velocity ratio close to unity

    NASA Technical Reports Server (NTRS)

    Higuera, F. J.; Jimenez, J.; Linan, A.

    1996-01-01

    The equations describing the first two terms of an asymptotic expansion of the solution of the planar turbulent mixing layer for values of the velocity ratio close to one are obtained. The first term of this expansion is the solution of the well-known time-evolving problem and the second, which includes the effects of the increase of the turbulence scales in the stream-wise direction, obeys a linear system of equations. Numerical solutions of these equations for a two-dimensional reacting mixing layer show that the correction to the time-evolving solution may explain the asymmetry of the entrainment and the differences in product generation observed in flip experiments.

  2. A Turbulence model taking into account the longitudinal flow inhomogeneity in mixing layers and jets

    NASA Astrophysics Data System (ADS)

    Troshin, A. I.

    2017-06-01

    The problem of potential core length overestimation of subsonic free jets by Reynolds-averaged Navier-Stokes (RANS) based turbulence models is addressed. It is shown that the issue is due to the incorrect velocity profile modeling of the jet mixing layers. An additional source term in ω equation is proposed which takes into account the effect of longitudinal flow inhomogeneity on turbulence in mixing layers. Computations confirm that the modified Speziale-Sarkar-Gatski/Launder- Reece-Rodi-omega (SSG/LRR-ω) turbulence model correctly predicts the mean velocity profiles in both initial and far-field regions of subsonic free plane jet as well as the centerline velocity decay rate.

  3. Analysis of Composite Panels Subjected to Thermo-Mechanical Loads

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Peters, Jeanne M.

    1999-01-01

    The results of a detailed study of the effect of cutout on the nonlinear response of curved unstiffened panels are presented. The panels are subjected to combined temperature gradient through-the-thickness combined with pressure loading and edge shortening or edge shear. The analysis is based on a first-order, shear deformation, Sanders-Budiansky-type shell theory with the effects of large displacements, moderate rotations, transverse shear deformation, and laminated anisotropic material behavior included. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, principal strains, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the nonlinear response to variations in the panel parameters, as well as in the material properties of the individual layers. Numerical results are presented for cylindrical panels and show the effects of variations in the loading and the size of the cutout on the global and local response quantities as well as their sensitivity to changes in the various panel, layer, and micromechanical parameters.

  4. Climate Response to Negative Greenhouse Gas Radiative Forcing in Polar Winter

    NASA Astrophysics Data System (ADS)

    Flanner, M. G.; Huang, X.; Chen, X.; Krinner, G.

    2018-02-01

    Greenhouse gas (GHG) additions to Earth's atmosphere initially reduce global outgoing longwave radiation, thereby warming the planet. In select environments with temperature inversions, however, increased GHG concentrations can actually increase local outgoing longwave radiation. Negative top of atmosphere and effective radiative forcing (ERF) from this situation give the impression that local surface temperatures could cool in response to GHG increases. Here we consider an extreme scenario in which GHG concentrations are increased only within the warmest layers of winter near-surface inversions of the Arctic and Antarctic. We find, using a fully coupled Earth system model, that the underlying surface warms despite the GHG addition exerting negative ERF and cooling the troposphere in the vicinity of the GHG increase. This unique radiative forcing and thermal response is facilitated by the high stability of the polar winter atmosphere, which inhibit thermal mixing and amplify the impact of surface radiative forcing on surface temperature. These findings also suggest that strategies to exploit negative ERF via injections of short-lived GHGs into inversion layers would likely be unsuccessful in cooling the planetary surface.

  5. Observed and modeled patterns of covariability between low-level cloudiness and the structure of the trade-wind layer

    DOE PAGES

    Nuijens, Louise; Medeiros, Brian; Sandu, Irina; ...

    2015-11-06

    We present patterns of covariability between low-level cloudiness and the trade-wind boundary layer structure using long-term measurements at a site representative of dynamical regimes with moderate subsidence or weak ascent. We compare these with ECMWF’s Integrated Forecast System and 10 CMIP5 models. By using single-time step output at a single location, we find that models can produce a fairly realistic trade-wind layer structure in long-term means, but with unrealistic variability at shorter-time scales. The unrealistic variability in modeled cloudiness near the lifting condensation level (LCL) is due to stronger than observed relationships with mixed-layer relative humidity (RH) and temperature stratificationmore » at the mixed-layer top. Those relationships are weak in observations, or even of opposite sign, which can be explained by a negative feedback of convection on cloudiness. Cloudiness near cumulus tops at the tradewind inversion instead varies more pronouncedly in observations on monthly time scales, whereby larger cloudiness relates to larger surface winds and stronger trade-wind inversions. However, these parameters appear to be a prerequisite, rather than strong controlling factors on cloudiness, because they do not explain submonthly variations in cloudiness. Models underestimate the strength of these relationships and diverge in particular in their responses to large-scale vertical motion. No model stands out by reproducing the observed behavior in all respects. As a result, these findings suggest that climate models do not realistically represent the physical processes that underlie the coupling between trade-wind clouds and their environments in present-day climate, which is relevant for how we interpret modeled cloud feedbacks.« less

  6. Observed and modeled patterns of covariability between low-level cloudiness and the structure of the trade-wind layer

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nuijens, Louise; Medeiros, Brian; Sandu, Irina

    We present patterns of covariability between low-level cloudiness and the trade-wind boundary layer structure using long-term measurements at a site representative of dynamical regimes with moderate subsidence or weak ascent. We compare these with ECMWF’s Integrated Forecast System and 10 CMIP5 models. By using single-time step output at a single location, we find that models can produce a fairly realistic trade-wind layer structure in long-term means, but with unrealistic variability at shorter-time scales. The unrealistic variability in modeled cloudiness near the lifting condensation level (LCL) is due to stronger than observed relationships with mixed-layer relative humidity (RH) and temperature stratificationmore » at the mixed-layer top. Those relationships are weak in observations, or even of opposite sign, which can be explained by a negative feedback of convection on cloudiness. Cloudiness near cumulus tops at the tradewind inversion instead varies more pronouncedly in observations on monthly time scales, whereby larger cloudiness relates to larger surface winds and stronger trade-wind inversions. However, these parameters appear to be a prerequisite, rather than strong controlling factors on cloudiness, because they do not explain submonthly variations in cloudiness. Models underestimate the strength of these relationships and diverge in particular in their responses to large-scale vertical motion. No model stands out by reproducing the observed behavior in all respects. As a result, these findings suggest that climate models do not realistically represent the physical processes that underlie the coupling between trade-wind clouds and their environments in present-day climate, which is relevant for how we interpret modeled cloud feedbacks.« less

  7. MODELING NON-PRECIPITATING CUMULUS CLOUDS AS FLOW-THROUGH-REACTOR TRANSFORMER AND VENTING TRANSPORTER OF MIXED LAYER POLLUTANTS

    EPA Science Inventory

    A simple diagnostic model of cumulus convective clouds is developed and used in a sensitivity study to examine the extent to which the rate of change of mixed and cloud layer pollutant concentration is influenced by vertical transport and chemical transformation processes occurri...

  8. A MULTI-STREAM MODEL FOR VERTICAL MIXING OF A PASSIVE TRACER IN THE CONVECTIVE BOUNDARY LAYER

    EPA Science Inventory

    We study a multi-stream model (MSM) for vertical mixing of a passive tracer in the convective boundary layer, in which the tracer is advected by many vertical streams with different probabilities and diffused by small scale turbulence. We test the MSM algorithm for investigatin...

  9. Passive scalar entrainment and mixing in a forced, spatially-developing mixing layer

    NASA Technical Reports Server (NTRS)

    Lowery, P. S.; Reynolds, W. C.; Mansour, N. N.

    1987-01-01

    Numerical simulations are performed for the forced, spatially-developing plane mixing layer in two and three dimensions. Transport of a passive scalar field is included in the computation. This, together with the allowance for spatial development in the simulations, affords the opportunity for study of the asymmetric entrainment of irrotational fluid into the layer. The inclusion of a passive scalar field provides a means for simulating the effect of this entrainment asymmetry on the generation of 'products' from a 'fast' chemical reaction. Further, the three-dimensional simulations provide useful insight into the effect of streamwise structures on these entrainment and 'fast' reaction processes. Results from a two-dimensional simulation indicate 1.22 parts high-speed fluid are entrained for every one part low-speed fluid. Inclusion of streamwise vortices at the inlet plane of a three-dimensional simulation indicate a further increase in asymmetric entrainment - 1.44:1. Results from a final three-dimensional simulation are presented. In this case, a random velocity perturbation is imposed at the inlet plane. The results indicate the 'natural' development of the large spanwise structures characteristic of the mixing layer.

  10. Airborne observation of mixing across the entrainment zone during PARADE 2011

    NASA Astrophysics Data System (ADS)

    Berkes, Florian; Hoor, Peter; Bozem, Heiko; Kunkel, Daniel; Sprenger, Michael; Henne, Stephan

    2016-05-01

    This study presents the analysis of the structure and air mass characteristics of the lower atmosphere during the field campaign PARADE (PArticles and RAdicals: Diel observations of the impact of urban and biogenic Emissions) on Mount Kleiner Feldberg in southwestern Germany during late summer 2011. We analysed measurements of meteorological variables (temperature, moisture, pressure, wind speed and direction) from radio soundings and of chemical tracers (carbon dioxide, ozone) from aircraft measurements. We focus on the thermodynamic and dynamic properties that control the chemical distribution of atmospheric constituents in the boundary layer. We show that the evolution of tracer profiles of CO2 and O3 indicate mixing across the inversion layer (or entrainment zone). This finding is supported by the analysis of tracer-tracer correlations which are indicative for mixing and the relation of tracer profiles in relation to the evolution of the boundary layer height deduced from radio soundings. The study shows the relevance of entrainment processes for the lower troposphere in general and specifically that the tracer-tracer correlation method can be used to identify mixing and irreversible exchange processes across the inversion layer.

  11. MAPLE prepared heterostructures with oligoazomethine: Fullerene derivative mixed layer for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Stanculescu, A.; Rasoga, O.; Socol, M.; Vacareanu, L.; Grigoras, M.; Socol, G.; Stanculescu, F.; Breazu, C.; Matei, E.; Preda, N.; Girtan, M.

    2017-09-01

    Mixed layers of azomethine oligomers containing 2,5-diamino-3,4-dicyanothiophene as central unit and triphenylamine (LV5) or carbazol (LV4) at both ends as donor and fullerene derivative, [6,6]-phenyl-C61 butyric acid butyl ester ([C60]PCB-C4) as acceptor, have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on glass/ITO and Si substrates. The effect of weight ratio between donor and acceptor (1:1; 1:2) and solvent type (chloroform, dimethylsulphoxide) on the optical (UV-vis transmission/absorption, photoluminescence) and morphological properties of LV4 (LV5): [C60]PCB-C4 mixed layers has been evidenced. Dark and under illumination I-V characteristics of the heterostructures realized with these mixed layers sandwiched between ITO and Al electrodes have revealed a solar cell behavior for the heterostructures prepared with both LV4 and LV5 using chloroform as matrix solvent. The solar cell structure realized with oligomer LV5, glass/ITO/LV5: [C60]PCB-C4 (1:1) has shown the best parameters.

  12. Method for forming silver-copper mixed kesterite semiconductor film

    DOEpatents

    Gershon, Talia S.; Gunawan, Oki; Lee, Yun S.; Mankad, Ravin

    2018-01-23

    After forming a layer of a Cu-deficient kesterite compound having the formula Cu.sub.2-xZn.sub.1+xSn(S.sub.ySe.sub.1-y).sub.4, wherein 0

  13. INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT

    EPA Science Inventory

    Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

  14. Proposed pushered single shell capsule design for the investigation of mid/high Z mix on the NIF

    NASA Astrophysics Data System (ADS)

    Sacks, Ryan; Tipton, Robert; Graziani, Frank

    2016-05-01

    The CD Mix campaign has given a detailed explination of the mix mechanics in the current ignition capsule designs by investigating the relationship between material mixing, shell-fuel interfaces, and the change in thermonuclear yield given a deuterated layer in the capsule. Alternative ignition scenarios include the use of double shell designs that incorporate high-Z material in the capsule. Simulations are conducted on a proposed capsule platform using the ARES code on a scaled capsule design using a partially reduced glass capsule design. This allows for the inclusion of deuterium on the inner surface of the pusher layer similar to the CD mix experiments. The presence of silicon dioxide allows for the investigation of the influence of higher Z material on the mixing characteristics.

  15. Large eddy simulation of heat entrainment under Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Ramudu, Eshwan; Gelderloos, Renske; Yang, Di; Meneveau, Charles; Gnanadesikan, Anand

    2017-11-01

    Sea ice cover in the Arctic has declined rapidly in recent decades. To better understand ice loss through bottom melting, we choose to study the Canada Basin of the Arctic Ocean, which is characterized by a perennial anomalously warm Pacific Summer Water (PSW) layer residing at the base of the mixed layer and a summertime Near-Surface Temperature Maximum (NSTM) layer trapping heat from solar radiation. The interaction of these warm layers with a moving ice basal surface is investigated using large eddy simulation. We find that the presence of the NSTM enhances heat entrainment from the mixed layer. Another conclusion from our work is that there is no heat entrained from the PSW layer, even at the largest ice-drift velocity of 0.3 m s-1 considered. We propose a scaling law for the heat flux at the ice basal surface which depends on the initial temperature anomaly in the NSTM layer and the ice-drift velocity. A case study of `The Great Arctic Cyclone of 2012' gives a turbulent heat flux from the mixed layer that is approximately 70% of the total ocean-to-ice heat flux estimated from the PIOMAS model often used for short-term predictions. Present results highlight the need for large-scale climate models to account for the NSTM layer. We acknowledge funding from NOAA Grant NA15OAR4310172, the NSF, and the University of Houston start-up fund.

  16. Vertical Mixing Effects on Phytoplankton Dynamics and Organic Carbon Export in the Western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Kessouri, Faycal; Ulses, Caroline; Estournel, Claude; Marsaleix, Patrick; D'Ortenzio, Fabrizio; Severin, Tatiana; Taillandier, Vincent; Conan, Pascal

    2018-03-01

    A 3-D high-resolution coupled hydrodynamic-biogeochemical model of the western Mediterranean was used to study phytoplankton dynamics and organic carbon export in three regions with contrasting vertical regimes, ranging from deep convection to a shallow mixed layer. One month after the initial increase in surface chlorophyll (caused by the erosion of the deep chlorophyll maximum), the autumnal bloom was triggered in all three regions by the upward flux of nutrients resulting from mixed layer deepening. In contrast, at the end of winter, the end of turbulent mixing favored the onset of the spring bloom in the deep convection region. Low grazing pressure allowed rapid phytoplankton growth during the bloom. Primary production in the shallow mixed layer region, the Algerian subbasin, was characterized by a long period (4 months) of sustained phytoplankton development, unlike the deep convection region where primary production was inhibited during 2 months in winter. Despite seasonal variations, annual primary production in all three regions is similar. In the deep convection region, total organic carbon export below the photic layer (150 m) and transfer to deep waters (800 m) was 5 and 8 times, respectively, higher than in the Algerian subbasin. Although some of the exported material will be injected back into the surface layer during the next convection event, lateral transport, and strong interannual variability of MLD in this region suggest that a significant amount of exported material is effectively sequestrated.

  17. Testing the usefulness of 222Rn to complement conventional hydrochemical data to trace groundwater provenance in complex multi-layered aquifers. Application to the Úbeda aquifer system (Jaén, SE Spain).

    PubMed

    Ortega, L; Manzano, M; Rodríguez-Arévalo, J

    2017-12-01

    The Úbeda aquifer system is a multi-layered aquifer intensively exploited for irrigation. It covers 1100km 2 and consists of piled up sedimentary aquifer and aquitard layers from Triassic sandstones and clays at the bottom, to Jurassic carbonates (main exploited layer) in the middle, and Miocene sandstones and marls at the top. Flow network modification by intense exploitation and the existence of deep faults favour vertical mixing of waters from different layers and with distinct chemical composition. This induces quality loss and fosters risk of quantity restrictions. To support future groundwater abstraction management, a hydrogeochemical (major and some minor solutes) and isotopic ( 222 Rn) study was performed to identify the chemical signatures of the different layers and their mixing proportions in mixed samples. The study of 134 groundwater samples allowed a preliminary identification of hydrochemical signatures and mixtures, but the existence of reducing conditions in the most exploited sector prevents the utility of sulphate as a tracer of Triassic groundwater in the Jurassic boreholes. The potential of 222 Rn to establish isotopic signatures and to trace groundwater provenance in mixtures was tested. 222 Rn was measured in 48 samples from springs and boreholes in most aquifer layers. At first, clear correlations were observed between 222 Rn, Cl and SO 4 in groundwater. Afterwards, very good correlations were observed between 222 Rn and the chemical facies of the different layers established with End Member Mixing Analysis (EMMA). Using 222 Rn as part of the signatures, EMMA helped to identify end-member samples, and to quantify the mixing proportions of water from the Triassic and the Deep Miocene layers in groundwater pumped by deep agricultural wells screened in the Jurassic. The incorporation of 222 Rn to the study also allowed identifying the impact of irrigation returns through the association of moderate NO 3 , Cl, and Br contents with very low 222 Rn activities. Copyright © 2017. Published by Elsevier B.V.

  18. One-pot in situ mixed film formation by azo coupling and diazonium salt electrografting.

    PubMed

    Esnault, Charles; Delorme, Nicolas; Louarn, Guy; Pilard, Jean-François

    2013-06-24

    So simple: The in situ synthesis of an aryldiazonium salt and an azo-aryldiazonium salt by azo coupling from sulfanilic acid and aniline is reported. Formation of a mixed organic layer is monitored by cyclic voltammetry and atomic force microscopy. A compact mixed layer is obtained with a global roughness of 0.4 nm and 10-15 % vertical extension in the range 1.5-6 nm. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Transport and Mixing Induced by Beating Cilia in Human Airways

    PubMed Central

    Chateau, Sylvain; D'Ortona, Umberto; Poncet, Sébastien; Favier, Julien

    2018-01-01

    The fluid transport and mixing induced by beating cilia, present in the bronchial airways, are studied using a coupled lattice Boltzmann—Immersed Boundary solver. This solver allows the simulation of both single and multi-component fluid flows around moving solid boundaries. The cilia are modeled by a set of Lagrangian points, and Immersed Boundary forces are computed onto these points in order to ensure the no-slip velocity conditions between the cilia and the fluids. The cilia are immersed in a two-layer environment: the periciliary layer (PCL) and the mucus above it. The motion of the cilia is prescribed, as well as the phase lag between two cilia in order to obtain a typical collective motion of cilia, known as metachronal waves. The results obtained from a parametric study show that antiplectic metachronal waves are the most efficient regarding the fluid transport. A specific value of phase lag, which generates the larger mucus transport, is identified. The mixing is studied using several populations of tracers initially seeded into the pericilary liquid, in the mucus just above the PCL-mucus interface, and in the mucus far away from the interface. We observe that each zone exhibits different chaotic mixing properties. The larger mixing is obtained in the PCL layer where only a few beating cycles of the cilia are required to obtain a full mixing, while above the interface, the mixing is weaker and takes more time. Almost no mixing is observed within the mucus, and almost all the tracers do not penetrate the PCL layer. Lyapunov exponents are also computed for specific locations to assess how the mixing is performed locally. Two time scales are introduced to allow a comparison between mixing induced by fluid advection and by molecular diffusion. These results are relevant in the context of respiratory flows to investigate the transport of drugs for patients suffering from chronic respiratory diseases. PMID:29559920

  20. Transport and Mixing Induced by Beating Cilia in Human Airways.

    PubMed

    Chateau, Sylvain; D'Ortona, Umberto; Poncet, Sébastien; Favier, Julien

    2018-01-01

    The fluid transport and mixing induced by beating cilia, present in the bronchial airways, are studied using a coupled lattice Boltzmann-Immersed Boundary solver. This solver allows the simulation of both single and multi-component fluid flows around moving solid boundaries. The cilia are modeled by a set of Lagrangian points, and Immersed Boundary forces are computed onto these points in order to ensure the no-slip velocity conditions between the cilia and the fluids. The cilia are immersed in a two-layer environment: the periciliary layer (PCL) and the mucus above it. The motion of the cilia is prescribed, as well as the phase lag between two cilia in order to obtain a typical collective motion of cilia, known as metachronal waves. The results obtained from a parametric study show that antiplectic metachronal waves are the most efficient regarding the fluid transport. A specific value of phase lag, which generates the larger mucus transport, is identified. The mixing is studied using several populations of tracers initially seeded into the pericilary liquid, in the mucus just above the PCL-mucus interface, and in the mucus far away from the interface. We observe that each zone exhibits different chaotic mixing properties. The larger mixing is obtained in the PCL layer where only a few beating cycles of the cilia are required to obtain a full mixing, while above the interface, the mixing is weaker and takes more time. Almost no mixing is observed within the mucus, and almost all the tracers do not penetrate the PCL layer. Lyapunov exponents are also computed for specific locations to assess how the mixing is performed locally. Two time scales are introduced to allow a comparison between mixing induced by fluid advection and by molecular diffusion. These results are relevant in the context of respiratory flows to investigate the transport of drugs for patients suffering from chronic respiratory diseases.

  1. Heat balances of the surface mixed layer in the equatorial Atlantic and Indian Ocean during FGGE

    NASA Technical Reports Server (NTRS)

    Molinari, R. L.

    1985-01-01

    Surface meteorological and surface and subsurface oceanographic data collected during FGGE in the equatorial Atlantic and Indian Oceans are used to estimate the terms in a heat balance relation for the mixed layer. The first balance tested is between changes in mixed layer temperature (MLT) and surface energy fluxes. Away from regions of low variance in MLT time series and equatorial and coastal upwelling, surface fluxes can account for 75 percent of the variance in the observed time series. Differences between observed and estimated MLTs indicate that on the average, maximum errors in surface flux are of the order of 20 to 30 W/sq m. In the Atlantic, the addition of zonal advection does not significantly improve the estimates. However in regions of equatorial upwelling, the eastern Atlantic vertical mixing and meridional advection can play an important role in the evolution of MLTs.

  2. Charge Transfer and Collection in Dilute Organic Donor-Acceptor Heterojunction Blends.

    PubMed

    Ding, Kan; Liu, Xiao; Forrest, Stephen R

    2018-05-09

    Experimental and theoretical approaches are used to understand the role of nanomorphology on exciton dissociation and charge collection at dilute donor-acceptor (D-A) organic heterojunctions (HJs). Specifically, two charge transfer (CT) states in D-A mixed HJs comprising nanocrystalline domains of tetraphenyldibenzoperiflanthene (DBP) as the donor and C 70 as the acceptor are unambiguously related to the nanomorphology of the mixed layer. Alternating DBP:C 70 multilayer stacks are used to identify and control the optical properties of the CT states, as well as to simulate the dilute mixed heterojunctions. A kinetic Monte Carlo model along with photoluminescence spectroscopy and scanning transmission electron microscopy are used to quantitatively evaluate the layer morphology under various growth conditions. As a result, we are able to understand the counterintuitive observation of high charge extraction efficiency and device performance of DBP:C 70 mixed layer photovoltaics at surprisingly low (∼10%) donor concentrations.

  3. Model free simulations of a high speed reacting mixing layer

    NASA Technical Reports Server (NTRS)

    Steinberger, Craig J.

    1992-01-01

    The effects of compressibility, chemical reaction exothermicity and non-equilibrium chemical modeling in a combusting plane mixing layer were investigated by means of two-dimensional model free numerical simulations. It was shown that increased compressibility generally had a stabilizing effect, resulting in reduced mixing and chemical reaction conversion rate. The appearance of 'eddy shocklets' in the flow was observed at high convective Mach numbers. Reaction exothermicity was found to enhance mixing at the initial stages of the layer's growth, but had a stabilizing effect at later times. Calculations were performed for a constant rate chemical rate kinetics model and an Arrhenius type kinetics prototype. The Arrhenius model was found to cause a greater temperature increase due to reaction than the constant kinetics model. This had the same stabilizing effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

  4. Understanding the desensitizing mechanism of olefin in explosives: shear slide of mixed HMX-olefin systems.

    PubMed

    Zhang, Chaoyang; Cao, Xia; Xiang, Bin

    2012-04-01

    We simulated the shear slide behavior of typical mixed HMX-olefin systems and the effect of thickness of olefin layers (4-22 Å) on the behavior at a molecular level by considering two cases: bulk shear and interfacial shear. The results show that: (1) the addition of olefin into HMX can reduce greatly the shear sliding barriers relative to the pure HMX in the two cases, suggesting that the desensitizing mechanism of olefin is controlled dominantly by its good lubricating property; (2) the change of interaction energy in both systoles of shear slide is strongly dominated by van der Waals interaction; and (3) the thickness of olefin layers in the mixed explosives can influence its desensitizing efficiency. That is, the excessive thinness of olefin layers in the mixed explosive systems, for example, several angstroms, can lead to very high sliding barriers.

  5. Nutrient interleaving below the mixed layer of the Kuroshio Extension Front

    NASA Astrophysics Data System (ADS)

    Nagai, Takeyoshi; Clayton, Sophie

    2017-08-01

    Nitrate interleaving structures were observed below the mixed layer during a cruise to the Kuroshio Extension in October 2009. In this paper, we investigate the formation mechanisms for these vertical nitrate anomalies, which may be an important source of nitrate to the oligotrphoc surface waters south of the Kuroshio Extension Front. We found that nitrate concentrations below the main stream of the Kuroshio Extension were elevated compared to the ambient water of the same density ( σ 𝜃 = 23.5-25). This appears to be analogous to the "nutrient stream" below the mixed layer, associated with the Gulf Stream. Strong turbulence was observed above the vertical nitrate anomaly, and we found that this can drive a large vertical turbulent nitrate flux >O (1 mmol N m-2 day-1). A realistic, high-resolution (2 km) numerical simulation reproduces the observed Kuroshio nutrient stream and nitrate interleaving structures, with similar lateral and vertical scales. The model results suggest that the nitrate interleaving structures are first generated at the western side of the meander crest on the south side of the Kuroshio Extension, where the southern tip of the mixed layer front is under frontogenesis. Lagrangian analyses reveal that the vertical shear of geostrophic and subinertial ageostrophic flow below the mixed layer tilts the existing along-isopycnal nitrate gradient of the Kuroshio nutrient stream to form nitrate interleaving structures. This study suggests that the multi-scale combination of (i) the lateral stirring of the Kuroshio nutrient stream by developed mixed layer fronts during fall to winter, (ii) the associated tilting of along-isopycnal nitrate gradient of the nutrient stream by subinertial shear, which forms vertical interleaving structures, and (iii) the strong turbulent diffusion above them, may provide a route to supply nutrients to oligotrophic surface waters on the south side of the Kuroshio Extension.

  6. High Winds and the Vertical Structure of Chl-a in the Southern Ocean: Insights from Remote Sensing and Novel in situ Sensors

    NASA Astrophysics Data System (ADS)

    Carranza, M. M.; Gille, S. T.; Franks, P. J. S.; Johnson, K. S.; Girton, J. B.

    2016-02-01

    The Southern Ocean is under the influence of strong atmospheric synoptic activity and contains some of the oceans deepest mixed layers. Deep mixed layers can transport phytoplankton below the euphotic zone, and phytoplankton growth is hypothesized to be co-limited by iron and light. Atmospheric forcing drives changes in the mixed-layer depth (MLD) that influence light levels and nutrient input to the euphotic zone. In summer, when the MLD is shallow and close to the euphotic depth, high satellite Chl-a correlate with high winds, consistent with wind-driven entrainment that can potentially increase nutrient concentrations in the euphotic zone. However, correlations between Chl-a and diurnal winds are largest at zero time lag. High winds can inject nutrients on short timescales (< 1 day), but in situ incubation experiments after iron addition indicate phytoplankton growth on slightly longer timescales (> 3-4 days), suggesting that the correlations are not a result of growth. High winds can also entrain Chl-a from a subsurface Chl-a maximum. Novel bio-optical sensors mounted on elephant seals and autonomous floats allow us to examine the vertical structure of Chl-a in the Southern Ocean. In this study, we investigate the occurrence of subsurface Chl-a maxima. We find that surface Chl-a is a relatively good proxy for depth-integrated Chl-a within the euphotic zone but gives an inadequate representation of biomass within the mixed layer, particularly in the summer. Subsurface Chl-a maxima are not uncommon and may occur in all seasons. Chl-a maxima that correlate with particle backscattering in summer and fall are found near the base of the mixed layer, closer to the nutrient maximum than the light maximum, suggesting that nutrient limitation (i.e., essentially iron) can play a greater role than light limitation in governing productivity, and that high winds potentially entrain a subsurface Chl-a maximum into the summer mixed layer.

  7. Atomic mixing induced by swift heavy ion irradiation of Fe/Zr multilayers

    NASA Astrophysics Data System (ADS)

    Jaouen, C.; Michel, A.; Pacaud, J.; Dufour, C.; Bauer, Ph.; Gervais, B.

    1999-01-01

    The mechanism of ion induced mixing and phase change was studied for Fe/Zr multilayers, and specifically for the case of swift heavy ions giving rise to a very large electronic excitation of the target. The multilayers had a modulation of 7.6 nm and an overall composition Fe 69Zr 31. The Zr layers were amorphous whereas the Fe ones were crystalline (bcc) with a very strong (1 1 0) texture in the growth direction. The phase transformation and the composition changes were analysed using the structural and magnetic properties of the Fe component by means of a detailed analysis of the X-ray diffraction profiles and with the aid of backscattering Mössbauer spectroscopy. A complete mixing was observed at a fluence of 10 13 U/cm 2. Both phenomena, the dose dependence of the ion beam mixed amorphous non-magnetic phase and the quantitative evolution of the crystalline iron layer thickness, suggest that mixing occurs in a two-stage process. At an initial stage, an anisotropic diffusion of iron atoms in the amorphous zirconium layers takes place along the interface, while subsequent ion bombardment leads to a generalised transformation through the whole of the Fe layer. Finally, the implications of these observations are discussed in comparison to the plastic deformation phenomena reported for amorphous alloys.

  8. The sensitivity of primary productivity to intra-seasonal mixed layer variability in the sub-Antarctic Zone of the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Joubert, W. R.; Swart, S.; Tagliabue, A.; Thomalla, S. J.; Monteiro, P. M. S.

    2014-03-01

    The seasonal cycle of primary productivity is impacted by seasonal and intra-seasonal dynamics of the mixed layer through the changing balance between mixing and buoyancy forcing, which regulates nutrient supply and light availability. Of particular recent interest is the role of synoptic scale events in supplying nutrients, particularly iron, to the euphotic zone in the Sub Antarctic Zone (SAZ), where phytoplankton blooms occur throughout summer. In this study, we present high resolution measurements of net community production (NCP) constrained by ΔO2/Ar ratios, and mixed layer depth (MLD) in the Atlantic SAZ. We found a non-linear relationship between NCP and MLD, with the highest and most variable NCP observed in shallow MLDs (< 45 m). We propose that NCP variability in the SAZ may be driven by alternating states of synoptic-scale deepening of the mixed layer, leading to the entrainment of iron (dFe), followed by restratification, allowing rapid growth in an iron replete, high light environment. Synoptic iron fluxes into the euphotic zone based on water column dFe profiles and high resolution glider MLD data, reveal a potentially significant contribution of "new iron" which could sustain NCP throughout summer. Future process studies will help elaborate these findings further.

  9. Simulations of arctic mixed-phase clouds in forecasts with CAM3 and AM2 for M-PACE

    DOE PAGES

    Xie, Shaocheng; Boyle, James; Klein, Stephen A.; ...

    2008-02-27

    [1] Simulations of mixed-phase clouds in forecasts with the NCAR Atmosphere Model version 3 (CAM3) and the GFDL Atmospheric Model version 2 (AM2) for the Mixed-Phase Arctic Cloud Experiment (M-PACE) are performed using analysis data from numerical weather prediction centers. CAM3 significantly underestimates the observed boundary layer mixed-phase cloud fraction and cannot realistically simulate the variations of liquid water fraction with temperature and cloud height due to its oversimplified cloud microphysical scheme. In contrast, AM2 reasonably reproduces the observed boundary layer cloud fraction while its clouds contain much less cloud condensate than CAM3 and the observations. The simulation of themore » boundary layer mixed-phase clouds and their microphysical properties is considerably improved in CAM3 when a new physically based cloud microphysical scheme is used (CAM3LIU). The new scheme also leads to an improved simulation of the surface and top of the atmosphere longwave radiative fluxes. Sensitivity tests show that these results are not sensitive to the analysis data used for model initialization. Increasing model horizontal resolution helps capture the subgrid-scale features in Arctic frontal clouds but does not help improve the simulation of the single-layer boundary layer clouds. AM2 simulated cloud fraction and LWP are sensitive to the change in cloud ice number concentrations used in the Wegener-Bergeron-Findeisen process while CAM3LIU only shows moderate sensitivity in its cloud fields to this change. Furthermore, this paper shows that the Wegener-Bergeron-Findeisen process is important for these models to correctly simulate the observed features of mixed-phase clouds.« less

  10. Simulations of Arctic mixed-phase clouds in forecasts with CAM3 and AM2 for M-PACE

    NASA Astrophysics Data System (ADS)

    Xie, Shaocheng; Boyle, James; Klein, Stephen A.; Liu, Xiaohong; Ghan, Steven

    2008-02-01

    Simulations of mixed-phase clouds in forecasts with the NCAR Atmosphere Model version 3 (CAM3) and the GFDL Atmospheric Model version 2 (AM2) for the Mixed-Phase Arctic Cloud Experiment (M-PACE) are performed using analysis data from numerical weather prediction centers. CAM3 significantly underestimates the observed boundary layer mixed-phase cloud fraction and cannot realistically simulate the variations of liquid water fraction with temperature and cloud height due to its oversimplified cloud microphysical scheme. In contrast, AM2 reasonably reproduces the observed boundary layer cloud fraction while its clouds contain much less cloud condensate than CAM3 and the observations. The simulation of the boundary layer mixed-phase clouds and their microphysical properties is considerably improved in CAM3 when a new physically based cloud microphysical scheme is used (CAM3LIU). The new scheme also leads to an improved simulation of the surface and top of the atmosphere longwave radiative fluxes. Sensitivity tests show that these results are not sensitive to the analysis data used for model initialization. Increasing model horizontal resolution helps capture the subgrid-scale features in Arctic frontal clouds but does not help improve the simulation of the single-layer boundary layer clouds. AM2 simulated cloud fraction and LWP are sensitive to the change in cloud ice number concentrations used in the Wegener-Bergeron-Findeisen process while CAM3LIU only shows moderate sensitivity in its cloud fields to this change. This paper shows that the Wegener-Bergeron-Findeisen process is important for these models to correctly simulate the observed features of mixed-phase clouds.

  11. Effects of Formation Heterogeneity in Semi-Confining Shale Layers in Enhancing Mixing and Storage of Dissolved CO2

    NASA Astrophysics Data System (ADS)

    Illangasekare, T. H.; Agartan Karacaer, E.; Vargas-Johnson, J.; Cihan, A.; Birkholzer, J. T.

    2017-12-01

    It is expected that heterogeneity of the deep geologic formation to play a key role in both trapping of supercritical CO2 and its mixing in the formation brine. In previously reported research by the authors, a set of laboratory experiments and field-scale simulations were used to show that convective mixing and diffusion controlled trapping are two important mechanisms that contribute to the dissolution trapping in multilayered systems with homogeneous low-permeability zones such as shale. However, these low-permeability layers (e.g. shale) are not always homogeneous due to their composition and texture variations in addition to the presence of faults, fractures and fissures. In this study, we investigated the potential outcomes of heterogeneity present within these semi-confining low-permeability layers in regards to mixing and storage of dissolved CO2. An intermediate-scale laboratory experiment was designed to investigate the contribution of convective mixing, diffusion controlled trapping and back diffusion to long-term storage of dissolved CO2 in multilayered formations with heterogeneous low-permeability layers. The experiment was performed using a surrogate fluid combination to represent dissolved CO2 and brine under ambient pressure and temperature conditions. After verifying the numerical model with the experimental results, different distributions of the same low-permeability materials having similar volume ratios with the experimentally studied scenario were tested numerically. The experiment and modeling results showed that connectivity of higher permeability material within the semi-confining low-permeability layers contributes to mixing through brine leakage between upper and lower aquifers, storage through diffusion, and in the long term, back diffusion of stored mass due to reversed concentration gradient.

  12. International Congress of Fluid Mechanics, 3rd, Cairo, Egypt, Jan. 2-4, 1990, Proceedings. Volumes 1, 2, 3, & 4

    NASA Astrophysics Data System (ADS)

    Nayfeh, A. H.; Mobarak, A.; Rayan, M. Abou

    This conference presents papers in the fields of flow separation, unsteady aerodynamics, fluid machinery, boundary-layer control and stability, grid generation, vorticity dominated flows, and turbomachinery. Also considered are propulsion, waves and sound, rotor aerodynamics, computational fluid dynamics, Euler and Navier-Stokes equations, cavitation, mixing and shear layers, mixing layers and turbulent flows, and fluid machinery and two-phase flows. Also addressed are supersonic and reacting flows, turbulent flows, and thermofluids.

  13. A Basin-Wide Examination of the Arctic Ocean's Double-Diffusive Staircase

    NASA Astrophysics Data System (ADS)

    Shibley, N.; Timmermans, M. L.; Carpenter, J. R.; Toole, J. M.

    2016-02-01

    The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure above the Atlantic Water Layer consisting of multiple mixed layers of order 1-m in height separated by sharp interfaces. This double-diffusive staircase structure is characterized across the entire Arctic Ocean through a detailed analysis of Ice-Tethered Profiler measurements acquired between 2004 and 2013. Staircase properties (mixed layer thicknesses and temperature-salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio for 50-m spanning the staircase stratification. It is shown that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (on the Eurasian side) and higher density ratio (on the Canadian side). We find that the diffusive staircase in the Eurasian Basin is characterized by fewer, thinner mixed layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin staircase mixed layers. Using a double-diffusive 4/3 flux law parameterization, the distribution of vertical heat fluxes through the staircase is estimated across the Arctic; it is found that heat fluxes in the Eurasian Basin [O(1) W/m^2] are generally an order of magnitude larger than those in the Canadian Basin [O(0.1) W/m^2].

  14. Liquid eutectic GaIn as an alternative electrode for PTB7:PCBM organic solar cells

    NASA Astrophysics Data System (ADS)

    Thanh Hau Pham, Viet; Kieu Trinh, Thanh; Tam Nguyen Truong, Nguyen; Park, Chinho

    2017-04-01

    Conventional vacuum deposition process of aluminum (Al) is costly, time-consuming and difficult to apply to the large-scale production of organic photovoltaic devices (OPV). This paper reports a vacuum-free fabrication process of poly[[4,8-bis(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b‧]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thienophenediyl]:[6,6]-phenyl C71 butyric acid methyl ester (PTB7:PCBM) bulk heterojunction organic solar cell with liquid eutectic gallium-indium (EGaIn) electrode as an alternative to the common Al electrode. The insertion of a thin poly(ethylene oxide) (PEO) layer after depositing organic photoactive layer could help prevent the diffusion of liquid EGaIn into the active layer and allow the deposition of the EGaIn electrode. The PEO interfacial layer was formed by spin-coating from a mixed solvent of alcohol and water. Among different alcohol+water (methanol, ethanol, ethylene glycol, n-propanol, isopropanol, and isobutanol) mixed solvent tested, the n-propanol+water mixed solvent showed the greatest enhancement to the performance of OPVs. The improved device performance was attributed to the reactivity of mixed solvent n-propanol+water toward the surface of PTB7:PCBM active layer, which could help optimize surface morphology.

  15. Main processes of the Atlantic cold tongue interannual variability

    NASA Astrophysics Data System (ADS)

    Planton, Yann; Voldoire, Aurore; Giordani, Hervé; Caniaux, Guy

    2018-03-01

    The interannual variability of the Atlantic cold tongue (ACT) is studied by means of a mixed-layer heat budget analysis. A method to classify extreme cold and warm ACT events is proposed and applied to ten various analysis and reanalysis products. This classification allows 5 cold and 5 warm ACT events to be selected over the period 1982-2007. Cold (warm) ACT events are defined by the presence of negative (positive) sea surface temperature (SST) anomalies at the center of the equatorial Atlantic in late boreal spring, preceded by negative (positive) zonal wind stress anomalies in the western equatorial Atlantic. An ocean general circulation model capable of reconstructing the interannual variability of the ACT correctly is used to demonstrate that cold ACT events develop rapidly from May to June mainly due to intense cooling by vertical mixing and horizontal advection. The simulated cooling at the center of the basin is the result of the combined effects of non-local and local processes. The non-local process is an upwelling associated with an eastward-propagating Kelvin wave, which makes the mixed-layer more shallow and preconditions the upper layers to be cooled by an intense heat loss at the base of the mixed-layer, which is amplified by a stronger local injection of energy from the atmosphere. The early cooling by vertical mixing in March is also shown to be a good predictor of June cooling. In July, horizontal advection starts to warm the mixed-layer abnormally and damps SST anomalies. The advection anomalies, which result from changes in the horizontal temperature gradient, are associated in some cases with the propagation of Rossby waves along the equator. During warm ACT events, processes are reversed, generating positive SST anomalies: a downwelling Kelvin wave triggers stratification anomalies and mixed-layer depth anomalies, amplified by a weaker injection of energy from the atmosphere in May-June. In July, warm ACT events are abnormally cooled due to negative horizontal advection anomalies resulting from processes similar to those that occur during cold ACT events. This additional cooling process extends the period of cooling of the ACT, reducing SST anomalies.

  16. Grazer responses to variable macroalgal resource conditions facilitate habitat structuring

    PubMed Central

    Perissinotto, Renzo; Bird, Matthew S.; Pelletier, Noémie

    2018-01-01

    Consumer responses to altered resource conditions can vary depending on dietary preference, resource characteristics and secondary resource features such as shelter. These can have cascading effects, especially if the consumed resource impacts on overall ecological functioning. In this study, we assessed the dietary composition of grazer communities following seasonal changes in the characteristics of their staple food-source (macroalgae). This was conducted in the living stromatolite pools growing along the coast of South Africa. Stable isotope mixing models suggested that following macroalgal bleaching in summer, metazoan consumers shifted their diet from predominantly macroalgae to a generalist composition. This has important implications for the integrity of the stromatolite matrix and its layered deposition. Where previously in winter stromatolite microalgae comprised a minor component of metazoan consumer diets, in summer, following a change in the resource conditions of macroalgae, microalgae featured more prominently in grazer diets. This seasonal grazing pressure on stromatolite-related resources probably promotes the pattern of annual layering observed in the stromatolite accretion. It also demonstrates a mechanism whereby grazer dietary shifts following a change in their preferred food resource can affect the ecosystem structure of their environment, specifically the stromatolite layering process which responds to microalgal growth or grazing conditions. PMID:29410845

  17. [Responses of soil microbial carbon metabolism to the leaf litter composition in Liaohe River Nature Reserve of northern Hebei Province, China].

    PubMed

    Li, Tian-yu; Kang, Feng-feng; Han, Hai-rong; Gao, Jing; Song, Xiao-shuai; Yu, Shu; Zhao, Jin-long; Yu, Xiao-wen

    2015-03-01

    Using litter bag method, we studied the effects of single and mixed litters from Betula platyphlla, Populus davidiana and Quercus mongolica on soil microbial biomass carbon (MBC), microbial respiration (MR) and microbial metabolic quotient (qCO2) in 0-5, 5-10 and 10-20 cm soil layers. The results showed that the average contents of MBC in 0-20 cm soil layer were 124.84, 325.29, 349.79 and 319.02 mg . kg-1 in the leaf litter removal treatment, Betula platyphlla treatment, Populus davidiana treatment and Quercus mongolica treatment, and the corresponding average rates of MR were 0.66, 1.12, 1.16 and 1.10 µg . g-1 . h-1, respectively. Meanwhile, in 0-20 cm soil layer, the average contents of MBC in the treatments with single leaf litter, mixed litter of two plant species and mixed litter of three plant species were 331. 37, 418. 52 and 529. 34 mg . kg-1, and the corresponding average rates of MR were 1.13, 1.30 and 1.46 µg . g-1 . h-1, respectively. In contrast to the MBC and MR, qCO2 in soil showed a reverse pattern. Our study suggested that characteristics of microbial carbolic metabolism were influenced by litter quality. Namely, the treatment with high litter quality had higher MBC, MR and utilization efficiency of soil carbon, compared with the treatment with low litter quality. Moreover, mixture of different species of leaf litter improved soil microbial activities, increased utilization efficiency on soil carbon and promoted diversity of microbial metabolic pathways, which could then contribute to maintaining and enhancing soil quality of forestland.

  18. Effect of dry air on interface smoothening in reactive sputter deposited Co/Ti multilayer

    NASA Astrophysics Data System (ADS)

    Biswas, A.; Porwal, A.; Bhattacharya, Debarati; Prajapat, C. L.; Ghosh, Arnab; Nand, Mangla; Nayak, C.; Rai, S.; Jha, S. N.; Singh, M. R.; Bhattacharyya, D.; Basu, S.; Sahoo, N. K.

    2017-09-01

    Top surface roughness and interface roughness are one of the key elements which determine the performance of X-ray and neutron thin film multilayer devices. It has been observed that by mixing air with argon in sputtering ambience during deposition of Co layers, polarized neutron reflectivity (PNR) of Co/Ti supermirror polarizers can be improved substantially. Cross-sectional HRTEM measurement reveals that sharper interfaces in the supermirror can be achieved in case of deposition of the multilayer under mixed ambience of argon and air. In order to investigate this interface modification mechanism further, in this communication two sets of tri-layer Co/Ti/Co samples and 20-layer Co/Ti periodic multilayer samples have been prepared; in one set all the layers are deposited only under argon ambience and in the other set, Co layers are deposited under a mixed ambience of argon and air. These samples have been characterized by measuring specular and non-specular X-ray reflectivities (GIXR) with X-rays of 1.54 Å wavelength and polarized neutron reflectivity (PNR) with neutron of 2.5 Å wavelength at grazing angle of incidence. It has been observed that the X-ray and neutron specular reflectivities at Bragg peaks of 20 layer periodic multilayer increase when Co layers are deposited under mixed ambience of argon and air. The detail information regarding the effect of air on the interfaces and magnetic properties has been obtained by fitting the measured spectra. The above information has subsequently been supplemented by XRD and magnetic measurements on the samples. XPS and XANES measurements have also been carried out to investigate whether cobalt oxide or cobalt nitride layers are being formed due to use of air in sputtering ambience.

  19. Rapid Near-inertial Internal Wave Group Propagation Through the Transition Layer from Float and Glider Observations in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Johnston, S.; Rudnick, D. L.; Sherman, J. T.

    2016-02-01

    Two Spray gliders and 1 SOLO-II float were deployed in 2013 and 2014 as components of ONR's Air-Sea Interactions in the Northern Indian Ocean (ASIRI) experiment. Shallow (10-50 m) salinity-controlled mixed layers in the Bay of Bengal isolate the rest of the deeper isothermal layer and ocean interior from winds. The transition layer is a deeper stratification maximum (20-100 m), which separates the upper ocean from the interior. Downward near-inertial internal wave (NIW) groups are observed here in potential density fluctuations and can rapidly (a few inertial periods) transfer energy out of the mixed layer into the stratified interior. (Inertial periods are T = 2*pi/f = 2 - 3 days from 9 - 17°N, where f is the Coriolis frequency.) When isopycnals shoal at fronts, the transition layer is brought closer to the mixed layer allowing for faster downward group speed due to the higher stratification. With about 10 inertial wind events in the NCEP reanalysis over the observation period of about 21 weeks, we find 3 NIW groups with clear downward energy (upward phase) propagation into the interior. The groups reach 200 m within 2-3 T and have vertical wavelengths of about 200 m. This implies horizontal wavelengths of about 200 km if the waves have a frequency of 1.1f. This horizontal wavelength and propagation time scale appear consistent with surface wind forcing correlation scales from 3-day highpassed wind products and decay estimates from surface drifters and theory (Park et al., 2009). Our results extend this previous work by making subsurface observations and measuring further equatorward. The mesoscale appears to mediate: (a) the conversion from mixed layer inertial oscillations into propagating NIW and (b) NIW propagation into the interior.

  20. Observed Aerosol Influence on Ice Water Content of Arctic Mixed-Phase Clouds

    NASA Astrophysics Data System (ADS)

    Norgren, M.; de Boer, G.; Shupe, M.

    2016-12-01

    The response of ice water content (IWC) in Arctic mixed-phase stratocumulus to atmospheric aerosols is observed. IWC retrievals from ground based radars operated by the Atmospheric Radiation Measurement (ARM) program in Barrow, Alaska are used to construct composite profiles of cloud IWC from a 9-year radar record starting in January of 2000. The IWC profiles for high (polluted) and low (clean) aerosol loadings are compared. Generally, we find that clean clouds exhibit statistically significant higher levels of IWC than do polluted clouds by a factor of 2-4 at cloud base. For springtime clouds, with a maximum relative humidity with respect to ice (RHI) above 110% in the cloud layer, the IWC at cloud base was a factor of 3.25 times higher in clean clouds than it was in polluted clouds. We infer that the aerosol loading of the cloud environment alters the liquid drop size distribution within the cloud, with larger drops being more frequent in clean clouds. Larger cloud drops promote riming within the cloud layer, which is one explanation for the higher IWC levels in clean clouds. The drop size distribution may also be a significant control of ice nucleation events within mixed-phase clouds. Whether the high IWC levels in clean clouds are due to increased riming or nucleation events is unclear at this time.

  1. The radiative effects of Saharan dust layer on the marine atmospheric layer

    NASA Astrophysics Data System (ADS)

    Abed, Mohammed

    2017-04-01

    The North African Saharan desert is one of the main sources of atmospheric dust. Since dust can be transported by winds for thousands of miles, reaching the Americas and extending across vast expanses of the tropical Atlantic Ocean, it is important to understand the influence that dust has on the radiative properties and the thermodynamic structure of the atmosphere. For climate models it is important that this is represented since the structure of the atmosphere can have important influences downwind on the development of convection, clouds, storms, precipitation and consequently radiative properties. In this study, we aim to understand the dynamic and thermodynamic properties of Saharan dust on the atmospheric structure of marine environment and to investigate the causes of the observed regions of well-mixed potential temperatures of the marine atmosphere in the presence of Saharan dust layers. We compare the influence of dust to other potentially important influences such as wind shear and air mass. To investigate this, we simulated the marine atmosphere in the presence and absence of dust using the UK Met Office Large Eddy Model (LEM) based the BOMEX case-study that is provided with the LEM and updated with observation taken during the FENNEC experiments of June 2011 and 2012. We performed LEM simulations with and without dust heating rates for an eight-hour time period. Data for meteorological profiles were used from the FENNEC aircraft measurements taken over the Atlantic Ocean near the Canary Islands. Our LEM results show that using a stratified (typical of non-dusty) atmosphere and then apply a dust heating rate the profile of potential temperature tends towards a well-mixed layer where the heating rates were applied and consistent with the observational cases. While LEM simulations for wind shear showed very little difference in the potential temperature profile and it was clear the well-mixed layer would not result. LEM simulations using dust heating rates were shown to create and maintain well-mixed layers if we initialised runs with either the dusty or non-dusty profiles; whereas, without the heating rates the layers progressed to a stratified layer consistent with non-dusty day observations. This illustrated independence of the well-mixed layers to the air mass type (other than the dust presence). We conclude from these tests that the well-mixed layers are explained by the presence of the dust. Until now it was not known if the well-mixed regions were a result of the different air masses, as air masses picking up dust over land then advecting out over the ocean are potentially very different to air masses that have been in more pristine oceanic environments, or other influences such as shear. Evaluation of CAPE and CIN with and without the influences of dust heating rates indicated that the atmospheric structure downwind was significantly altered by the presence of the dust layer. It is important as a follow-on from this work to investigate whether the climate models can capture these dust layer influences and potential impacts downwind.

  2. Turbulent properties of oceanic near-surface stable boundary layers subject to wind, fresh water, and thermal forcing.

    NASA Astrophysics Data System (ADS)

    St. Laurent, Louis; Clayson, Carol Anne

    2015-04-01

    The near-surface oceanic boundary layer is generally regarded as convectively unstable due to the effects of wind, evaporation, and cooling. However, stable conditions also occur often, when rain or low-winds and diurnal warming provide buoyancy to a thin surface layer. These conditions are prevalent in the tropical and subtropical latitude bands, and are underrepresented in model simulations. Here, we evaluate cases of oceanic stable boundary layers and their turbulent processes using a combination of measurements and process modeling. We focus on the temperature, salinity and density changes with depth from the surface to the upper thermocline, subject to the influence of turbulent processes causing mixing. The stabilizing effects of freshwater from rain as contrasted to conditions of high solar radiation and low winds will be shown, with observations providing surprising new insights into upper ocean mixing in these regimes. Previous observations of freshwater lenses have demonstrated a maximum of dissipation near the bottom of the stable layer; our observations provide a first demonstration of a similar maximum near the bottom of the solar heating-induced stable layer and a fresh-water induced barrier layer. Examples are drawn from recent studies in the tropical Atlantic and Indian oceans, where ocean gliders equipped with microstructure sensors were used to measure high resolution hydrographic properties and turbulence levels. The limitations of current mixing models will be demonstrated. Our findings suggest that parameterizations of near-surface mixing rates during stable stratification and low-wind conditions require considerable revision, in the direction of larger diffusivities.

  3. Characterising the structure of quasi-periodic mixing events in stratified turbulent Taylor-Couette flow

    NASA Astrophysics Data System (ADS)

    Singh, Kanwar Nain; Partridge, Jamie; Dalziel, Stuart; Caulfield, C. P.; Mathematical Underpinnings of Stratified Turbulence (MUST) Team

    2017-11-01

    We present results from experiments conducted to study mixing in a two-layer stably-stratified turbulent Taylor-Couette flow. It has previously been observed that there is a quasi-periodic mixing event located at the interface separating the layers. We observe, through conductivity probe measurements, that the power of the mixing event in the frequency spectrum of the density data at the interface is higher when measured near the inner cylinder than in the middle of the annular gap. This is consistent with Oglethorpe's (2014) hypothesis that the mixing structure is triggered near the inner cylinder, and then advects and decays or disperses radially. We also observe that at Ri =g/'Ro (RiΩi)2 7 , where Ri, Ro are the inner and outer cylinder radius, respectively, g ' the reduced gravity characterising the density jump between the layers and Ωi is the rotation rate of the inner cylinder, the power drops significantly at all radial locations, which is reminiscent of the onset of the enhanced flux regime as observed by Oglethorpe et al. (2013). We perform experiments to characterise the spatial extent and dynamics of this mixing structure using particle image velocimetry (PIV) giving further insights into this important mixing process. EPSRC programme Grant EP/K034529/1 & SGPC-CCT Scholarship.

  4. A Preliminary Study Associated with the Experimental Measurement of the Aero-Optic Characteristics of Hypersonic Configurations

    DTIC Science & Technology

    1992-06-01

    of the mixing layer. Optical propagation through the nonuniform media induces wavefront distortion in the collected target radiation, as different...body, before, during and after a run. The chopper frequency will be up to 10Khz. Sensor response will be available up to lOms and in the MWIR and LWIR ...bands. The IR spectrometer (Figure 5-13) will be available to measure spectral radiance in the SWIR, MWIR and LWIR bands. The spectral resolution will

  5. Crossed hot-wire data acquisition and reduction system

    NASA Technical Reports Server (NTRS)

    Westphal, R. V.; Mehta, R. D.

    1984-01-01

    The report describes a system for rapid computerized calibration acquisition, and processing of data from a crossed hot-wire anemometer is described. Advantages of the system are its speed, minimal use of analog electronics, and improved accuracy of the resulting data. Two components of mean velocity and turbulence statistics up to third order are provided by the data reduction. Details of the hardware, calibration procedures, response equations, software, and sample results from measurements in a turbulent plane mixing layer are presented.

  6. Chromatic response of polydiacetylene vesicle induced by the permeation of methotrexate.

    PubMed

    Shin, Min Jae; Kim, Ye Jin; Kim, Jong-Duk

    2015-07-07

    The noble vesicular system of polydiacetylene showed a red shift using two types of detecting systems. One of the systems involves the absorption of target materials from the outer side of the vesicle, and the other system involves the permeation through the vesicular layers from within the vesicle. The chromatic mixed vesicles of N-(2-aminoethyl)pentacosa-10,12-diynamide (AEPCDA) and dimethyldioctadecylammonium chloride (DODAC) were fabricated by sonication, followed by polymerization by UV irradiation. The stability of monomeric vesicles was observed to increase with the polymerization of the vesicles. Methotrexate was used as a target material. The polymerized mixed vesicles having a blue color were exposed to a concentration gradient of methotrexate, and a red shift was observed indicating the adsorption of methotrexate on the polydiacetylene bilayer. In order to check the chromatic change by the permeation of methotrexate, we separated the vesicle portion, which contained methotrexate inside the vesicle, and checked chromatic change during the permeation of methotrexate through the vesicle. The red shift apparently indicates the disturbance in the bilayer induced by the permeation of methotrexate. The maximum contrast of color appeared at the equal molar ratio of AEPCDA and DODAC, indicating that the formation of flexible and deformable vesicular layers is important for red shift. Therefore, it is hypothesized that the system can be applicable for the chromatic detection of the permeation of methotrexate through the polydiacetylene layer.

  7. Physical control of interannual variations of the winter chlorophyll bloom in the northern Arabian Sea

    NASA Astrophysics Data System (ADS)

    Girijakumari Keerthi, Madhavan; Lengaigne, Matthieu; Levy, Marina; Vialard, Jerome; Parvathi, Vallivattathillam; de Boyer Montégut, Clément; Ethé, Christian; Aumont, Olivier; Suresh, Iyyappan; Parambil Akhil, Valiya; Moolayil Muraleedharan, Pillathu

    2017-08-01

    The northern Arabian Sea hosts a winter chlorophyll bloom, triggered by convective overturning in response to cold and dry northeasterly monsoon winds. Previous studies of interannual variations of this bloom only relied on a couple of years of data and reached no consensus on the associated processes. The current study aims at identifying these processes using both ˜ 10 years of observations (including remotely sensed chlorophyll data and physical parameters derived from Argo data) and a 20-year-long coupled biophysical ocean model simulation. Despite discrepancies in the estimated bloom amplitude, the six different remotely sensed chlorophyll products analysed in this study display a good phase agreement at seasonal and interannual timescales. The model and observations both indicate that the interannual winter bloom fluctuations are strongly tied to interannual mixed layer depth anomalies ( ˜ 0.6 to 0.7 correlation), which are themselves controlled by the net heat flux at the air-sea interface. Our modelling results suggest that the mixed layer depth control of the bloom amplitude ensues from the modulation of nutrient entrainment into the euphotic layer. In contrast, the model and observations both display insignificant correlations between the bloom amplitude and thermocline depth, which precludes a control of the bloom amplitude by daily dilution down to the thermocline depth, as suggested in a previous study.

  8. Mixed-layered bismuth--oxygen--iodine materials for capture and waste disposal of radioactive iodine

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Krumhansl, James L; Nenoff, Tina M

    2015-01-06

    Materials and methods of synthesizing mixed-layered bismuth oxy-iodine materials, which can be synthesized in the presence of aqueous radioactive iodine species found in caustic solutions (e.g. NaOH or KOH). This technology provides a one-step process for both iodine sequestration and storage from nuclear fuel cycles. It results in materials that will be durable for repository conditions much like those found in Waste Isolation Pilot Plant (WIPP) and estimated for Yucca Mountain (YMP). By controlled reactant concentrations, optimized compositions of these mixed-layered bismuth oxy-iodine inorganic materials are produced that have both a high iodine weight percentage and a low solubility inmore » groundwater environments.« less

  9. A unified view of convective transports by stratocumulus clouds, shallow cumulus clouds, and deep convection

    NASA Technical Reports Server (NTRS)

    Randall, David A.

    1990-01-01

    A bulk planetary boundary layer (PBL) model was developed with a simple internal vertical structure and a simple second-order closure, designed for use as a PBL parameterization in a large-scale model. The model allows the mean fields to vary with height within the PBL, and so must address the vertical profiles of the turbulent fluxes, going beyond the usual mixed-layer assumption that the fluxes of conservative variables are linear with height. This is accomplished using the same convective mass flux approach that has also been used in cumulus parameterizations. The purpose is to show that such a mass flux model can include, in a single framework, the compensating subsidence concept, downgradient mixing, and well-mixed layers.

  10. Large-Eddy Simulation (LES) of a Compressible Mixing Layer and the Significance of Inflow Turbulence

    NASA Technical Reports Server (NTRS)

    Mankbadi, Mina Reda; Georgiadis, Nicholas J.; Debonis, James R.

    2017-01-01

    In the context of Large Eddy Simulations (LES), the effects of inflow turbulence are investigated through the Synthetic Eddy Method (SEM). The growth rate of a turbulent compressible mixing layer corresponding to operating conditions of GeobelDutton Case 2 is investigated herein. The effects of spanwise width on the growth rate of the mixing layer is investigated such that spanwise width independence is reached. The error in neglecting inflow turbulence effects is quantified by comparing two methodologies: (1) Hybrid-RANS-LES methodology and (2) SEM-LES methodology. Best practices learned from Case 2 are developed herein and then applied to a higher convective mach number corresponding to Case 4 experiments of GeobelDutton.

  11. Cumulus cloud venting of mixed layer ozone

    NASA Technical Reports Server (NTRS)

    Ching, J. K. S.; Shipley, S. T.; Browell, E. V.; Brewer, D. A.

    1985-01-01

    Observations are presented which substantiate the hypothesis that significant vertical exchange of ozone and aerosols occurs between the mixed layer and the free troposphere during cumulus cloud convective activity. The experiments utilized the airborne Ultra-Violet Differential Absorption Lidar (UV-DIAL) system. This system provides simultaneous range resolved ozone concentration and aerosol backscatter profiles with high spatial resolution. Evening transects were obtained in the downwind area where the air mass had been advected. Space-height analyses for the evening flight show the cloud debris as patterns of ozone typically in excess of the ambient free tropospheric background. This ozone excess was approximately the value of the concentration difference between the mixed layer and free troposphere determined from independent vertical soundings made by another aircraft in the afternoon.

  12. Evaluation of wind regimes and their impact on vertical mixing and coupling in a moderately dense forest

    NASA Astrophysics Data System (ADS)

    Wunder, Tobias; Ehrnsperger, Laura; Thomas, Christoph

    2017-04-01

    In the last decades much attention has been devoted to improving our understanding of organized motions in plant canopies. Particularly the impact of coherent structures on turbulent flows and vertical mixing in near-neutral conditions has been the focus of many experimental and modeling studies. Despite this progress, the weak-wind subcanopy airflow in concert with stable or weak-wind above-canopy conditions remains poorly understood. In these conditions, evidence is mounting that larger-scale motions, so called sub-meso motions which occupy time scales from minutes to hours and spatial scales from tens of meters to kilometers, dominate transport and turbulent mixing particularly in the subcanopy, because of generally weaker background flow as a result of the enhanced friction due to the plant material. We collected observations from a network of fast-response sensor across the vertical and horizontal dimensions during the INTRAMIX experiment at the Fluxnet site Waldstein/ Weidenbrunnen (DE-Bay) in a moderately dense Norway spruce (Picea Abies) forest over a period of ten weeks. Its main goal was to investigate the role of the submeso-structures on the turbulent wind field and the mixing mechanisms including coherent structures. In a first step, coupling regimes differentiating between weak and strong flows and day- and nighttime-conditions are determined. Subsequently, each of the regimes is analyzed for its dominant flow dynamics identified by wavelet analysis. It is hypothesized that strong vertical wind directional shear does not necessarily indicate a decoupling of vertical layers, but on the contrary may create situations of significant coupling of the sub-canopy with the canopy layers above. Moreover, rapid changes of wind direction or even reversals may generate substantial turbulence and induce intermittent coupling on a variety of time scales. The overarching goal is to improve diagnostics for vertical mixing in plant canopies incorporating turbulence and submeso-motions and to develop a classification of flow modes capable of representing the main driving mechanisms of mixing in forest canopies.

  13. Special Specification 3XXX, dense-graded hot-mix asphalt.

    DOT National Transportation Integrated Search

    2004-01-01

    Construct a hot-mix asphalt (HMA) pavement layer composed of a compacted, dense-graded mixture of aggregate and asphalt binder mixed hot in a mixing plant. Pay adjustments will apply to HMA placed under this specification unless the HMA is deemed exe...

  14. Measurements of the aerosol chemical composition and mixing state in the Po Valley using multiple spectroscopic techniques

    NASA Astrophysics Data System (ADS)

    Decesari, S.; Allan, J.; Plass-Duelmer, C.; Williams, B. J.; Paglione, M.; Facchini, M. C.; O'Dowd, C.; Harrison, R. M.; Gietl, J. K.; Coe, H.; Giulianelli, L.; Gobbi, G. P.; Lanconelli, C.; Carbone, C.; Worsnop, D.; Lambe, A. T.; Ahern, A. T.; Moretti, F.; Tagliavini, E.; Elste, T.; Gilge, S.; Zhang, Y.; Dall'Osto, M.

    2014-11-01

    The use of co-located multiple spectroscopic techniques can provide detailed information on the atmospheric processes regulating aerosol chemical composition and mixing state. So far, field campaigns heavily equipped with aerosol mass spectrometers have been carried out mainly in large conurbations and in areas directly affected by their outflow, whereas lesser efforts have been dedicated to continental areas characterised by a less dense urbanisation. We present here the results obtained at a background site in the Po Valley, Italy, in summer 2009. For the first time in Europe, six state-of-the-art spectrometric techniques were used in parallel: aerosol time-of-flight mass spectrometer (ATOFMS), two aerosol mass spectrometers (high-resolution time-of-flight aerosol mass spectrometer - HR-ToF-AMS and soot particle aerosol mass spectrometer - SP-AMS), thermal desorption aerosol gas chromatography (TAG), chemical ionisation mass spectrometry (CIMS) and (offline) proton nuclear magnetic resonance (1H-NMR) spectroscopy. The results indicate that, under high-pressure conditions, atmospheric stratification at night and early morning hours led to the accumulation of aerosols produced by anthropogenic sources distributed over the Po Valley plain. Such aerosols include primary components such as black carbon (BC), secondary semivolatile compounds such as ammonium nitrate and amines and a class of monocarboxylic acids which correspond to the AMS cooking organic aerosol (COA) already identified in urban areas. In daytime, the entrainment of aged air masses in the mixing layer is responsible for the accumulation of low-volatility oxygenated organic aerosol (LV-OOA) and also for the recycling of non-volatile primary species such as black carbon. According to organic aerosol source apportionment, anthropogenic aerosols accumulating in the lower layers overnight accounted for 38% of organic aerosol mass on average, another 21% was accounted for by aerosols recirculated in residual layers but still originating in northern Italy, while a substantial fraction (41%) was due to the most aged aerosols imported from transalpine areas. The different meteorological regimes also affected the BC mixing state: in periods of enhanced stagnation and recirculation of pollutants, the number fraction of the BC-containing particles determined by ATOFMS was 75% of the total, while in the days of enhanced ventilation of the planetary boundary layer (PBL), such fraction was significantly lower (50%) because of the relative greater influence of non-BC-containing aerosol local sources in the Po Valley. Overall, a full internal mixing between BC and the non-refractory aerosol chemical components was not observed during the experiment in this environment.

  15. Ternary metal-rich sulfide with a layered structure

    DOEpatents

    Franzen, Hugo F.; Yao, Xiaoqiang

    1993-08-17

    A ternary Nb-Ta-S compound is provided having the atomic formula, Nb.sub.1.72 Ta.sub.3.28 S.sub.2, and exhibiting a layered structure in the sequence S-M3-M2-M1-M2-M3-S wherein S represents sulfur layers and M1, M2, and M3 represent Nb/Ta mixed metal layers. This sequence generates seven sheets stacked along the [001] direction of an approximate body centered cubic crystal structure with relatively weak sulfur-to-sulfur van der Waals type interactions between adjacent sulfur sheets and metal-to-metal bonding within and between adjacent mixed metal sheets.

  16. Energy and water vapor transport across a simplified cloud-clear air interface

    NASA Astrophysics Data System (ADS)

    Gallana, L.; Di Savino, S.; De Santi, F.; Iovieno, M.; Tordella, D.

    2014-11-01

    We consider a simplified physics of the could interface where condensation, evaporation and radiation are neglected and momentum, thermal energy and water vapor transport is represented in terms of the Boussinesq model coupled to a passive scalar transport equation for the vapor. The interface is modeled as a layer separating two isotropic turbulent regions with different kinetic energy and vapor concentration. In particular, we focus on the small scale part of the inertial range of the atmospheric boundary layer as well as on the dissipative range of scales which are important to the micro-physics of warm clouds. We have numerically investigated stably stratified interfaces by locally perturbing at an initial instant the standard temperature lapse rate at the cloud interface and then observing the temporal evolution of the system. When the buoyancy term becomes of the same order of the inertial one, we observe a spatial redistribution of the kinetic energy which produce a concomitant pit of kinetic energy within the mixing layer. In this situation, the mixing layer contains two interfacial regions with opposite kinetic energy gradient, which in turn produces two intermittent sublayers in the velocity fluctuations field. This changes the structure of the field with respect to the corresponding non-stratified shearless mixing: the communication between the two turbulent region is weak, and the growth of the mixing layer stops. These results are discussed with respect to Large Eddy Simulations data for the Planetary Boundary Layers.

  17. Improving scattering layer through mixture of nanoporous spheres and nanoparticles in ZnO-based dye-sensitized solar cells.

    PubMed

    Kim, Chohui; Choi, Hongsik; Kim, Jae Ik; Lee, Sangheon; Kim, Jinhyun; Lee, Woojin; Hwang, Taehyun; Kang, Suji; Moon, Taeho; Park, Byungwoo

    2014-01-01

    A scattering layer is utilized by mixing nanoporous spheres and nanoparticles in ZnO-based dye-sensitized solar cells. Hundred-nanometer-sized ZnO spheres consisting of approximately 35-nm-sized nanoparticles provide not only effective light scattering but also a large surface area. Furthermore, ZnO nanoparticles are added to the scattering layer to facilitate charge transport and increase the surface area as filling up large voids. The mixed scattering layer of nanoparticles and nanoporous spheres on top of the nanoparticle-based electrode (bilayer geometry) improves solar cell efficiency by enhancing both the short-circuit current (J sc) and fill factor (FF), compared to the layer consisting of only nanoparticles or nanoporous spheres.

  18. Lead bromide-based layered perovskite Langmuir-Blodgett films having π-conjugated molecules as organic layer prepared by using squeezed out technique

    NASA Astrophysics Data System (ADS)

    Era, Masanao; Shironita, Yu; Soda, Koichi

    2018-03-01

    Using the squeezed out technique, we successfully prepared PbBr-based layered perovskite Langmuir-Blodgett (LB) films, which have π-conjugated materials as an organic layer (i.e., a phenylenevinylene oligomer, a dithienylethene derivative, and a π-conjugated polyfluorene derivative). The mixed monolayers of π-conjugated materials and octadecylammonium bromide were spread on an aqueous subphase containing saturated PbBr2. During pressing, octadecylammonium molecules were squeezed from the mixed monolayer, and the squeezed ammonium molecules formed the PbBr-based layered perovskite structure at the air-aqueous subphase interface. The monolayers with the PbBr-based layered perovskite structure could be deposited on fused quartz substrates by the LB technique. In addition to the preparation procedure, the structural and optical properties of the layered perovskite LB films and their formation mechanism are reported in this paper.

  19. Effects of polymer additives on Rayleigh-Taylor turbulence.

    PubMed

    Boffetta, G; Mazzino, A; Musacchio, S

    2011-05-01

    The role of polymer additives on the turbulent convective flow of a Rayleigh-Taylor system is investigated by means of direct numerical simulations of Oldroyd-B viscoelastic model. The dynamics of polymer elongations follows adiabatically the self-similar evolution of the turbulent mixing layer and shows the appearance of a strong feedback on the flow which originates a cutoff for polymer elongations. The viscoelastic effects on the mixing properties of the flow are twofold. Mixing is appreciably enhanced at large scales (the mixing layer growth rate is larger than that of the purely Newtonian case) and depleted at small scales (thermal plumes are more coherent with respect to the Newtonian case). The observed speed up of the thermal plumes, together with an increase of the correlations between temperature field and vertical velocity, contributes to a significant enhancement of heat transport. Our findings are consistent with a scenario of drag reduction induced by polymers. A weakly nonlinear model proposed by Fermi for the growth of the mixing layer is reported in the Appendix. © 2011 American Physical Society

  20. Effects of Transition-Metal Mixing on Na Ordering and Kinetics in Layered P 2 Oxides

    NASA Astrophysics Data System (ADS)

    Zheng, Chen; Radhakrishnan, Balachandran; Chu, Iek-Heng; Wang, Zhenbin; Ong, Shyue Ping

    2017-06-01

    Layered P 2 oxides are promising cathode materials for rechargeable sodium-ion batteries. In this work, we systematically investigate the effects of transition-metal (TM) mixing on Na ordering and kinetics in the NaxCo1 -yMnyO2 model system using density-functional-theory (DFT) calculations. The DFT-predicted 0-K stability diagrams indicate that Co-Mn mixing reduces the energetic differences between Na orderings, which may account for the reduction of the number of phase transformations observed during the cycling of mixed-TM P 2 layered oxides compared to a single TM. Using ab initio molecular-dynamics simulations and nudged elastic-band calculations, we show that the TM composition at the Na(1) (face-sharing) site has a strong influence on the Na site energies, which in turn impacts the kinetics of Na diffusion towards the end of the charge. By employing a site-percolation model, we establish theoretical upper and lower bounds for TM concentrations based on their effect on Na(1) site energies, providing a framework to rationally tune mixed-TM compositions for optimal Na diffusion.

  1. Modeling condensation with a noncondensable gas for mixed convection flow

    NASA Astrophysics Data System (ADS)

    Liao, Yehong

    2007-05-01

    This research theoretically developed a novel mixed convection model for condensation with a noncondensable gas. The model developed herein is comprised of three components: a convection regime map; a mixed convection correlation; and a generalized diffusion layer model. These components were developed in a way to be consistent with the three-level methodology in MELCOR. The overall mixed convection model was implemented into MELCOR and satisfactorily validated with data covering a wide variety of test conditions. In the development of the convection regime map, two analyses with approximations of the local similarity method were performed to solve the multi-component two-phase boundary layer equations. The first analysis studied effects of the bulk velocity on a basic natural convection condensation process and setup conditions to distinguish natural convection from mixed convection. It was found that the superimposed velocity increases condensation heat transfer by sweeping away the noncondensable gas accumulated at the condensation boundary. The second analysis studied effects of the buoyancy force on a basic forced convection condensation process and setup conditions to distinguish forced convection from mixed convection. It was found that the superimposed buoyancy force increases condensation heat transfer by thinning the liquid film thickness and creating a steeper noncondensable gas concentration profile near the condensation interface. In the development of the mixed convection correlation accounting for suction effects, numerical data were obtained from boundary layer analysis for the three convection regimes and used to fit a curve for the Nusselt number of the mixed convection regime as a function of the Nusselt numbers of the natural and forced convection regimes. In the development of the generalized diffusion layer model, the driving potential for mass transfer was expressed as the temperature difference between the bulk and the liquid-gas interface using the Clausius-Clapeyron equation. The model was developed on a mass basis instead of a molar basis to be consistent with general conservation equations. It was found that vapor diffusion is not only driven by a gradient of the molar fraction but also a gradient of the mixture molecular weight at the diffusion layer.

  2. Modeling the purging of dense fluid from a street canyon driven by an interfacial mixing flow and skimming flow

    NASA Astrophysics Data System (ADS)

    Baratian-Ghorghi, Z.; Kaye, N. B.

    2013-07-01

    An experimental study is presented to investigate the mechanism of flushing a trapped dense contaminant from a canyon by turbulent boundary layer flow. The results of a series of steady-state experiments are used to parameterize the flushing mechanisms. The steady-state experimental results for a canyon with aspect ratio one indicate that dense fluid is removed from the canyon by two different processes, skimming of dense fluid from the top of the dense layer; and by an interfacial mixing flow that mixes fresh fluid down into the dense lower layer (entrainment) while mixing dense fluid into the flow above the canyon (detrainment). A model is developed for the time varying buoyancy profile within the canyon as a function of the Richardson number which parameterizes both the interfacial mixing and skimming processes observed. The continuous release steady-state experiments allowed for the direct measurement of the skimming and interfacial mixing flow rates for any layer depth and Richardson number. Both the skimming rate and the interfacial mixing rate were found to be power-law functions of the Richardson number of the layer. The model results were compared to the results of previously published finite release experiments [Z. Baratian-Ghorghi and N. B. Kaye, Atmos. Environ. 60, 392-402 (2012)], 10.1016/j.atmosenv.2012.06.077. A high degree of consistency was found between the finite release data and the continuous release data. This agreement acts as an excellent check on the measurement techniques used, as the finite release data was based on curve fitting through buoyancy versus time data, while the continuous release data was calculated directly by measuring the rate of addition of volume and buoyancy once a steady-state was established. Finally, a system of ordinary differential equations is presented to model the removal of dense fluid from the canyon based on empirical correlations of the skimming and interfacial mixing taken form the steady-state experiments. The ODE model predicts well the time taken for a finite volume of dense fluid to be flushed from a canyon.

  3. Inner Plasma Structure of the Low-Latitude Reconnection Layer

    NASA Technical Reports Server (NTRS)

    Zhang, Q.-H.; Dunlop, M. W.; Lockwood, M.; Lavraud, B.; Bogdanova, Y. V.; Hasegawa, H.; Yang, H. -G.; Liu, R. -Y.; Hu, H. -Q.; Zhang, B. -C.; hide

    2012-01-01

    We report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (Ssp and Ssh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RDsp and RDsh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer.

  4. Physical-Biological Coupling in the Western South China Sea: The Response of Phytoplankton Community to a Mesoscale Cyclonic Eddy.

    PubMed

    Wang, Lei; Huang, Bangqin; Chiang, Kuo-Ping; Liu, Xin; Chen, Bingzhang; Xie, Yuyuan; Xu, Yanping; Hu, Jianyu; Dai, Minhan

    2016-01-01

    It is widely recognized that the mesoscale eddies play an important part in the biogeochemical cycle in ocean ecosystem, especially in the oligotrophic tropical zones. So here a heterogeneous cyclonic eddy in its flourishing stage was detected using remote sensing and in situ biogeochemical observation in the western South China Sea (SCS) in early September, 2007. The high-performance liquid chromatography method was used to identify the photosynthetic pigments. And the CHEMical TAXonomy (CHEMTAX) was applied to calculate the contribution of nine phytoplankton groups to the total chlorophyll a (TChl a) biomass. The deep chlorophyll a maximum layer (DCML) was raised to form a dome structure in the eddy center while there was no distinct enhancement for TChl a biomass. The integrated TChl a concentration in the upper 100 m water column was also constant from the eddy center to the surrounding water outside the eddy. However the TChl a biomass in the surface layer (at 5 m) in the eddy center was promoted 2.6-fold compared to the biomass outside the eddy (p < 0.001). Thus, the slight enhancement of TChl a biomass of euphotic zone integration within the eddy was mainly from the phytoplankton in the upper mixed zone rather than the DCML. The phytoplankton community was primarily contributed by diatoms, prasinophytes, and Synechococcus at the DCML within the eddy, while less was contributed by haptophytes_8 and Prochlorococcus. The TChl a biomass for most of the phytoplankton groups increased at the surface layer in the eddy center under the effect of nutrient pumping. The doming isopycnal within the eddy supplied nutrients gently into the upper mixing layer, and there was remarkable enhancement in phytoplankton biomass at the surface layer with 10.5% TChl a biomass of water column in eddy center and 3.7% at reference stations. So the slight increasing in the water column integrated phytoplankton biomass might be attributed to the stimulated phytoplankton biomass at the surface layer.

  5. Localized application of soil organic matter shifts distribution of cluster roots of white lupin in the soil profile due to localized release of phosphorus

    PubMed Central

    Li, Hai-Gang; Shen, Jian-Bo; Zhang, Fu-Suo; Lambers, Hans

    2010-01-01

    Background and Aims Phosphorus (P) is a major factor controlling cluster-root formation. Cluster-root proliferation tends to concentrate in organic matter (OM)-rich surface-soil layers, but the nature of this response of cluster-root formation to OM is not clear. Cluster-root proliferation in response to localized application of OM was characterized in Lupinus albus (white lupin) grown in stratified soil columns to test if the stimulating effect of OM on cluster-root formation was due to (a) P release from breakdown of OM; (b) a decrease in soil density; or (c) effects of micro-organisms other than releasing P from OM. Methods Lupin plants were grown in three-layer stratified soil columns where P was applied at 0 or 330 mg P kg−1 to create a P-deficient or P-sufficient background, and OM, phytate mixed with OM, or perlite was applied to the top or middle layers with or without sterilization. Key Results Non-sterile OM stimulated cluster-root proliferation and root length, and this effect became greater when phytate was supplied in the presence of OM. Both sterile OM and perlite significantly decreased cluster-root formation in the localized layers. The OM position did not change the proportion of total cluster roots to total roots in dry biomass among no-P treatments, but more cluster roots were concentrated in the OM layers with a decreased proportion in other places. Conclusions Localized application of non-sterile OM or phytate plus OM stimulated cluster-root proliferation of L. albus in the localized layers. This effect is predominantly accounted for by P release from breakdown of OM or phytate, but not due to a change in soil density associated with OM. No evidence was found for effects of micro-organisms in OM other than those responsible for P release. PMID:20150198

  6. Decadal change of the south Atlantic ocean Angola-Benguela frontal zone since 1980

    NASA Astrophysics Data System (ADS)

    Vizy, Edward K.; Cook, Kerry H.; Sun, Xiaoming

    2018-01-01

    High-resolution simulations with a regional atmospheric model coupled to an intermediate-level mixed layer ocean model along with multiple atmospheric and oceanic reanalyses are analyzed to understand how and why the Angola-Benguela frontal Zone (ABFZ) has changed since 1980. A southward shift of 0.05°-0.55° latitude decade-1 in the annual mean ABFZ position accompanied by an intensification of + 0.05 to + 0.13 K/100-km decade-1 has occurred as ocean mixed layer temperatures have warmed (cooled) equatorward (poleward) of the front over the 1980-2014 period. These changes are captured in a 35-year model integration. The oceanic warming north of the ABFZ is associated with a weakening of vertical entrainment, reduced cooling associated with vertical diffusion, and a deepening of the mixed layer along the Angola coast. These changes coincide with a steady weakening of the onshore atmospheric flow as the zonal pressure gradient between the eastern equatorial Atlantic and the Congo Basin weakens. Oceanic cooling poleward of the ABFZ is primarily due to enhanced advection of cooler water from the south and east, increased cooling by vertical diffusion, and shoaling of the mixed layer depth. In the atmosphere, these changes are related to an intensification and poleward shift of the South Atlantic sub-tropical anticyclone as surface winds, hence the westward mixed layer ocean currents, intensify in the Benguela upwelling region along the Namibian coast. With a few caveats, these findings demonstrate that air/sea interactions play a prominent role in influencing the observed decadal variability of the ABFZ over the southeastern Atlantic since 1980.

  7. Observations of the Summertime Boundary Layer over the Ross Ice Shelf, Antarctica Using SUMO UAVs

    NASA Astrophysics Data System (ADS)

    Nigro, M. A.; Cassano, J. J.; Jolly, B.; McDonald, A.

    2014-12-01

    During January 2014 Small Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe the boundary layer over the Ross Ice Shelf, Antarctica. A total of 41 SUMO flights were completed during a 9-day period with a maximum of 11 flights during a single day. Flights occurred as frequently as every 1.5 hours so that the time evolution of the boundary layer could be documented. On almost all of the flights the boundary layer was well mixed from the surface to a depth of less than 50 m to over 350 m. The depth of the well-mixed layer was observed to both increase and decrease over the course of an individual day suggesting that processes other than entrainment were altering the boundary layer depth. The well-mixed layer was observed to both warm and cool during the field campaign indicating that advective processes as well as surface fluxes were acting to control the temporal evolution of the boundary layer temperature. Only a small number of weakly stably stratified boundary layers were observed. Strong, shallow inversions, of up to 6 K, were observed above the top of the boundary layer. Observations from a 30 m automatic weather station and two temporary automatic weather stations 10 km south and west of the main field campaign location provide additional data for understanding the boundary layer evolution observed by the SUMO UAVs during this 9-day period. This presentation will discuss the observed evolution of the summertime boundary layer as well as comment on lessons learned operating the SUMO UAVs at a remote Antarctic field camp.

  8. Climate Response of Direct Radiative Forcing of Anthropogenic Black Carbon

    NASA Technical Reports Server (NTRS)

    Chung, Serena H.; Seinfeld,John H.

    2008-01-01

    The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) is examined by 100-year simulations in the Goddard Institute for Space Studies General Circulation Model II-prime coupled to a mixed-layer ocean model. Anthropogenic BC is predicted to raise globally and annually averaged equilibrium surface air temperature by 0.20 K if BC is assumed to be externally mixed. The predicted increase is significantly greater in the Northern Hemisphere (0.29 K) than in the Southern Hemisphere (0.11 K). If BC is assumed to be internally mixed with the present day level of sulfate aerosol, the predicted annual mean surface temperature increase rises to 0.37 K globally, 0.54 K for the Northern Hemisphere, and 0.20 K for the Southern Hemisphere. The climate sensitivity of BC direct radiative forcing is calculated to be 0.6 K W (sup -1) square meters, which is about 70% of that of CO2, independent of the assumption of BC mixing state. The largest surface temperature response occurs over the northern high latitudes during winter and early spring. In the tropics and midlatitudes, the largest temperature increase is predicted to occur in the upper troposphere. Direct radiative forcing of anthropogenic BC is also predicted to lead to a change of precipitation patterns in the tropics; precipitation is predicted to increase between 0 and 20 N and decrease between 0 and 20 S, shifting the intertropical convergence zone northward. If BC is assumed to be internally mixed with sulfate instead of externally mixed, the change in precipitation pattern is enhanced. The change in precipitation pattern is not predicted to alter the global burden of BC significantly because the change occurs predominantly in regions removed from BC sources.

  9. Combining Airborne and Lidar Measurements for Attribution of Aerosol Layers

    NASA Astrophysics Data System (ADS)

    Nikandrova, A.; Väänänen, R.; Tabakova, K.; Kerminen, V. M.; O'Connor, E.

    2016-12-01

    The aim of this work was to identify discrete aerosol layers and diagnose their origin, investigate the strength of mixing within the free-troposphere and with the boundary layer (BL), and understand the impact that mixing has on local and long-range transport of aerosol. For these purposes we combined airborne in-situ aerosol measurements with data obtained by a High Spectral Resolution Lidar (HSRL). The HSRL was deployed in Hyytiälä, Southern Finland, from January to September 2014 as a part of the US DoE ARM (Atmospheric Radiation Measurement) Mobile Facility during the BAECC (Biogenic Aerosols - Effects on Cloud and Climate) Campaign. Two airborne campaigns took place in April and August 2014 during the BAECC campaign. The vertical profile of backscatter coefficient from the HSRL was used to diagnose the location and depth of significant aerosol layers in the atmosphere. Frequently, in addition to the BL, one or two tropospheric layers were identified. In-situ measurements of the aerosol size distribution in these layers were obtained from a Scanning Mobility Particle Sizer (SMPS) and Optical Particle Sizer (OPS), that were installed on board the aircraft; these measurements were combined to cover sizes ranging from 10 nm to 10 µm. As expected, the highest number concentration of aerosol particles at all size ranges was found predominantly in the BL. Many upper layers had size distributions with a similar shape to that in the BL but with overall lower concentrations attributed to dilution of particles into a large volume of air. Hence, these layers were likely of very similar origin to the air in the BL and presumably were the result of lofted residual layers. Intervening layers however, could contain markedly different distribution shapes, which could be attributed to both different air mass origins, and different ambient relative humidity. Potential for mixing between two discreet elevated layers was often seen as a thin interface layer, which exhibited a combination of properties from both layers. Strong turbulent mixing ensured lower variability in the size distribution in the BL on short timescales, with more variability seen in the free troposphere. 96-hour back trajectories from multiple altitudes were used to diagnose the air mass origin of each discrete layer.

  10. Mixed ternary heterojunction solar cell

    DOEpatents

    Chen, Wen S.; Stewart, John M.

    1992-08-25

    A thin film heterojunction solar cell and a method of making it has a p-type layer of mixed ternary I-III-VI.sub.2 semiconductor material in contact with an n-type layer of mixed binary II-VI semiconductor material. The p-type semiconductor material includes a low resistivity copper-rich region adjacent the back metal contact of the cell and a composition gradient providing a minority carrier mirror that improves the photovoltaic performance of the cell. The p-type semiconductor material preferably is CuInGaSe.sub.2 or CuIn(SSe).sub.2.

  11. Mixing Regimes in a Spatially Confined, Two-Dimensional, Supersonic Shear Layer

    DTIC Science & Technology

    1992-07-31

    MODEL ................................... 3 THE MODEL PROBLEMS .............................................. 6 THE ONE-DIMENSIONAL PROBLEM...the effects of the numerical diffusion on the spectrum. Guirguis et al.ś and Farouk et al."’ have studied spatially evolving mixing layers for equal...approximations. Physical and Numerical Model General Formulation We solve the time-dependent, two-dimensional, compressible, Navier-Stokes equations for a

  12. Near-field Development of a Turbulent Mixing Layer Periodically Forced by a Bimorph PVDF Film Actuator

    NASA Astrophysics Data System (ADS)

    Naka, Yoshitsugu; Tsuboi, Ken-Ichiro; Kametani, Yukinori; Fukagata, Koji; Obi, Shinnosuke

    We have performed experiments in a turbulent mixing layer with periodic forcing introduced by a Piezo Film Actuator (PFA). Three different lengths of PFAs have been used, and the effects of various combinations of forcing amplitudes and frequencies are investigated. The forcing at the first and second sub-harmonic frequencies against the natural frequency enhances the development of the thickness of the mixing layer: the mixing layer spreads due to the forcing. On the other hand, the forcing near the natural frequency suppresses the development: the mean velocity gradient becomes steeper than the no control case. The vector pattern of the periodic velocity components indicated the formation of the vortical structure. By forcing at the natural and its first sub-harmonic frequencies, two counter-rotating vortices are clearly observed in one period of forcing. By forcing at second sub-harmonic frequency, the vortical structure is found only in the downstream region. The distribution of the periodic Reynolds shear stress significantly varies with the forcing frequency and it takes a positive value when forcing occurs near the natural frequency. However, the total value of the Reynolds shear stress remains negative due to the contribution of the turbulent components.

  13. Mixed Layer Heat and Fresh Water Balance in North Bay of Bengal (18N, 90E) Using a Seaglider and Mooring

    NASA Astrophysics Data System (ADS)

    Thangaprakash, V. P.; Girishkumar, M. S.; S, S.; Chaudhuri, D.; Sureshkumar, N.; Ravichandran, M.; Sengupta, D.; Weller, R. A.

    2016-02-01

    The Bay of Bengal (BoB) receives the large quantity of freshwater by excess precipitation over evaporation and runoff. This large freshwater flux into the BoB leads to strong haline stratification in the near surface layer, which have significant impact on the evolution of near thermo-haline structure and air-sea interactions process in those areas. However, lack of systematic measurements of observations, the factors that are modulating near mixed layer salinity and temperature in these freshwater pool in the northern BoB is not yet understood clearly. Under OMM - ASIRI (Ocean mixing and monsoon - Air sea interaction regional initiatives in the Northern Indian Ocean) programme, 3 month repeated hydrographic survey using seaglider in a butterfly (or bowtie) track centered around a mooring in the North Bay of Bengal (18N, 89E) equipped with near surface ASIMET sensors and subsurface temperature and salinity measurements, which provides unprecedental data source to quantify the relative contribution of different process on the evolution of near surface thermo-haline field through mixed layer heat and salt budget. The results of the analysis will be presented.

  14. Equilibrium of adsorption of mixed milk protein/surfactant solutions at the water/air interface.

    PubMed

    Kotsmar, C; Grigoriev, D O; Xu, F; Aksenenko, E V; Fainerman, V B; Leser, M E; Miller, R

    2008-12-16

    Ellipsometry and surface profile analysis tensiometry were used to study and compare the adsorption behavior of beta-lactoglobulin (BLG)/C10DMPO, beta-casein (BCS)/C10DMPO and BCS/C12DMPO mixtures at the air/solution interface. The adsorption from protein/surfactant mixed solutions is of competitive nature. The obtained adsorption isotherms suggest a gradual replacement of the protein molecules at the interface with increasing surfactant concentration for all studied mixed systems. The thickness, refractive index, and the adsorbed amount of the respective adsorption layers, determined by ellipsometry, decrease monotonically and reach values close to those for a surface covered only by surfactant molecules, indicating the absence of proteins from a certain surfactant concentration on. These results correlate with the surface tension data. A continuous increase of adsorption layer thickness was observed up to this concentration, caused by the desorption of segments of the protein and transforming the thin surface layer into a rather diffuse and thick one. Replacement and structural changes of the protein molecules are discussed in terms of protein structure and surface activity of surfactant molecules. Theoretical models derived recently were used for the quantitative description of the equilibrium state of the mixed surface layers.

  15. Understanding the dimensional and mechanical properties of coastal Langmuir Circulations

    NASA Astrophysics Data System (ADS)

    Shrestha, Kalyan; Kuehl, Joseph; Anderson, William

    2017-11-01

    Non-linear interaction of surface waves and wind-driven shear instability in the upper ocean mixed layer form counter-rotating vortical structures called Langmuir Circulations. This oceanic microscale turbulence is one of the key contributors of mixing and vertical transport in the upper ocean mixed layer. Langmuir turbulence in the open (deep) ocean has already been the topic of a large research effort. However, coastal Langmuir cells are distinctly different from Langmuir cells in open-ocean regions, where additional bottom-boundary layer shear alters the kinematic properties of Langmuir cells. For this study, we have conducted a wide-ranging numerical study (solving the grid-filtered Craik-Leibovich equations) of coastal Langmuir turbulence, assessing which parameters affect Langmuir cells and defining the parametric hierarchy. The Stokes profile (aggregate velocity due to orbital wave motion) is functionally dependent on Stokes drift velocity and wavenumber of the surface waves. We explain that these parameters, which correspond to the environmental forcing variables, control the horizontal and vertical length scales of Langmuir cell respectively. This result is important in understanding the transport and dispersion of materials in the upper mixed layer of coastal ocean. We argue that wind stress is a parameter governing the strength of Langmuir cells.

  16. The effects of temporal variability of mixed layer depth on primary productivity around Bermuda

    NASA Technical Reports Server (NTRS)

    Bissett, W. Paul; Meyers, Mark B.; Walsh, John J.; Mueller-Karger, Frank E.

    1994-01-01

    Temporal variations in primary production and surface chlorophyll concentrations, as measured by ship and satellite around Bermuda, were simulated with a numerical model. In the upper 450 m of the water column, population dynamics of a size-fractionated phytoplankton community were forced by daily changes of wind, light, grazing stress, and nutrient availability. The temporal variations of production and chlorophyll were driven by changes in nutrient introduction to the euphotic zone due to both high- and low-frequency changes of the mixed layer depth within 32 deg-34 deg N, 62 deg-64 deg W between 1979 and 1984. Results from the model derived from high-frequency (case 1) changes in the mixed layer depth showed variations in primary production and peak chlorophyll concentrations when compared with results from the model derived from low-frequency (case 2) mixed layer depth changes. Incorporation of size-fractionated plankton state variables in the model led to greater seasonal resolution of measured primary production and vertical chlorophyll profiles. The findings of this study highlight the possible inadequacy of estimating primary production in the sea from data of low-frequency temporal resolution and oversimplified biological simulations.

  17. Unexpected winter phytoplankton blooms in the North Atlantic subpolar gyre

    NASA Astrophysics Data System (ADS)

    Lacour, L.; Ardyna, M.; Stec, K. F.; Claustre, H.; Prieur, L.; Poteau, A.; D'Alcala, M. Ribera; Iudicone, D.

    2017-11-01

    In mid- and high-latitude oceans, winter surface cooling and strong winds drive turbulent mixing that carries phytoplankton to depths of several hundred metres, well below the sunlit layer. This downward mixing, in combination with low solar radiation, drastically limits phytoplankton growth during the winter, especially that of the diatoms and other species that are involved in seeding the spring bloom. Here we present observational evidence for widespread winter phytoplankton blooms in a large part of the North Atlantic subpolar gyre from autonomous profiling floats equipped with biogeochemical sensors. These blooms were triggered by intermittent restratification of the mixed layer when mixed-layer eddies led to a horizontal transport of lighter water over denser layers. Combining a bio-optical index with complementary chemotaxonomic and modelling approaches, we show that these restratification events increase phytoplankton residence time in the sunlight zone, resulting in greater light interception and the emergence of winter blooms. Restratification also caused a phytoplankton community shift from pico- and nanophytoplankton to phototrophic diatoms. We conclude that transient winter blooms can maintain active diatom populations throughout the winter months, directly seeding the spring bloom and potentially making a significant contribution to over-winter carbon export.

  18. The evaporatively driven cloud-top mixing layer

    NASA Astrophysics Data System (ADS)

    Mellado, Juan Pedro

    2010-11-01

    Turbulent mixing caused by the local evaporative cooling at the top cloud-boundary of stratocumuli will be discussed. This research is motivated by the lack of a complete understanding of several phenomena in that important region, which translates into an unacceptable variability of order one in current models, including those employed in climate research. The cloud-top mixing layer is a simplified surrogate to investigate, locally, particular aspects of the fluid dynamics at the boundary between the stratocumulus clouds and the upper cloud-free air. In this work, direct numerical simulations have been used to study latent heat effects. The problem is the following: When the cloud mixes with the upper cloud-free layer, relatively warm and dry, evaporation tends to cool the mixture and, if strong enough, the buoyancy reversal instability develops. This instability leads to a turbulent convection layer growing next to the upper boundary of the cloud, which is, in several aspects, similar to free convection below a cold horizontal surface. In particular, results show an approximately self-preserving behavior that is characterized by the molecular buoyancy flux at the inversion base, fact that helps to explain the difficulties found when doing large-eddy simulations of this problem using classical subgrid closures.

  19. Improved performances of organic light-emitting diodes with mixed layer and metal oxide as anode buffer

    NASA Astrophysics Data System (ADS)

    Xue, Qin; Liu, Shouyin; Zhang, Shiming; Chen, Ping; Zhao, Yi; Liu, Shiyong

    2013-01-01

    We fabricated organic light-emitting devices (OLEDs) employing 2-methyl-9,10-di(2-naphthyl)-anthracene (MADN) as hole-transport material (HTM) instead of commonly used N,N'-bis-(1-naphthyl)-N,N'-diphenyl,1,1'-biphenyl-4,4'-diamine (NPB). After inserting a 0.9 nm thick molybdenum oxide (MoOx) layer at the indium tin oxide (ITO)/MADN interface and a 5 nm thick mixed layer at the organic/organic heterojunction interface, the power conversion efficiency of the device can be increased by 4-fold.

  20. Dynamics of the transition zone in coastal zone color scanner-sensed ocean color in the North Pacific during oceanographic spring

    NASA Technical Reports Server (NTRS)

    Glover, David M.; Wroblewski, J. S.; Mcclain, Charles R.

    1994-01-01

    A transition zone in phytoplankton concentration running across the North Pacific basin at 30 deg to 40 deg north latitude corresponds to a basin-wide front in surface chlorophyll observed in a composite of coastal zone color scanner (CZCS) images for May, June, and July 1979-1986. This transition zone with low chlorophyll to the south and higher chlorophyll to the north can be simulated by a simple model of the concentration of phytoplankton, zooplankton, and dissolved nutrient (nitrate) in the surface mixed layer of the ocean applied to the North Pacific basin for the climatological conditions during oceanographic springtime (May, June, and July). The model is initialized with a 1 deg x 1 deg gridded estimate of wintertime (February, March, and April) mixed layer nitrate concentrations calculated from an extensive nutrient database and a similarly gridded mixed layer depth data set. Comparison of model predictions with CZCS data provides a means of evaluating the dynamics of the transition zone. We conclude that in the North Pacific, away from major boundary currents and coastal upwelling zones, wintertime vertical mixing determines the total nutrient available to the plankton ecosystem in the spring. The transition zone seen in basin-scale CZCS images is a reflection of the geographic variation in the wintertime mixed layer depth and the nitracline, leading to a latitudinal gradient in phytoplankton chlorophyll.

  1. Observations of the Early Morning Boundary-Layer Transition with Small Remotely-Piloted Aircraft

    NASA Astrophysics Data System (ADS)

    Wildmann, Norman; Rau, Gerrit Anke; Bange, Jens

    2015-12-01

    A remotely-piloted aircraft (RPA), equipped with a high resolution thermodynamic sensor package, was used to investigate physical processes during the morning transition of the atmospheric boundary layer over land. Experiments were conducted at a test site in heterogeneous terrain in south-west Germany on 5 days from June to September 2013 in an evolving shallow convective boundary layer, which then developed into a well-mixed layer later in the day. A combination of vertical profiling and constant-altitude profiling (CAP) at 100 m height above ground level was chosen as the measuring strategy throughout the experiment. The combination of flight strategies allows the application of mixed-layer scaling using the boundary-layer height z_i, convective velocity scale w_* and convective temperature scale θ _*. The hypothesis that mixed-layer theory is valid during the whole transition was not confirmed for all parameters. A good agreement is found for temperature variances, especially in the upper half of the boundary layer, and the normalized heat-flux profile. The results were compared to a previous study with the helicopter-borne turbulence probe Helipod, and it was found that similar data quality can be achieved with the RPA. On all days, the CAP flight level was within the entrainment zone for a short time, and the horizontal variability of temperature and water vapour along the flight path is presented as an example of the inhomogeneity of layer interfaces in the boundary layer. The study serves as a case study of the possibilities and limitations with state-of-the-art RPA technology in micrometeorology.

  2. Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet

    NASA Technical Reports Server (NTRS)

    Hingst, W. R.; Towne, C. E.

    1974-01-01

    An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.

  3. Mass and energy transfer across the Earth's magnetopause caused by vortex-induced reconnection: Mass and energy transfer by K-H vortex

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nakamura, T. K. M.; Eriksson, S.; Hasegawa, H.

    When the interplanetary magnetic field (IMF) is strongly northward, a boundary layer that contains a considerable amount of plasma of magnetosheath origin is often observed along and earthward of the low-latitude magnetopause. Such a pre-existing boundary layer, with a higher density than observed in the adjacent magnetosphere, reduces the local Alfvén speed and allows the Kelvin-Helmholtz instability (KHI) to grow more strongly. We employ a three-dimensional fully kinetic simulation to model an event observed by the Magnetospheric Multiscale (MMS) mission in which the spacecraft detected substantial KH waves between a pre-existing boundary layer and the magnetosheath during strong northward IMF.more » Initial results of this simulation [Nakamura et al., 2017] have successfully demonstrated ion-scale signatures of magnetic reconnection induced by the non-linearly developed KH vortex, which are quantitatively consistent with MMS observations. Furthermore, we quantify the simulated mass and energy transfer processes driven by this vortex-induced reconnection (VIR) and show that during this particular MMS event (i) mass enters a new mixing layer formed by the VIR more efficiently from the pre-existing boundary layer side than from the magnetosheath side, (ii) mixed plasmas within the new mixing layer convect tailward along the magnetopause at more than half the magnetosheath flow speed, and (iii) energy dissipation in localized VIR dissipation regions results in a strong parallel electron heating within the mixing layer. Finally, the quantitative agreements between the simulation and MMS observations allow new predictions that elucidate how the mass and energy transfer processes occur near the magnetopause during strong northward IMF.« less

  4. Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project

    NASA Astrophysics Data System (ADS)

    Halios, Christos H.; Barlow, Janet F.

    2018-03-01

    The study of the boundary layer can be most difficult when it is in transition and forced by a complex surface, such as an urban area. Here, a novel combination of ground-based remote sensing and in situ instrumentation in central London, UK, is deployed, aiming to capture the full evolution of the urban boundary layer (UBL) from night-time until the fully-developed convective phase. In contrast with the night-time stable boundary layer observed over rural areas, the night-time UBL is weakly convective. Therefore, a new approach for the detection of the morning-transition and rapid-growth phases is introduced, based on the sharp, quasi-linear increase of the mixing height. The urban morning-transition phase varied in duration between 0.5 and 4 h and the growth rate of the mixing layer during the rapid-growth phase had a strong positive relationship with the convective velocity scale, and a weaker, negative relationship with wind speed. Wind shear was found to be higher during the night-time and morning-transition phases than the rapid-growth phase and the shear production of turbulent kinetic energy near the mixing-layer top was around six times larger than surface shear production in summer, and around 1.5 times larger in winter. In summer under low winds, low-level jets dominated the UBL, and shear production was greater than buoyant production during the night-time and the morning-transition phase near the mixing-layer top. Within the rapid-growth phase, buoyant production dominated at the surface, but shear production dominated in the upper half of the UBL. These results imply that regional flows such as low-level jets play an important role alongside surface forcing in determining UBL structure and growth.

  5. Fronts and intrusions in the upper Deep Polar Water of the Eurasian and Makarov basins

    NASA Astrophysics Data System (ADS)

    Kuzmina, Natalia; Rudels, Bert; Zhurbas, Natalia; Lyzhkov, Dmitry

    2013-04-01

    CTD data obtained in the Arctic Basin are analyzed to describe structural features of intrusive layers and fronts encountered in the upper Deep Polar Water. This work is an extension of Arctic intrusions studies by Rudels et al. (1999) and Kuzmina et al. (2011). Numerous examples of fronts and intrusions observed in a deep layer (depth range of 600-1300 m) in the Eurasian and Makarov basins where salinity is increasing, and temperature is decreasing with depth (stable-stable thermohaline stratification), are described. The data are used to estimate hydrological parameters capable of determining different types of fronts and characterizing intrusive layers depending on the front structure. Coherence of intrusive layers is shown to get broken with the change of front structure. An evidence is found that enhanced turbulent mixing above local bottom elevations can prevent from intrusive layering. A linear stability model description of the observed intrusions is developed based on the Merryfield's (2000) assumption that interleaving is caused by differential mixing. Theoretical analysis is focused on prediction of the slopes of unstable modes at baroclinic and thermohaline fronts. Apparent vertical diffusivity due to turbulent mixing at baroclinic and thermohaline fronts is estimated on the basis of comparison of observed intrusion slopes with modeled slopes of the most unstable modes. Apparent lateral diffusivity is estimated too, based on Joyce (1980) approach. These estimates show that intrusive instability of fronts caused by differential mixing can result in sizable values of apparent lateral heat diffusivity in the deep Arctic layer that are quite comparable with those of the upper and intermediate Arctic layers (Walsh, Carmack, 2003; Kuzmina et al., 2011).

  6. Mass and energy transfer across the Earth's magnetopause caused by vortex-induced reconnection: Mass and energy transfer by K-H vortex

    DOE PAGES

    Nakamura, T. K. M.; Eriksson, S.; Hasegawa, H.; ...

    2017-10-23

    When the interplanetary magnetic field (IMF) is strongly northward, a boundary layer that contains a considerable amount of plasma of magnetosheath origin is often observed along and earthward of the low-latitude magnetopause. Such a pre-existing boundary layer, with a higher density than observed in the adjacent magnetosphere, reduces the local Alfvén speed and allows the Kelvin-Helmholtz instability (KHI) to grow more strongly. We employ a three-dimensional fully kinetic simulation to model an event observed by the Magnetospheric Multiscale (MMS) mission in which the spacecraft detected substantial KH waves between a pre-existing boundary layer and the magnetosheath during strong northward IMF.more » Initial results of this simulation [Nakamura et al., 2017] have successfully demonstrated ion-scale signatures of magnetic reconnection induced by the non-linearly developed KH vortex, which are quantitatively consistent with MMS observations. Furthermore, we quantify the simulated mass and energy transfer processes driven by this vortex-induced reconnection (VIR) and show that during this particular MMS event (i) mass enters a new mixing layer formed by the VIR more efficiently from the pre-existing boundary layer side than from the magnetosheath side, (ii) mixed plasmas within the new mixing layer convect tailward along the magnetopause at more than half the magnetosheath flow speed, and (iii) energy dissipation in localized VIR dissipation regions results in a strong parallel electron heating within the mixing layer. Finally, the quantitative agreements between the simulation and MMS observations allow new predictions that elucidate how the mass and energy transfer processes occur near the magnetopause during strong northward IMF.« less

  7. Wastewater microalgal production, nutrient removal and physiological adaptation in response to changes in mixing frequency.

    PubMed

    Sutherland, Donna L; Turnbull, Matthew H; Broady, Paul A; Craggs, Rupert J

    2014-09-15

    Laminar flows are a common problem in high rate algal ponds (HRAP) due to their long channels and gentle mixing by a single paddlewheel. Sustained laminar flows may modify the amount of light microalgal cells are exposed to, increase the boundary layer between the cell and the environment and increase settling out of cells onto the pond bottom. To date, there has been little focus on the effects of the time between mixing events (frequency of mixing) on the performance of microalgae in wastewater treatment HRAPs. This paper investigates the performance of three morphologically distinct microalgae in wastewater treatment high rate algal mesocosms operated at four different mixing frequencies (continuous, mixed every 45 min, mixed every 90 min and no mixing). Microalgal performance was measured in terms of biomass concentration, nutrient removal efficiency, light utilisation and photosynthetic performance. Microalgal biomass increased significantly with increasing mixing frequency for the two colonial species but did not differ for the single celled species. All three species were more efficient at NH4-N uptake as the frequency of mixing increased. Increased frequency of mixing supported larger colonies with improved harvest-ability by gravity but at the expense of efficient light absorption and maximum rate of photosynthesis. However, maximum quantum yield was highest in the continuously mixed cultures due to higher efficiency of photosynthesis under light limited conditions. Based on these results, higher microalgal productivity, improved wastewater treatment and better gravity based harvest-ability can be achieved with the inclusion of more mixing points and reduced laminar flows in full-scale HRAP. Copyright © 2014 Elsevier Ltd. All rights reserved.

  8. The interactive role of subsynoptic scale jet streak and planetary boundary layer processes in organizing an isolated convective complex

    NASA Technical Reports Server (NTRS)

    Kaplan, M. L.; Zack, J. W.; Wong, V. C.; Coats, G. D.

    1984-01-01

    Surface analyses and numerical simulation sensitivity studies are compared in order to determine the role played by deep, well-mixed, and well-heated boundary layers in perturbing a weak jet streak in proximity to the development of an isolated but intense convective complex associated with the Grand Island, Nebraska tornado outbreak of June 3-4, 1980. A brief description of the case is first presented, emphasizing three-hourly surface analyses, radar, and satellite data. The results of numerical experiments comparing differences in the runs with and without diurnal surface sensible heating are discussed and related to observations. The dynamical processes responsible for these simulation differences are discussed, and the significance of these differences are considered in terms of their effect on the preconvective environment.

  9. Atmospheric Boundary Layer temperature and humidity from new-generation Raman lidar

    NASA Astrophysics Data System (ADS)

    Froidevaux, Martin; Higgins, Chad; Simeonov, Valentin; Pardyjak, Eric R.; Parlange, Marc B.

    2010-05-01

    Mixing ratio and temperature data, obtained with EPFL Raman lidar during the TABLE-08 experiment are presented. The processing methods will be discussed along with fundamental physics. An independent calibration is performed at different distances along the laser beam, demonstrating that the multi-telescopes design of the lidar system is reliable for field application. The maximum achievable distance as a function of time and/or space averaging will also be discussed. During the TABLE-08 experiment, different type of lidar measurements have been obtained including: horizontal and vertical time series, as well as boundary layer "cuts", during day and night. The high resolution data, 1s in time and 1.25 m in space, are used to understand the response of the atmosphere to variations in surface variability.

  10. A Lagrangian analysis of the impact of transport and transformation on the ozone stratification observed in the free troposphere during the ESCOMPTE campaign

    NASA Astrophysics Data System (ADS)

    Colette, A.; Ancellet, G.; Menut, L.; Arnold, S. R.

    2006-03-01

    The ozone variability observed by tropospheric ozone lidars during the ESCOMPTE campaign is analyzed by means of a hybrid-Lagrangian modeling study. Transport processes responsible for the formation of ozone-rich layers are identified using a semi-Lagrangian analysis of mesoscale simulations to identify the planetary boundary layer (PBL) footprint in the free troposphere. High ozone concentrations are related to polluted air masses exported from the Iberian PBL. The chemical composition of air masses coming from the PBL and transported in the free troposphere is evaluated using a Lagrangian chemistry model. The initial concentrations are provided by a model of chemistry and transport. Different scenarios are tested for the initial conditions and for the impact of mixing with background air in order to perform a quantitative comparison with the lidar observations. For this meteorological situation, the characteristic mixing time is of the order of 2 to 5 days depending on the initial conditions. Ozone is produced in the free troposphere within most air masses exported from the Iberian PBL at an average rate of 0.2 ppbv h-1, with a maximum ozone production of 0.4 ppbv h-1. Transport processes from the PBL are responsible for an increase of 13.3 ppbv of ozone concentrations in the free troposphere compared to background levels; about 45% of this increase is attributed to in situ production during the transport rather than direct export of ozone.

  11. A Lagrangian analysis of the impact of transport and transformation on the ozone stratification observed in the free troposphere during the ESCOMPTE campaign

    NASA Astrophysics Data System (ADS)

    Colette, A.; Ancellet, G.; Menut, L.; Arnold, S. R.

    2006-08-01

    The ozone variability observed by tropospheric ozone lidars during the ESCOMPTE campaign is analyzed by means of a hybrid-Lagrangian modeling study. Transport processes responsible for the formation of ozone-rich layers are identified using a semi-Lagrangian analysis of mesoscale simulations to identify the planetary boundary layer (PBL) footprint in the free troposphere. High ozone concentrations are related to polluted air masses exported from the Iberian PBL. The chemical composition of air masses coming from the PBL and transported in the free troposphere is evaluated using a Lagrangian chemistry model. The initial concentrations are provided by a model of chemistry and transport. Different scenarios are tested for the initial conditions and for the impact of mixing with background air in order to perform a quantitative comparison with the lidar observations. For this meteorological situation, the characteristic mixing time is of the order of 2 to 6 days depending on the initial conditions. Ozone is produced in the free troposphere within most air masses exported from the Iberian PBL at an average rate of 0.2 ppbv h-1, with a maximum ozone production of 0.4 ppbv h-1. Transport processes from the PBL are responsible for an increase of 13.3 ppbv of ozone concentrations in the free troposphere compared to background levels; about 45% of this increase is attributed to in situ production during the transport rather than direct export of ozone.

  12. Vortex-scalar element calculations of a diffusion flame stabilized on a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Ghoniem, Ahmed F.; Givi, Peyman

    1987-01-01

    The vortex-scalar element method, a scheme which utilizes vortex elements to discretize the region of high vorticity and scalar elements to represent species or temperature fields, is utilized in the numerical simulations of a two-dimensional reacting mixing layer. Computations are performed for a diffusion flame at high Reynolds and Peclet numbers without resorting to turbulence models. In the nonreacting flow, the mean and fluctuation profiles of a conserved scalar show good agreement with experimental measurements. Results for the reacting flow indicate that for temperature independent kinetics, the chemical reaction begins immediately downstream of the splitter plate where mixing starts. Results for the reacting flow with Arrhenius kinetics show an ignition delay, which depends on reactant temperature, before significant chemical reaction occurs. Harmonic forcing changes the structure of the layer, and concomitantly the rates of mixing and reaction, in accordance with experimental results. Strong stretch within the braids in the nonequilibrium kinetics case causes local flame quenching due to the temperature drop associated with the large convective fluxes.

  13. Mesoscale Eddies Control the Timing of Spring Phytoplankton Blooms: A Case Study in the Japan Sea

    NASA Astrophysics Data System (ADS)

    Maúre, E. R.; Ishizaka, J.; Sukigara, C.; Mino, Y.; Aiki, H.; Matsuno, T.; Tomita, H.; Goes, J. I.; Gomes, H. R.

    2017-11-01

    Satellite Chlorophyll a (CHL) data were used to investigate the influence of mesoscale anticyclonic eddies (AEs) and cyclonic eddies (CEs) on the timing of spring phytoplankton bloom initiation around the Yamato Basin (133-139°E and 35-39.5°N) in the Japan Sea, for the period 2002-2011. The results showed significant differences between AEs and CEs in the timing and initiation mechanism of the spring phytoplankton bloom. Blooms were initiated earlier in CEs which were characterized by shallow mixed-layer depths (< 100 m). The early blooming preceded the end of winter cooling (i.e., while net heat flux (Q0) is still negative) and is initiated by the increased average light within the shallow mixed-layer depth. Conversely, blooms appeared in the AEs despite deeper mixed-layer depth (> 100 m) but close to the commencement of positive Q0. This suggests that the relaxation of turbulent mixing is crucial for the bloom initiation in AEs.

  14. Mixed and mixing layer depths in the ocean surface boundary layer under conditions of diurnal stratification

    NASA Astrophysics Data System (ADS)

    Sutherland, G.; Reverdin, G.; Marié, L.; Ward, B.

    2014-12-01

    A comparison between mixed (MLD) and mixing (XLD) layer depths is presented from the SubTRopical Atlantic Surface Salinity Experiment (STRASSE) cruise in the subtropical Atlantic. This study consists of 400 microstructure profiles during fairly calm and moderate conditions (2 < U10 < 10 m s-1) and strong solar heating O(1000 W m-2). The XLD is determined from a decrease in the turbulent dissipation rate to an assumed background level. Two different thresholds for the background dissipation level are tested, 10-8 and 10-9 m2 s-3, and these are compared with the MLD as calculated using a density threshold. The larger background threshold agrees with the MLD during restratification but only extends to half the MLD during nighttime convection, while the lesser threshold agrees well during convection but is deeper by a factor of 2 during restratification. Observations suggest the use of a larger density threshold to determine the MLD in a buoyancy driven regime.

  15. Solar Irradiance Changes and Phytoplankton Productivity in Earth's Ocean Following Astrophysical Ionizing Radiation Events

    NASA Astrophysics Data System (ADS)

    Neale, Patrick J.; Thomas, Brian C.

    2016-04-01

    Two atmospheric responses to simulated astrophysical ionizing radiation events significant to life on Earth are production of odd-nitrogen species, especially NO2, and subsequent depletion of stratospheric ozone. Ozone depletion increases incident short-wavelength ultraviolet radiation (UVB, 280-315 nm) and longer (>600 nm) wavelengths of photosynthetically available radiation (PAR, 400-700 nm). On the other hand, the NO2 haze decreases atmospheric transmission in the long-wavelength UVA (315-400 nm) and short-wavelength PAR. Here, we use the results of previous simulations of incident spectral irradiance following an ionizing radiation event to predict changes in terran productivity focusing on photosynthesis of marine phytoplankton. The prediction is based on a spectral model of photosynthetic response, which was developed for the dominant genera in central regions of the ocean (Synechococcus and Prochlorococcus), and on remote-sensing-based observations of spectral water transparency, temperature, wind speed, and mixed layer depth. Predicted productivity declined after a simulated ionizing event, but the effect integrated over the water column was small. For integrations taking into account the full depth range of PAR transmission (down to 0.1% of utilizable PAR), the decrease was at most 2-3% (depending on strain), with larger effects (5-7%) for integrations just to the depth of the surface mixed layer. The deeper integrations were most affected by the decreased utilizable PAR at depth due to the NO2 haze, whereas shallower integrations were most affected by the increased surface UV. Several factors tended to dampen the magnitude of productivity responses relative to increases in surface-damaging radiation, for example, most inhibition in the modeled strains is caused by UVA and PAR, and the greatest relative increase in damaging exposure is predicted to occur in the winter when UV and productivity are low.

  16. Depth and Extent of Gas-Ablator Mix in Symcap Implosions at the National Ignition Facility

    NASA Astrophysics Data System (ADS)

    Pino, Jesse; Ma, T.; MacLaren, S. A.; Salmonson, J. D.; Ho, D.; Khan, S. F.; Masse, L.; Ralph, J. E.; Czajka, C.; Casey, D.; Sacks, R.; Smalyuk, V. A.; Tipton, R. E.; Kyrala, G. A.

    2017-10-01

    A longstanding question in ICF physics has been the extent to which capsule ablator material mixes into the burning fusion fuel and degrades performance. Several recent campaigns at the National Ignition Facility have examined this question through the use of separated reactants. A layer of CD plastic is placed on the inner surface of the CH shell and the shell is filled with a gas mixture of H and T. This allows for simultaneous neutron signals that inform different aspects of the physics; we get core TT neutron yield, atomic mix from the DT neutrons, and information about shell heating from the DD neutron signal. By systematically recessing the CD layer away from the gas boundary we gain an inference of the depth of the mixing layer. This presentation will cover three campaigns to look at mixing depth: An ignition-like design (``Low-foot'') at two convergence ratios, as well as a robust, nearly one-dimensional, low convergence, symmetric platform designed to minimize ablation front feed-through (HED 2-shock). We show that the 2-shock capsule has less ablator-gas mix, and compare the experimental results to mix-model simulations. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344, LLNS, LLC.

  17. Parametric resonant triad interactions in a free shear layer

    NASA Technical Reports Server (NTRS)

    Mallier, R.; Maslowe, S. A.

    1993-01-01

    We investigate the weakly nonlinear evolution of a triad of nearly-neutral modes superimposed on a mixing layer with velocity profile u bar equals Um + tanh y. The perturbation consists of a plane wave and a pair of oblique waves each inclined at approximately 60 degrees to the mean flow direction. Because the evolution occurs on a relatively fast time scale, the critical layer dynamics dominate the process and the amplitude evolution of the oblique waves is governed by an integro-differential equation. The long-time solution of this equation predicts very rapid (exponential of an exponential) amplification and we discuss the pertinence of this result to vortex pairing phenomena in mixing layers.

  18. A Direct Numerical Simulation of a Temporally Evolving Liquid-Gas Turbulent Mixing Layer

    NASA Astrophysics Data System (ADS)

    Vu, Lam Xuan; Chiodi, Robert; Desjardins, Olivier

    2017-11-01

    Air-blast atomization occurs when streams of co-flowing high speed gas and low speed liquid shear to form drops. Air-blast atomization has numerous industrial applications from combustion engines in jets to sprays used for medical coatings. The high Reynolds number and dynamic pressure ratio of a realistic air-blast atomization case requires large eddy simulation and the use of multiphase sub-grid scale (SGS) models. A direct numerical simulations (DNS) of a temporally evolving mixing layer is presented to be used as a base case from which future multiphase SGS models can be developed. To construct the liquid-gas mixing layer, half of a channel flow from Kim et al. (JFM, 1987) is placed on top of a static liquid layer that then evolves over time. The DNS is performed using a conservative finite volume incompressible multiphase flow solver where phase tracking is handled with a discretely conservative volume of fluid method. This study presents statistics on velocity and volume fraction at different Reynolds and Weber numbers.

  19. Buoyant production and consumption of turbulence kinetic energy in cloud-topped mixed layers

    NASA Technical Reports Server (NTRS)

    Randall, D. A.

    1984-01-01

    It is pointed out that studies of the entraining planetary boundary layer (PBL) have generally emphasized the role of buoyancy fluxes in driving entrainment. The buoyancy flux is proportional to the rate of conversion of the potential energy of the mean flow into the kinetic energy of the turbulence. It is not unusual for conversion to proceed in both directions simultaneously. This occurs, for instance, in both clear and cloudy convective mixed layers which are capped by inversions. A partitioning of the net conversion into positive parts, generating turbulence kinetic energy (TKE), and negative parts (TKE-consuming), would make it possible to include the positive part in the gross production rate, and closure would be achieved. Three different approaches to partitioning have been proposed. The present investigation is concerned with a comparison of the three partitioning theories. Particular attention is given to the cloud-topped mixed layer because in this case the differences between two partitioning approaches are most apparent.

  20. Photovoltaic Performance Enhancement of Silicon Solar Cells Based on Combined Ratios of Three Species of Europium-Doped Phosphors.

    PubMed

    Ho, Wen-Jeng; You, Bang-Jin; Liu, Jheng-Jie; Bai, Wen-Bin; Syu, Hong-Jhang; Lin, Ching-Fuh

    2018-05-18

    This paper presents a scheme for the enhancement of silicon solar cells in terms of luminescent emission band and photovoltaic performance. The proposed devices are coated with an luminescent down-shifting (LDS) layer comprising three species of europium (Eu)-doped phosphors mixed within a silicate film (SiO₂) using a spin-on film deposition. The three species of phosphor were mixed at ratios of 0.5:1:1.5, 1:1:1, or 1.5:1:0.5 in weight percentage (wt %). The total quantity of Eu-doped phosphors in the silicate solution was fixed at 3 wt %. The emission wavelengths of the Eu-doped phosphors were as follows: 518 nm (specie-A), 551 nm (specie-B), and 609 nm (specie-C). We examined the extended luminescent emission bands via photoluminescence measurements at room temperature. Closely matching the luminescent emission band to the high responsivity band of the silicon semiconductor resulted in good photovoltaic performance. Impressive improvements in efficiency were observed in all three samples: 0.5:1:1.5 (20.43%), 1:1:1 (19.67%), 1.5:1:0.5 (16.81%), compared to the control with a layer of pure SiO₂ (13.80%).

  1. Streamwise Vorticity Generation in Laminar and Turbulent Jets

    NASA Technical Reports Server (NTRS)

    Demuren, Aodeji O.; Wilson, Robert V.

    1999-01-01

    Complex streamwise vorticity fields are observed in the evolution of non-circular jets. Generation mechanisms are investigated via Reynolds-averaged (RANS), large-eddy (LES) and direct numerical (DNS) simulations of laminar and turbulent rectangular jets. Complex vortex interactions are found in DNS of laminar jets, but axis-switching is observed only when a single instability mode is present in the incoming mixing layer. With several modes present, the structures are not coherent and no axis-switching occurs, RANS computations also produce no axis-switching. On the other hand, LES of high Reynolds number turbulent jets produce axis-switching even for cases with several instability modes in the mixing layer. Analysis of the source terms of the mean streamwise vorticity equation through post-processing of the instantaneous results shows that, complex interactions of gradients of the normal and shear Reynolds stresses are responsible for the generation of streamwise vorticity which leads to axis-switching. RANS computations confirm these results. k - epsilon turbulence model computations fail to reproduce the phenomenon, whereas algebraic Reynolds stress model (ASM) computations, in which the secondary normal and shear stresses are computed explicitly, succeeded in reproducing the phenomenon accurately.

  2. Effects of different feeder layers on culture of bovine embryonic stem cell-like cells in vitro.

    PubMed

    Cong, Shan; Cao, Guifang; Liu, Dongjun

    2014-12-01

    To find a suitable feeder layer is important for successful culture conditions of bovine embryonic stem cell-like cells. In this study, expression of pluripotency-related genes OCT4, SOX2 and NANOG in bovine embryonic stem cell-like cells on mouse embryonic fibroblast feeder layers at 1-5 passages were monitored in order to identify the possible reason that bovine embryonic stem cell-like cells could not continue growth and passage. Here, we developed two novel feeder layers, mixed embryonic fibroblast feeder layers of mouse and bovine embryonic fibroblast at different ratios and sources including mouse fibroblast cell lines. The bovine embryonic stem cell-like cells generated in our study displayed typical stem cell morphology and expressed specific markers such as OCT4, stage-specific embryonic antigen 1 and 4, alkaline phosphatase, SOX2, and NANOG mRNA levels. When feeder layers and cell growth factors were removed, the bovine embryonic stem cell-like cells formed embryoid bodies in a suspension culture. Furthermore, we compared the expression of the pluripotent markers during bovine embryonic stem cell-like cell in culture on mixed embryonic fibroblast feeder layers, including mouse fibroblast cell lines feeder layers and mouse embryonic fibroblast feeder layers by real-time quantitative polymerase chain reaction. Results suggested that mixed embryonic fibroblast and sources including mouse fibroblast cell lines feeder layers were more suitable for long-term culture and growth of bovine embryonic stem cell-like cells than mouse embryonic fibroblast feeder layers. The findings may provide useful experimental data for the establishment of an appropriate culture system for bovine embryonic stem cell lines.

  3. Sedimentary record of sub-glacial outburst floods at Laurentian Fan

    NASA Astrophysics Data System (ADS)

    Leng, Wei; von Dobeneck, Tilo

    2016-04-01

    Large-scale glacial meltwater discharge could be widely recognized off the eastern Canadian continental margin. At Laurentian Fan, sub-glacial outburst floods eroded Permian-Carboniferous redbeds at Gulf of St. Lawrence and then delivered the reddish sediments by Laurentian Channel. Sedimentary record from four gravity cores (GeoB18514-2, 18515-1, 18516-2 and 18517-1) at the SW slope of the Grand Banks of Newfoundland revealed the major depositional processes since Heinrich event 2 (ca. 22 ka). In the cores, the upper thick Holocene olive-grey silty mud units overly IRD-rich Heinrich 1 layer, five reddish units are distinguished in the lower part. Reddish units get proportionally thinner along the SW slope at higher and more distal positions; instead, separating olive-grey layers get thicker with height and distance. Reddish and olive grey units have sharp boundaries and no signs of erosion. Mean grain size changes abruptly from coarse in grey layers to fine in reddish layers, terrigenous elements (as Al, K, Ti, Fe) and clays (Al/Si) are highly elevated in reddish layers and low in Heinrich layers, which are instead enriched in detrital continental carbonates. Both Heinrich layers and reddish layers have enhanced magnetic susceptibility, but Heinrich layer have higher ferromagnetic (SIRM) content (mafic rocks), while reddish layers have more hematite (HIRM). These five reddish layers differ from event to event, which seems to reflect different mixing ratios of event-related and background sedimentation. This mixing will allow estimating event-specific sedimentation rates. Using mixing ratio combined with 14C dating data could contribute to estimate the sedimentation rate and duration of outburst floods, which could help to build ice sheet retreat history and find the connection with paleoclimate changes.

  4. Pigment Identification on "The Ecstasy of St. Theresa" Painting by Raman Microscopy

    NASA Astrophysics Data System (ADS)

    Marano, D.; Marmontelli, M.; De Benedetto, G. E.; Catalano, I. M.; Sabbatini, L.; Vona, F.

    A study of the pigments of "The Ecstasy of St. Theresa," a seventeenth century oil painting on canvas, was performed by Raman microscopy. Lazurite was identified in both Jesus Christ's and St. Theresa's mantles as the pigment responsible for the blue coloration. Litharge was identified inside the black bitumen layer. Usually the bitumen needed a lot of time to dry in the air when mixed with drying oil. Litharge was used by the artist to decrease the oil drying time. A complementary study, using micro-Raman and SEM, allowed us to identify red ochre as the pigment responsible for the red coloration in the altar on the left side of the painting.

  5. Gamma-based Measurement of ``Dark Mix'' in ICF Capsules

    NASA Astrophysics Data System (ADS)

    Meaney, Kevin; Herrmann, H.; Kim, Yh; Zylstra, Ab; Geppert-Kleinrath, H.; Hoffman, Nm; Yi, As

    2017-10-01

    Mix of capsule ablator material into the fusion fuel is a source of yield degradation in inertial confinement fusion. Jetting or chunk mix, such as the elusive ``meteors'' that have been observed at NIF, can be difficult to diagnose because the chunks may not get hot enough to excite dopant x-rays, nor atomized enough for separated-reactants to fuse. Using the gamma reaction history (GRH-6m) diagnostic, (n,n') gammas from strategically placed carbon layer within a beryllium capsule gives a measure of the time-resolved areal density of this carbon during the burn and hence an indication of the compression and spatial distribution of this layer. As the carbon moves further from the fuel, the areal density nominally decreases as 1/r2 for unablated material. However, mix of this carbon into the cold dense fuel layer or hot spot will have a significant effect on the carbon gamma signal. Different types of mix (e.g., jetting, Rayleigh-Taylor fingers, diffusive, ...) as well as features that can seed this mix (eg., tents, fill,...) will be discussed along with their expected effect on the carbon signal. The design for upcoming OMEGA shots, which will demonstrate this technique, and the potential for use on the NIF will be presented.

  6. Vertical velocity variance in the mixed layer from radar wind profilers

    USGS Publications Warehouse

    Eng, K.; Coulter, R.L.; Brutsaert, W.

    2003-01-01

    Vertical velocity variance data were derived from remotely sensed mixed layer turbulence measurements at the Atmospheric Boundary Layer Experiments (ABLE) facility in Butler County, Kansas. These measurements and associated data were provided by a collection of instruments that included two 915 MHz wind profilers, two radio acoustic sounding systems, and two eddy correlation devices. The data from these devices were available through the Atmospheric Boundary Layer Experiment (ABLE) database operated by Argonne National Laboratory. A signal processing procedure outlined by Angevine et al. was adapted and further built upon to derive vertical velocity variance, w_pm???2, from 915 MHz wind profiler measurements in the mixed layer. The proposed procedure consisted of the application of a height-dependent signal-to-noise ratio (SNR) filter, removal of outliers plus and minus two standard deviations about the mean on the spectral width squared, and removal of the effects of beam broadening and vertical shearing of horizontal winds. The scatter associated with w_pm???2 was mainly affected by the choice of SNR filter cutoff values. Several different sets of cutoff values were considered, and the optimal one was selected which reduced the overall scatter on w_pm???2 and yet retained a sufficient number of data points to average. A similarity relationship of w_pm???2 versus height was established for the mixed layer on the basis of the available data. A strong link between the SNR and growth/decay phases of turbulence was identified. Thus, the mid to late afternoon hours, when strong surface heating occurred, were observed to produce the highest quality signals.

  7. A review of turbulent-boundary-layer heat transfer research at Stanford, 1958-1983

    NASA Technical Reports Server (NTRS)

    Moffat, R. J.; Kays, W. M.

    1984-01-01

    For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers. In the early phases of the program, the topics considered were the simple zero-pressure-gradient turbulent boundary layer with constant and with varying surface temperature, and the accelerated boundary layer. Later equilibrium boundary layers were considered along with factors affecting the boundary layer, taking into account transpired flows, flows with axial pressure gradients, transpiration, acceleration, deceleration, roughness, full-coverage film cooling, surface curvature, free convection, and mixed convection. A description is provided of the apparatus and techniques used, giving attention to the smooth plate rig, the rough plate rig, the full-coverage film cooling rig, the curvature rig, the concave wall rig, the mixed convection tunnel, and aspects of data reduction and uncertainty analysis.

  8. An experimental study of scalar mixing in curved shear layers

    NASA Technical Reports Server (NTRS)

    Karasso, P. S.; Mungal, M. G.

    1990-01-01

    This report describes the work being undertaken to study the scalar mixing in curved shear layers. First, the motivation for this work and its objectives are described. Second, a description of the experimental rig that has been built is given. Third, some preliminary results (flow visualizations) are discussed, and finally, future steps that will be taken to complete the study are outlined.

  9. Mathematical modeling of the kinetics of deposition of particles during their pulse introduction through the free surface of a mixed-medium plane layer

    NASA Astrophysics Data System (ADS)

    Boger, A. A.; Ryazhskikh, V. I.; Slyusarev, M. I.

    2012-01-01

    Based on diffusion concepts of transfer of slightly concentrated polydisperse suspensions in the gravity field, we propose a mathematical model of the kinetics of deposition of such suspensions in a plane layer of a homogeneously mixed medium through the free surface of which Stokesian particles penetrate according to the rectangular pulse law.

  10. Quantifying Ozone Production throughout the Boundary Layer from High Frequency Tethered Profile Measurements during a High Ozone Episode in the Uinta Basin, Utah

    NASA Astrophysics Data System (ADS)

    Sterling, C. W.; Johnson, B.; Schnell, R. C.; Oltmans, S. J.; Cullis, P.; Hall, E. G.; Jordan, A. F.; Windell, J.; McClure-Begley, A.; Helmig, D.; Petron, G.

    2015-12-01

    During the Uinta Basin Winter Ozone Study (UBWOS) in Jan - Feb 2013, 735 tethered ozonesonde profiles were obtained at 3 sites including during high wintertime photochemical ozone production events that regularly exceeded 125 ppb. High resolution profiles of ozone and temperature with altitude, measured during daylight hours, showed the development of approximately week long high ozone episodes building from background levels of ~40 ppb to >150 ppb. The topography of the basin combined with a strong temperature inversion trapped oil and gas production effluents in the basin and the snow covered surface amplified the sun's radiation driving the photochemical ozone production at rates up to 13 ppb/hour in a cold layer capped at 1600-1700 meters above sea level. Beginning in mid-morning, ozone mixing ratios throughout the cold layer increased until late afternoon. Ozone mixing ratios were generally constant with height indicating that ozone production was nearly uniform throughout the depth of the cold pool. Although there was strong diurnal variation, ozone mixing ratios increased during the day more than decreased during the night, resulting in elevated levels the next morning; an indication that nighttime loss processes did not compensate for daytime production. Even though the 3 tethersonde sites were at elevations differing by as much as 140 m, the top of the high ozone layer was nearly uniform in altitude at the 3 locations. Mobile van surface ozone measurements across the basin confirmed this capped structure of the ozone layer; the vehicle drove out of high ozone mixing ratios at an elevation of ~1900 meters above sea level, above which free tropospheric ozone mixing ratios of ~50 ppb were measured. Exhaust plumes from a coal-fired power plant in the eastern portion of the basin were intercepted by the tethersondes. The structure of the profiles clearly showed that effluents in the plumes were not mixed downward and thus did not contribute precursor nitrogen oxides to the observed ozone production in the boundary layer.

  11. DNS and LES of a Shear-Free Mixing Layer

    NASA Technical Reports Server (NTRS)

    Knaepen, B.; Debliquy, O.; Carati, D.

    2003-01-01

    The purpose of this work is twofold. First, given the computational resources available today, it is possible to reach, using DNS, higher Reynolds numbers than in Briggs et al.. In the present study, the microscale Reynolds numbers reached in the low- and high-energy homogeneous regions are, respectively, 32 and 69. The results reported earlier can thus be complemented and their robustness in the presence of increased turbulence studied. The second aim of this work is to perform a detailed and documented LES of the shear-free mixing layer. In that respect, the creation of a DNS database at higher Reynolds number is necessary in order to make meaningful LES assessments. From the point of view of LES, the shear-free mixing-layer is interesting since it allows one to test how traditional LES models perform in the presence of an inhomogeneity without having to deal with difficult numerical issues. Indeed, as argued in Briggs et al., it is possible to use a spectral code to study the shear-free mixing layer and one can thus focus on the accuracy of the modelling while avoiding contamination of the results by commutation errors etc. This paper is organized as follows. First we detail the initialization procedure used in the simulation. Since the flow is not statistically stationary, this initialization procedure has a fairly strong influence on the evolution. Although we will focus here on the shear-free mixing layer, the method proposed in the present work can easily be used for other flows with one inhomogeneous direction. The next section of the article is devoted to the description of the DNS. All the relevant parameters are listed and comparison with the Veeravalli & Warhaft experiment is performed. The section on the LES of the shear-free mixing layer follows. A detailed comparison between the filtered DNS data and the LES predictions is presented. It is shown that simple eddy viscosity models perform very well for the present test case, most probably because the flow seems to be almost isotropic in the small-scale range that is not resolved by the LES.

  12. Ocean Mixed Layer responses to intense meteorological events during HyMeX-SOP1 from a high-resolution ocean simulation

    NASA Astrophysics Data System (ADS)

    Lebeaupin Brossier, Cindy; Arsouze, Thomas; Béranger, Karine; Bouin, Marie-Noëlle; Bresson, Emilie; Ducrocq, Véronique; Giordani, Hervé; Nuret, Mathieu; Rainaud, Romain; Taupier-Letage, Isabelle

    2014-12-01

    The western Mediterranean Sea is a source of heat and humidity for the atmospheric low-levels in autumn. Large exchanges take place at the air-sea interface, especially during intense meteorological events, such as heavy precipitation and/or strong winds. The Ocean Mixed Layer (OML), which is quite thin at this time of year (∼ 20 m-depth), evolves rapidly under such intense fluxes. This study investigates the ocean responses under intense meteorological events that occurred during HyMeX SOP1 (5 September-6 November 2012). The OML conditions and tendencies are derived from a high-resolution ocean simulation using the sub-regional eddy-resolving NEMO-WMED36 model (1/36°-resolution), driven at the surface by hourly air-sea fluxes from the AROME-WMED forecasts (2.5 km-resolution). The high space-time resolution of the atmospheric forcing allows the highly variable surface fluxes, which induce rapid changes in the OML, to be well represented and linked to small-scale atmospheric processes. First, the simulation results are compared to ocean profiles from several platforms obtained during the campaign. Then, this study focuses on the short-term OML evolution during three events. In particular, we examine the OML cooling and mixing under strong wind events, potentially associated with upwelling, as well as the surface freshening under heavy precipitation events, producing low-salinity lenses. Tendencies demonstrate the major role of the surface forcing in the temperature and/or salinity anomaly formation. At the same time, mixing [restratification] rapidly occurs. As expected, the sign of this tendency term is very dependent on the local vertical stratification which varies at fine scale in the Mediterranean. It also controls [disables] the vertical propagation. In the Alboran Sea, the strong dynamics redistribute the OML anomalies, sometimes up to 7 days after their formation. Elsewhere, despite local amplitude modulations due to internal wave excitation by strong winds, the integrated effect of the horizontal advection is almost null on the anomalies' spread and decay. Finally, diffusion has a small contribution.

  13. A second-order bulk boundary-layer model

    NASA Technical Reports Server (NTRS)

    Randall, David A.; Shao, Qingqiu; Moeng, Chin-Hoh

    1992-01-01

    Bulk mass-flux models represent the large eddies that are primarily responsible for the turbulent fluxes in the planetary boundary layer as convective circulations, with an associated convective mass flux. In order for such models to be useful, it is necessary to determine the fractional area covered by rising motion in the convective circulations. This fraction can be used as an estimate of the cloud amount, under certain conditions. 'Matching' conditions have been developed that relate the convective mass flux to the ventilation and entrainment mass fluxes. These are based on conservation equations for the scalar means and variances in the entrainment and ventilation layers. Methods are presented to determine both the fractional area covered by rising motion and the convective mass flux. The requirement of variance balance is used to relax the 'well-mixed' assumption. The vertical structures of the mean state and the turbulent fluxes are determined analytically. Several aspects of this simple model's formulation are evaluated using results from large-eddy simulations.

  14. Response of the Land-Atmosphere System Over North-Central Oklahoma During the 2017 Eclipse

    DOE PAGES

    Turner, D. D.; Wulfmeyer, V.; Behrendt, A.; ...

    2018-02-05

    On 21 August 2017, a solar eclipse occurred over the continental United States resulting in a rapid reduction and subsequent increase of solar radiation over a large region of the country. The eclipse’s effect on the land-atmosphere system is documented in unprecedented detail using a unique array of sensors deployed at three sites in north-central Oklahoma. The observations showed that turbulent fluxes of heat and momentum at the surface responded quickly to the change in solar radiation. The decrease in the sensible heat flux resulted in a decrease in the air temperature below 200 m, and a large decrease inmore » turbulent motions throughout the boundary layer. Furthermore, the turbulent mixing in the boundary layer lagged behind the change in the surface fluxes, and this lag depended on the height above the surface. The turbulent motions increased and the convective boundary layer was reestablished as the sensible heat flux recovered.« less

  15. Low Voltage Electrowetting on Ferroelectric PVDF-HFP Insulator with Highly Tunable Contact Angle Range.

    PubMed

    Sawane, Yogesh B; Ogale, Satishchandra B; Banpurkar, Arun G

    2016-09-14

    We demonstrate a consistent electrowetting response on ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) insulator covered with a thin Teflon AF layer. This bilayer exhibits a factor of 3 enhancement in the contact angle modulation compared to that of conventional single-layered Teflon AF dielectric. On the basis of the proposed model the enhancement is attributed to the high value of effective dielectric constant (εeff ≈ 6) of the bilayer. Furthermore, the bilayer dielectric exhibits a hysteresis-free contact angle modulation over many AC voltage cycles. But the contact angle modulation for DC voltage shows a hysteresis because of the field-induced residual polarization in the ferroelectric layer. Finally, we show that a thin bilayer exhibits contact angle modulation of Δθ (U) ≈ 60° at merely 15 V amplitude of AC voltage indicating a potential dielectric for practical low voltage electrowetting applications. A proof of concept confirms electrowetting based rapid mixing of a fluorescent dye in aqueous glycerol solution for 15 V AC signal.

  16. Response of the Land-Atmosphere System Over North-Central Oklahoma During the 2017 Eclipse

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Turner, D. D.; Wulfmeyer, V.; Behrendt, A.

    On 21 August 2017, a solar eclipse occurred over the continental United States resulting in a rapid reduction and subsequent increase of solar radiation over a large region of the country. The eclipse’s effect on the land-atmosphere system is documented in unprecedented detail using a unique array of sensors deployed at three sites in north-central Oklahoma. The observations showed that turbulent fluxes of heat and momentum at the surface responded quickly to the change in solar radiation. The decrease in the sensible heat flux resulted in a decrease in the air temperature below 200 m, and a large decrease inmore » turbulent motions throughout the boundary layer. Furthermore, the turbulent mixing in the boundary layer lagged behind the change in the surface fluxes, and this lag depended on the height above the surface. The turbulent motions increased and the convective boundary layer was reestablished as the sensible heat flux recovered.« less

  17. Polysulfide intercalated layered double hydroxides for metal capture applications

    DOEpatents

    Kanatzidis, Mercouri G.; Ma, Shulan

    2017-04-04

    Polysulfide intercalated layered double hydroxides and methods for their use in vapor and liquid-phase metal capture applications are provided. The layered double hydroxides comprise a plurality of positively charged host layers of mixed metal hydroxides separated by interlayer spaces. Polysulfide anions are intercalated in the interlayer spaces.

  18. Shock compression response of highly reactive Ni + Al multilayered thin foils

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kelly, Sean C.; Thadhani, Naresh N., E-mail: naresh.thadhani@mse.gatech.edu

    2016-03-07

    The shock-compression response of Ni + Al multilayered thin foils is investigated using laser-accelerated thin-foil plate-impact experiments over the pressure range of 2 to 11 GPa. The foils contain alternating Ni and Al layers (parallel but not flat) of nominally 50 nm bilayer spacing. The goal is to determine the equation of state and shock-induced reactivity of these highly reactive fully dense thin-foil materials. The laser-accelerated thin-foil impact set-up involved combined use of photon-doppler-velocimetry to monitor the acceleration and impact velocity of an aluminum flyer, and VISAR interferometry was used to monitor the back free-surface velocity of the impacted Ni + Al multilayered target. The shock-compressionmore » response of the Ni + Al target foils was determined using experimentally measured parameters and impedance matching approach, with error bars identified considering systematic and experimental errors. Meso-scale CTH shock simulations were performed using real imported microstructures of the cross-sections of the multilayered Ni + Al foils to compute the Hugoniot response (assuming no reaction) for correlation with their experimentally determined equation of state. It was observed that at particle velocities below ∼150 m/s, the experimentally determined equation of state trend matches the CTH-predicted inert response and is consistent with the observed unreacted state of the recovered Ni + Al target foils from this velocity regime. At higher particle velocities, the experimentally determined equation of state deviates from the CTH-predicted inert response. A complete and self-sustained reaction is also seen in targets recovered from experiments performed at these higher particle velocities. The deviation in the measured equation of state, to higher shock speeds and expanded volumes, combined with the observation of complete reaction in the recovered multilayered foils, confirmed via microstructure characterization, is indicative of the occurrence of shock-induced chemical reaction occurring in the time-scale of the high-pressure state. TEM characterization of recovered shock-compressed (unreacted) Ni + Al multilayered foils exhibits distinct features of constituent mixing revealing jetted layers and inter-mixed regions. These features were primarily observed in the proximity of the undulations present in the alternating layers of the Ni + Al starting foils, suggesting the important role of such instabilities in promoting shock-induced intermetallic-forming reactions in the fully dense highly exothermic multilayered thin foils.« less

  19. Aircraft measurements to characterize polluted winter boundary layers: Overview of twin otter flights during the Utah Winter Fine Particulate Matter Study

    NASA Astrophysics Data System (ADS)

    Brown, S. S.; Baasandorj, M.; Franchin, A.; Middlebrook, A. M.; Goldberger, L.; Thornton, J. A.; Dube, W. P.; McDuffie, E. E.; Womack, C.; Fibiger, D. L.; Moravek, A.; Clark, J. C.; Murphy, J. G.; Mitchell, R.

    2017-12-01

    Winter air pollution is a significant public health concern. In many regions of the U.S., Europe and Asia, wintertime particulate matter concentrations exceed national and / or international air quality standards. Winter air pollution also represents a scientific challenge because these events occur during stagnation events in shallow, vertically stratified boundary layers whose composition is difficult to probe from surface level measurements. Chemical processes responsible for the conversion of primary emissions to secondary pollutants such as ammonium nitrate aerosol vary with height above ground level. Sources of oxidants are poorly understood and may result from both local chemical production and mixing between shallow inversion layers and background air. During the Utah Winter Fine Particulate Study (UWFPS) in January - February 2017, the NOAA twin otter executed 23 research flights with a payload designed to characterize the formation of ammonium nitrate aerosol in three mountain valleys of northern Utah (Salt Lake, Cache, and Utah). These valleys are subject to periodic episodes of winter aerosol pollution well in excess of U.S. national ambient air quality standards. This presentation will describe the measurement strategy of the twin otter flights to address the specific features of aerosol pollution within winter boundary layer of this region. This strategy is relevant to understanding the broader issue of winter air pollution in other regions and potentially to the design of future studies. The presentation will summarize findings from UWFPS related to boundary layer structure, emissions and chemical processes responsible for ammonium nitrate aerosol in this region.

  20. Changes in the depth habitat of the Oligocene planktic foraminifera (Dentoglobigerina venezuelana) induced by thermocline deepening in the eastern equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Matsui, Hiroki; Nishi, Hiroshi; Takashima, Reishi; Kuroyanagi, Azumi; Ikehara, Minoru; Takayanagi, Hideko; Iryu, Yasufumi

    2016-06-01

    Understanding planktic foraminiferal depth habitat along with consistent taxonomic concepts is key to accurate reconstruction of paleoceanographic records. The Oligocene-Pliocene long-ranging and widely distributed species Dentoglobigerina venezuelana lived in the mixed layer (shallower) during the early Oligocene, whereas the same species calcified at thermocline or subthermocline depths (deeper) during the late Oligocene and Miocene. The exact timing of the species' depth habitat change and its possible relationships with Oligocene climate dynamics remain unknown. Here we reveal isotopic records of D. venezuelana along with the Paragloborotalia siakensis group (a mixed-layer dweller) by using sediments at Integrated Ocean Drilling Program Site U1334 in the eastern equatorial Pacific throughout the Oligocene. A two-step depth habitat change of D. venezuelana is apparent: (1) from upper to lower mixed layer (~27.4 Ma) and (2) from lower mixed layer to thermocline depth (~26.3 Ma). In addition, the planktic foraminiferal faunal assemblage experienced a marked change from dominantly thermocline (deeper) species to abundant mixed-layer (shallower) species, suggesting that depth habitat shifts of D. venezuelana were clearly related to thermocline deepening in the eastern equatorial Pacific. Comparison of the first isotopic shift (~27.4 Ma) at multiple sites (U1334, U1333, and 1218) revealed a southward depth habitat change of D. venezuelana within ~200 kyr, implying overall thermocline deepening with reduced steepness in the eastern equatorial Pacific. We consider that global warming conditions during the late Oligocene likely caused thermocline deepening with upwelling decrease in the eastern equatorial Pacific, guiding D. venezuelana to adapt to greater depths in the water column.

  1. An Assessment of Southern Ocean Water Masses and Sea Ice During 1988-2007 in a Suite of Interannual CORE-II Simulations

    NASA Technical Reports Server (NTRS)

    Downes, Stephanie M.; Farneti, Riccardo; Uotila, Petteri; Griffies, Stephen M.; Marsland, Simon J.; Bailey, David; Behrens, Erik; Bentsen, Mats; Bi, Daohua; Biastoch, Arne; hide

    2015-01-01

    We characterise the representation of the Southern Ocean water mass structure and sea ice within a suite of 15 global ocean-ice models run with the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) protocol. The main focus is the representation of the present (1988-2007) mode and intermediate waters, thus framing an analysis of winter and summer mixed layer depths; temperature, salinity, and potential vorticity structure; and temporal variability of sea ice distributions. We also consider the interannual variability over the same 20 year period. Comparisons are made between models as well as to observation-based analyses where available. The CORE-II models exhibit several biases relative to Southern Ocean observations, including an underestimation of the model mean mixed layer depths of mode and intermediate water masses in March (associated with greater ocean surface heat gain), and an overestimation in September (associated with greater high latitude ocean heat loss and a more northward winter sea-ice extent). In addition, the models have cold and fresh/warm and salty water column biases centred near 50 deg S. Over the 1988-2007 period, the CORE-II models consistently simulate spatially variable trends in sea-ice concentration, surface freshwater fluxes, mixed layer depths, and 200-700 m ocean heat content. In particular, sea-ice coverage around most of the Antarctic continental shelf is reduced, leading to a cooling and freshening of the near surface waters. The shoaling of the mixed layer is associated with increased surface buoyancy gain, except in the Pacific where sea ice is also influential. The models are in disagreement, despite the common CORE-II atmospheric state, in their spatial pattern of the 20-year trends in the mixed layer depth and sea-ice.

  2. Origin of non-spherical particles in the boundary layer over Beijing, China: based on balloon-borne observations.

    PubMed

    Chen, Bin; Yamada, Maromu; Iwasaka, Yasunobu; Zhang, Daizhou; Wang, Hong; Wang, Zhenzhu; Lei, Hengchi; Shi, Guangyu

    2015-10-01

    Vertical structures of aerosols from the ground to about 1,000 m altitude in Beijing were measured with a balloon-borne optical particle counter. The results showed that, in hazy days, there were inversions at approximately 500-600 m, below which the particulate matters were well mixed vertically, while the concentration of particles decreased sharply above the mixing layer. Electron microscopic observation of the particles collected with the balloon-borne impactor indicates that the composition of particles is different according to weather conditions in the boundary mixing layer of Beijing city and suggests that dust particles are always dominant in coarse-mode particles. Interestingly, sea-salt particles are frequently identified, suggesting the importance of marine air inflow to the Beijing area even in summer. The Ca-rich spherical particles are also frequently identified, suggesting chemical modification of dust particle by NOx or emission of CaO and others from local emission. Additionally, those types of particles showed higher concentration above the mixing layer under the relatively calm weather condition of summer, suggesting the importance of local-scale convection found in summer which rapidly transported anthropogenic particles above the mixing layer. Lidar extinction profiles qualitatively have good consistency with the balloon-borne measurements. Attenuation effects of laser pulse intensity are frequently observed due to high concentration of particulate matter in the Beijing atmosphere, and therefore quantitative agreement of lidar return and aerosol concentration can be hardly observed during dusty condition. Comparing the depolarization ratio obtained from the lidar measurements with the balloon-borne measurements, the contribution of the dry sea-salt particles, in addition to the dust particles, is suggested as an important factor causing depolarization ratio in the Beijing atmosphere.

  3. Southern Ocean vertical iron fluxes; the ocean model effect

    NASA Astrophysics Data System (ADS)

    Schourup-Kristensen, V.; Haucke, J.; Losch, M. J.; Wolf-Gladrow, D.; Voelker, C. D.

    2016-02-01

    The Southern Ocean plays a key role in the climate system, but commonly used large-scale ocean general circulation biogeochemical models give different estimates of current and future Southern Ocean net primary and export production. The representation of the Southern Ocean iron sources plays an important role for the modeled biogeochemistry. Studies of the iron supply to the surface mixed layer have traditionally focused on the aeolian and sediment contributions, but recent work has highlighted the importance of the vertical supply from below. We have performed a model study in which the biogeochemical model REcoM2 was coupled to two different ocean models, the Finite Element Sea-ice Ocean Model (FESOM) and the MIT general circulation model (MITgcm) and analyzed the magnitude of the iron sources to the surface mixed layer from below in the two models. Our results revealed a remarkable difference in terms of mechanism and magnitude of transport. The mean iron supply from below in the Southern Ocean was on average four times higher in MITgcm than in FESOM and the dominant pathway was entrainment in MITgcm, whereas diffusion dominated in FESOM. Differences in the depth and seasonal amplitude of the mixed layer between the models affect on the vertical iron profile, the relative position of the base of the mixed layer and ferricline and thereby also on the iron fluxes. These differences contribute to differences in the phytoplankton composition in the two models, as well as in the timing of the onset of the spring bloom. The study shows that the choice of ocean model has a significant impact on the iron supply to the Southern Ocean mixed layer and thus on the modeled carbon cycle, with possible implications for model runs predicting the future carbon uptake in the region.

  4. Aspects of turbulent-shear-layer dynamics and mixing

    NASA Astrophysics Data System (ADS)

    Slessor, Michael David

    Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of high-Reynolds-number, turbulent, shear-layer flows in both incompressible- and compressible-flow regimes. Experiments designed to address several issues were performed; effects of inflow boundary conditions, freestream conditions (supersonic/subsonic flow), and compressibility, on both large-scale dynamics and small-scale mixing, are described. Chemically-reacting and non-reacting flows were investigated, the former relying on the (Hsb2 + NO)/Fsb2 chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing through use of "flip" experiments. A variety of experimental techniques, including a color-schlieren visualization system developed as part of this work, were used to study the flows. Both inflow conditions and compressibility are found to have significant effects on the flow. In particular, inflow conditions are "remembered" for long distances downstream, a sensitivity similar to that observed in low-dimensionality, non-linear (chaotic) systems. The global flowfields (freestreams coupled by the shear layer) of transonic flows exhibit a sensitivity to imposed boundary conditions, a.e., local area ratios. A previously-proposed mode-selection rule for turbulent-structure convection speeds, based on the presence of a lab-frame subsonic freestream, was experimentally demonstrated to be incorrect. Compressibility, when decoupled from ail other parameters, e.g., Reynolds number, velocity and density ratios, etc., reduces large-scale entrainment and turbulent growth, but slightly enhances small-scale mixing, with an associated change in the structure of the molecularly-mixed fluid. This reduction in shear-layer growth rate is examined and a new parameter that interprets compressibility as an energy-exchange mechanism is proposed. The parameter reconciles and collapses experimentally-observed growth rates.

  5. Understanding rapid changes in phase partitioning between cloud liquid and ice in an Arctic stratiform mixed-phase cloud

    NASA Astrophysics Data System (ADS)

    Kalesse, Heike; de Boer, Gijs; Solomon, Amy; Oue, Mariko; Ahlgrimm, Maike; Zhang, Damao; Shupe, Matthew; Luke, Edward; Protat, Alain

    2016-04-01

    In the Arctic, a region particularly sensitive to climate change, mixed-phase clouds occur as persistent single or multiple stratiform layers. For many climate models, the correct partitioning of hydrometeor phase (liquid vs. ice) remains a challenge. However, this phase partitioning plays an important role for precipitation processes and the radiation budget. To better understand the partitioning of phase in Arctic clouds, observations using a combination of surface-based remote sensors are useful. In this study, the focus is on a persistent low-level single-layer stratiform Arctic mixed-phase cloud observed during March 11-12, 2013 at the US Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) permanent site in Barrow, Alaska. This case is of particular interest due to two significant shifts in observed precipitation intensity over a 36 hour period. For the first 12 hours of this case, the observed liquid portion of the cloud cover featured a stable cloud top height with a gradually descending liquid cloud base and continuous ice precipitation. Then the ice precipitation intensity significantly decreased. A second decrease in ice precipitation intensity was observed a few hours later coinciding with the advection of a cirrus over the site. Through analysis of the data collected by extensive ground-based remote-sensing and in-situ observing systems as well as Nested Weather Research and Forecasting (WRF) simulations and ECMWF radiation scheme simulations, we try to shed light on the processes responsible for these rapid changes in precipitation rates. A variety of parameters such as the evolution of the internal dynamics and microphysics of the low-level mixed-phase cloud and the influence of the cirrus cloud are evaluated.

  6. Diffusive tunneling for alleviating Knudsen-layer reactivity reduction under hydrodynamic mix

    NASA Astrophysics Data System (ADS)

    Tang, Xianzhu; McDevitt, Chris; Guo, Zehua

    2017-10-01

    Hydrodynamic mix will produce small features for intermixed deuterium-tritium fuel and inert pusher materials. The geometrical characteristics of the mix feature have a large impact on Knudsen layer yield reduction. We considered two features. One is planar structure, and the other is fuel cells segmented by inert pusher material which can be represented by a spherical DT bubble enclosed by a pusher shell. The truly 3D fuel feature, the spherical bubble, has the largest degree of yield reduction, due to fast ions being lost in all directions. The planar fuel structure, which can be regarded as 1D features, has modest amount of potential for yield degradation. While the increasing yield reduction with increasing Knudsen number of the fuel region is straightforwardly anticipated, we also show, by a combination of direct simulation and simple model, that once the pusher materials is stretched sufficiently thin by hydrodynamic mix, the fast fuel ions diffusively tunnel through them with minimal energy loss, so the Knudsen layer yield reduction becomes alleviated. This yield recovery can occur in a chunk-mixed plasma, way before the far more stringent, asymptotic limit of an atomically homogenized fuel and pusher assembly. Work supported by LANL LDRD program.

  7. Solid-state membrane module

    DOEpatents

    Hinklin, Thomas Ray; Lewinsohn, Charles Arthur

    2015-06-30

    A module for separating oxygen from an oxygen-containing gaseous mixture comprising planar solid-state membrane units, each membrane unit comprising planar dense mixed conducting oxides layers, planar channel-free porous support layers, and one or more planar intermediate support layers comprising at least one channeled porous support layer. The porosity of the planar channeled porous support layers is less than the porosity of the planar channel-free porous support layers.

  8. Complex and noncentrosymmetric stacking of layered metal dichalcogenide materials created by screw dislocations

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shearer, Melinda J.; Samad, Leith; Zhang, Yi

    The interesting and tunable properties of layered metal dichalcogenides heavily depend on their phase and layer stacking. Here, we show and explain how the layer stacking and physical properties of WSe 2 are influenced by screw dislocations. A one-to-one correlation of atomic force microscopy and high- and low-frequency Raman spectroscopy of many dislocated WSe 2 nanoplates reveals variations in the number and shapes of dislocation spirals and different layer stackings that are determined by the number, rotation, and location of the dislocations. Plates with triangular dislocation spirals form noncentrosymmetric stacking that gives rise to strong second-harmonic generation and enhanced photoluminescence,more » plates with hexagonal dislocation spirals form the bulk 2H layer stacking commonly observed, and plates containing mixed dislocation shapes have intermediate noncentrosymmetric stackings with mixed properties. Multiple dislocation cores and other complexities can lead to more complex stackings and properties. Finally, these previously unobserved properties and layer stackings in WSe 2 will be interesting for spintronics and valleytronics.« less

  9. Complex and noncentrosymmetric stacking of layered metal dichalcogenide materials created by screw dislocations

    DOE PAGES

    Shearer, Melinda J.; Samad, Leith; Zhang, Yi; ...

    2017-02-08

    The interesting and tunable properties of layered metal dichalcogenides heavily depend on their phase and layer stacking. Here, we show and explain how the layer stacking and physical properties of WSe 2 are influenced by screw dislocations. A one-to-one correlation of atomic force microscopy and high- and low-frequency Raman spectroscopy of many dislocated WSe 2 nanoplates reveals variations in the number and shapes of dislocation spirals and different layer stackings that are determined by the number, rotation, and location of the dislocations. Plates with triangular dislocation spirals form noncentrosymmetric stacking that gives rise to strong second-harmonic generation and enhanced photoluminescence,more » plates with hexagonal dislocation spirals form the bulk 2H layer stacking commonly observed, and plates containing mixed dislocation shapes have intermediate noncentrosymmetric stackings with mixed properties. Multiple dislocation cores and other complexities can lead to more complex stackings and properties. Finally, these previously unobserved properties and layer stackings in WSe 2 will be interesting for spintronics and valleytronics.« less

  10. Response of the Water Cycle of West Africa and Atlantic to Radiative Forcing by Saharan Dust

    NASA Technical Reports Server (NTRS)

    Lau, K. M.; Kim, Kyu-Myong; Sud, Yogesh C.; Walker, Gregory L.

    2010-01-01

    The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence in support of the "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feed back triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Easter Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean. region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while long wave has the opposite response. The elevated dust layer warms the air over Nest Africa and the eastern Atlantic. The condensation heating associated with the induced deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface energy fluxes, resulting in cooling of the Nest African land and the eastern Atlantic, and a warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

  11. Crossover between two- and three-dimensional turbulence in spatial mixing layers

    NASA Astrophysics Data System (ADS)

    Biancofiore, Luca

    2016-11-01

    We investigate how the domain depth affects the turbulent behaviour in spatially developing mixing layers by means of large-eddy simulations (LES) based on a spectral vanishing viscosity technique. Analyses of spectra of the vertical velocity, of Lumley's diagrams, of the turbulent kinetic energy and of the vortex stretching show that a two-dimensional behaviour of the turbulence is promoted in spatial mixing layers by constricting the fluid motion in one direction. This finding is in agreement with previous works on turbulent systems constrained by a geometric anisotropy, pioneered by Smith, Chasnov & Waleffe. We observe that the growth of the momentum thickness along the streamwise direction is damped in a confined domain. A full two-dimensional turbulent behaviour is observed when the momentum thickness is of the same order of magnitude as the confining scale.

  12. Inviscid spatial stability of a compressible mixing layer. II - The flame sheet model

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.; Grosch, C. E.

    1990-01-01

    The results of an inviscid spatial calculation for a compressible reacting mixing layer are reported. The limit of infinitive activation energy is taken and the diffusion flame is approximated by a flame sheet. Results are reported for the phase speeds of the neutral waves and maximum growth rates of the unstable waves as a function of the parameters of the problem: the ratio of the temperature of the stationary stream to that of the moving stream, the Mach number of the moving streams, the heat release per unit mass fraction of the reactant, the equivalence ratio of the reaction, and the frequency of the disturbance. These results are compared to the phase speeds and growth rates of the corresponding nonreacting mixing layer. We show that the addition of combustion has important and complex effects on the flow stability.

  13. The prediction of sea-surface temperature variations by means of an advective mixed-layer ocean model

    NASA Technical Reports Server (NTRS)

    Atlas, R. M.

    1976-01-01

    An advective mixed layer ocean model was developed by eliminating the assumption of horizontal homogeneity in an already existing mixed layer model, and then superimposing a mean and anomalous wind driven current field. This model is based on the principle of conservation of heat and mechanical energy and utilizes a box grid for the advective part of the calculation. Three phases of experiments were conducted: evaluation of the model's ability to account for climatological sea surface temperature (SST) variations in the cooling and heating seasons, sensitivity tests in which the effect of hypothetical anomalous winds was evaluated, and a thirty-day synoptic calculation using the model. For the case studied, the accuracy of the predictions was improved by the inclusion of advection, although nonadvective effects appear to have dominated.

  14. Control of shock-wave boundary-layer interactions by bleed in supersonic mixed compression inlets

    NASA Technical Reports Server (NTRS)

    Fukuda, M. K.; Reshotko, E.; Hingst, W. R.

    1975-01-01

    An experimental investigation has been conducted to determine the effect of bleed region geometry and bleed rate on shock wave-boundary layer interactions in an axisymmetric, mixed-compression inlet at a Mach number of 2.5. The full realizable reduction in transformed form factor is obtained by bleeding off about half the incident boundary layer mass flow. Bleeding upstream or downstream of the shock-induced pressure rise is preferable to bleeding across the shock-induced pressure rise. Slanted holes are more effective than normal holes. Two different bleed hole sizes were tested without detectable difference in performance.

  15. Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Throckmorton, Heather M.; Newman, Brent D.; Heikoop, Jeffrey M.

    Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO 2 and CH 4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ 2H and δ 18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface activemore » layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ 2H vs δ 18O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.« less

  16. Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

    DOE PAGES

    Throckmorton, Heather M.; Newman, Brent D.; Heikoop, Jeffrey M.; ...

    2016-04-16

    Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO 2 and CH 4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ 2H and δ 18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface activemore » layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ 2H vs δ 18O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.« less

  17. Magnetic induction constraints on electrical conductivity within Europa

    NASA Astrophysics Data System (ADS)

    Bills, B. G.; Vance, S.

    2017-12-01

    We examine the problem of inferring radial variations in electrical conductivity within Europa, from measurements of the magnetic field induced within Europa by its motion through Jupiter's magnetic field. The Europa Clipper mission is expected to make multiple encounters with Europa, sampling several periods at which significant magnetic induction forcing occurs. Most previous analyses have considered a simple 3-layer model of Europa's internal structure, with an insulating core, a uniform conductivity ocean, and an insulating ice shell, and have only examined responses at 2 forcing periods. We attempt to address the broader issues of what level of detail can be inferred from plausible estimates of induced field response at several additional forcing periods. We will present results of an analysis of the periods and amplitudes of magnetic field variations at Europa, and at the Europa Clipper spacecraft. It appears likely that useful information on the induction response will be attained at 6 forcing frequencies, spanning the interval from 1 to just over 15 cycles per orbital period, in Europa's motion about Jupiter. The range of periods is 5.6 to 85 hours. The induced field diffuses into the interior, and signals at longer periods penetrate more deeply. Having measurements at a range of forcing periods thus helps resolve radial structure. Even if the ocean is well mixed and has uniform salinity, there will be some depth-dependent variations in electrical conductivity due to temperature and pressure variations. Much larger variations would be present if the ocean were stably stratified, with a denser brine underlying a fresher upper layer. While vigorous convection within the ocean would likely mix and homogenize the water column, a stratified ocean is at least possible. Could such a feature of the ocean be detected via magnetic induction? Also, the conductivities in the ice shell above, and silicate layer beneath the ocean are expected to be substantially smaller than in a salty ocean. However, they are not zero. We will consider the extent to which these regions might also be interrogated via magnetic induction.

  18. Enhancing charge transfer kinetics by nanoscale catalytic cermet interlayer.

    PubMed

    An, Jihwan; Kim, Young-Beom; Gür, Turgut M; Prinz, Fritz B

    2012-12-01

    Enhancing the density of catalytic sites is crucial for improving the performance of energy conversion devices. This work demonstrates the kinetic role of 2 nm thin YSZ/Pt cermet layers on enhancing the oxygen reduction kinetics for low temperature solid oxide fuel cells. Cermet layers were deposited between the porous Pt cathode and the dense YSZ electrolyte wafer using atomic layer deposition (ALD). Not only the catalytic role of the cermet layer itself but the mixing effect in the cermet was explored. For cells with unmixed and fully mixed cermet interlayers, the maximum power density was enhanced by a factor of 1.5 and 1.8 at 400 °C, and by 2.3 and 2.7 at 450 °C, respectively, when compared to control cells with no cermet interlayer. The observed enhancement in cell performance is believed to be due to the increased triple phase boundary (TPB) density in the cermet interlayer. We also believe that the sustained kinetics for the fully mixed cermet layer sample stems from better thermal stability of Pt islands separated by the ALD YSZ matrix, which helped to maintain the high-density TPBs even at elevated temperature.

  19. The Effect of Eu Doping on Microstructure, Morphology and Methanal-Sensing Performance of Highly Ordered SnO2 Nanorods Array

    PubMed Central

    Zhao, Yanping; Li, Yuehua; Ren, Xingping; Gao, Fan; Zhao, Heyun

    2017-01-01

    Layered Eu-doped SnO2 ordered nanoarrays constructed by nanorods with 10 nm diameters and several hundred nanometers length were synthesized by a substrate-free hydrothermal route using alcohol and water mixed solvent of sodium stannate and sodium hydroxide at 200 °C. The Eu dopant acted as a crystal growth inhibitor to prevent the SnO2 nanorods growth up, resulting in tenuous SnO2 nanorods ordered arrays. The X-ray diffraction (XRD) revealed the tetragonal rutile-type structure with a systematic average size reduction and unit cell volume tumescence, while enhancing the residual strain as the Eu-doped content increases. The surface defects that were caused by the incorporation of Eu ions within the surface oxide matrix were observed by high-resolution transmission electron microscope (HRTEM). The results of the response properties of sensors based on the different levels of Eu-doped SnO2 layered nanoarrays demonstrated that the 0.5 at % Eu-doped SnO2 layered nanorods arrays exhibited an excellent sensing response to methanal at 278 °C. The reasons of the enhanced sensing performance were discussed from the complicated defect surface structure, the large specific surface area, and the excellent catalytic properties of Eu dopant. PMID:29168796

  20. Under-ice turbulent microstructure and upper ocean vertical fluxes in the Makarov and Eurasian basins, Arctic Ocean, during late spring and late summer / autumn in 2015

    NASA Astrophysics Data System (ADS)

    Rabe, Benjamin; Janout, Markus; Graupner, Rainer; Hoelemann, Jens; Hampe, Hendrik; Hoppmann, Mario; Horn, Myriel; Juhls, Bennet; Korhonen, Meri; Nikolopoulos, Anna; Pisarev, Sergey; Randelhoff, Achim; Savy, Jean-Philippe; Villacieros Robineau, Nicolas

    2017-04-01

    The Arctic Ocean is generally assumed to be fairly quiescent when compared to many other oceans. The sea-ice cover, a strong halocline and a shallow, cold mixed-layer prevents much of the ocean to be affected by atmospheric conditions and properties of the ocean mixed-layer. In turn, the mixed-layer and the sea-ice is largely isolated from the warm layer of Atlantic origin below by the lower halocline. Yet, the content of heat, freshwater and biologically important nutrients differs strongly between these different layers. Hence, it is crucial to be able to estimate vertical fluxes of salt, heat and nutrients to understand variability in the upper Arctic Ocean and the sea-ice, including the ecosystem. Yet, it is difficult to obtain direct flux measurements, and estimates are sparse. We present several sets of under-ice turbulent microstructure profiles in the Eurasian and Makarov Basin of the Arctic Ocean from two expeditions, in 2015. These cover melt during late spring north of Svalbard and freeze-up during late summer / autumn across the Eurasian and Makarov basins. Our results are presented against a background of the anomalously warm atmospheric conditions during summer 2015 followed by unusually low temperatures in September. 4 - 24 h averages of the measurements generally show elevated dissipation rates at the base of the mixed-layer. We found highest levels of dissipation near the Eurasian continental slope and smaller peaks in the profiles where Bering Sea Summer Water (sBSW) lead to additional stratification within the upper halocline in the Makarov Basin. The elevated levels of dissipation associated with sBSW and the base of the mixed-layer were associated with the relatively low levels of vertical eddy diffusivity. We discuss these findings in the light of the anomalous conditions in the upper ocean, sea-ice and the atmosphere during 2015 and present estimates of vertical fluxes of heat, salt and other dissolved substances measured in water samples.

  1. Ultraviolet radiation and the photobiology of earth's early oceans.

    PubMed

    Cockell, C S

    2000-10-01

    During the Archean era (3.9-2.5 Ga ago) the earth was dominated by an oceanic lithosphere. Thus, understanding how life arose and persisted in the Archean oceans constitutes a major challenge in understanding early life on earth. Using a radiative transfer model of the late Archean oceans, the photobiological environment of the photic zone and the surface microlayer is explored at the time before the formation of a significant ozone column. DNA damage rates might have been approximately three orders of magnitude higher in the surface layer of the Archean oceans than on the present-day oceans, but at 30 m depth, damage may have been similar to the surface of the present-day oceans. However at this depth the risk of being transported to surface waters in the mixed layer was high. The mixed layer may have been inhabited by a low diversity UV-resistant biota. But it could have been numerically abundant. Repair capabilities similar to Deinococcus radiodurans would be sufficient to survive in the mixed layer. Diversity may have been greater in the region below the mixed layer and above the light compensation point corresponding to today's 'deep chlorophyll maximum'. During much of the Archean the air-water interface was probably an uninhabitable extreme environment for neuston. The habitability of some regions of the photic zone is consistent with the evidence embodied in the geologic record, which suggests an oxygenated upper layer in the Archean oceans. During the early Proterozoic, as ozone concentrations increased to a column abundance above 1 x 10(17) cm-2, UV stress would have been reduced and possibly a greater diversity of organisms could have inhabited the mixed layer. However, nutrient upwelling from newly emergent continental crusts may have been more significant in increasing total planktonic abundance in the open oceans and coastal regions than photobiological factors. The phohobiological environment of the Archean oceans has implications for the potential cross-transfer of life between other water bodies of the early Solar System, possibly on early Mars or the water bodies of a wet, early Venus.

  2. Observation and modeling of mixing-layer development in HED blast-wave-driven shear flow

    NASA Astrophysics Data System (ADS)

    di Stefano, Carlos

    2013-10-01

    This talk describes work exploring the sensitivity to initial conditions of hydrodynamic mixing-layer growth due to shear flow in the high-energy-density regime. This work features an approach in two parts, experimental and theoretical. First, an experiment, conducted at the OMEGA-60 laser facility, seeks to measure the development of such a mixing layer. This is accomplished by placing a layer of low-density (initially of either 0.05 or 0.1 g/cm3, to vary the system's Atwood number) carbon foam against a layer of higher-density (initially 1.4 g/cm3) polyamide-imide that has been machined to a nominally-flat surface at its interface with the foam. Inherent roughness of this surface's finish is precisely measured and varied from piece to piece. Ten simultaneous OMEGA beams, comprising a 4.5 kJ, 1-ns pulse focused to a roughly 1-mm-diameter spot, irradiate a thin polycarbonate ablator, driving a blast wave into the foam, parallel to its interface with the polyamide-imide. The ablator is framed by a gold washer, such that the blast wave is driven only into the foam, and not into the polyamide-imide. The subsequent forward motion of the shocked foam creates the desired shear effect, and the system is imaged by X-ray radiography 35 ns after the beginning of the driving laser pulse. Second, a simulation is performed, intending to replicate the flow observed in the experiment as closely as possible. Using the resulting simulated flow parameters, an analytical model can be used to predict the evolution of the mixing layer, as well as track the motion of the fluid in the experiment prior to the snapshot seen in the radiograph. The ability of the model to predict growth of the mixing layer under the various conditions observed in the experiment is then examined. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, and by the National Laser Use.

  3. Turbulent mixing induced by Richtmyer-Meshkov instability

    NASA Astrophysics Data System (ADS)

    Krivets, V. V.; Ferguson, K. J.; Jacobs, J. W.

    2017-01-01

    Richtmyer-Meshkov instability is studied in shock tube experiments with an Atwood number of 0.7. The interface is formed in a vertical shock tube using opposed gas flows, and three-dimensional random initial interface perturbations are generated by the vertical oscillation of gas column producing Faraday waves. Planar Laser Mie scattering is used for flow visualization and for measurements of the mixing process. Experimental image sequences are recorded at 6 kHz frequency and processed to obtain the time dependent variation of the integral mixing layer width. Measurements of the mixing layer width are compared with Mikaelian's [1] model in order to extract the growth exponent θ where a fairly wide range of values is found varying from θ ≈ 0.2 to 0.6.

  4. Interaction of Sound with Sound by Novel Mechanisms: Ultrasonic Four-Wave Mixing Mediated by a Suspension and Ultrasonic Three-Wave Mixing at a Free Surface

    NASA Astrophysics Data System (ADS)

    Simpson, Harry Jay

    Two mechanisms of sound interacting with sound are experimentally and theoretically investigated. Ultrasonic four-wave mixing in a dilute particle suspension, analogous to optical four-wave mixing in photorefractive materials, involves the interaction of three ultrasonic wavefields that produces a fourth scattered wavefield. The experimental configuration consists of two ultrasonic (800 kHz) pump waves that are used to produce a grating in a suspension of 25 μm diameter polymer particles in salt water. The pump waves are counter-propagating, which form a standing wavefield in the suspension and the less compressible particles are attracted to the pressure nodes in response to the time averaged radiation pressure. A higher frequency (2-10 MHz) ultrasonic wavefield is used to probe the resulting grating. The ultrasonic Bragg scattering is then measured. The scattering depends strongly on the response to the pump wave and is an unusual class of acoustical nonlinearity. Investigation of very small amplitude gratings are done by studying the temporal response of the Bragg scattering to a sudden turn on of a moderate amplitude pump wavefield in a previously homogeneous particle suspension. The Bragg scattering has been verified experimentally and is modeled for early-time grating formations using a sinusoidal grating. The larger amplitude gratings are studied in equilibrium and are modeled using an Epstein layer approximation. Ultrasonic three-wave mixing at a free surface involves the interaction of a high amplitude 400 kHz plane wavefield incident at 33^circ on a water-air interface with a normally incident high frequency (4.6 MHz) focused wavefield. The 400 kHz "pump" wavefield reflects from the surface and produces an oscillating surface displacement that forms a local traveling phase grating. Simultaneously the 4.6 MHz "probe" wavefield is reflected from the free surface. The grating scatters the focused probe wavefield and produces (or contributes to) spatially and Doppler shifted foci relative to the main focus.

  5. Interaction of sound with sound by novel mechanisms: Ultrasonic four-wave mixing mediated by a suspension and ultrasonic three-wave mixing at a free surface

    NASA Astrophysics Data System (ADS)

    Simpson, Harry Jay

    Two mechanisms of sound interacting with sound are experimentally and theoretically investigated. Ultrasonic four-wave mixing in a dilute particle suspension, analogous to optical four-wave mixing in photorefractive materials, involves the interaction of three ultrasonic wavefields that produces a fourth scattered wavefield. The experimental configuration consists of two ultrasonic (800 kHz) pump waves that are used to produce a grating in a suspension of 25 micron diameter polymer particles in salt water. The pump waves are counter-propagating, which form a standing wavefield in the suspension and the less compressible particles are attracted to the pressure nodes in response to the time averaged radiation pressure. A higher frequency (2 to 10 MHz) ultrasonic wavefield is used to probe the resulting grating. The ultrasonic Bragg scattering is then measured. The scattering depends strongly on the response to the pump wave and is an unusual class of acoustical nonlinearity. Investigation of very small amplitude gratings are done by studying the temporal response of the Bragg scattering to a sudden turn on of a moderate amplitude pump wavefield in a previously homogeneous particle suspension. The Bragg scattering has been verified experimentally and is modeled for early-time grating formations using a sinusoidal grating. The larger amplitude gratings are studied in equilibrium and are modeled using an Epstein layer approximation. Ultrasonic three-wave mixing at a free surface involves the interaction of a high amplitude 400 kHz plane wavefield incident at 33 degrees on a water-air interface with a normally incident high frequency (4.6 MHz) focused wavefield. The 400 kHz 'pump' wavefield reflects from the surface and produces an oscillating surface displacement that forms a local traveling phase grating. Simultaneously the 4.6 MHz 'probe' wavefield is reflected from the free surface. The grating scatters the focused probe wavefield and produces (or contributes to) spatially and Doppler shifted foci relative to the main focus.

  6. The Provenance of Sulfur that Becomes Non-Seasalt Sulfate (NSS)

    NASA Astrophysics Data System (ADS)

    Huebert, B. J.; Simpson, R. M.; Howell, S. G.

    2012-12-01

    As a part of the Pacific Atmospheric Sulfur Experiment (PASE), we measured sulfur gases and aerosol chemistry (vs size) from the NCAR C-130 near Christmas Island. Monthly (project) average concentrations in the Marine Boundary Layer (MBL, the lowest mixed layer) and Buffer Layer (BuL, a more stable layer atop the MBL, with clouds) are used to evaluate the formation, loss, and exchange rates for DMS, SO2, and NSS in each layer. We evaluate entrainment, divergence, vertical mixing, chemical formation and loss for each to make a self-consistent budget of oxidized sulfur in the remote marine atmosphere. We find that long-range transport of sulfur from continental sources can be larger than the sulfur source from biogenic dimethyl sulfide, DMS. DMS does not appear to control either the number of NSS particles or NSS mass.

  7. Mixed-layer kerolite/stevensite from the Amargosa Desert, Nevada

    USGS Publications Warehouse

    Eberl, Dennis D.; Jones, Blair F.; Khoury, Hani N.

    1982-01-01

    Mixed-layer clays composed of randomly interstratified kerolite/stevensite occur as lake and/or spring deposits of probable Pliocene and Pleistocene age in the Amargosa Desert of southern Nevada, U.S.A. The percentage of expandable layers of these clays, determined from computer-simulated X-ray diffractograms, ranges from almost 0 to about 80%. This range in expandabilities most likely results from differences in solution chemistry and/or temperature at the time of formation. An average structural formula for the purest clay (sample P-7), a clay with about 70% expandable layers, is:[(Mg2.72Al0.07Fe0.03Li0.09)(Si3.96Al0.04)O10(OH)0.2]-0.21[X+0.21]+0.21The data suggest that talc, kerolite, and stevensite form a continuous structural series based on layer charge.

  8. Observed ocean thermal response to Hurricanes Gustav and Ike

    NASA Astrophysics Data System (ADS)

    Meyers, Patrick C.; Shay, Lynn K.; Brewster, Jodi K.; Jaimes, Benjamin

    2016-01-01

    The 2008 Atlantic hurricane season featured two hurricanes, Gustav and Ike, crossing the Gulf of Mexico (GOM) within a 2 week period. Over 400 airborne expendable bathythermographs (AXBTs) were deployed in a GOM field campaign before, during, and after the passage of Gustav and Ike to measure the evolving upper ocean thermal structure. AXBT and drifter deployments specifically targeted the Loop Current (LC) complex, which was undergoing an eddy-shedding event during the field campaign. Hurricane Gustav forced a 50 m deepening of the ocean mixed layer (OML), dramatically altering the prestorm ocean conditions for Hurricane Ike. Wind-forced entrainment of colder thermocline water into the OML caused sea surface temperatures to cool by over 5°C in GOM common water, but only 1-2°C in the LC complex. Ekman pumping and a near-inertial wake were identified by fluctuations in the 20°C isotherm field observed by AXBTs and drifters following Hurricane Ike. Satellite estimates of the 20° and 26°C isotherm depths and ocean heat content were derived using a two-layer model driven by sea surface height anomalies. Generally, the satellite estimates correctly characterized prestorm conditions, but the two-layer model inherently could not resolve wind-forced mixing of the OML. This study highlights the importance of a coordinated satellite and in situ measurement strategy to accurately characterize the ocean state before, during, and after hurricane passage, particularly in the case of two consecutive storms traveling through the same domain.

  9. Linkages Between Boundary-Layer Structure and the Development of Nocturnal Low-Level Jets in Central Oklahoma

    NASA Astrophysics Data System (ADS)

    Klein, Petra M.; Hu, Xiao-Ming; Shapiro, Alan; Xue, Ming

    2016-03-01

    In the Southern Great Plains, nocturnal low-level jets (LLJs) develop frequently after sunset and play an important role in the transport and dispersion of moisture and atmospheric pollutants. However, our knowledge regarding the LLJ evolution and its feedback on the structure of the nocturnal boundary layer (NBL) is still limited. In the present study, NBL characteristics and their interdependencies with LLJ evolution are investigated using datasets collected across the Oklahoma City metropolitan area during the Joint Urban field experiment in July 2003 and from three-dimensional simulations with the Weather Research and Forecasting (WRF) model. The strength of the LLJs and turbulent mixing in the NBL both increase with the geostrophic forcing. During nights with the strongest LLJs, turbulent mixing persisted after sunset in the NBL and a strong surface temperature inversion did not develop. However, the strongest increase in LLJ speed relative to the mixed-layer wind speed in the daytime convective boundary layer (CBL) occurred when the geostrophic forcing was relatively weak and thermally-induced turbulence in the CBL was strong. Under these conditions, turbulent mixing at night was typically much weaker and a strong surface-based inversion developed. Sensitivity tests with the WRF model confirm that weakening of turbulent mixing during the decay of the CBL in the early evening transition is critical for LLJ formation. The cessation of thermally-induced CBL turbulence during the early evening transition triggers an inertial oscillation, which contributes to the LLJ formation.

  10. Structural Response Prediction: Full-field, Dynamic Pressure and Displacement Measurements of a Panel Excited by Shock Boundary-layer Interaction

    DTIC Science & Technology

    2015-02-01

    research cell14. The RC-19 facility is a continuous flow wind tunnel designed to study the mechanisms that govern the mixing and combustion process... angle of 39° from the tunnel bottom wall. The shock generator can translate 170 mm in the flow direction to allow for the shock wave to impinge from...approximate absolute pressure of 20.5 kPa. A series of “ wind -off” images for PSP were collected at that time. The tunnel was then started by setting the

  11. Cloud Effects on Ocean Mixed Layer in the Northeast Pacific Ocean

    DTIC Science & Technology

    1991-06-01

    examining this phenomenon is the disproportionate darkness of the long January nights (-16 hours). The greenhouse effect was particularly active...increase in entrainment velocity thereby deepening the mixed layer and cooling the ocean surface. The greenhouse effect had little significant impact...This result is similar to the results found in the short-term experiment of Event #1, where the greenhouse effect is the dominant factor on the MLD

  12. The effects of stabilizing and destabilizing longitudinal curvature on the structure of turbulent, two-stream mixing layers

    NASA Technical Reports Server (NTRS)

    Plesniak, Michael W.; Johnston, J. P.

    1989-01-01

    The construction and development of the multi-component traversing system and associated control hardware and software are presented. A hydrogen bubble/laser sheet flow visualization technique was developed to visually study the characteristics of the mixing layers. With this technique large-scale rollers arising from the Taylor-Gortler instability and its interaction with the primary Kelvin-Helmholtz structures can be studied.

  13. Ill-posedness in modeling mixed sediment river morphodynamics

    NASA Astrophysics Data System (ADS)

    Chavarrías, Víctor; Stecca, Guglielmo; Blom, Astrid

    2018-04-01

    In this paper we analyze the Hirano active layer model used in mixed sediment river morphodynamics concerning its ill-posedness. Ill-posedness causes the solution to be unstable to short-wave perturbations. This implies that the solution presents spurious oscillations, the amplitude of which depends on the domain discretization. Ill-posedness not only produces physically unrealistic results but may also cause failure of numerical simulations. By considering a two-fraction sediment mixture we obtain analytical expressions for the mathematical characterization of the model. Using these we show that the ill-posed domain is larger than what was found in previous analyses, not only comprising cases of bed degradation into a substrate finer than the active layer but also in aggradational cases. Furthermore, by analyzing a three-fraction model we observe ill-posedness under conditions of bed degradation into a coarse substrate. We observe that oscillations in the numerical solution of ill-posed simulations grow until the model becomes well-posed, as the spurious mixing of the active layer sediment and substrate sediment acts as a regularization mechanism. Finally we conduct an eigenstructure analysis of a simplified vertically continuous model for mixed sediment for which we show that ill-posedness occurs in a wider range of conditions than the active layer model.

  14. GenoQuery: a new querying module for functional annotation in a genomic warehouse

    PubMed Central

    Lemoine, Frédéric; Labedan, Bernard; Froidevaux, Christine

    2008-01-01

    Motivation: We have to cope with both a deluge of new genome sequences and a huge amount of data produced by high-throughput approaches used to exploit these genomic features. Crossing and comparing such heterogeneous and disparate data will help improving functional annotation of genomes. This requires designing elaborate integration systems such as warehouses for storing and querying these data. Results: We have designed a relational genomic warehouse with an original multi-layer architecture made of a databases layer and an entities layer. We describe a new querying module, GenoQuery, which is based on this architecture. We use the entities layer to define mixed queries. These mixed queries allow searching for instances of biological entities and their properties in the different databases, without specifying in which database they should be found. Accordingly, we further introduce the central notion of alternative queries. Such queries have the same meaning as the original mixed queries, while exploiting complementarities yielded by the various integrated databases of the warehouse. We explain how GenoQuery computes all the alternative queries of a given mixed query. We illustrate how useful this querying module is by means of a thorough example. Availability: http://www.lri.fr/~lemoine/GenoQuery/ Contact: chris@lri.fr, lemoine@lri.fr PMID:18586731

  15. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Morgan, B. E.; Olson, B. J.; White, J. E.

    High-fidelity large eddy simulation (LES) of a low-Atwood number (A = 0.05) Rayleigh-Taylor mixing layer is performed using the tenth-order compact difference code Miranda. An initial multimode perturbation spectrum is specified in Fourier space as a function of mesh resolution such that a database of results is obtained in which each successive level of increased grid resolution corresponds approximately to one additional doubling of the mixing layer width, or generation. The database is then analyzed to determine approximate requirements for self-similarity, and a new metric is proposed to quantify how far a given simulation is from the limit of self-similarity.more » It is determined that mixing layer growth reaches a high degree of self-similarity after approximately 4.5 generations. Statistical convergence errors and boundary effects at late time, however, make it impossible to draw similar conclusions regarding the self-similar growth of more sensitive turbulence parameters. Finally, self-similar turbulence profiles from the LES database are compared with one-dimensional simulations using the k-L-a and BHR-2 Reynolds-averaged Navier-Stokes (RANS) models. The k-L-a model, which is calibrated to reproduce a quadratic turbulence kinetic energy profile for a self-similar mixing layer, is found to be in better agreement with the LES than BHR-2 results.« less

  16. Statistical anisotropy in free turbulence for mixing layers at high Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.; Luke, Theodore E.

    1996-08-01

    A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after propagating through free turbulent mixing layers. Shearing interferometers provide a two-dimensional flow visualization that is nonintrusive. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Experiments were performed on an unbounded, plane shear mixing layer of helium and nitrogen gas at fixed velocities and high Reynolds numbers for six locations in the flow development. Statistical autocorrelation functions and structure functions were computed on the reconstructed phase maps. The autocorrelation function results indicated that the turbulence-induced phase fluctuations were not wide-sense stationary. The structure functions exhibited statistical homogeneity, indicating that the phase fluctuations were stationary in first increments. However, the turbulence-corrupted phase was not isotropic. A five-thirds power law is shown to fit orthogonal slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence. Strehl ratios were computed from the phase structure functions and compared with classical estimates that assume isotropy. The isotropic models are shown to overestimate the optical degradation by nearly 3 orders of magnitude compared with the structure function calculations.

  17. Transient natural ventilation of a room with a distributed heat source

    NASA Astrophysics Data System (ADS)

    Fitzgerald, Shaun D.; Woods, Andrew W.

    We report on an experimental and theoretical study of the transient flows which develop as a naturally ventilated room adjusts from one temperature to another. We focus on a room heated from below by a uniform heat source, with both high- and low-level ventilation openings. Depending on the initial temperature of the room relative to (i) the final equilibrium temperature and (ii) the exterior temperature, three different modes of ventilation may develop. First, if the room temperature lies between the exterior and the equilibrium temperature, the interior remains well-mixed and gradually heats up to the equilibrium temperature. Secondly, if the room is initially warmer than the equilibrium temperature, then a thermal stratification develops in which the upper layer of originally hot air is displaced upwards by a lower layer of relatively cool inflowing air. At the interface, some mixing occurs owing to the effects of penetrative convection. Thirdly, if the room is initially cooler than the exterior, then on opening the vents, the original air is displaced downwards and a layer of ambient air deepens from above. As this lower layer drains, it is eventually heated to the ambient temperature, and is then able to mix into the overlying layer of external air, and the room becomes well-mixed. For each case, we present new laboratory experiments and compare these with some new quantitative models of the transient flows. We conclude by considering the implications of our work for natural ventilation of large auditoria.

  18. White organic light-emitting diodes with ultra-thin mixed emitting layer

    NASA Astrophysics Data System (ADS)

    Jeon, T.; Forget, S.; Chenais, S.; Geffroy, B.; Tondelier, D.; Bonnassieux, Y.; Ishow, E.

    2012-02-01

    White light can be obtained from Organic Light Emitting Diodes by mixing three primary colors, (i.e. red, green and blue) or two complementary colors in the emissive layer. In order to improve the efficiency and stability of the devices, a host-guest system is generally used as an emitting layer. However, the color balance to obtain white light is difficult to control and optimize because the spectrum is very sensitive to doping concentration (especially when a small amount of material is used). We use here an ultra-thin mixed emitting layer (UML) deposited by thermal evaporation to fabricate white organic light emitting diodes (WOLEDs) without co-evaporation. The UML was inserted in the hole-transporting layer consisting of 4, 4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (α-NPB) instead of using a conventional doping process. The UML was formed from a single evaporation boat containing a mixture of two dipolar starbust triarylamine molecules (fvin and fcho) presenting very similar structures and thermal properties and emitting in complementary spectral regions (orange and blue respectively) and mixed according to their weight ratio. The composition of the UML specifically allows for fine tuning of the emission color despite its very thin thickness down to 1 nm. Competitive energy transfer processes from fcho and the host interface toward fvin are key parameters to control the relative intensity between red and blue emission. White light with very good CIE 1931 color coordinate (0.34, 0.34) was obtained by simply adjusting the UML film composition.

  19. Polar Amplification of Global Warming in Models Without Ice-Albedo Feedbacks

    NASA Astrophysics Data System (ADS)

    Alexeev, V. A.; Langen, P. L.

    2004-12-01

    Non-ice-albedo feedback mechanisms leading to polar amplification, as reported by Alexeev (2003), are explored in three aquaplanet climate model systems of different complexity. We analyze this pattern using three different "ghost forcing" experiments (Hansen et al, 1997). In the first one we uniformly add 4W/m2 to the oceanic mixed layer in order to roughly simulate a 2xCO2 forcing at the surface. The second forcing, of the same magnitude, is applied only within the tropics and the third forcing is applied only polewards of 30 degrees (north and south). It turns out that our systems' equilibrium responses are linear with respect to these forcings. Surprisingly, the response to the tropical-only forcing is essentially non-local with quite significant warming at higher latitudes. The response to the high-latitude-only forcing is more local and has higher amplitude near the poles. Our explanation of the polar amplification obtained in the uniform forcing experiment is therefore two-fold. Firstly, the tropics are much more difficult to warm because of the higher sensitivity of the surface budget to SST changes at higher temperatures. Secondly, any extra heat deposited in the tropics is not easily radiated to outer space because of the high opaqueness of the tropical atmosphere. The energy, most of which is latent, needs to be redistributed by transports to the extra-tropics. Consequently, the tropical "ghost forcing" results in an essentially non-local response, while the extra-tropical one yields a more localized response, because the energy in the atmosphere cannot propagate effectively equator-wards from high latitudes. The paper deals with these mechanisms in three climate model systems with no ice-albedo feedbacks - an EBM and two different GCMs - one with cloud feedbacks and the other with cloud feedbacks excluded. References. Alexeev, V.A., (2003) Sensitivity to CO2 doubling of an atmospheric GCM coupled to an oceanic mixed layer: a linear analysis. Climate Dynamics, 20: p.775-787. Hansen, J., Sato M, and R. Ruedy, (1997) Radiative forcing and climate response, JGR, 102, No. D6, 6831-6864.

  20. Analysis of the polar amplification pattern of global warming on an aquaplanet in "ghost forcing" experiments with no ice-albedo feedbacks

    NASA Astrophysics Data System (ADS)

    Alexeev, V. A.; Langen, P. L.

    2004-05-01

    Non-ice-albedo feedback mechanisms leading to polar amplification, as reported by Alexeev (2003), are explored in three aquaplanet climate model systems of different complexity. We analyze this pattern using three different "ghost forcing" experiments (Hansen et al, 1997). In the first one we uniformly add 4W/m2 to the oceanic mixed layer in order to roughly simulate a 2xCO2 forcing at the surface. The second forcing, of the same magnitude, is applied only within the tropics and the third forcing is applied only polewards of 30 degrees (north and south). It turns out that our systems' equilibrium responses are linear with respect to these forcings. Surprisingly, the response to the tropical-only forcing is essentially non-local with quite significant warming at higher latitudes. The response to the high-latitude-only forcing is more local and has higher amplitude near the poles. Our explanation of the polar amplification obtained in the uniform forcing experiment is therefore two-fold. Firstly, the tropics are much more difficult to warm because of the higher sensitivity of the surface budget to SST changes at higher temperatures. Secondly, any extra heat deposited in the tropics is not easily radiated to outer space because of the high opaqueness of the tropical atmosphere. The energy, most of which is latent, needs to be redistributed by transports to the extra-tropics. Consequently, the tropical "ghost forcing" results in an essentially non-local response, while the extra-tropical one yields a more localized response, because the energy in the atmosphere cannot propagate effectively equator-wards from high latitudes. The paper deals with these mechanisms in three climate model systems with no ice-albedo feedback - an EBM and two different GCMs - one with cloud feedbacks and the other with cloud feedbacks excluded. References. Alexeev, V.A., (2003) Sensitivity to CO2 doubling of an atmospheric GCM coupled to an oceanic mixed layer: a linear analysis. Climate Dynamics, 20: p.775-787. Hansen, J., Sato M, and R. Ruedy, (1997) Radiative forcing and climate response, JGR, 102, No. D6, 6831-6864.

  1. The effect of fringe fields from patterned magnetic domains on the electroluminescence of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas J.; Wohlgennant, Markus; Flatté, Michael E.

    2016-10-01

    Large magnetic field effects, either in conduction or luminescence, have been observed in organic light-emitting diodes (OLEDs) for over a decade now. The physical processes are largely understood when exciton formation and recombination lead to the magnetic field effects. Recently, magnetic field effects in some co-evaporated blends have shown that exciplexes deliver even larger responses. In either case, the magnetic field effects arise from some spin-mixing mechanism and spin-selective processes in either the exciton formation or the exciplex recombination. Precise control of light output is not possible when the spin mixing is either due to hyper-fine fields or differences in the Lande g-factor. We theoretically examine the optical output when a patterned magnetic film is deposited near the OLED. The fringe fields from the magnetic layers supply an additionally source of spin mixing that can be easily controlled. In the absence of other spin mixing mechanisms, the luminescence from exciplexes can be modified by 300%. When other spin-mixing mechanisms are present, fringe fields from remanent magnetic states act as a means to either boost or reduce light emission from those mechanisms. Lastly, we examine the influence of spin decoherence on the optical output.

  2. Total Mercury and Methylmercury Response in Water, Sediment, and Biota to Destratification of the Great Salt Lake, Utah, United States.

    PubMed

    Valdes, Carla; Black, Frank J; Stringham, Blair; Collins, Jeffrey N; Goodman, James R; Saxton, Heidi J; Mansfield, Christopher R; Schmidt, Joshua N; Yang, Shu; Johnson, William P

    2017-05-02

    Measurements of chemical and physical parameters made before and after sealing of culverts in the railroad causeway spanning the Great Salt Lake in late 2013 documented dramatic alterations in the system in response to the elimination of flow between the Great Salt Lake's north and south arms. The flow of denser, more-saline water through the culverts from the north arm (Gunnison Bay) to the south arm (Gilbert Bay) previously drove the perennial stratification of the south arm and the existence of oxic shallow brine and anoxic deep brine layers. Closure of the causeway culverts occurred concurrently with a multiyear drought that resulted in a decrease in the lake elevation and a concomitant increase in top-down erosion of the upper surface of the deep brine layer by wind-forced mixing. The combination of these events resulted in the replacement of the formerly stratified water column in the south arm with one that was vertically homogeneous and oxic. Total mercury concentrations in the deep waters of the south arm decreased by approximately 81% and methylmercury concentrations in deep waters decreased by roughly 86% due to destratification. Methylmercury concentrations decreased by 77% in underlying surficial sediment, whereas there was no change observed in total mercury. The dramatic mercury loss from deep waters and methylmercury loss from underlying sediment in response to causeway sealing provides new understanding of the potential role of the deep brine layer in the accumulation and persistence of methylmercury in the Great Salt Lake. Additional mercury measurements in biota appear to contradict the previously implied connection between elevated methylmercury concentrations in the deep brine layer and elevated mercury in avian species reported prior to causeway sealing.

  3. Streaked X Ray Spectra from Polar Direct Drive Capsules with an Equatorial Defect

    NASA Astrophysics Data System (ADS)

    Murphy, T. J.; Bradley, P. A.; Cobble, J. A.; Hsu, S. C.; Krasheninnikova, N. S.; Magelssen, G. R.; Schmitt, M. J.; Tregillis, I. L.; Wysocki, F. J.

    2011-10-01

    In the Defect Implosion Experiment (DIME) on Omega, capsules with an equatorial ``trench'' defect have been imploded to study defect-induced mix processes. The capsules contain layers doped with titanium and/or vanadium, with doped layers in contact with the deuterium fill gas on some targets, and separated from the gas by a layer of undoped plastic in others. Streaked x-ray spectra from the capsule implosions provide information on conditions in the mix layer. Polar direct drive was utilized in preparation for experiments planned for the National Ignition Facility in 2012. This work is supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under contract DE-AC52-06NA25396.

  4. Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Debarati; Basu, Saibal; Singh, Surendra; Roy, Sumalay; Dev, Bhupendra Nath

    2012-12-01

    Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni-Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

  5. Rayleigh-Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. I

    NASA Astrophysics Data System (ADS)

    Zhou, Ye

    2017-12-01

    Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities play an important role in a wide range of engineering, geophysical, and astrophysical flows. They represent a triggering event that, in many cases, leads to large-scale turbulent mixing. Much effort has been expended over the past 140 years, beginning with the seminal work of Lord Rayleigh, to predict the evolution of the instabilities and of the instability-induced mixing layers. The objective of Part I of this review is to provide the basic properties of the flow, turbulence, and mixing induced by RT, RM, and Kelvin-Helmholtz (KH) instabilities. Historical efforts to study these instabilities are briefly reviewed, and the significance of these instabilities is discussed for a variety of flows, particularly for astrophysical flows and for the case of inertial confinement fusion. Early experimental efforts are described, and analytical attempts to model the linear, and nonlinear regimes of these mixing layers are examined. These analytical efforts include models for both single-mode and multi-mode initial conditions, as well as multi-scale models to describe the evolution. Comparisons of these models and theories to experimental and simulation studies are then presented. Next, attention is paid to the issue of the influence of stabilizing mechanisms (e.g., viscosity, surface tension, and diffuse interface) on the evolution of these instabilities, as well as the limitations and successes of numerical methods. Efforts to study these instabilities and mixing layers using group-theoretic ideas, as well as more formal notions of turbulence cascade processes during the later stages of the induced mixing layers, are inspected. A key element of the review is the discussion of the late-time self-similar scaling for the RT and RM growth factors, α and θ. These parameters are influenced by the initial conditions and much of the observed variation can be explained by this. In some cases, these instabilities induced flows can transition to turbulence. Both the spatial and temporal criteria to achieve the transition to turbulence have been examined. Finally, a description of the energy-containing scales in the mixing layers, including energy "injection" and cascade processes are presented in greater detail. Part II of this review is designed to provide a much broader and in-depth understanding of this critical area of research (Zhou, 2017. Physics Reports, 723-725, 1-160).

  6. The dependence of entrainment and drizzle in marine stratiform clouds on biomass burning aerosols derived from stable isotope and thermodynamic profiles

    NASA Astrophysics Data System (ADS)

    Henze, D.; Noone, D.

    2017-12-01

    A third of the world's biomass burning aerosol (BBA) particles are generated in southern Africa, and these particles are swept into the midlevel troposphere over the southeast Atlantic Ocean. The presence of these aerosols over the marine environment of the south east Atlantic offers a unique natural laboratory for studying aerosol effects on climate, and specifically a modification to the hydrologic cycle and microphysical characteristics of clouds. Different rates of condensation with high aerosol numbers change the precipitation rates in drizzling stratiform clouds, while the mixing of aerosols into the cloud layer is synonymous with entrainment from above cloud top near the top of the subtropical inversion. To better understanding the magnitude of the aerosol influence on southeast Atlantic boundary layer clouds we analyze the cloud-top entrainment and drizzle as a function of aerosol loading to determine the impact of BBA. Entrainment was determined from mixing line analysis based on profile measurements of moist static energy, total water, and the two most common heavy isotopes of water - HDO and H218O. Data was collected on the P-3 Orion aircraft during the NASA 2017 ORACLES campaign. Using these measurements, a box model was constructed using the combined conservation laws associated with all four of these quantities to estimate the entrainment and rainout of cloud liquid. The population of profiles sampled by the aircraft over the course of the 30 day mission spans varying concentrations of BBA. Initial plots of the water isotope mixing lines show where and to what degree the BBA air mass has mixed into the boundary layer air mass from above. This is demonstrated by the fact that the mixing end-members are the same for the different areas sampled, but the rate at which the various mixing lines are traversed as a function of altitude varies. Further, the mixing lines as a function of height traverse back and forth between end members multiple times over one profile. This suggests that air masses are mixing by `layering' into each other, and helps us to better represent entrainment in our box model. Meanwhile, isotope ratios measured below vs above the cloud layer show that the air above the clouds is depleted of heavy water isotopes in comparison to below - the degree of depletion could correspond to drizzle amount.

  7. Spatiotemporal structure of wind farm-atmospheric boundary layer interactions

    NASA Astrophysics Data System (ADS)

    Cervarich, Matthew; Baidya Roy, Somnath; Zhou, Liming

    2013-04-01

    Wind power is currently one of the fastest growing energy sources in the world. Most of the growth is in the utility sector consisting of large wind farms with numerous industrial-scale wind turbines. Wind turbines act as a sink of mean kinetic energy and a source of turbulent kinetic energy in the atmospheric boundary layer (ABL). In doing so, they modify the ABL profiles and land-atmosphere exchanges of energy, momentum, mass and moisture. This project explores theses interactions using remote sensing data and numerical model simulations. The domain is central Texas where 4 of the world's largest wind farms are located. A companion study of seasonally-averaged Land Surface Temperature data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on TERRA and AQUA satellites shows a warming signal at night and a mixed cooling/warming signal during the daytime within the wind farms. In the present study, wind farm-ABL interactions are simulated with the Weather Research and Forecasting (WRF) model. The simulations show that the model is capable of replicating the observed signal in land surface temperature. Moreover, similar warming/cooling effect, up to 1C, was observed in seasonal mean 2m air temperature as well. Further analysis show that enhanced turbulent mixing in the rotor wakes is responsible for the impacts on 2m and surface air temperatures. The mixing is due to 2 reasons: (i) turbulent momentum transport to compensate the momentum deficit in the wakes of the turbines and (ii) turbulence generated due to motion of turbine rotors. Turbulent mixing also alters vertical profiles of moisture. Changes in land-atmosphere temperature and moisture gradient and increase in turbulent mixing leads to more than 10% change in seasonal mean surface sensible and latent heat flux. Given the current installed capacity and the projected installation across the world, wind farms are likely becoming a major driver of anthropogenic land use change on Earth. Hence, understanding WF-ABL interactions and its effects is of significant scientific and societal importance.

  8. Resilient modulus and the fatigue properties of Kansas hot mix asphalt mixes

    DOT National Transportation Integrated Search

    2006-08-01

    This research study aimed to determine the dynamic modulus, bending stiffness and fatigue properties of four representative Superpave Hot Mix Asphalt (HMA) mixtures used in the construction of base layers of Kansas flexible pavements and to compare t...

  9. Natural remanent magnetization acquisition in bioturbated sediment: General theory and implications for relative paleointensity reconstructions

    NASA Astrophysics Data System (ADS)

    Egli, R.; Zhao, X.

    2015-04-01

    We present a general theory for the acquisition of natural remanent magnetizations (NRM) in sediment under the influence of (a) magnetic torques, (b) randomizing torques, and (c) torques resulting from interaction forces. Dynamic equilibrium between (a) and (b) in the water column and at the sediment-water interface generates a detrital remanent magnetization (DRM), while much stronger randomizing torques may be provided by bioturbation inside the mixed layer. These generate a so-called mixed remanent magnetization (MRM), which is stabilized by mechanical interaction forces. During the time required to cross the surface mixed layer, DRM is lost and MRM is acquired at a rate that depends on bioturbation intensity. Both processes are governed by a MRM lock-in function. The final NRM intensity is controlled mainly by a single parameter γ that is defined as the product of rotational diffusion and mixed-layer thickness, divided by sedimentation rate. This parameter defines three regimes: (1) slow mixing (γ < 0.2) leading to DRM preservation and insignificant MRM acquisition, (2) fast mixing (γ > 10) with MRM acquisition and full DRM randomization, and (3) intermediate mixing. Because the acquisition efficiency of DRM is larger than that of MRM, NRM intensity is particularly sensitive to γ in case of mixed regimes, generating variable NRM acquisition efficiencies. This model explains (1) lock-in delays that can be matched with empirical reconstructions from paleomagnetic records, (2) the existence of small lock-in depths that lead to DRM preservation, (3) specific NRM acquisition efficiencies of magnetofossil-rich sediments, and (4) some relative paleointensity artifacts.

  10. Double layer mixed matrix membrane adsorbers improving capacity and safety hemodialysis

    NASA Astrophysics Data System (ADS)

    Saiful; Borneman, Z.; Wessling, M.

    2018-05-01

    Double layer mixed matrix membranes adsorbers have been developed for blood toxin removal by embedding activated carbon into cellulose acetate macroporous membranes. The membranes are prepared by phase inversion method via water vapor induced phase separation followed by an immersion precipitation step. Double layer MMM consisting of an active support and a separating layer. The active support layer consists of activated carbon particles embedded in macroporous cellulose acetate; the separating layer consists of particle free cellulose acetate. The double layer membrane possess an open and interconnected macroporous structure with a high loading of activated carbon available for blood toxins removal. The MMM AC has a swelling degree of 6.5 %, porosity of 53 % and clean water flux of 800 Lm-2h-1bar-1. The prepared membranes show a high dynamic Creatinine (Crt) removal during hemodilysis process. The Crt removal by adsorption contributes to amore than 83 % of the total removal. The double layer adsorptive membrane proves hemodialysis membrane can integrated with adsorption, in which blood toxins are removed in one step.

  11. Controlling the surface‐mediated release of DNA using ‘mixed multilayers’

    PubMed Central

    Appadoo, Visham; Carter, Matthew C. D.

    2016-01-01

    Abstract We report the design of erodible ‘mixed multilayer’ coatings fabricated using plasmid DNA and combinations of both hydrolytically degradable and charge‐shifting cationic polymer building blocks. Films fabricated layer‐by‐layer using combinations of a model poly(β‐amino ester) (polymer 1) and a model charge‐shifting polymer (polymer 2) exhibited DNA release profiles that were substantially different than those assembled using DNA and either polymer 1 or polymer 2 alone. In addition, the order in which layers of these two cationic polymers were deposited during assembly had a profound impact on DNA release profiles when these materials were incubated in physiological buffer. Mixed multilayers ∼225 nm thick fabricated by depositing layers of polymer 1/DNA onto films composed of polymer 2/DNA released DNA into solution over ∼60 days, with multi‐phase release profiles intermediate to and exhibiting some general features of polymer 1/DNA or polymer 2/DNA films (e.g., a period of rapid release, followed by a more extended phase). In sharp contrast, ‘inverted’ mixed multilayers fabricated by depositing layers of polymer 2/DNA onto films composed of polymer 1/DNA exhibited release profiles that were almost completely linear over ∼60‐80 days. These and other results are consistent with substantial interdiffusion and commingling (or mixing) among the individual components of these compound materials. Our results reveal this mixing to lead to new, unanticipated, and useful release profiles and provide guidance for the design of polymer‐based coatings for the local, surface‐mediated delivery of DNA from the surfaces of topologically complex interventional devices, such as intravascular stents, with predictable long‐term release profiles. PMID:27981243

  12. Natural remananent magnetization acquisition through sediment mixing: theory and implications for relative paleointensity

    NASA Astrophysics Data System (ADS)

    Egli, Ramon; Zhao, Xiangyu

    2015-04-01

    We present a general theory on the acquisition of natural remanent magnetizations (NRM) in sediment under the influence of (a) magnetic torques, (b) randomizing torques (e.g. from bioturbation), and (c) torques resulting from interaction forces between remanence carriers and other particles. Dynamic equilibrium between (a) and (b) in the water column and sediment-water interface produce a detrital remanent magnetization (DRM), while much stronger randomizing forces occur in the mixed layer of sediment due to bioturbation forces. These generate a so-called mixing remanent magnetization (MRM), which is stabilized by interaction forces. During the time required to cross the mixed layer, DRM is lost and MRM is acquired at a rate that depends on bioturbation intensity. Both processes are governed by the same MRM lock-in function. The final NRM intensity is controlled mainly by a single parameter defined as the product of rotational diffusion constant and mixed layer thickness, divided by the sedimentation rate. This parameter defines three regimes: (1) slow mixing, leading to DRM preservation and insignificant MRM acquisition, (2) fast mixing with MRM acquisition and full randomization of the original DRM, and (3) intermediate mixing. Because the acquisition efficiency of DRM is expectedly larger than that of a MRM, MRM is particularly sensitive to the mixing rate in case of intermediate regimes, and generates variable NRM acquisition efficiencies. Our model explains (1) lock-in delays that can be matched with empirical reconstructions from paleomagnetic records, (2) the existence of small lock-in depths leading to DRM preservation, (3) NRM acquisition efficiencies of magnetofossil-rich sediments, and (4) relative paleointensity artifacts reported in some recent studies.

  13. Fabrication of nanostructures and nanostructure based interfaces for biosensor application

    NASA Astrophysics Data System (ADS)

    Srivastava, Devesh

    Nanoparticles have applications from electronics, composites, drug-delivery, imaging and sensors etc. Fabricating and controlling shape and size of nanoparticles and also controlling the positioning of these particles in 1, 2 or 3-d structures is of most interest. The underlying theme of this study is to develop simple and efficient techniques to fabricate nanoparticles from polymers, and also achieve control in shape, size and functionalization of nanoparticles, while applying them in biosensor applications. First part of the dissertation studies the fabrication of nanostructures using anodized alumina membrane as template. It discusses the fabrication design for injecting polystyrene nanoparticles inside the pores of anodized alumina membranes and heating the membrane to coalesce the particles into tapered nanoparticles. Various parameters like temperature and amount of injected particles can vary the size and shape of fabricated nanoparticles. Later it focuses on the fabrication of metallic nanostructures using the alumina membranes without the aid of the injection system. It utilizes the difference in the functionality of the pore edges of cleaved alumina membrane with respect to the pore walls to first deposit charged polymers using layer-by-layer deposition followed by deposition of nickel. Second part of this study involves immobilization of enzymes for biosensor applications. It describes a biosensor interface developed by immobilization of tyrosinase using layer-by-layer (LBL) deposition process. The interface was modified with functional nanoparticles and their influence on the response of biosensor was studied. Tyrosinase sensor was further extended to develop a novel biosensor which was used to study real time inhibition of NEST, a subunit of the medically relevant membrane protein, neuropathy target esterase. The biosensor was developed to give real time monitoring of dose dependent decrease in activity of NEST. Final part of this study emphasizes on the influence of high shear rate mixer from PRIMIX, Japan on polymer particle formation. This mixer can process specific volume of liquid and subject it to high shear conditions. The mixing geometry consists of concentric cylinders, 52 mm inner turbine diameter and 58 mm vessel diameter, with inner turbine rotating at high peripheral speeds ranging from 10 m/s to 50m/s. The mixing is in turbulent regime at all the speeds. Poly-lactic acid (PLA) nanoparticles were fabricated by nanoprecipitation and emulsion diffusion process. Nanoprecipitation process was independent of shear rate at low mixing speeds and particle size went up at high speeds due to coalescence of PLA particles. Emulsion diffusion was done by making oil in water emulsion. PLA dissolved in ethyl acetate was used as oil phase. It was followed by diffusion of ethyl acetate in excess amount of DI water. It followed expected trend of smaller size at high mixing speeds but was very sensitive to mixing time where particles coalesced at longer time duration. The influence of viscosity was also studied and particles changed shape from spherical nanoparticles to micron sized open shells at high viscosity and high mixing speeds due to heating combined with mixing occurring in viscous turbulent regime.

  14. Vertical distribution and composition of phytoplankton under the influence of an upper mixed layer.

    PubMed

    Ryabov, Alexei B; Rudolf, Lars; Blasius, Bernd

    2010-03-07

    The vertical distribution of phytoplankton is of fundamental importance for the dynamics and structure of aquatic communities. Here, using an advection-reaction-diffusion model, we investigate the distribution and competition of phytoplankton species in a water column, in which inverse resource gradients of light and a nutrient can limit growth of the biomass. This problem poses a challenge for ecologists, as the location of a production layer is not fixed, but rather depends on many internal parameters and environmental factors. In particular, we study the influence of an upper mixed layer (UML) in this system and show that it leads to a variety of dynamic effects: (i) Our model predicts alternative density profiles with a maximum of biomass either within or below the UML, thereby the system may be bistable or the relaxation from an unstable state may require a long-lasting transition. (ii) Reduced mixing in the deep layer can induce oscillations of the biomass; we show that a UML can sustain these oscillations even if the diffusivity is less than the critical mixing for a sinking phytoplankton population. (iii) A UML can strongly modify the outcome of competition between different phytoplankton species, yielding bistability both in the spatial distribution and in the species composition. (iv) A light limited species can obtain a competitive advantage if the diffusivity in the deep layers is reduced below a critical value. This yields a subtle competitive exclusion effect, where the oscillatory states in the deep layers are displaced by steady solutions in the UML. Finally, we present a novel graphical approach for deducing the competition outcome and for the analysis of the role of a UML in aquatic systems. 2009 Elsevier Ltd. All rights reserved.

  15. The Summertime Arctic Atmosphere: Meteorological Measurements during the Arctic Ocean Experiment 2001.

    NASA Astrophysics Data System (ADS)

    Tjernström, Michael; Leck, Caroline; Persson, P. Ola G.; Jensen, Michael L.; Oncley, Steven P.; Targino, Admir

    2004-09-01

    An atmospheric boundary layer experiment into the high Arctic was carried out on the Swedish ice-breaker Oden during the summer of 2001, with the primary boundary layer observations obtained while the icebreaker drifted with the ice near 89°N during 3 weeks in August. The purposes of the experiment were to gain an understanding of atmospheric boundary layer structure and transient mixing mechanisms, in addition to their relationships to boundary layer clouds and aerosol production. Using a combination of in situ and remote sensing instruments, with temporal and spatial resolutions previously not deployed in the Arctic, continuous measurements of the lower-troposphere structure and boundary layer turbulence were taken concurrently with atmospheric gas and particulate chemistry, and marine biology measurements.The boundary layer was strongly controlled by ice thermodynamics and local turbulent mixing. Near-surface temperatures mostly remained between near the melting points of the sea- and freshwater, and near-surface relative humidity was high. Low clouds prevailed and fog appeared frequently. Visibility outside of fog was surprisingly good even with very low clouds, probably due to a lack of aerosol particles preventing the formation of haze. The boundary layer was shallow but remained well mixed, capped by an occasionally very strong inversion. Specific humidity often increased with height across the capping inversion.In contrast to the boundary layer, the free troposphere often retained its characteristics from well beyond the Arctic. Elevated intrusions of warm, moist air from open seas to the south were frequent. The picture that the Arctic atmosphere is less affected by transport from lower latitudes in summer than the winter may, thus, be an artifact of analyzing only surface measurements. The transport of air from lower latitudes at heights above the boundary layer has a major impact on the Arctic boundary layer, even very close to the North Pole. During a few week-long periods synoptic-scale weather systems appeared, while weaker and shallower mesoscale fronts were frequent. While frontal passages changed the properties of the free troposphere, changes in the boundary layer were more determined by local effects that often led to changes contrary to those aloft. For example, increasing winds associated with a cold front often led to a warming of the near-surface air by mixing and entrainment.

  16. Effect of N2 annealing on AlZrO oxide

    NASA Astrophysics Data System (ADS)

    Pétry, J.; Richard, O.; Vandervorst, W.; Conard, T.; Chen, J.; Cosnier, V.

    2003-07-01

    In the path to the introduction of high-k dielectric into integrated circuit components, a large number of challenges has to be solved. Subsequent to the film deposition, the high-k film is exposed to additional high-temperature anneals for polycrystalline Si activation but also to improve its own electrical properties. Hence, concerns can be raised regarding the thermal stability of these stacks upon annealing. In this study, we investigated the effect of N2 annealing (700 to 900 °C) of atomic layer chemical vapor deposition AlZrO layers using x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The effect of the Si surface preparation [H-Si, 0.5 nm rapid thermal oxide (RTO), Al2O3] on the modification of the high-k oxide and the interfacial layer upon annealing was also analyzed. Compositional changes can be observed for all temperature and surface preparations. In particular, we observe a segregation of Al(oxide) toward the surface of the mixed oxide. In addition, an increase of the Si concentration in the high-k film itself can be seen with a diffusion profile extending toward the surface of the film. On the other hand, the modification of the interfacial layer is strongly dependent on the system considered. In the case of mixed oxide grown on 0.5 nm RTO, no differences are observed between the as-deposited layer and the layer annealed at 700 °C. At 800 °C, a radical change occurs: The initial RTO layer seems to be converted into a mixed layer composed of the initial SiO2 and Al2O3 coming from the mixed oxide, however without forming an Al-silicate layer. A similar situation is found for anneals at 900 °C, as well. When grown on 1.5 nm Al2O3 on 0.5 nm RTO, the only difference with the previous system is the observation of an Al-silicate fraction in the interfacial layer for the as-deposited and 700 °C annealed samples, which disappears at higher temperatures. Finally, considering layers deposited on a H-Si surface, we observe a slight increase of the interfacial thickness after annealing at 700 °C and no further changes for a higher annealing temperature.

  17. Theory of plasmonic effects in nonlinear optics: the case of graphene

    NASA Astrophysics Data System (ADS)

    Rostami, Habib; Katsnelson, Mikhail I.; Polini, Marco; Mikhail I. Katsnelson Collaboration; Habib Rostami; Marco Polini Collaboration

    The nonlinear optical properties of two-dimensional electronic systems are beginning to attract considerable interest both in the theoretical and experimental sectors. Recent experiments on the nonlinear optical properties of graphene reveal considerably strong third harmonic generation and four-wave mixing of this single-atomic-layer electronic system. We develop a large-N theory of electron-electron interaction corrections to multi-legged Feynman diagrams describing second- and third-order nonlinear response functions. Our theory is completely general and is useful to understand all second- and third-order nonlinear effects, including harmonic generation, wave mixing, and photon drag. We apply our theoretical framework to the case of graphene, by carrying out microscopic calculations of the second- and third-order nonlinear response functions of an interacting two-dimensional gas of massless Dirac fermions. We compare our results with recent measurements, where all-optical launching of graphene plasmons has been achieved. This work was supported by Fondazione Istituto Italiano di Tecnologia, the European Union's Horizon 2020 research and innovation programme under Grant agreement No. 696656 GrapheneCore, and the ERC Advanced Grant 338957 FEMTO/NANO (M.I.K.).

  18. Charge Separation at Mixed-Dimensional Single and Multilayer MoS2/Silicon Nanowire Heterojunctions.

    PubMed

    Henning, Alex; Sangwan, Vinod K; Bergeron, Hadallia; Balla, Itamar; Sun, Zhiyuan; Hersam, Mark C; Lauhon, Lincoln J

    2018-05-16

    Layered two-dimensional (2-D) semiconductors can be combined with other low-dimensional semiconductors to form nonplanar mixed-dimensional van der Waals (vdW) heterojunctions whose charge transport behavior is influenced by the heterojunction geometry, providing a new degree of freedom to engineer device functions. Toward that end, we investigated the photoresponse of Si nanowire/MoS 2 heterojunction diodes with scanning photocurrent microscopy and time-resolved photocurrent measurements. Comparison of n-Si/MoS 2 isotype heterojunctions with p-Si/MoS 2 heterojunction diodes under varying biases shows that the depletion region in the p-n heterojunction promotes exciton dissociation and carrier collection. We measure an instrument-limited response time of 1 μs, which is 10 times faster than the previously reported response times for planar Si/MoS 2 devices, highlighting the advantages of the 1-D/2-D heterojunction. Finite element simulations of device models provide a detailed understanding of how the electrostatics affect charge transport in nanowire/vdW heterojunctions and inform the design of future vdW heterojunction photodetectors and transistors.

  19. Ocean acidification alters the photosynthetic responses of a coccolithophorid to fluctuating ultraviolet and visible radiation.

    PubMed

    Jin, Peng; Gao, Kunshan; Villafañe, Virginia E; Campbell, Douglas A; Helbling, E Walter

    2013-08-01

    Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400-700 nm) and ultraviolet radiation (UVR; 280-400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 μatm) and low, current (390 μatm) CO₂ levels, under regimes of fluctuating irradiances with or without UVR. Under both CO₂ levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO₂ showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280-315 nm)-induced inhibition. Ultraviolet A (315-400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO₂-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.

  20. Effects of Exsolution Lamellae on Magnetic Properties of Crustal Rocks and Contributions to Remanent Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    McEnroe, S. A.; Robinson, P.; Fabian, K.; Brown, L. L.; Harrison, R. J.

    2011-12-01

    Magnetic anomalies from crustal sources are measured over a wide range of scales and elevations, from near-surface to satellites. They reflect magnetic minerals in rocks, which respond to the changing planetary magnetic field. Anomalies are influenced by the geometry of the geological bodies, and magnetic properties of the minerals. Commonly, magnetism of continental crust has been described in terms of bulk ferrimagnetism of minerals, and much attributed to induced magnetization. Though remanent magnetization was crucial for dating the ocean floor, and is important in mineral exploration, its contribution to continental magnetic anomalies is commonly ignored. Over the last decade studying remanent anomalies in crustal rocks, we discovered a new type of remanence, 'lamellar magnetism'. This is due to layers of mixed Fe2+/Fe3+ valence at (001) contacts between exsolution lamellae and hosts of ilmenite and hematite. The mixed-valence contact layers are placed by chemistry between hematite Fe3+ layers and ilmenite Ti4+ layers, where they provide reduction of ionic charge imbalance. Placement requires that the uncompensated spin of contact layers on opposite sides of a lamella be in-phase magnetically. This produces a net ferrimagnetic moment per lamella of ~4 uB per formula unit, regardless of lamella thickness, thus net moment is greatest with the greatest density of magnetically in-phase fine lamellae created during slow cooling. We can show that in-phase magnetization of lamellae is greatly enhanced in foliated samples, where the statistical (001) plane is parallel to the Earth field at the time of exsolution. Strictly speaking, the resulting magnetization is a chemical remanence with very high stability. Lamellar magnetism is responsible for numerous remanent magnetic anomalies in continental rocks we present here. We highlight some bodies with NRMs > 20 A/m which are possible analogs for sources of remanent anomalies on Mars.

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