Winter ocean-ice interactions under thin sea ice observed by IAOOS platforms during N-ICE2015: Salty surface mixed layer and active basal melt

NASA Astrophysics Data System (ADS)

Koenig, Zoé; Provost, Christine; Villacieros-Robineau, Nicolas; Sennéchael, Nathalie; Meyer, Amelie

2016-10-01

IAOOS (Ice Atmosphere Arctic Ocean Observing System) platforms, measuring physical parameters at the atmosphere-snow-ice-ocean interface deployed as part of the N-ICE2015 campaign, provide new insights on winter conditions North of Svalbard. The three regions crossed during the drifts, the Nansen Basin, the Sofia Deep, and the Svalbard northern continental slope featured distinct hydrographic properties and ice-ocean exchanges. In the Nansen Basin, the quiescent warm layer was capped by a stepped halocline (60 and 110 m) and a deep thermocline (110 m). Ice was forming and the winter mixed layer salinity was larger by ˜0.1 g/kg than previously observed. Over the Svalbard continental slope, the Atlantic Water (AW) was very shallow (20 m from the surface) and extended offshore from the 500 m isobath by a distance of about 70 km, sank along the slope (40 m from the surface) and probably shed eddies into the Sofia Deep. In the Sofia Deep, relatively warm waters of Atlantic origin extended from 90 m downward. Resulting from different pathways, these waters had a wide range of hydrographic characteristics. Sea-ice melt was widespread over the Svalbard continental slope and ocean-to-ice heat fluxes reached values of 400 W m-2 (mean of ˜150 W m-2 over the continental slope). Sea-ice melt events were associated with near 12 h fluctuations in the mixed-layer temperature and salinity corresponding to the periodicity of tides and near-inertial waves potentially generated by winter storms, large barotropic tides over steep topography, and/or geostrophic adjustments.

A two-dimensional ocean model for long-term climatic simulations: Stability and coupling to atmospheric and sea ice models

NASA Astrophysics Data System (ADS)

Harvey, L. D. Danny

1992-06-01

A two-dimensional (latitude-depth) deep ocean model is presented which is coupled to a sea ice model and an Energy Balance Climate Model (EBCM), the latter having land-sea and surface-air resolution. The processes which occur in the ocean model are thermohaline overturning driven by the horizontal density gradient, shallow wind-driven overturning cells, convective overturning, and vertical and horizontal diffusion of heat and salt. The density field is determined from the temperature and salinity fields using a nonlinear equation of state. Mixed layer salinity is affected by evaporation, precipitation, runoff from continents, and sea ice freezing and melting, as well as by advective, convective, and diffusive exchanges with the deep ocean. The ocean model is first tested in an uncoupled mode, in which hemispherically symmetric mixed layer temperature and salinity, or salinity flux, are specified as upper boundary conditions. An experiment performed with previous models is repeated in which a mixed layer salinity perturbation is introduced in the polar half of one hemisphere after switching from a fixed salinity to a fixed salinity flux boundary condition. For small values of the vertical diffusion coefficient KV, the model undergoes self-sustained oscillations with a period of about 1500 years. With larger values of KV, the model locks into either an asymmetric mode with a single overturning cell spanning both hemispheres, or a symmetric quiescent state with downwelling near the equator, upwelling at high latitudes, and a warm deep ocean (depending on the value of KV). When the ocean model is forced with observed mixed layer temperature and salinity, no oscillations occur. The model successfully simulates the very weak meridional overturning and strong Antarctic Circumpolar Current at the latitudes of the Drake Passage. The coupled EBCM-deep ocean model displays internal oscillations with a period of 3000 years if the ocean fraction is uniform with latitude and KV and the horizontal diffusion coefficient in the mixed layer are not too large. Globally averaged atmospheric temperature changes of 2 K are driven by oscillations in the heat flux into or out of the deep ocean, with the sudden onset of a heat flux out of the deep ocean associated with the rapid onset of thermohaline overturning after a quiescent period, and the sudden onset of a heat flux into the deep ocean associated with the collapse of thermohaline overturning. When the coupled model is run with prescribed parameters (such as land-sea fraction and precipitation) varying with latitude based on observations, the model does not oscillate and produces a reasonable deep ocean temperature field but a completely unrealistic salinity field. Resetting the mixed layer salinity to observations on each time step (equivalent to the "flux correction" method used in atmosphere-ocean general circulation models) is sufficient to give a realistic salinity field throughout the ocean depth, but dramatically alters the flow field and associated heat transport. Although the model is highly idealized, the finding that the maximum perturbation in globally averaged heat flux from the deep ocean to the surface over a 100-year period is 1.4 W m-2 suggests that effect of continuing greenhouse gas increases, which could result in a heating perturbation of 10 W m-2 by the end of the next century, will swamp possible surface heating perturbations due to changes in oceanic circulation. On the other hand, the extreme sensitivity of the oceanic flow field to variations in precipitation and evaporation suggests that it will not be possible to produce accurate projections of regional climatic change in the near term, if at all.

Seasonal Variation of Barrier Layer in the Southern Ocean

NASA Astrophysics Data System (ADS)

Pan, Li; Zhong, Yisen; Liu, Hailong; Zhou, Lei; Zhang, Zhaoru; Zhou, Meng

2018-03-01

The seasonal variability of barrier layer (BL) and its formation mechanism in the Southern Ocean are investigated using the most recent Argo data. The results reveal that the BL is a persistent feature in the Southern Ocean with a strong seasonal cycle. The thickest BL appears in winter with the maximum amplitude exceeding 250 m while it dramatically decreases to less than 50 m in summer. The spatial distribution of BL is zonally oriented in the Pacific and Indian Ocean sectors, which is in agreement with that of the mixed layer depth (MLD) and the isothermal layer depth (ILD). Two areas with the most prominent BL are identified. One is located south of Australia and the other in the southeastern Pacific. The BL formation in both areas is generally attributed to a shallow mixed layer controlled by surface freshwater intrusion and a deep isothermal layer modulated by seasonal vertical convection. In the former region, the cold and fresh Antarctic Surface Water (ASW) is transported northward across the Subantarctic Front (SAF) by the Ekman effect and overlies the warm Subantarctic Mode Water (SAMW). The resulting inverse temperature structure facilitates the development of thick BLs. In the latter region, the BL emerges in the ventilation area where the shallow Surface Salinity Minimum Water (SSMW) coming from north leans against the deep vertical isotherms. In summer, positive surface heat flux into the ocean overwhelms other thermodynamic effects in the mixed layer heat budget. The MLD and ILD coincide and thus the BL is destroyed.

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.

The Sinking and Spreading of The Antarctic Deep Ice Shelf Water In The Ross Sea Studied By In Situ Observaions and Numerical Modeling

NASA Astrophysics Data System (ADS)

Rubino, A.; Budillon, G.; Pierini, S.; Spezie, G.

The sinking and spreading of the Deep Ice Shelf Water (DISW) in the Ross Sea are analyzed using in situ observations and the results of a nonlinear, reduced-gravity, frontal layered numerical "plume" model which is able to simulate the motion of a bottom-arrested current over realistic topography. The model is forced by prescribing the thickness of the DISW vein as well as its density structure at the southern model boundary. The ambient temperature and salinity are imposed using hydrographic data acquired by the Italian PNRA-CLIMA project. In the model water of the quiescent ambient ocean is allowed to entrain in the active deep layer due to a simple param- eterization of turbulent mixing. The importance of forcing the model with a realistic ambient density is demonstrated by carrying out a numerical simulation in which the bottom active layer is forced using an idealized ambient density. In a more realis- tic simulation the path and the density structure of the DISW vein flowing over the Challenger Basin are obtained and are found to be in good agreement with data. The evolution of the deep current beyond the continental shelf is also simulated. It provides useful information on the water flow and mixing in a region of the Ross Sea where the paucity of experimental data does not allow for a detailed description of the deep ocean dynamics.

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.

Seasonal Variation of Submesoscale Flow Features in a Mesoscale Eddy-dominant Region in the East Sea

NASA Astrophysics Data System (ADS)

Chang, Yeon S.; Choi, Byoung-Ju; Park, Young-Gyu

2018-03-01

Seasonal changes in the distribution of submesoscale (SM) flow features were examined using a fine-resolution numerical simulation. The SM flows are expected to be strong where mesoscale (MS) eddies actively develop and also when the mixed layer depth (MLD) is deep due to enhanced baroclinic instability. In the East Sea (ES), MS eddies more actively develop in summer while the MLD is deeper in winter, which provided the motivation to conduct this study to test the effects of MLD and MS eddies on the SM activity in this region. Finite-scale Liapunov exponents and the vertical velocity components were employed to analyze the SM activities. It was found that the SM intensity was marked by seasonality: it is stronger in winter when the mixed layer is deep but weaker in summer - despite the greater eddy kinetic energy. This is because in summer the mixed layer is so thin that there is not enough available potential energy. When the SM activity was quantified based on parameterization, (MLD × density gradient), it was determined that the seasonal variation of MLD plays a more important role than the lateral density gradient variation on SM flow motion in the ES.

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.

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

Spatial patterns of mixing in the Solomon Sea

NASA Astrophysics Data System (ADS)

Alberty, M. S.; Sprintall, J.; MacKinnon, J.; Ganachaud, A.; Cravatte, S.; Eldin, G.; Germineaud, C.; Melet, A.

2017-05-01

The Solomon Sea is a marginal sea in the southwest Pacific that connects subtropical and equatorial circulation, constricting transport of South Pacific Subtropical Mode Water and Antarctic Intermediate Water through its deep, narrow channels. Marginal sea topography inhibits internal waves from propagating out and into the open ocean, making these regions hot spots for energy dissipation and mixing. Data from two hydrographic cruises and from Argo profiles are employed to indirectly infer mixing from observations for the first time in the Solomon Sea. Thorpe and finescale methods indirectly estimate the rate of dissipation of kinetic energy (ɛ) and indicate that it is maximum in the surface and thermocline layers and decreases by 2-3 orders of magnitude by 2000 m depth. Estimates of diapycnal diffusivity from the observations and a simple diffusive model agree in magnitude but have different depth structures, likely reflecting the combined influence of both diapycnal mixing and isopycnal stirring. Spatial variability of ɛ is large, spanning at least 2 orders of magnitude within isopycnal layers. Seasonal variability of ɛ reflects regional monsoonal changes in large-scale oceanic and atmospheric conditions with ɛ increased in July and decreased in March. Finally, tide power input and topographic roughness are well correlated with mean spatial patterns of mixing within intermediate and deep isopycnals but are not clearly correlated with thermocline mixing patterns.

Interface dissolution control of the 14C profile in marine sediment

USGS Publications Warehouse

Keir, R.S.; Michel, R.L.

1993-01-01

The process of carbonate dissolution at the sediment-water interface has two possible endmember boundary conditions. Either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation (interface dissolution), or the vertical mixing is rapid relative to their extermination rate (homogeneous dissolution). In this study, a detailed radiocarbon profile was determined in deep equatorial Pacific sediment that receives a high rate of carbonate supply. In addition, a box model of sediment mixing was used to simulate radiocarbon, carbonate content and excess thorium profiles that result from either boundary process following a dissolution increase. Results from homogeneous dissolution imply a strong, very recent erosional event, while interface dissolution suggests that moderately increased dissolution began about 10,000 years ago. In order to achieve the observed mixed layer radiocarbon age, increased homogeneous dissolution would concentrate a greater amount of clay and 230Th than is observed, while for interface dissolution the predicted concentrations are too small. These results together with small discontinuities beneath the mixed layer in 230Th profiles suggest a two-stage increase in interface dissolution in the deep Pacific, the first occurring near the beginning of the Holocene and the second more recently, roughly 5000 years ago. ?? 1993.

Crop response to deep tillage - a meta-analysis

NASA Astrophysics Data System (ADS)

Schneider, Florian; Don, Axel; Hennings, Inga; Schmittmann, Oliver; Seidel, Sabine J.

2017-04-01

Subsoil, i.e. the soil layer below the topsoil, stores tremendous stocks of nutrients and can keep water even under drought conditions. Deep tillage may be a method to enhance the plant-availability of subsoil resources. However, in field trials, deep tillage effects on crop yields were inconsistent. Therefore, we conducted a meta-analysis of crop yield response to subsoiling, deep ploughing and deep mixing of soil profiles. Our search resulted in 1530 yield comparisons following deep and conventional control tillage on 67 experimental cropping sites. The vast majority of the data derived from temperate latitudes, from trials conducted in the USA (679 observations) and Germany (630 observations). On average, crop yield response to deep tillage was slightly positive (6% increase). However, individual deep tillage effects were highly scattered including about 40% yield depressions after deep tillage. Deep tillage on soils with root restrictive layers increased crop yields about 20%, while soils containing >70% silt increased the risk of yield depressions following deep tillage. Generally, deep tillage effects increased with drought intensity indicating deep tillage as climate adaptation measure at certain sites. Our results suggest that deep tillage can facilitate the plant-availability of subsoil nutrients, which increases crop yields if (i) nutrients in the topsoil are growth limiting, and (ii) deep tillage does not come at the cost of impairing topsoil fertility. On sites with root restrictive soil layers, deep tillage can be an effective measure to mitigate drought stress and improve the resilience of crops. However, deep tillage should only be performed on soils with a stable structure, i.e. <70% silt content. We will discuss the contribution of deep tillage options to enhance the sustainability of agricultural production by facilitating the uptake of nutrients and water from the subsoil.

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.

Predicting The Intrusion Layer From Deep Ocean Oil Spills

NASA Astrophysics Data System (ADS)

Wang, Dayang; Chow, Aaron; Adams, E. Eric

2015-11-01

Oil spills from deep ocean blowout events motivate our study of multiphase plumes in a water column. Key to understanding the long-term fate of these plumes is the ability to predict the depth and persistence of intrusion layers. While intrusion layers from multiphase plumes have been studied under stagnant conditions, their behavior in the presence of crossflow, especially in mild crossflow, remains poorly understood. The classical classification of plume behavior identifies two regimes: crossflow-dominant and stratification-dominant--but it does not account for the interplay between the two effects, leaving the transition region unexplored. We conduct laboratory tank experiments to investigate the behavior of intrusion layers under the simultaneous action of crossflow and stratification. Our experiments use an inverted frame of reference, using glass beads with a range of sizes to simulate oil droplets. We find that crossflow creates enhanced mixing, which in turn leads to a shallower intrusion layer of the released fluid (correspondingly, a deeper layer in the case of a deep ocean blowout). We develop a mathematical formulation that extends previous models to account for crossflow effects, and use field observations to validate the analytical and experimental findings.

Contribution of topographically generated submesoscale turbulence to Southern Ocean overturning

NASA Astrophysics Data System (ADS)

Ruan, Xiaozhou; Thompson, Andrew F.; Flexas, Mar M.; Sprintall, Janet

2017-11-01

The ocean's global overturning circulation regulates the transport and storage of heat, carbon and nutrients. Upwelling across the Southern Ocean's Antarctic Circumpolar Current and into the mixed layer, coupled to water mass modification by surface buoyancy forcing, has been highlighted as a key process in the closure of the overturning circulation. Here, using twelve high-resolution hydrographic sections in southern Drake Passage, collected with autonomous ocean gliders, we show that Circumpolar Deep Water originating from the North Atlantic, known as Lower Circumpolar Deep Water, intersects sloping topography in narrow and strong boundary currents. Observations of strong lateral buoyancy gradients, enhanced bottom turbulence, thick bottom mixed layers and modified water masses are consistent with growing evidence that topographically generated submesoscale flows over continental slopes enhance near-bottom mixing, and that cross-density upwelling occurs preferentially over sloping topography. Interactions between narrow frontal currents and topography occur elsewhere along the path of the Antarctic Circumpolar Current, which leads us to propose that such interactions contribute significantly to the closure of the overturning in the Southern Ocean.

Role of Deep Convection in Establishing the Isotopic Composition of Water Vapor in the Tropical Transition Layer

NASA Technical Reports Server (NTRS)

Smith, Jamison A.; Ackerman, Andrew S.; Jensen, Eric J.; Toon, Owen B.

2006-01-01

The transport of H2O and HDO within deep convection is investigated with 3-D large eddy simulations (LES) using bin microphysics. The lofting and sublimation of HDO-rich ice invalidate the Rayleigh fractionation model of isotopologue distribution within deep convection. Bootstrapping the correlation of the ratio of HDO to H2O (deltaD) to water vapor mixing ratio (q(sub v)) through a sequence of convective events produced non-Rayleigh correlations resembling observations. These results support two mechanisms for stratospheric entry. Deep convection can inject air with water vapor of stratospheric character directly into the tropical transition layer (TTL). Alternatively, moister air detraining from convection may be dehydrated via cirrus formation n the TTL to produce stratospheric water vapor. Significant production of subsaturated air in the TTL via convective dehydration is not observed in these simulations, nor is it necessary to resolve the stratospheric isotope paradox.

The interactive role of subsynoptic scale jet sreak and planetary boundary layer adjustments in organizing an apparently isolated convective complex

NASA Technical Reports Server (NTRS)

Kaplan, M. L.; Zack, J. W.; Wong, V. C.; Tuccillo, J. J.; Coats, G. D.

1982-01-01

A mesoscale atmospheric simulation system is described that is being developed in order to improve the simulation of subsynoptic and mesoscale adjustments associated with cyclogenesis, severe storm development, and significant atmospheric transport processes. Present emphasis in model development is in the parameterization of physical processes, time-dependent boundary conditions, sophisticated initialization and analysis procedures, nested grid solutions, and applications software development. Basic characteristics of the system as of March 1982 are listed. In a case study, the Grand Island tornado outbreak of 3 June 1980 is considered in substantial detail. Results of simulations with a mesoscale atmospheric simulation system indicate that over the high plains subtle interactions between existing jet streaks and deep well mixed boundary layers can lead to well organized patterns of mesoscale divergence and pressure falls. The amplitude and positioning of these mesoscale features is a function of the subtle nonlinear interaction between the pre-existing jet-streak and deep well mixed boundary layers. Model results for the case study indicate that the model has the potential for forecasting the precursor mesoscale convective environment.

Transparent conductive oxide films mixed with gallium oxide nanoparticle/single-walled carbon nanotube layer for deep ultraviolet light-emitting diodes

PubMed Central

2013-01-01

We propose a transparent conductive oxide electrode scheme of gallium oxide nanoparticle mixed with a single-walled carbon nanotube (Ga2O3 NP/SWNT) layer for deep ultraviolet light-emitting diodes using spin and dipping methods. We investigated the electrical, optical and morphological properties of the Ga2O3 NP/SWNT layers by increasing the thickness of SWNTs via multiple dipping processes. Compared with the undoped Ga2O3 films (current level 9.9 × 10-9 A @ 1 V, transmittance 68% @ 280 nm), the current level flowing in the Ga2O3 NP/SWNT increased by approximately 4 × 105 times and the transmittance improved by 9% after 15 times dip-coating (current level 4 × 10-4 A at 1 V; transmittance 77.0% at 280 nm). These improvements result from both native high transparency of Ga2O3 NPs and high conductivity and effective current spreading of SWNTs. PMID:24295342

Moisture Vertical Structure, Deep Convective Organization, and Convective Transition in the Amazon

NASA Astrophysics Data System (ADS)

Schiro, K. A.; Neelin, J. D.

2017-12-01

Constraining precipitation processes in climate models with observations is crucial to accurately simulating current climate and reducing uncertainties in future projections. Results from the Green Ocean Amazon (GOAmazon) field campaign (2014-2015) provide evidence that deep convection is strongly controlled by the availability of moisture in the free troposphere over the Amazon, much like over tropical oceans. Entraining plume buoyancy calculations confirm that CWV is a good proxy for the conditional instability of the environment, yet differences in convective onset as a function of CWV exist over land and ocean, as well as seasonally and diurnally over land. This is largely due to variability in the contribution of lower tropospheric humidity to the total column moisture. Boundary layer moisture shows a strong relationship to the onset during the day, which largely disappears during nighttime. Using S-Band radar, these transition statistics are examined separately for unorganized and mesoscale-organized convection, which exhibit sharp increases in probability of occurrence with increasing moisture throughout the column, particularly in the lower free troposphere. Retrievals of vertical velocity from a radar wind profiler indicate updraft velocity and mass flux increasing with height through the lower troposphere. A deep-inflow mixing scheme motivated by this — corresponding to deep inflow of environmental air into a plume that grows with height — provides a weighting of boundary layer and free tropospheric air that yields buoyancies consistent with the observed onset of deep convection across seasons and times of day, across land and ocean sites, and for all convection types. This provides a substantial improvement relative to more traditional constant mixing assumptions, and a dramatic improvement relative to no mixing. Furthermore, it provides relationships that are as strong or stronger for mesoscale-organized convection as for unorganized convection.

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.

Interannual variability (1979-2013) of the North-Western Mediterranean deep water mass formation: past observation reanalysis and coupled ocean-atmosphere high-resolution modelling

NASA Astrophysics Data System (ADS)

Somot, Samuel; Houpert, Loic; Sevault, Florence; Testor, Pierre; Bosse, Anthony; Durrieu de Madron, Xavier; Dubois, Clotilde; Herrmann, Marine; Waldman, Robin; Bouin, Marie-Noëlle; Cassou, Christophe

2015-04-01

The North-Western Mediterranean Sea is known as one of the only place in the world where open-sea deep convection occurs (often up to more than 2000m) with the formation of the Western Mediterranean Deep Water (WMDW). This phenomena is mostly driven by local preconditioning of the water column and strong buoyancy losses during Winter. At the event scale, the WMDW formation is characterized by different phases (preconditioning, strong mixing, restratification and spreading), intense air-sea interaction and strong meso-scale activity but, on a longer time scale, it also shows a large interannual variability and may be strongly affected by climate change with impact on the regional biogeochemistry. Therefore observing, simulating and understanding the long-term temporal variability of the North-Western Mediterranean deep water formation is still today a very challenging task. We try here to tackle those issues thanks to (1) a thorough reanalysis of past in-situ observations (CTD, Argo, surface and deep moorings, gliders) and (2) an ERA-Interim driven simulation using a recently-developed fully coupled Regional Climate System Model (CNRM-RCSM4, Sevault et al. 2014). The multi-decadal simulation (1979-2013) is designed to be temporally and spatially homogeneous with a realistic chronology, a high resolution representation of both the regional ocean and atmosphere, specific initial conditions, a long-term spin-up and a full ocean-atmosphere coupling without constraint at the air-sea interface. The observation reanalysis allows to reconstruct interannual time series of deep water formation indicators (ocean surface variables, mixed layer depth, surface of the convective area, dense water volumes and characteristics of the deep water). Using the observation-based indicators and the model outputs, the 34 Winters of the period 1979-2013 are analysed in terms of weather regimes, related Winter air-sea fluxes, ocean preconditioning, mixed layer depth, surface of the convective area, deep water formation rate and long-term evolution of the deep water hydrology.

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.

Tracing the source of deep water in the Arctic Ocean with 17Oexcess of dissolved O2

NASA Astrophysics Data System (ADS)

Smethie, W. M., Jr.; Luz, B.; Barkan, E.; Broecker, W. S.

2014-12-01

The 17Oexcess of dissolved O2 (17Δ) in the ocean is a unique property which is useful for telling apart O2 produced by marine photosynthesis (bio-O2) from atmospheric O2. Unlike O2 concentration, 17Δ is not affected by respiration and thus behaves conservatively in the deep sea. In general, 17Δ in the oceanic mixed layer is low due to the dominance of air-sea gas exchange. In contrast, in the Arctic mixed-layer 17Δ is higher because sufficient light penetrates through the sea-ice cover and drives photosynthesis, but air-sea gas exchange is retarded by sea ice cover. We have preliminary 17Δ data from depth profiles in the Eurasian and Makarov basins. In both, the fraction of bio-O2 is about 20 % in the surface mixed layer. However, the vertical distribution beneath the mixed layer at the two stations is substantially different. In the Makarov Basin there is a layer of Pacific Water centered at about 100 m, which enters the Arctic Ocean through Bering Strait and is modified as it flows across the wide Chukchi and Siberian shelves. It has a strong maximum in 17Δ, equivalent to ~30% bio-O2. 17Δ then decreases through the underlying halocline to a minimum between 500 and 700 m, which lies within the Barents Sea Branch of Atlantic Water (BSBW) indicating ~15% bio-O2. At the Eurasian Basin station, 17Δ decreases from the mixed layer through the halocline reaching a minimum at the temperature maximum of Atlantic Water. This temperature maximum marks the core of the Fram Strait Branch of Atlantic Water (FSBW). 17Δ then increases to a maximum indicating ~20% bio-O2 between 500 and 700 m. The BSBW is produced as Atlantic Water flows through the shallow Barents Sea becoming denser than FSBW and enters the Eurasian Basin through the Santa Anna Trough beneath the FSBW. Our 17Δ measurements suggest that waters of Pacific and Atlantic origin that transit across the wide Arctic continental shelves acquire a high 17Δ signal indicative of photosynthesis in ice covered water.

Surface wind mixing in the Regional Ocean Modeling System (ROMS)

NASA Astrophysics Data System (ADS)

Robertson, Robin; Hartlipp, Paul

2017-12-01

Mixing at the ocean surface is key for atmosphere-ocean interactions and the distribution of heat, energy, and gases in the upper ocean. Winds are the primary force for surface mixing. To properly simulate upper ocean dynamics and the flux of these quantities within the upper ocean, models must reproduce mixing in the upper ocean. To evaluate the performance of the Regional Ocean Modeling System (ROMS) in replicating the surface mixing, the results of four different vertical mixing parameterizations were compared against observations, using the surface mixed layer depth, the temperature fields, and observed diffusivities for comparisons. The vertical mixing parameterizations investigated were Mellor- Yamada 2.5 level turbulent closure (MY), Large- McWilliams- Doney Kpp (LMD), Nakanishi- Niino (NN), and the generic length scale (GLS) schemes. This was done for one temperate site in deep water in the Eastern Pacific and three shallow water sites in the Baltic Sea. The model reproduced the surface mixed layer depth reasonably well for all sites; however, the temperature fields were reproduced well for the deep site, but not for the shallow Baltic Sea sites. In the Baltic Sea, the models overmixed the water column after a few days. Vertical temperature diffusivities were higher than those observed and did not show the temporal fluctuations present in the observations. The best performance was by NN and MY; however, MY became unstable in two of the shallow simulations with high winds. The performance of GLS nearly as good as NN and MY. LMD had the poorest performance as it generated temperature diffusivities that were too high and induced too much mixing. Further observational comparisons are needed to evaluate the effects of different stratification and wind conditions and the limitations on the vertical mixing parameterizations.

The Northeast Monsoon's Impact on Mixing, Phytoplankton Biomass and Nutrient Cycling in the Arabian Sea

NASA Technical Reports Server (NTRS)

Wiggert, J. D.; Jones, B. H.; Dickey, T. D.; Brink, K. H.; Weller, R. A.; Marra, J.; Codispoti, L. A.

2000-01-01

In the northern Arabian Sea, atmospheric conditions during the Northeast (winter) Monsoon lead to deep convective mixing. Due to the proximity of the permanent pyncnocline to the sea surface, this mixing does not penetrate below 125 m. However, a strong nitracline is also present and the deep convection results in significant nitrate flux into the surface waters. This leads to nitrate concentrations over the upper 100 m that exceed 4 micrometers toward the end of the Monsoon. During the 1994/1995 US JGOFS/Arabian Sea expedition, the mean areal gross primary production over two successive Northeast Monsoons was determined to be 1.35gC/sq m/d. Thus, despite the deep penetrative convection, high rates of primary productivity were maintained. An interdisciplinary model was developed to elucidate the biogeochemical processes involved in supporting the elevated productivity. This model consists of a 1-D mixed-layer model coupled to a set of equations that tracked phytoplankton growth and the concentration of the two major nutrients (nitrate and ammonium). Zooplankton grazing was parameterized by rate constant determined by shipboard experiments. Model boundary conditions consist of meteorological time-series measured from the surface buoy that was part of the ONR Arabian Sea Experiment's central mooring. Our numerical experiments show that elevated surface evaporation, and the associated salinization of the mixed layer, strongly contributes to the frequency and penetration depth of the observed convective mixing. Cooler surface temperatures, increased nitrate entrainment, reduced water column stratification, and lower near-surface chlorophyll a concentrations all result from this enhanced mixing. The model also captured a dependence on regenerated nitrogen observed in nutrient uptake experiments performed during the Northeast Monsoon. Our numerical experiments also indicate that variability in mean pycnocline depth causes up to a 25% reduction in areal chlorophyll a concentration. We hypothesize that such shifts in pycnocline depth may contribute to the interannual variations in primary production and surface chlorophyll a concentration that have been previously observed in this region.

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.

Evolution of the Marginal Ice Zone: Adaptive Sampling with Autonomous Gliders

DTIC Science & Technology

2015-09-30

kinetic energy (ε). Gliders also sampled dissolved oxygen, optical backscatter ( chlorophyll and CDOM fluorescence) and multi-spectral downwelling...Fig. 2). In the pack, Pacific Summer Water and a deep chlorophyll maximum form distinct layers at roughly 60 m and 80 m, respectively, which become...Sections across the ice edge just prior to recovery, during freeze-up, reveal elevated chlorophyll fluorescence throughout the mixed layer (Fig. 4

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

Fronts and frontogenesis as revealed by high time resolution data

NASA Technical Reports Server (NTRS)

Frank, A. E.; Barber, D. A.

1977-01-01

Upper air sounding are used to examine a cold front of average intensity. Vertical cross sections of potential temperature and wind, and horizontal analyses were compared and adjusted for consistency. These analyses were then used to study the evolution of the front, found to consist of a complex system of fronts occurring at all levels of the troposphere. Low level fronts were strongest at the surface and rapidly weakened with height. Fronts in the midddle troposphere were much more intense. The warm air ahead of the fronts was nearly barotropic, while the cold air behind was baroclinic through deep layers. A deep mixed layer was observed to grow in this cold air.

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.

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.

Comparing the behaviour of two ocean surface models in simulating dissolved O 2 concentration at O.W.S.P.

NASA Astrophysics Data System (ADS)

Thomas, F.; Minster, J. F.; Gaspar, P.; Gregoris, Y.

1993-02-01

We compare the simulation of the O 2 concentration in the mixed layer at Sta. P using two different mixed layer models with the same biological production-consumption function. One is the integral mixed layer model already used by THOMASet al. (Deep-Sea Research, 37, 463-491, 1990). The other is the eddy kinetic energy (EKE) model of GASPARet al. (Journal of Geophysical Research, 95, 16179-16194, 1990). The latter simulates better both the seasonal and the short time evolution of the oxygen concentration. The submixed layer summer supersaturation is also closer to observations, by about 25%, though a factor of 2 too high: this could be improved by adjustment of the production function. The net annual gas exchange flux with the atmosphere is always a degassing of the order of 10% of the total biological production. In general, the model values are smaller (within a factor of 3 for the EKE model) than the data. However, the latter may not be robust as 96 measurements per year are necessary to estimate this flux within a factor of 10.

One hundred years of Arctic ice cover variations as simulated by a one-dimensional, ice-ocean model

NASA Astrophysics Data System (ADS)

Hakkinen, S.; Mellor, G. L.

1990-09-01

A one-dimensional ice-ocean model consisting of a second moment, turbulent closure, mixed layer model and a three-layer snow-ice model has been applied to the simulation of Arctic ice mass and mixed layer properties. The results for the climatological seasonal cycle are discussed first and include the salt and heat balance in the upper ocean. The coupled model is then applied to the period 1880-1985, using the surface air temperature fluctuations from Hansen et al. (1983) and from Wigley et al. (1981). The analysis of the simulated large variations of the Arctic ice mass during this period (with similar changes in the mixed layer salinity) shows that the variability in the summer melt determines to a high degree the variability in the average ice thickness. The annual oceanic heat flux from the deep ocean and the maximum freezing rate and associated nearly constant minimum surface salinity flux did not vary significantly interannually. This also implies that the oceanic influence on the Arctic ice mass is minimal for the range of atmospheric variability tested.

Predator-guided sampling reveals biotic structure in the bathypelagic.

PubMed

Benoit-Bird, Kelly J; Southall, Brandon L; Moline, Mark A

2016-02-24

We targeted a habitat used differentially by deep-diving, air-breathing predators to empirically sample their prey's distributions off southern California. Fine-scale measurements of the spatial variability of potential prey animals from the surface to 1,200 m were obtained using conventional fisheries echosounders aboard a surface ship and uniquely integrated into a deep-diving autonomous vehicle. Significant spatial variability in the size, composition, total biomass, and spatial organization of biota was evident over all spatial scales examined and was consistent with the general distribution patterns of foraging Cuvier's beaked whales (Ziphius cavirostris) observed in separate studies. Striking differences found in prey characteristics between regions at depth, however, did not reflect differences observed in surface layers. These differences in deep pelagic structure horizontally and relative to surface structure, absent clear physical differences, change our long-held views of this habitat as uniform. The revelation that animals deep in the water column are so spatially heterogeneous at scales from 10 m to 50 km critically affects our understanding of the processes driving predator-prey interactions, energy transfer, biogeochemical cycling, and other ecological processes in the deep sea, and the connections between the productive surface mixed layer and the deep-water column. © 2016 The Author(s).

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.

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.

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.

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.

GoAmazon2014/5 campaign points to deep-inflow approach to deep convection across scales.

PubMed

Schiro, Kathleen A; Ahmed, Fiaz; Giangrande, Scott E; Neelin, J David

2018-05-01

A substantial fraction of precipitation is associated with mesoscale convective systems (MCSs), which are currently poorly represented in climate models. Convective parameterizations are highly sensitive to the assumptions of an entraining plume model, in which high equivalent potential temperature air from the boundary layer is modified via turbulent entrainment. Here we show, using multiinstrument evidence from the Green Ocean Amazon field campaign (2014-2015; GoAmazon2014/5), that an empirically constrained weighting for inflow of environmental air based on radar wind profiler estimates of vertical velocity and mass flux yields a strong relationship between resulting buoyancy measures and precipitation statistics. This deep-inflow weighting has no free parameter for entrainment in the conventional sense, but to a leading approximation is simply a statement of the geometry of the inflow. The structure further suggests the weighting could consistently apply even for coherent inflow structures noted in field campaign studies for MCSs over tropical oceans. For radar precipitation retrievals averaged over climate model grid scales at the GoAmazon2014/5 site, the use of deep-inflow mixing yields a sharp increase in the probability and magnitude of precipitation with increasing buoyancy. Furthermore, this applies for both mesoscale and smaller-scale convection. Results from reanalysis and satellite data show that this holds more generally: Deep-inflow mixing yields a strong precipitation-buoyancy relation across the tropics. Deep-inflow mixing may thus circumvent inadequacies of current parameterizations while helping to bridge the gap toward representing mesoscale convection in climate models.

The formation of Greenland Sea Deep Water: double diffusion or deep convection?

NASA Astrophysics Data System (ADS)

Clarke, R. Allyn; Swift, James H.; Reid, Joseph L.; Koltermann, K. Peter

1990-09-01

An examination of the extensive hydrographic data sets collected by C.S.S. Hudson and F.S. Meteor in the Norwegian and Greenland Seas during February-June 1982 reveals property distributions and circulation patterns broadly similar to those seen in earlier data sets. These data sets, however, reveal the even stronger role played by topography, with evidence of separate circulation patterns and separate water masses in each of the deep basins. The high precision temperature, salinity and oxygen data obtained reveals significant differences in the deep and bottom waters found in the various basins of the Norwegian and Greenland Seas. A comparison of the 1982 data set with earlier sets shows that the renewal of Greenland Sea Deep Water must have taken place sometime over the last decade; however there is no evidence that deep convective renewal of any of the deep and bottom waters in this region was taking place at the time of the observations. The large-scale density fields, however, do suggest that deep convection to the bottom is most likely to occure in the Greenland Basin due to its deep cyclonic circulation. The hypothesis that Greenland Sea Deep Water (GSDW) is formed through dipycnal mixing processes acting on the warm salty core of Atlantic Water entering the Greenland Sea is examined. θ-S correlations and oxygen concentrations suggest that the salinity maxima in the Greenland Sea are the product of at least two separate mixing processes, not the hypothesized single mixing process leading to GSDW. A simple one-dimensional mixed layer model with ice growth and decay demonstrates that convective renewal of GSDW would have occurred within the Greenland Sea had the winter been a little more severe. The new GSDW produced would have only 0.003 less salt and less than 0.04 ml 1 -1 greater oxygen concentration than that already in the basin. Consequently, detection of whether new deep water has been produced following a winter cooling season could be difficult even with the best of modern accuracy.

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.

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.

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.

Possible Sea Ice Impacts on Oceanic Deep Convection

NASA Technical Reports Server (NTRS)

Parkinson, C. L.

1984-01-01

Many regions of the world ocean known or suspected to have deep convection are sea-ice covered for at least a portion of the annual cycle. As this suggests that sea ice might have some impact on generating or maintaining this phenomenon, several mechanisms by which sea ice could exert an influence are presented in the following paragraphs. Sea ice formation could be a direct causal factor in deep convection by providing the surface density increase necessary to initiate the convective overturning. As sea ice forms, either by ice accretion or by in situ ice formation in open water or in lead areas between ice floes, salt is rejected to the underlying water. This increases the water salinity, thereby increasing water density in the mixed layer under the ice. A sufficient increase in density will lead to mixing with deeper waters, and perhaps to deep convection or even bottom water formation. Observations are needed to establish whether this process is actually occurring; it is most likely in regions with extensive ice formation and a relatively unstable oceanic density structure.

Enhancement of free tropospheric ozone production by deep convection

NASA Technical Reports Server (NTRS)

Pickering, Kenneth E.; Thompson, Anne M.; Scala, John R.; Tao, Wei-Kuo; Simpson, Joanne

1994-01-01

It is found from model simulations of trace gas and meteorological data from aircraft campaigns that deep convection may enhance the potential for photochemical ozone production in the middle and upper troposphere by up to a factor of 60. Examination of half a dozen individual convective episodes show that the degree of enhancement is highly variable. Factors affecting enhancement include boundary layer NO(x) mixing ratios, differences in the strength and structure of convective cells, as well as variation in the amount of background pollution already in the free troposphere.

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.

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.

Tritium in the western Mediterranean Sea during 1981 Phycemed cruise

NASA Astrophysics Data System (ADS)

Andrie, Chantal; Merlivat, Liliane

1988-02-01

We report on simultaneous hydrological and tritium data taken in the western Mediterranean Sea during April 1981 and which implement our knowledge of the spatial and temporal variability of the convection process occurring in the Northern Basin (Gulf of Lion, Ligurian Sea). The renewal time of the deep waters in the Medoc area is calculated to be 11 ± 2 years using a box-model assymption. An important local phenomenon of "cascading" off the Ebro River near the Spanish coast is, noticeable by the use of tritium data. In the Sardinia Straits area tritium data indicate very active mixing between 100 and 500 m depth. The tritium subsurface maxima in Sardinia Straits suggests the influence of not only the Levantine Intermediate Water (LIW) but also an important shallower component. In waters deeper than 500m, an active mixing occurs between the deep water and the LIW via an intermediate water mass from the Tyrrhenian Sea by "salt-fingering". Assuming a two end-member mixing. We determine the deep tritium content in the Sardinia Channel to be 1.8 TU. For comparison, the deep tritium content of the Northern Basin is equal to 1.3 TU. Tritium data relative to the Alboran Sea show that a layer of high tritium content persists all along its path from Sardifia to Gibraltar on a density surface shallower than the intermediate water. The homogeneity of the deep tritium concentrations between 1200 m depth and the bottom corroborate the upward "pumping" and westward circulation of deep waters along the continental slope of the North African Shelf. From the data measured in the Sardinia Straits and in the Alboran Sea, and upper limit of the deep advection rate of the order of 0.5 cm s-1 is estimated.

Improved Bilayer Resist System Using Contrast-Enhanced Lithography With Water-Soluble Photopolymer

NASA Astrophysics Data System (ADS)

Sasago, Masaru; Endo, Masayuki; Hirai, Yoshihiko; Ogawa, Kazufurni; Ishihara, Takeshi

1986-07-01

A new water-soluble contract enhanced material, WSP (Water-soluble Photopolymer), has been developed. The WSP is composed of a mainpolymer and a photobleachable reagents. The mainpolymer is a water-soluble polymer mixed with pullulan (refined through biotechnological process) and polyvinyl-pyrolidone (PVP). The photo-bleachable reagent is of a diazonium compound gorup. The introduction of the mainpolymer and photobleach-able reagent mixture has improved filmity, gas transparency, photobleaching characteristics and solubility in alkaline which are essential to the device fabrication. Submicron photoresist patterns are successfully fabricated by a simple sequence of photolithography process. The WSP layer has been applied to the bilayer resist system--deep-UV portable conformable masking (PCM)--that is not affected by VLSI's topography, and is able to fabricate highly accurate pattern. The aqueous developable layer, PMGI, with high organic solvent resistance is used in the bottom layer. Therefore, no interfacial mixing with conventional positive resist top layer is observed. Furthermore, deep-UV exposure method has been used for the KrF excimer laser optical system in order to increase high throughput. From the experiments, it has been confirmed that good resist transfer profile can be realized by the use of WSP, and that the submicron resist patterns with high aspect-ratio can be developed on the nonplaner wafer with steps of up to 41m by the combination of the WSP with the PCM system. By this technology, has been improved the weak point: variation in the line width due to the thickness of contrast-enhanced layer when the CEL technology is applied, and dependency of both the finished resist profile and the line-width accuracy on the thickness of the top layer resist when the PCM system is adopted.

Temporal variability of chlorophyll distribution in the Gulf of Mexico: bio-optical data from profiling floats

NASA Astrophysics Data System (ADS)

Pasqueron de Fommervault, Orens; Perez-Brunius, Paula; Damien, Pierre; Camacho-Ibar, Victor F.; Sheinbaum, Julio

2017-12-01

Chlorophyll concentration is a key oceanic biogeochemical variable. In the Gulf of Mexico (GOM), its distribution, which is mainly obtained from satellite surface observations and scarce in situ experiments, is still poorly understood. In 2011-2012, eight profiling floats equipped with biogeochemical sensors were deployed for the first time in the GOM and generated an unprecedented dataset that significantly increased the number of chlorophyll vertical distribution measurements in the region. The analysis of these data, once calibrated, permits us to reconsider the spatial and temporal variability of the chlorophyll concentration in the water column. At a seasonal scale, results confirm the surface signal seen by satellites, presenting maximum concentrations in winter and low values in summer. It is shown that the deepening of the mixed layer is the primary factor triggering the chlorophyll surface increase in winter. In the GOM, a possible interpretation is that this surface increase corresponds to a biomass increase. However, the present dataset suggests that the basin-scale climatological surface increase in chlorophyll content results from a vertical redistribution of subsurface chlorophyll and/or photoacclimation processes, rather than a net increase of biomass. One plausible explanation for this is the decoupling between the mixed-layer depth and the deep nutrient reservoir since mixed-layer depth only reaches the nitracline in sporadic events in the observations. Float measurements also provide evidence that the depth and the magnitude of the deep chlorophyll maximum is strongly controlled by the mesoscale variability, with higher chlorophyll biomass generally observed in cyclones rather than anticyclones.

Interannual control of plankton communities by deep winter mixing and prey/predator interactions in the NW Mediterranean: Results from a 30-year 3D modeling study

NASA Astrophysics Data System (ADS)

Auger, P. A.; Ulses, C.; Estournel, C.; Stemmann, L.; Somot, S.; Diaz, F.

2014-05-01

A realistic modeling approach is designed to address the role of winter mixing on the interannual variability of plankton dynamics in the north-western (NW) Mediterranean basin. For the first time, a high-resolution coupled hydrodynamic-biogeochemical model (Eco3m-S) covering a 30-year period (1976-2005) is validated on available in situ and satellite data for the NW Mediterranean. In this region, cold, dry winds in winter often lead to deep convection and strong upwelling of nutrients into the euphotic layer. High nutrient contents at the end of winter then support the development of a strong spring bloom of phytoplankton. Model results indicate that annual primary production is not affected by winter mixing due to seasonal balance (minimum in winter and maximum in spring). However, the total annual water column-integrated phytoplankton biomass appears to be favored by winter mixing because zooplankton grazing activity is low in winter and early spring. This reduced grazing is explained here by the rarefaction of prey due to both light limitation and the effect of mixing-induced dilution on prey/predator interactions. A negative impact of winter mixing on winter zooplankton biomass is generally simulated except for mesozooplankton. This difference is assumed to stem from the lower parameterized mortality, top trophic position and detritivorous diet of mesozooplankton in the model. Moreover, model suggests that the variability of annual mesozooplankton biomass is principally modulated by the effects of winter mixing on winter biomass. Thus, interannual variability of winter nutrient contents in the euphotic layer, resulting from winter mixing, would control spring primary production and thus annual mesozooplankton biomass. Our results show a bottom-up control of mesozooplankton communities, as observed at a coastal location of the Ligurian Sea.

Wind-Tunnel Simulation of Weakly and Moderately Stable Atmospheric Boundary Layers

NASA Astrophysics Data System (ADS)

Hancock, Philip E.; Hayden, Paul

2018-07-01

The simulation of horizontally homogeneous boundary layers that have characteristics of weakly and moderately stable atmospheric flow is investigated, where the well-established wind engineering practice of using `flow generators' to provide a deep boundary layer is employed. Primary attention is given to the flow above the surface layer, in the absence of an overlying inversion, as assessed from first- and second-order moments of velocity and temperature. A uniform inlet temperature profile ahead of a deep layer, allowing initially neutral flow, results in the upper part of the boundary layer remaining neutral. A non-uniform inlet temperature profile is required but needs careful specification if odd characteristics are to be avoided, attributed to long-lasting effects inherent of stability, and to a reduced level of turbulent mixing. The first part of the wind-tunnel floor must not be cooled if turbulence quantities are to vary smoothly with height. Closely horizontally homogeneous flow is demonstrated, where profiles are comparable or closely comparable with atmospheric data in terms of local similarity and functions of normalized height. The ratio of boundary-layer height to surface Obukhov length, and the surface heat flux, are functions of the bulk Richardson number, independent of horizontal homogeneity. Surface heat flux rises to a maximum and then decreases.

Wind-Tunnel Simulation of Weakly and Moderately Stable Atmospheric Boundary Layers

NASA Astrophysics Data System (ADS)

Hancock, Philip E.; Hayden, Paul

2018-02-01

The simulation of horizontally homogeneous boundary layers that have characteristics of weakly and moderately stable atmospheric flow is investigated, where the well-established wind engineering practice of using `flow generators' to provide a deep boundary layer is employed. Primary attention is given to the flow above the surface layer, in the absence of an overlying inversion, as assessed from first- and second-order moments of velocity and temperature. A uniform inlet temperature profile ahead of a deep layer, allowing initially neutral flow, results in the upper part of the boundary layer remaining neutral. A non-uniform inlet temperature profile is required but needs careful specification if odd characteristics are to be avoided, attributed to long-lasting effects inherent of stability, and to a reduced level of turbulent mixing. The first part of the wind-tunnel floor must not be cooled if turbulence quantities are to vary smoothly with height. Closely horizontally homogeneous flow is demonstrated, where profiles are comparable or closely comparable with atmospheric data in terms of local similarity and functions of normalized height. The ratio of boundary-layer height to surface Obukhov length, and the surface heat flux, are functions of the bulk Richardson number, independent of horizontal homogeneity. Surface heat flux rises to a maximum and then decreases.

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.

Irminger Sea deep convection injects oxygen and anthropogenic carbon to the ocean interior

PubMed Central

Fröb, F.; Olsen, A.; Våge, K.; Moore, G. W. K.; Yashayaev, I.; Jeansson, E.; Rajasakaren, B.

2016-01-01

Deep convection in the subpolar North Atlantic ventilates the ocean for atmospheric gases through the formation of deep water masses. Variability in the intensity of deep convection is believed to have caused large variations in North Atlantic anthropogenic carbon storage over the past decades, but observations of the properties during active convection are missing. Here we document the origin, extent and chemical properties of the deepest winter mixed layers directly observed in the Irminger Sea. As a result of the deep convection in winter 2014–2015, driven by large oceanic heat loss, mid-depth oxygen concentrations were replenished and anthropogenic carbon storage rates almost tripled compared with Irminger Sea hydrographic section data in 1997 and 2003. Our observations provide unequivocal evidence that ocean ventilation and anthropogenic carbon uptake take place in the Irminger Sea and that their efficiency can be directly linked to atmospheric forcing. PMID:27786263

Toward Exploring the Synergy Between Cloud Radar Polarimetry and Doppler Spectral Analysis in Deep Cold Precipitating Systems in the Arctic

NASA Astrophysics Data System (ADS)

Oue, Mariko; Kollias, Pavlos; Ryzhkov, Alexander; Luke, Edward P.

2018-03-01

The study of Arctic ice and mixed-phase clouds, which are characterized by a variety of ice particle types in the same cloudy volume, is challenging research. This study illustrates a new approach to qualitative and quantitative analysis of the complexity of ice and mixed-phase microphysical processes in Arctic deep precipitating systems using the combination of Ka-band zenith-pointing radar Doppler spectra and quasi-vertical profiles of polarimetric radar variables measured by a Ka/W-band scanning radar. The results illustrate the frequent occurrence of multimodal Doppler spectra in the dendritic/planar growth layer, where locally generated, slower-falling particle populations are well separated from faster-falling populations in terms of Doppler velocity. The slower-falling particle populations contribute to an increase of differential reflectivity (ZDR), while an enhanced specific differential phase (KDP) in this dendritic growth temperature range is caused by both the slower and faster-falling particle populations. Another area with frequent occurrence of multimodal Doppler spectra is in mixed-phase layers, where both populations produce ZDR and KDP values close to 0, suggesting the occurrence of a riming process. Joint analysis of the Doppler spectra and the polarimetric radar variables provides important insight into the microphysics of snow formation and allows the separation of the contributions of ice of different habits to the values of reflectivity and ZDR.

Underground structures increasing the intrinsic vulnerability of urban groundwater: Sensitivity analysis and development of an empirical law based on a groundwater age modelling approach

NASA Astrophysics Data System (ADS)

Attard, Guillaume; Rossier, Yvan; Eisenlohr, Laurent

2017-09-01

In a previous paper published in Journal of Hydrology, it was shown that underground structures are responsible for a mixing process between shallow and deep groundwater that can favour the spreading of urban contamination. In this paper, the impact of underground structures on the intrinsic vulnerability of urban aquifers was investigated. A sensitivity analysis was performed using a 2D deterministic modelling approach based on the reservoir theory generalized to hydrodispersive systems to better understand this mixing phenomenon and the mixing affected zone (MAZ) caused by underground structures. It was shown that the maximal extent of the MAZ caused by an underground structure is reached approximately 20 years after construction. Consequently, underground structures represent a long-term threat for deep aquifer reservoirs. Regarding the construction process, draining operations have a major impact and favour large-scale mixing between shallow and deep groundwater. Consequently, dewatering should be reduced and enclosed as much as possible. The role played by underground structures' dimensions was assessed. The obstruction of the first aquifer layer caused by construction has the greatest influence on the MAZ. The cumulative impact of several underground structures was assessed. It was shown that the total MAZ area increases linearly with underground structures' density. The role played by materials' properties and hydraulic gradient were assessed. Hydraulic conductivity, anisotropy and porosity have the strongest influence on the development of MAZ. Finally, an empirical law was derived to estimate the MAZ caused by an underground structure in a bi-layered aquifer under unconfined conditions. This empirical law, based on the results of the sensitivity analysis developed in this paper, allows for the estimation of MAZ dimensions under known material properties and underground structure dimensions. This empirical law can help urban planners assess the area of influence of underground structures and protect urban strategic reservoirs.

Kuroshio Graduate Student Support

DTIC Science & Technology

2018-06-06

875 North Randolph Street Arlington, VA 22203-1995 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION / AVAILABILITY ...strong horizontal density gradients (e.g., midlatitude subtropical gyres), with a small fraction occurring in regions of deep mixed layers (e.g., high ...Society homogenous in the presence of sharp horizontal density contrasts (e.g., Fig. 1a). These sharp gradients provide a source of available

Does deep ocean mixing drive upwelling or downwelling of abyssal waters?

NASA Astrophysics Data System (ADS)

Ferrari, R. M.; McDougall, T. J.; Mashayek, A.; Nikurashin, M.; Campin, J. M.

2016-02-01

It is generally understood that small-scale mixing, such as is caused by breaking internal waves, drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes. However the observational evidence that the turbulent fluxes generated by small-scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom than above implies that small-scale mixing converts light waters into denser ones, thus driving a net sinking of abyssal water. Using a combination of numerical models and observations, it will be shown that abyssal waters return to the surface along weakly stratified boundary layers, where the small-scale mixing of density decays to zero. The net ocean meridional overturning circulation is thus the small residual of a large sinking of waters, driven by small-scale mixing in the stratified interior, and a comparably large upwelling, driven by the reduced small-scale mixing along the ocean boundaries.

Investigation of the Charge Balance in Green Phosphorescent Organic Light-Emitting Diodes by Controlling the Mixed Host Emission Layer.

PubMed

Lee, Jeonghyun; Choi, Pyungho; Kim, Minsoo; Lim, Kiwon; Hyeon, Younghwan; Kim, Soonkon; Koo, Kwangjun; Kim, Sangsoo; Choi, Byoungdeog

2018-09-01

In this paper, we investigated the use of a mixed host emission layer (MH-EML) in green phosphorescent organic light-emitting diodes (OLEDs). The hole transport type (p-type) material (4,4'-Bis(N-carbazolyl)-1,1'-biphenyl (CBP)) and electron transport type (N-type) material (2,2',2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)) were mixed with different ratios. The electrons were easily injected through the lowest unoccupied molecular orbital (LUMO) of TPBi in the mixed host system. Also, holes were confined in the EML because of the deep highest occupied molecular orbital (HOMO) level of TPBi (6.7 eV). These results indicate that excitons were formed effectively and the recombination zone became wider under a high electric field in MH-EML devices. For these reasons, the lifetime of the MH-OLED device was 1.36 times higher than that of a single host emission layer (SH-EML) device and showed a reduction in Joule heating. Finally, the external quantum efficiency (EQE) roll-off ratio from 1 mA/cm2 to 100 mA/cm2 in the optimized device (30.46%) was 18.12%p lower than that of the SH-EML (48.58%).

On Suspended matter grain size in Baltic sea

NASA Astrophysics Data System (ADS)

Bubnova, Ekaterina; Sivkov, Vadim; Zubarevich, Victor

2016-04-01

Suspended matter grain size data were gathered during the 25th research vessel "Akademik Mstislav Keldysh" cruise (1991, September-October). Initial quantitative data were obtained with a use of the Coulter counter and subsequently modified into volume concentrations (mm3/l) for size intervals. More than 80 samples from 15 stations were analyzed (depth range 0-355 m). The main goal of research was to illustrate the spatial variability of suspended matter concentration and dispersion in Baltic Sea. The mutual feature of suspended matter grain size distribution is the logical rise of particle number along with descending of particle's size. Vertical variability of grain size distribution was defined by Baltic Sea hydrological structure, including upper mixed layer - from the surface to the thermocline - with 35 m thick, cold intermediate layer - from the thermocline to the halocline- and bottom layer, which lied under the halocline. Upper layer showed a rise in total suspended matter concentration (up to 0.6 mm3/l), while cold intermediate level consisted of far more clear water (up to 0.1 mm3/l). Such a difference is caused by the thermocline boarding role. Meanwhile, deep bottom water experienced surges in suspended matter concentration owing to the nepheloid layer presence and "liquid bottom" effect. Coastal waters appeared to have the highest amount of particles (up to 5.0 mm3/l). Suspended matter grain size distribution in the upper mixed layer revealed a peak of concentration at 7 μ, which can be due to autumn plankton bloom. Another feature in suspended matter grain size distribution appeared at the deep layer below halocline, where both O2 and H2S were observed and red/ox barrier is. The simultaneous presence of Fe and Mn (in solutions below red/ox barrier) and O2 leads to precipitation of oxyhydrates Fe and Mn and grain size distribution graph peaking at 4.5 μ.

How Choice of Depth Horizon Influences the Estimated Spatial Patterns and Global Magnitude of Ocean Carbon Export Flux

NASA Astrophysics Data System (ADS)

Palevsky, Hilary I.; Doney, Scott C.

2018-05-01

Estimated rates and efficiency of ocean carbon export flux are sensitive to differences in the depth horizons used to define export, which often vary across methodological approaches. We evaluate sinking particulate organic carbon (POC) flux rates and efficiency (e-ratios) in a global earth system model, using a range of commonly used depth horizons: the seasonal mixed layer depth, the particle compensation depth, the base of the euphotic zone, a fixed depth horizon of 100 m, and the maximum annual mixed layer depth. Within this single dynamically consistent model framework, global POC flux rates vary by 30% and global e-ratios by 21% across different depth horizon choices. Zonal variability in POC flux and e-ratio also depends on the export depth horizon due to pronounced influence of deep winter mixing in subpolar regions. Efforts to reconcile conflicting estimates of export need to account for these systematic discrepancies created by differing depth horizon choices.

A charge carrier transport model for donor-acceptor blend layers

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

Fischer, Janine, E-mail: janine.fischer@iapp.de; Widmer, Johannes; Koerner, Christian

2015-01-28

Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C{sub 60} in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for themore » characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (E{sub t} = 0.14 eV, N{sub t} = 1.2 × 10{sup 18 }cm{sup −3}) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.« less

[Soil organic carbon mineralization of Black Locust forest in the deep soil layer of the hilly region of the Loess Plateau, China].

PubMed

Ma, Xin-Xin; Xu, Ming-Xiang; Yang, Kai

2012-11-01

The deep soil layer (below 100 cm) stores considerable soil organic carbon (SOC). We can reveal its stability and provide the basis for certification of the deep soil carbon sinks by studying the SOC mineralization in the deep soil layer. With the shallow soil layer (0-100 cm) as control, the SOC mineralization under the condition (temperature 15 degrees C, the soil water content 8%) of Black Locust forest in the deep soil layer (100-400 cm) of the hilly region of the Loess Plateau was studied. The results showed that: (1) There was a downward trend in the total SOC mineralization with the increase of soil depth. The total SOC mineralization in the sub-deep soil (100-200 cm) and deep soil (200-400 cm) were equivalent to approximately 88.1% and 67.8% of that in the shallow layer (0-100 cm). (2) Throughout the carbon mineralization process, the same as the shallow soil, the sub-deep and deep soil can be divided into 3 stages. In the rapid decomposition phase, the ratio of the mineralization or organic carbon to the total mineralization in the sub-deep and deep layer (0-10 d) was approximately 50% of that in the shallow layer (0-17 d). In the slow decomposition phase, the ratio of organic carbon mineralization to total mineralization in the sub-deep, deep layer (11-45 d) was 150% of that in the shallow layer (18-45 d). There was no significant difference in this ratio among these three layers (46-62 d) in the relatively stable stage. (3) There was no significant difference (P > 0.05) in the mineralization rate of SOC among the shallow, sub-deep, deep layers. The stability of SOC in the deep soil layer (100-400 cm) was similar to that in the shallow soil layer and the SOC in the deep soil layer was also involved in the global carbon cycle. The change of SOC in the deep soil layer should be taken into account when estimating the effects of soil carbon sequestration in the Hilly Region of the Loess Plateau, China.

Ocean impact on Nioghalvfjerdsfjorden Glacier, Northeast Greenland

NASA Astrophysics Data System (ADS)

Schaffer, Janin; Kanzow, Torsten; von Appen, Wilken-Jon; Mayer, Christoph

2017-04-01

The ocean plays an important role in modulating the mass balance of the Greenland Ice Sheet by delivering heat to the marine-terminating outlet glaciers around Greenland. The largest of three outlet glaciers draining the Northeast Greenland Ice Stream is Nioghalvfjerdsfjorden Glacier (also referred to as 79 North Glacier). Historic observations showed that warm waters of Atlantic origin are present in the subglacial cavity below the 80 km long floating ice tongue of the Nioghalvfjerdsfjorden Glacier and cause strong basal melt at the grounding line, but to date it has been unknown how those warm water enter the cavity. In order to understand how Atlantic origin waters carry heat into the subglacial cavity beneath Nioghalvfjerdsfjorden Glacier, we performed bathymetric, hydrographic, and velocity observations in the vicinity of the main glacier calving front aboard RV Polarstern in summer 2016. The bathymetric multibeam data shows a 500 m deep and 2 km narrow passage downstream of a 310 m deep sill. This turned out to be the only location deep enough for an exchange of Atlantic waters between the glacier cavity and the continental shelf. Hydrographic and velocity measurements revealed a density driven plume in the vicinity of the glacier calving front causing a rapid flow of waters of Atlantic origin warmer 1°C into the subglacial cavity through the 500 m deep passage. In addition, glacially modified waters flow out of the glacier cavity below the 80 m deep ice base. In the vicinity of the glacier, the glacially modified waters form a distinct mixed layer situated above the Atlantic waters and below the ambient Polar water. At greater distances from the glacier this layer is eroded by lateral mixing with ambient water. Based on our observations we will present an estimate of the ocean heat transport into the subglacial cavity. In comparison with historic observations we find an increase in Atlantic water temperatures throughout the last 20 years. The resulting enhanced basal melt rates may explain the observed thinning of the glacier tongue.

Toward Exploring the Synergy Between Cloud Radar Polarimetry and Doppler Spectral Analysis in Deep Cold Precipitating Systems in the Arctic

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

Oue, Mariko; Kollias, Pavlos; Ryzhkov, Alexander

The study of Arctic ice and mixed-phase clouds, which are characterized by a variety of ice particle types in the same cloudy volume, is challenging research. This study illustrates a new approach to qualitative and quantitative analysis of the complexity of ice and mixed-phase microphysical processes in Arctic deep precipitating systems using the combination of Ka-band zenith-pointing radar Doppler spectra and quasi-vertical profiles of polarimetric radar variables measured by a Ka/W-band scanning radar. The results illustrate the frequent occurrence of multimodal Doppler spectra in the dendritic/planar growth layer, where locally generated, slower-falling particle populations are well separated from faster-falling populationsmore » in terms of Doppler velocity. The slower-falling particle populations contribute to an increase of differential reflectivity (Z DR), while an enhanced specific differential phase (K DP) in this dendritic growth temperature range is caused by both the slower and faster-falling particle populations. Another area with frequent occurrence of multimodal Doppler spectra is in mixed-phase layers, where both populations produce Z DR and K DP values close to 0, suggesting the occurrence of a riming process. A Joint analysis of the Doppler spectra and the polarimetric radar variables provides important insight into the microphysics of snow formation and allows the separation of the contributions of ice of different habits to the values of reflectivity and Z DR.« less

Toward Exploring the Synergy Between Cloud Radar Polarimetry and Doppler Spectral Analysis in Deep Cold Precipitating Systems in the Arctic

DOE PAGES

Oue, Mariko; Kollias, Pavlos; Ryzhkov, Alexander; ...

2018-03-16

The study of Arctic ice and mixed-phase clouds, which are characterized by a variety of ice particle types in the same cloudy volume, is challenging research. This study illustrates a new approach to qualitative and quantitative analysis of the complexity of ice and mixed-phase microphysical processes in Arctic deep precipitating systems using the combination of Ka-band zenith-pointing radar Doppler spectra and quasi-vertical profiles of polarimetric radar variables measured by a Ka/W-band scanning radar. The results illustrate the frequent occurrence of multimodal Doppler spectra in the dendritic/planar growth layer, where locally generated, slower-falling particle populations are well separated from faster-falling populationsmore » in terms of Doppler velocity. The slower-falling particle populations contribute to an increase of differential reflectivity (Z DR), while an enhanced specific differential phase (K DP) in this dendritic growth temperature range is caused by both the slower and faster-falling particle populations. Another area with frequent occurrence of multimodal Doppler spectra is in mixed-phase layers, where both populations produce Z DR and K DP values close to 0, suggesting the occurrence of a riming process. A Joint analysis of the Doppler spectra and the polarimetric radar variables provides important insight into the microphysics of snow formation and allows the separation of the contributions of ice of different habits to the values of reflectivity and Z DR.« less

Deep learning based classification of morphological patterns in RCM to guide noninvasive diagnosis of melanocytic lesions (Conference Presentation)

NASA Astrophysics Data System (ADS)

Kose, Kivanc; Bozkurt, Alican; Ariafar, Setareh; Alessi-Fox, Christi A.; Gill, Melissa; Dy, Jennifer G.; Brooks, Dana H.; Rajadhyaksha, Milind

2017-02-01

In this study we present a deep learning based classification algorithm for discriminating morphological patterns that appear in RCM mosaics of melanocytic lesions collected at the dermal epidermal junction (DEJ). These patterns are classified into 6 distinct types in the literature: background, meshwork, ring, clod, mixed, and aspecific. Clinicians typically identify these morphological patterns by examination of their textural appearance at 10X magnification. To mimic this process we divided mosaics into smaller regions, which we call tiles, and classify each tile in a deep learning framework. We used previously acquired DEJ mosaics of lesions deemed clinically suspicious, from 20 different patients, which were then labelled according to those 6 types by 2 expert users. We tried three different approaches for classification, all starting with a publicly available convolutional neural network (CNN) trained on natural image, consisting of a series of convolutional layers followed by a series of fully connected layers: (1) We fine-tuned this network using training data from the dataset. (2) Instead, we added an additional fully connected layer before the output layer network and then re-trained only last two layers, (3) We used only the CNN convolutional layers as a feature extractor, encoded the features using a bag of words model, and trained a support vector machine (SVM) classifier. Sensitivity and specificity were generally comparable across the three methods, and in the same ranges as our previous work using SURF features with SVM . Approach (3) was less computationally intensive to train but more sensitive to unbalanced representation of the 6 classes in the training data. However we expect CNN performance to improve as we add more training data because both the features and the classifier are learned jointly from the data. *First two authors share first authorship.

The suborbicularis oculi fat (SOOF) and the fascial planes: has everything already been explained?

PubMed

Andretto Amodeo, Chiara; Casasco, Andrea; Icaro Cornaglia, Antonia; Kang, Robert; Keller, Gregory S

2014-01-01

During anatomic and surgical dissections, a connection was seen between the superficial layer of the deep temporal fascia and the prezygomatic area. These findings were in contrast to previous evaluations. This study defines this connection, which is important to understand from both surgical and anatomic standpoints. To define the connection between the superficial layer of the deep temporal fascia and the prezygomatic area and demonstrate the presence of a deep fascial layer in the midface. Anatomical study performed at the Laboratoire d'Anatomie de la Faculté de Médecine de Nice, Sophia Antipolis, France; at the Centre du Don des Corps de l'Université Paris Descartes, Paris, France; and at the Department of Experimental Medicine, Histology, and Embryology Unit of the University of Pavia, Pavia, Italy. Twenty-four hemifaces of 14 white cadavers were dissected to define the relationship between deep temporal fascia and the midface. Four biopsy samples were harvested for histologic analysis. Dissection of 24 hemifaces from the fresh cadavers revealed the following findings. There is a connection of the deep fascia of the temple (superficial layer of deep temporal fascia) to the midface that divides the fat deep to the orbicularis muscle into 2 layers. One layer of fat is the so-called suborbicularis oculi fat (SOOF), which is superficial to the deep fascia, and the other layer of fat (preperiosteal) is deep to the deep fascia and adherent to malar bone. These findings are in contrast to previous anatomical findings. RESULTS In 12 hemifaces, the superficial layer of the deep temporal fascia directly reached the prezygomatic area as a continuous fascial layer. In 16 hemifaces, the superficial sheet of the deep temporal fascia inserted at the level of the zygomatic and lateral orbital rim and continued as a deep fascial layer over the prezygomatic area. In all specimens, a deep fascial layer was present in the prezygomatic-infraorbital area. This deep fascial layer is adherent to the muscles of the infraorbital area, and it divided the fat located deep to the orbicularis oculi muscle into 2 layers: the SOOF and a deeper layer. Histologic examination of the biopsy samples confirmed these findings. This study demonstrates the existence of a deep fascial layer in the midface. This fascia is connected to the superficial layer of the deep temporal fascia, and it divides the fat deep to the orbicularis oculi muscle into 2 layers. This new finding carries interesting implications related to the classic concept of the superficial musculoaponeurotic system. NA.

Modification of deep waters in Marguerite Bay, western Antarctic Peninsula, caused by topographic overflows

NASA Astrophysics Data System (ADS)

Venables, Hugh J.; Meredith, Michael P.; Brearley, J. Alexander

2017-05-01

Circumpolar Deep Water (CDW) intrudes from the mid-layers of the Antarctic Circumpolar Current onto the shelf of the western Antarctic Peninsula, providing a source of heat and nutrients to the regional ocean. It is well known that CDW is modified as it flows across the shelf, but the mechanisms responsible for this are not fully known. Here, data from underwater gliders with high spatial resolution are used to demonstrate the importance of detailed bathymetry in inducing multiple local mixing events. Clear evidence for overflows is observed in the glider data as water flows along a deep channel with multiple transverse ridges. The ridges block the densest waters, with overflowing water descending several hundred metres to fill subsequent basins. This vertical flow leads to entrainment of overlying colder and fresher water in localised mixing events. Initially this process leads to an increase in bottom temperatures due to the temperature maximum waters descending to greater depths. After several ridges, however, the mixing is sufficient to remove the temperature maximum completely and the entrainment of colder thermocline waters to depth reduces the bottom temperature, to approximately the same as in the source region of Marguerite Trough. Similarly, it is shown that deep waters of Palmer Deep are warmer than at the same depth at the shelf break. The exact details of the transformations observed are heavily dependent on the local bathymetry and water column structure, but glacially-carved troughs and shallow sills are a common feature of the bathymetry of polar shelves, and these types of processes may be a factor in determining the hydrographic conditions close to the coast across a wider area.

Comparison of Four Mixed Layer Mesoscale Parameterizations and the Equation for an Arbitrary Tracer

NASA Technical Reports Server (NTRS)

Canuto, V. M.; Dubovikov, M. S.

2011-01-01

In this paper we discuss two issues, the inter-comparison of four mixed layer mesoscale parameterizations and the search for the eddy induced velocity for an arbitrary tracer. It must be stressed that our analysis is limited to mixed layer mesoscales since we do not treat sub-mesoscales and small turbulent mixing. As for the first item, since three of the four parameterizations are expressed in terms of a stream function and a residual flux of the RMT formalism (residual mean theory), while the fourth is expressed in terms of vertical and horizontal fluxes, we needed a formalism to connect the two formulations. The standard RMT representation developed for the deep ocean cannot be extended to the mixed layer since its stream function does not vanish at the ocean's surface. We develop a new RMT representation that satisfies the surface boundary condition. As for the general form of the eddy induced velocity for an arbitrary tracer, thus far, it has been assumed that there is only the one that originates from the curl of the stream function. This is because it was assumed that the tracer residual flux is purely diffusive. On the other hand, we show that in the case of an arbitrary tracer, the residual flux has also a skew component that gives rise to an additional bolus velocity. Therefore, instead of only one bolus velocity, there are now two, one coming from the curl of the stream function and other from the skew part of the residual flux. In the buoyancy case, only one bolus velocity contributes to the mean buoyancy equation since the residual flux is indeed only diffusive.

Evaluation of vertical coordinate and vertical mixing algorithms in the HYbrid-Coordinate Ocean Model (HYCOM)

NASA Astrophysics Data System (ADS)

Halliwell, George R.

Vertical coordinate and vertical mixing algorithms included in the HYbrid Coordinate Ocean Model (HYCOM) are evaluated in low-resolution climatological simulations of the Atlantic Ocean. The hybrid vertical coordinates are isopycnic in the deep ocean interior, but smoothly transition to level (pressure) coordinates near the ocean surface, to sigma coordinates in shallow water regions, and back again to level coordinates in very shallow water. By comparing simulations to climatology, the best model performance is realized using hybrid coordinates in conjunction with one of the three available differential vertical mixing models: the nonlocal K-Profile Parameterization, the NASA GISS level 2 turbulence closure, and the Mellor-Yamada level 2.5 turbulence closure. Good performance is also achieved using the quasi-slab Price-Weller-Pinkel dynamical instability model. Differences among these simulations are too small relative to other errors and biases to identify the "best" vertical mixing model for low-resolution climate simulations. Model performance deteriorates slightly when the Kraus-Turner slab mixed layer model is used with hybrid coordinates. This deterioration is smallest when solar radiation penetrates beneath the mixed layer and when shear instability mixing is included. A simulation performed using isopycnic coordinates to emulate the Miami Isopycnic Coordinate Ocean Model (MICOM), which uses Kraus-Turner mixing without penetrating shortwave radiation and shear instability mixing, demonstrates that the advantages of switching from isopycnic to hybrid coordinates and including more sophisticated turbulence closures outweigh the negative numerical effects of maintaining hybrid vertical coordinates.

Water mass dynamics shape Ross Sea protist communities in mesopelagic and bathypelagic layers

NASA Astrophysics Data System (ADS)

Zoccarato, Luca; Pallavicini, Alberto; Cerino, Federica; Fonda Umani, Serena; Celussi, Mauro

2016-12-01

Deep-sea environments host the largest pool of microbes and represent the last largely unexplored and poorly known ecosystems on Earth. The Ross Sea is characterized by unique oceanographic dynamics and harbors several water masses deeply involved in cooling and ventilation of deep oceans. In this study the V9 region of the 18S rDNA was targeted and sequenced with the Ion Torrent high-throughput sequencing technology to unveil differences in protist communities (>2 μm) correlated with biogeochemical properties of the water masses. The analyzed samples were significantly different in terms of environmental parameters and community composition outlining significant structuring effects of temperature and salinity. Overall, Alveolata (especially Dinophyta), Stramenopiles and Excavata groups dominated mesopelagic and bathypelagic layers, and protist communities were shaped according to the biogeochemistry of the water masses (advection effect and mixing events). Newly-formed High Salinity Shelf Water (HSSW) was characterized by high relative abundance of phototrophic organisms that bloom at the surface during the austral summer. Oxygen-depleted Circumpolar Deep Water (CDW) showed higher abundance of Excavata, common bacterivores in deep water masses. At the shelf-break, Antarctic Bottom Water (AABW), formed by the entrainment of shelf waters in CDW, maintained the eukaryotic genetic signature typical of both parental water masses.

Long-period variability of oxygen dissolved in Black Sea waters

NASA Astrophysics Data System (ADS)

Polonsky, A. B.; Kotolypova, A. A.

2017-09-01

Using an archival database from the Institute of Natural and Technical Systems, the low-frequency variability of oxygen dissolved in the deep-water and northwestern parts of the Black Sea for the period of 1955-2004 is analyzed. The upper mixed layer (UML) is characterized by quasi-periodic variability in the dissolved oxygen concentration in the interdecadal scale. Deeper, a long-term decrease in the oxygen concentration is recorded.

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.

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.

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. II - Wall shear stress

NASA Technical Reports Server (NTRS)

Liou, M. S.; Adamson, T. C., Jr.

1980-01-01

Asymptotic methods are used to calculate the shear stress at the wall for the interaction between a normal shock wave and a turbulent boundary layer on a flat plate. A mixing length model is used for the eddy viscosity. The shock wave is taken to be strong enough that the sonic line is deep in the boundary layer and the upstream influence is thus very small. It is shown that unlike the result found for laminar flow an asymptotic criterion for separation is not found; however, conditions for incipient separation are computed numerically using the derived solution for the shear stress at the wall. Results are compared with available experimental measurements.

Phosphorus doping a semiconductor particle

DOEpatents

Stevens, G.D.; Reynolds, J.S.

1999-07-20

A method of phosphorus doping a semiconductor particle using ammonium phosphate is disclosed. A p-doped silicon sphere is mixed with a diluted solution of ammonium phosphate having a predetermined concentration. These spheres are dried with the phosphorus then being diffused into the sphere to create either a shallow or deep p-n junction. A good PSG glass layer is formed on the surface of the sphere during the diffusion process. A subsequent segregation anneal process is utilized to strip metal impurities from near the p-n junction into the glass layer. A subsequent HF strip procedure is then utilized to removed the PSG layer. Ammonium phosphate is not a restricted chemical, is inexpensive, and does not pose any special shipping, handling, or disposal requirement. 1 fig.

Phosphorous doping a semiconductor particle

DOEpatents

Stevens, Gary Don; Reynolds, Jeffrey Scott

1999-07-20

A method (10) of phosphorus doping a semiconductor particle using ammonium phosphate. A p-doped silicon sphere is mixed with a diluted solution of ammonium phosphate having a predetermined concentration. These spheres are dried (16, 18), with the phosphorus then being diffused (20) into the sphere to create either a shallow or deep p-n junction. A good PSG glass layer is formed on the surface of the sphere during the diffusion process. A subsequent segregation anneal process is utilized to strip metal impurities from near the p-n junction into the glass layer. A subsequent HF strip procedure is then utilized to removed the PSG layer. Ammonium phosphate is not a restricted chemical, is inexpensive, and does not pose any special shipping, handling, or disposal requirement.

How Diffusivity, Thermocline and Incident Light Intensity Modulate the Dynamics of Deep Chlorophyll Maximum in Tyrrhenian Sea

PubMed Central

Valenti, Davide; Denaro, Giovanni; Spagnolo, Bernardo; Conversano, Fabio; Brunet, Christophe

2015-01-01

During the last few years theoretical works have shed new light and proposed new hypotheses on the mechanisms which regulate the spatio-temporal behaviour of phytoplankton communities in marine pelagic ecosystems. Despite this, relevant physical and biological issues, such as effects of the time-dependent mixing in the upper layer, competition between groups, and dynamics of non-stationary deep chlorophyll maxima, are still open questions. In this work, we analyze the spatio-temporal behaviour of five phytoplankton populations in a real marine ecosystem by using a one-dimensional reaction-diffusion-taxis model. The study is performed, taking into account the seasonal variations of environmental variables, such as light intensity, thickness of upper mixed layer and profiles of vertical turbulent diffusivity, obtained starting from experimental findings. Theoretical distributions of phytoplankton cell concentration was converted in chlorophyll concentration, and compared with the experimental profiles measured in a site of the Tyrrhenian Sea at four different times (seasons) of the year, during four different oceanographic cruises. As a result we find a good agreement between theoretical and experimental distributions of chlorophyll concentration. In particular, theoretical results reveal that the seasonal changes of environmental variables play a key role in the phytoplankton distribution and determine the properties of the deep chlorophyll maximum. This study could be extended to other marine ecosystems to predict future changes in the phytoplankton biomass due to global warming, in view of devising strategies to prevent the decline of the primary production and the consequent decrease of fish species. PMID:25629963

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.

Does the Deep Layer of the Deep Temporalis Fascia Really Exist?

PubMed

Li, Hui; Li, Kaide; Jia, Wenhao; Han, Chaoying; Chen, Jinlong; Liu, Lei

2018-04-14

It has been widely accepted that a split of the deep temporal fascia occurs approximately 2 to 3 cm above the zygomatic arch and extends into the superficial and deep layers. The deep layer of the deep temporal fascia is between the superficial temporal fat pad and the temporal muscle. However, during procedures, the authors noted the absence of the deep layer of the deep temporal fascia between the superficial temporal fat pad and the temporal muscle. This prospective study was conducted to clarify the presence or absence of a deep layer of the deep temporal fascia. Anatomic layers of the soft tissues of the temporal region, with reference to the deep temporal fascia, were investigated in 130 cases operated on for zygomaticofacial fractures using the supratemporal approach from June 2013 to June 2017. Of 130 surgeries, the authors found the absence of a thick, obviously identifiable, fascial layer between the superficial temporal fat pad and the temporal muscle. In fact, the authors found nothing above the temporal muscle in most cases. In a few cases, the authors observed only a small amount of scattered loose connective tissue between the superficial temporal fat pad and the temporal muscle. This clinical study showed the absence of a thick, obviously identifiable, fascial layer between the superficial temporal fat pad and the temporal muscle, which suggests that a "deep layer of the deep temporal fascia" might not exist. Copyright © 2018. Published by Elsevier Inc.

Some Remarks on Practical Aspects of Laboratory Testing of Deep Soil Mixing Composites Achieved in Organic Soils

NASA Astrophysics Data System (ADS)

Kanty, Piotr; Rybak, Jarosław; Stefaniuk, Damian

2017-10-01

This paper presents the results of laboratory testing of organic soil-cement samples are presented in the paper. The research program continues previously reported the authors’ experiences with cement-fly ash-soil sample testing. Over 100 of compression and a dozen of tension tests have been carried out altogether. Several samples were waiting for failure test for over one year after they were formed. Several factors, like: the large amount of the tested samples, a long observation time, carrying out the tests in complex cycles of loading and the possibility of registering the loads and deformation in the axial and lateral direction - have made it possible to take into consideration numerous interdependencies, three of which have been presented in this work: the increments of compression strength, the stiffness of soil-cement in relation to strength and the tensile strength. Compressive strength, elastic modulus and tensile resistance of cubic samples were examined. Samples were mixed and stored in the laboratory conditions. Further numerical analysis in the Finite Element Method numerical code Z_Soil, were performed on the basis of laboratory test results. Computations prove that cement-based stabilization of organic soil brings serious risks (in terms of material capacity and stiffness) and Deep Soil Mixing technology should not be recommended for achieving it. The numerical analysis presented in the study below includes only one type of organic and sandy soil and several possible geometric combinations. Despite that, it clearly points to the fact that designing the DSM columns in the organic soil may be linked with a considerable risk and the settlement may reach too high values. During in situ mixing, the organic material surrounded by sand layers surely mixes with one another in certain areas. However, it has not been examined and it is difficult to assume such mixing already at the designing stage. In case of designing the DSM columns which goes through a thin layer of organic soil it is recommended to carry out each time the core drilling which checks the degree of material mixing and their strength.

The Effects of Storm Runoff on Water Quality and the Coping Strategy of a Deep Canyon-Shaped Source Water Reservoir in China

PubMed Central

Ma, Weixing; Huang, Tinglin; Li, Xuan; Zhou, Zizhen; Li, Yang; Zeng, Kang

2015-01-01

Storm runoff events in the flooding season affect the water quality of reservoirs and increase risks to the water supply, but coping strategies have seldom been reported. The phenomenon of turbid current intrusion resulting in water turbidity and anoxic conditions reappearing after storm runoff, resulting in the deterioration of water quality, was observed in the flooding season in the deep canyon-shaped Heihe Reservoir. The objective of this work was to elucidate the effects of storm runoff on the Heihe Reservoir water quality and find a coping strategy. In this study, an intensive sampling campaign measuring water temperature, dissolved oxygen, turbidity, nutrients, and metals were conducted in the reservoir over a period of two years, and the water-lifting aerators were improved to achieve single aeration and a full layer of mixing and oxygenation functions using different volumes of gas. The operation of the improved water-lifting aerators mixed the reservoir three months ahead of the natural mixing time, and good water quality was maintained during the induced mixing period, thereby extending the good water quality period. The results can provide an effective coping strategy to improve the water quality of a source water reservoir and ensure the safety of drinking water. PMID:26184258

Investigation of Deep Ocean Circulation and Mixing Using Ar-39 (Invited)

NASA Astrophysics Data System (ADS)

Smethie, W. M.; Schlosser, P.

2013-12-01

Ar-39 is a radioactive noble gas that forms in the atmosphere by cosmic ray interaction with Ar-40. It has a half-life of 269 years and its production rate in the atmosphere has varied no more than 7% during the past 1000 years. It enters the surface ocean with an average equilibration time of about one month and thus the entire surface ocean, except for ice covered regions at high latitudes, is in quasi-equilibrium with the atmospheric Ar-39:Ar ratio. The well known input to the ocean, radioactive decay constant and chemical inertness make Ar-39 an ideal tracer of circulation and mixing in the deep ocean, where anthropogenic transient tracers such as CFCs and tritium have not yet penetrated. However, due to the difficult measurement, only about 125 oceanic Ar-39 samples have been measured to date. This was done by counting the decays of Ar-39 atoms and required a half liter of argon gas per sample, extracted from about 1500 liters of water. The 125 samples that have been measured provide a glimpse of the information that can be gained from Ar-39 observations. In the Pacific Ocean three vertical profiles show a decrease in Ar-39 from the surface mixed layer through the thermocline to a minimum at intermediate depths and an increase from there to the bottom. This reflects formation of bottom water around the Antarctic continent, spreading of this water northward and upwelling and mixing into intermediate depths. The lowest concentration was 6×4% modern which is equivalent to a 900-1600 year isolation time from the surface. In the Atlantic Ocean newly formed North Atlantic Deep Water has an Ar-39 concentration of about 85% modern compared to 55% modern for newly formed Antarctic Bottom Water and reach values as low as about 40% modern in the interior reflecting the more rapid ventilation of the deep Atlantic Ocean relative to the deep Pacific Ocean. In the Arctic Ocean the mean residence time of deep water in the Nansen, Amundsen and Makarov Basins based on Ar-39 are about 270, 190, and 330 years respectively. Radiocarbon also provides information on circulation and mixing in the deep ocean and thousands of measurements have been made. However, the distributions of Ar-39 and C-14 are different due to the large difference in their half-lives (269 years and 5730 years respectively). Measurement of both tracers provides information on the relative importance of advection and mixing in the deep ocean and provides more accurate transit times than can be obtained with only one of these tracers. In the Atlantic Ocean, where the deep water is roughly a two-end member mixture of northern component and southern component water, the age of the two components can be estimated from simultaneous measurement of Ar-39 and C-14. The few existing measurements suggest that the northern component water has an age range of 40-200 years and the southern component water a range of 60-600 years. Development of the ATTA method for measuring radioactive noble gases offers great potential to dramatically increase the number of samples that can be measured for Ar-39, which could greatly improve our understanding of mixing and circulation in the deep ocean.

Seasonality of Red Sea Mixed-Layer Depth and Density Budget

NASA Astrophysics Data System (ADS)

Kartadikaria, A. R.; Cerovecki, I.; Krokos, G.; Hoteit, I.

2016-02-01

The Red Sea is an active area of water mass formation. Dense water initially formed in the northern Red Sea, in the Gulf of Aqaba and the Gulf of Suez, spreads southward and finally flows to the open ocean through the Gulf of Aden via the narrow strait of Bab Al Mandeb. The signature of this outflow can be traced until the southern Indian Ocean, and is characterized by potential density of σθ ≈ 27.4. This water mass is important because it represents a significant source of heat and salt for the Indian Ocean. Using a high-resolution 1km regional MITgcm ocean model for the period 1992-2001 configured for the Red Sea, we examine the spatio-temporal characteristics of water mass formation inside the basin by analyzing closed and complete temperature and salinity budgets. The deepest mixed-layers (MLD) always develop in the northern part of the basin where surface ocean buoyancy loss leads to the Red Sea Intermediate and Deep Water formation. As this water is advected south, it is strongly modified by diapycnal mixing of heat and salt.

Thermodynamic Controls on Deep Convection in the Tropics: Observations and Applications to Modeling

NASA Astrophysics Data System (ADS)

Schiro, Kathleen Anne

Constraining precipitation processes in climate models with observations is crucial to accurately simulating current climate and reducing uncertainties in future projections. This work presents robust relationships between tropical deep convection, column-integrated water vapor (CWV), and other thermodynamic quantities analyzed with data from the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility in Manacapuru, Brazil as part of the GOAmazon campaign and are directly compared to such relationships at DOE ARM sites in the tropical western Pacific. A robust relationship between CWV and precipitation, as explained by variability in lower tropospheric humidity, exists just as strongly in a tropical continental region as it does in a tropical oceanic region. Given sufficient mixing in the lower troposphere, higher CWV generally results in greater plume buoyancies through a deep convective layer. Although sensitivity of convection to other controls is suggested, such as microphysical processes and dynamical lifting mechanisms, the increase in buoyancy with CWV is consistent with the sharp increase in precipitation observed. Entraining plume buoyancy calculations confirm that CWV is a good proxy for the conditional instability of the environment, yet differences in convective onset as a function of CWV exist over land and ocean, as well as seasonally and diurnally over land. This is largely due to variability in the contribution of lower tropospheric humidity to the total column moisture. Over land, the relationship between deep convection and lower free tropospheric moisture is robust across all seasons and times of day, whereas the relation to boundary layer moisture is robust for the daytime only. Using S-Band radar, these transition statistics are examined separately for unorganized and mesoscale-organized convection, which exhibit sharp increases in probability of occurrence with increasing moisture throughout the column, particularly in the lower free troposphere. An observational basis for an integrated buoyancy measure from a single plume buoyancy formulation that provides a strong relation to precipitation can be useful for constraining convective parameterizations. A mixing scheme corresponding to deep inflow of environmental air into a plume that grows with height provides a weighting of boundary layer and free tropospheric air that yields buoyancies consistent with the observed onset of deep convection across seasons and times of day, across land and ocean sites, and for all convection types. This provides a substantial improvement relative to more traditional constant mixing assumptions, and a dramatic improvement relative to no mixing. Furthermore, it provides relationships that are as strong or stronger for mesoscale-organized convection as for unorganized convection. Downdrafts and their associated parameters are poorly constrained in models, as physical and microphysical processes of leading order importance are difficult to observe with sufficient frequency for development of robust statistics. Downdrafts and cold pool characteristics for mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection in the Amazon are composited and both exhibit similar signatures in wind speed, surface fluxes, surface equivalent potential temperature (theta e) and precipitation. For both MCSs and unorganized convection, downdrafts associated with the strongest modifications to surface thermodynamics have increasing probability of occurrence with decreasing height through the lowest 4 km and show similar mean downdraft magnitudes with height. If theta e is approximately conserved following descent, a large fraction of the air reaching the surface likely originates at altitudes in the lowest 2 km. Mixing computations suggest that, on average, air originating at heights greater than 3 km would require substantial mixing, particularly in the case of isolated cells, to match the observed cold pool thetae . Statistics from two years of surface meteorological data at the GOAmazon site and 15 years of data at the DOE ARM site on Manus Island in the tropical western Pacific show that Deltathetae conditioned on precipitation levels off with increasing precipitation rate, bounded by the maximum difference between surface thetae and its minimum in the profile aloft. Robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.

Lidar Observations of the Vertical Structure of Ozone and Aerosol during Wintertime High-Ozone Episodes Associated with Oil and Gas Exploration in the Uintah Basin

NASA Astrophysics Data System (ADS)

Senff, C. J.; Langford, A. O.; Banta, R. M.; Alvarez, R. J.; Weickmann, A.; Sandberg, S.; Marchbanks, R. D.; Brewer, A.; Hardesty, R. M.

2013-12-01

The Uintah Basin in northeast Utah has been experiencing extended periods of poor air quality in the winter months including very high levels of surface ozone. To investigate the causes of these wintertime ozone pollution episodes, two comprehensive studies were undertaken in January/February of 2012 and 2013. As part of these Uintah Basin Ozone Studies (UBOS), NOAA deployed its ground-based, scanning Tunable Optical Profiler for Aerosol and oZone (TOPAZ) lidar to document the vertical structure of ozone and aerosol backscatter from near the surface up to about 3 km above ground level (AGL). TOPAZ, along with a comprehensive set of chemistry and meteorological measurements, was situated in both years at the Horse Pool site at the northern edge of a large concentration of gas producing wells in the eastern part of the Uintah Basin. The 2012 study was characterized by unusually warm and snow-free condition and the TOPAZ lidar observed deep boundary layers (BL) and mostly well-mixed vertical ozone profiles at or slightly above tropospheric background levels. During UBOS 2013, winter weather conditions in the Uintah Basin were more typical with snow-covered ground and a persistent, shallow cold-pool layer. The TOPAZ lidar characterized with great temporal and spatial detail the evolution of multiple high-ozone episodes as well as cleanout events caused by the passage of synoptic-scale storm systems. Despite the snow cover, the TOPAZ observations show well-mixed afternoon ozone and aerosol profiles up to about 100 m AGL. After several days of pollutant buildup, BL ozone values reached 120-150 ppbv. Above the mixed layer, ozone values gradually decreased to tropospheric background values of around 50 ppbv throughout the several-hundred-meter-deep cold-pool layer and then stayed constant above that up to about 3 km AGL. During the ozone episodes, the lidar observations show no indication of either vertical or horizontal transport of high ozone levels to the surface, thus supporting the notion that ozone is locally produced in the Uintah Basin. In both winters, TOPAZ occasionally observed ozone titration as the NOx-rich plume from the nearby Bonanza power plant was advected over the Horse Pool site. In 2012, low ozone values due to titration were observed at the surface and throughout the well-mixed BL, while in 2013 low ozone values were confined to the upper part of the cold-pool layer above the BL. This suggests that power plant NOx was very likely not part of the precursor mix that led to the high surface ozone values observed in 2013.

1/f model for long-time memory of the ocean surface temperature

NASA Astrophysics Data System (ADS)

Fraedrich, Klaus; Luksch, Ute; Blender, Richard

2004-09-01

The 1/f spectrum of the ocean surface temperature in the Atlantic and Pacific midlatitudes is explained by a simple vertical diffusion model with a shallow mixed layer on top of a deep ocean. The model is forced at the air-sea interface with the total surface heat flux from a 1000 year climate simulation. The analysis reveals the role of ocean advection and substantiates estimates of internal thermal diffusivities.

Depth evolution of the Meirama pit lake, A Coruña, NW Spain

NASA Astrophysics Data System (ADS)

Delgado, Jordi; Juncosa-Rivera, Ricardo; Cereijo-Arango, José Luis; García-Morrondo, David; Muñoz-Ibáñez, Andrea; Grande-García, Elisa; Rodríguez-Cedrún, Borja

2016-04-01

The Meirama pit lake is a water mass in the process of controlled flooding that, by the end of December 2015, can be described as a steadily stratified meromictic system. The deepest portion of the lake (monimolimnion) is isolated regarding the annual mixing dynamics (December/January) of the upper water body (mixolimnion), for which the depth of mixing is restricted to a water column of 35-40 m thick. Due to the contrasting flooding history (access of groundwater at the beginning and mixed access of stream/groundwater (being dominant the stream water) the deepest portion of the lake is separated from the upper, non-mixed layer by a marked chemocline. Strictly speaking, the monimolimnion of a meromictic lake extends to the waters located beneath the mixed lake layer. In the case of the Meirama Lake the monimolimnion is internally stratified and made of two major water bodies. From hereafter the deep and upper monimolimnion will be identified as bottom and middle sections of the lake while the mixolimnion is referred to as the surface layer. The general characteristics and evolution of the Meirama Lake have been reported elsewhere. In this work we focus on a summary description of the chemical evolution of the monimolimnion of the lake based on data gathered between 2009 and 2015 from the still on-going monitoring survey. The chemical evolution of the monimolimnion of the lake differs significantly from that of the mixolimnion. In general, surface water is sensible to seasonal fluctuations due to weather conditions, rainfall and biogeochemical processes. The middle and bottom sections are not sensible, in general, to this effects and their evolution obeys to a number of internal processes. In the case of temperature we observe a nearly constant gradient increase (0.001 °C/day) in the middle and deep lake waters up to the beginning of 2012, where it remains constant. The rise in temperature is likely due to the heat provided by groundwater seepage whose temperature is above that of the lake water at the corresponding depth. Likewise, electrical conductance shows a similar constant-rate increasing rate (0.223 and 0.115 S/cm-day in the bottom and middle sections, respectively) whose origin we also associate with groundwater seepage. Based on a wide number of parameters (O2, Cl, SO4, NO3, NO2, NH4, Fe, Mn…) we observe that the monimolimnion of the lake, either in its bottom or middle layer is a rather dynamic (transient) geochemical system.

Application of interleaving models to describe intrusive layers in the Deep Polar Water of the Arctic Basin

NASA Astrophysics Data System (ADS)

Zhurbas, Nataliya; Kuzmina, Natalia; Lyzhkov, Dmitry; Izvekova, Yulia N.

2016-04-01

Interleaving models of pure thermohaline and baroclinic frontal zones of finite width are applied to describe intrusions at the fronts found in the upper part of the Deep Polar Water, the Eurasian basin, under stable-stable thermohaline stratification. It is assumed that differential mixing is the main mechanism of the intrusion formation. Different parameterizations of differential mixing (Merrryfield, 2002; Kuzmina et al., 2011) are used in the models. Important parameters of interleaving such as the growth rate, vertical scale, and slope of the most unstable modes are calculated. It is found that the interleaving model of a pure thermohaline front can satisfactory describe the important parameters of intrusions observed at a thermohaline, very low baroclinicity front in the Eurasian basin, just in accordance to Merryfield (2002) findings. In the case of baroclinic front, satisfactory agreement over all the interleaving parameters is found between the model calculations and observations provided that the vertical momentum diffusivity significantly exceeds the corresponding mass diffusivity. Under specific (reasonable) constraints of the vertical momentum diffusivity, the most unstable mode has a vertical scale approximately two-three times smaller than the vertical scale of the observed intrusions. A thorough discussion of the results is presented. References Kuzmina N., Rudels B., Zhurbas V., Stipa T. On the structure and dynamical features of intrusive layering in the Eurasian Basin in the Arctic Ocean. J. Geophys. Res., 2011, 116, C00D11, doi:10.1029/2010JC006920. Merryfield W. J. Intrusions in Double-Diffusively Stable Arctic Waters: Evidence for Differential mixing? J. Phys. Oceanogr., 2002, 32, 1452-1439.

A three-dimensional ocean mesoscale simulation using data from the SEMAPHORE experiment: Mixed layer heat budget

NASA Astrophysics Data System (ADS)

Caniaux, Guy; Planton, Serge

1998-10-01

A primitive equation model is used to simulate the mesoscale circulation associated with a portion of the Azores Front investigated during the intensive observation period (IOP) of the Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment in fall 1993. The model is a mesoscale version of the ocean general circulation model (OGCM) developed at the Laboratoire d'Océanographie Dynamique et de Climatologie (LODYC) in Paris and includes open lateral boundaries, a 1.5-level-order turbulence closure scheme, and fine mesh resolution (0.11° for latitude and 0.09° for longitude). The atmospheric forcing is provided by satellite data for the solar and infrared fluxes and by analyzed (or reanalyzed for the wind) atmospheric data from the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast model. The extended data set collected during the IOP of SEMAPHORE enables a detailed initialization of the model, a coupling with the rest of the basin through time dependent open boundaries, and a model/data comparison for validation. The analysis of model outputs indicates that most features are in good agreement with independent available observations. The surface front evolution is subject to an intense deformation different from that of the deep front system, which evolves only weakly. An estimate of the upper layer heat budget is performed during the 22 days of the integration of the model. Each term of this budget is analyzed according to various atmospheric events that occurred during the experiment, such as the passage of a strong storm. This facilitates extended estimates of mixed layer or relevant surface processes beyond those which are obtainable directly from observations. Surface fluxes represent 54% of the heat loss in the mixed layer and 70% in the top 100-m layer, while vertical transport at the mixed layer bottom accounts for 31% and three-dimensional processes account for 14%.

On sharp vorticity gradients in elongating baroclinic eddies and their stabilization with a solid-body rotation

NASA Astrophysics Data System (ADS)

Sutyrin, Georgi G.

2016-06-01

Wide compensated vortices are not able to remain circular in idealized two-layer models unless the ocean depth is assumed to be unrealistically large. Small perturbations on both cyclonic and anticyclonic eddies grow slower if a middle layer with uniform potential vorticity (PV) is added, owing to a weakening of the vertical coupling between the upper and lower layers and a reduction of the PV gradient in the deep layer. Numerical simulations show that the nonlinear development of the most unstable elliptical mode causes self-elongation of the upper vortex core and splitting of the deep PV anomaly into two corotating parts. The emerging tripolar flow pattern in the lower layer results in self-intensification of the fluid rotation in the water column around the vortex center. Further vortex evolution depends on the model parameters and initial conditions, which limits predictability owing to multiple equilibrium attractors existing in the dynamical system. The vortex core strips thin filaments, which roll up into submesoscale vortices to result in substantial mixing at the vortex periphery. Stirring and damping of vorticity by bottom friction are found to be essential for subsequent vortex stabilization. The development of sharp PV gradients leads to nearly solid-body rotation inside the vortex core and formation of transport barriers at the vortex periphery. These processes have important implications for understanding the longevity of real-ocean eddies.

A case study of microphysical structures and hydrometeor phase in convection using radar Doppler spectra at Darwin, Australia

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

Riihimaki, Laura D.; Comstock, Jennifer M.; Luke, Edward

To understand the microphysical processes that impact diabatic heating and cloud lifetimes in convection, we need to characterize the spatial distribution of supercooled liquid water. To address this observational challenge, vertically pointing active sensors at the Darwin Atmospheric Radiation Measurement (ARM) site are used to classify cloud phase within a deep convective cloud in a shallow to deep convection transitional case. The cloud cannot be fully observed by a lidar due to signal attenuation. Thus we develop an objective method for identifying hydrometeor classes, including mixed-phase conditions, using k-means clustering on parameters that describe the shape of the Doppler spectramore » from vertically pointing Ka band cloud radar. This approach shows that multiple, overlapping mixed-phase layers exist within the cloud, rather than a single region of supercooled liquid, indicating complexity to how ice growth and diabatic heating occurs in the vertical structure of the cloud.« less

The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink.

PubMed

Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

2015-09-18

Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.

The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

PubMed Central

Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

2015-01-01

Reduced surface–deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface–subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring–summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall–winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink. PMID:26382319

Convective Formation of Pileus Cloud Near the Tropopause

NASA Technical Reports Server (NTRS)

Garrett, Timothy J.; Dean-Day, Jonathan; Liu, Chuntao; Barnett, Brian K.; Mace, Gerald G.; Baumgardner, Darrel G.; Webster, Christopher R.; Bui, T. Paul; Read, William G.; Minnis, Patrick

2005-01-01

Pileus clouds form where humid, stably stratified air is mechanically displaced vertically ahead of rising convection. This paper describes convective formation of pileus cloud in the tropopause transition layer (TTL), and explores a possible link to the formation of long-lasting cirrus at cold temperatures. In-situ measurements from off the coast of Honduras during the July 2002 CRYSTALFACE experiment show an example of TTL cirrus associated with, and penetrated by, deep convection. The cirrus was enriched with total water compared to its surroundings, but composed of extremely small ice crystals with effective radii between 2 and 4 m. Through gravity wave analysis, and intercomparison of measured and simulated cloud microphysics, it is argued that the TTL cirrus in this case originated neither from convectively-forced gravity wave motions nor environmental mixing alone. Rather, it is hypothesized that some combination was involved in which, first, convection forced pileus cloud to form from TTL air; second, it punctured the pileus layer, contributing larger ice crystals through interfacial mixing; third, the addition of condensate inhibited evaporation of the original pileus ice crystals in the warm phase of the ensuing gravity wave; fourth, through successive pulses, deep convection formed the observed layer of TTL cirrus. While the general incidence and longevity of pileus cloud remains unknown, in-situ measurements, and satellite-based Microwave Limb Sounder retrievals, suggest that much of the tropical TTL is sufficiently humid to be susceptible to its formation. Where these clouds form and persist, there is potential for an irreversible repartition from water vapor to ice at cold temperatures.

The atmospheric boundary layer in the CSIRO global climate model: simulations versus observations

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Rotstayn, L. D.; Krummel, P. B.

2002-07-01

A 5-year simulation of the atmospheric boundary layer in the CSIRO global climate model (GCM) is compared with detailed boundary-layer observations at six locations, two over the ocean and four over land. Field observations, in the form of surface fluxes and vertical profiles of wind, temperature and humidity, are generally available for each hour over periods of one month or more in a single year. GCM simulations are for specific months corresponding to the field observations, for each of five years. At three of the four land sites (two in Australia, one in south-eastern France), modelled rainfall was close to the observed climatological values, but was significantly in deficit at the fourth (Kansas, USA). Observed rainfall during the field expeditions was close to climatology at all four sites. At the Kansas site, modelled screen temperatures (Tsc), diurnal temperature amplitude and sensible heat flux (H) were significantly higher than observed, with modelled evaporation (E) much lower. At the other three land sites, there is excellent correspondence between the diurnal amplitude and phase and absolute values of each variable (Tsc, H, E). Mean monthly vertical profiles for specific times of the day show strong similarities: over land and ocean in vertical shape and absolute values of variables, and in the mixed-layer and nocturnal-inversion depths (over land) and the height of the elevated inversion or height of the cloud layer (over the sea). Of special interest is the presence climatologically of early morning humidity inversions related to dewfall and of nocturnal low-level jets; such features are found in the GCM simulations. The observed day-to-day variability in vertical structure is captured well in the model for most sites, including, over a whole month, the temperature range at all levels in the boundary layer, and the mix of shallow and deep mixed layers. Weaknesses or unrealistic structure include the following, (a) unrealistic model mixed-layer temperature profiles over land in clear skies, related to use of a simple local first-order turbulence closure, (b) a tendency to overpredict cloud liquid water near the surface.

Glacial to interglacial surface nutrient variations of Bering Deep Basins recorded by δ13C and δ15N of sedimentary organic matter

NASA Astrophysics Data System (ADS)

Nakatsuka, Takeshi; Watanabe, Kazuki; Handa, Nobuhiko; Matsumoto, Eiji; Wada, Eitaro

1995-12-01

Stable carbon and nitrogen isotopic ratios (δ13C and δ15N) of organic matter were measured in three sediment cores from deep basins of the Bering Sea to investigate past changes in surface nutrient conditions. For surface water reconstructions, hemipelagic layers in the cores were distinguished from turbidite layers (on the basis of their sedimentary structures and 14C ages) and analyzed for isotopic studies. Although δ13C profiles may have been affected by diagenesis, both δ15N and δ13C values showed common positive anomalies during the last deglaciation. We explain these anomalies as reflecting suppressed vertical mixing and low nutrient concentrations in surface waters caused by injection of meltwater from alpine glaciers around the Bering Sea. Appendix tables are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington , DC 20009. Document P95-003; $2.50. Payment must accompany order.

Observations of near-bottom currents in Bornholm Basin, Slupsk Furrow and Gdansk Deep

NASA Astrophysics Data System (ADS)

Bulczak, A. I.; Rak, D.; Schmidt, B.; Beldowski, J.

2016-06-01

Dense bottom currents are responsible for transport of the salty inflow waters from the North Sea driving ventilation and renewal of Baltic deep waters. This study characterises dense currents in three deep locations of the Baltic Proper: Bornholm Basin (BB), Gdansk Basin (GB) and Slupsk Furrow (SF). These locations are of fundamental importance for the transport and pollution associated with chemical munitions deposited in BB and GB after 2nd World War. Of further importance the sub-basins are situated along the pathway of dense inflowing water.Current velocities were measured in the majority of the water column during regular cruises of r/v Oceania and r/v Baltica in 2001-2012 (38 cruises) by 307 kHz vessel mounted (VM), downlooking ADCP. Additionally, the high-resolution CTD and oxygen profiles were collected. Three moorings measured current velocity profiles in SF and GB over the summer 2012. In addition, temperature, salinity, oxygen and turbidity were measured at about 1 m above the bottom in GB. The results showed that mean current speed across the Baltic Proper was around 12 cm s-1 and the stronger flow was characteristic to the regions located above the sills, in the Bornholm and Slupsk Channels, reaching on average about 20 cm s-1. The results suggest that these regions are important for the inflow of saline waters into the eastern Baltic and are the areas of intense vertical mixing. The VM ADCP observations indicate that the average near-bottom flow across the basin can reach 35±6 cm s-1. The mooring observations also showed similar near-bottom flow velocities. However, they showed that the increased speed of the near-bottom layer occurred frequently in SF and GB during short time periods lasting for about few to several days or 10-20% of time. The observations showed that the bottom mixed layer occupies at least 10% of the water column and the turbulent mixing induced by near-bottom currents is likely to produce sediment resuspension and transport within the layer in all three sub-basins. The turbidity measurements, performed for 5-month-long time period over the summer 2012 in GB show that increased sediment resuspension is associated with a faster near-bottom flow.

Monsoon dependent ecosystems: Implications of the vertical distribution of soil moisture on land surface-atmosphere interactions

NASA Astrophysics Data System (ADS)

Sanchez-Mejia, Zulia M.

Uncertainty of predicted change in precipitation frequency and intensity motivates the scientific community to better understand, quantify, and model the possible outcome of dryland ecosystems. In pulse dependent ecosystems (i.e. monsoon driven) soil moisture is tightly linked to atmospheric processes. Here, I analyze three overarching questions; Q1) How does soil moisture presence or absence in a shallow or deep layer influence the surface energy budget and planetary boundary layer characteristics?, Q2) What is the role of vegetation on ecosystem albedo in the presence or absence of deep soil moisture?, Q3) Can we develop empirical relationships between soil moisture and the planetary boundary layer height to help evaluate the role of future precipitation changes in land surface atmosphere interactions? . To address these questions I use a conceptual framework based on the presence or absence of soil moisture in a shallow or deep layer. I define these layers by using root profiles and establish soil moisture thresholds for each layer using four years of observations from the Santa Rita Creosote Ameriflux site. Soil moisture drydown curves were used to establish the shallow layer threshold in the shallow layer, while NEE (Net Ecosystem Exchange of carbon dioxide) was used to define the deep soil moisture threshold. Four cases were generated using these thresholds: Case 1, dry shallow layer and dry deep layer; Case 2, wet shallow layer and dry deep layer; Case 3, wet shallow layer and wet deep layer, and Case 4 dry shallow and wet deep layer. Using this framework, I related data from the Ameriflux site SRC (Santa Rita Creosote) from 2008 to 2012 and from atmospheric soundings from the nearby Tucson Airport; conducted field campaigns during 2011 and 2012 to measure albedo from individual bare and canopy patches that were then evaluated in a grid to estimate the influence of deep moisture on albedo via vegetation cover change; and evaluated the potential of using a two-layer bucket model and empirical relationships to evaluate the link between deep soil moisture and the planetary boundary layer height under changing precipitation regime. My results indicate that (1) the presence or absence of water in two layers plays a role in surface energy dynamics, (2) soil moisture presence in the deep layer is linked with decreased ecosystem albedo and planetary boundary layer height, (3) deep moisture sustains vegetation greenness and decreases albedo, and (4) empirical relationships are useful in modeling planetary boundary layer height from dryland ecosystems. Based on these results we argue that deep soil moisture plays an important role in land surface-atmosphere interactions.

Constraints on Lunar Structure from Combined Geochemical, Mineralogical, and Geophysical modeling

NASA Astrophysics Data System (ADS)

Bremner, P. M.; Fuqua, H.; Mallik, A.; Diamond, M. R.; Lock, S. J.; Panovska, S.; Nishikawa, Y.; Jiménez-Pérez, H.; Shahar, A.; Panero, W. R.; Lognonne, P. H.; Faul, U.

2016-12-01

The internal physical and geochemical structure of the Moon is still poorly constrained. Here, we take a multidisciplinary approach to attempt to constrain key parameters of the lunar structure. We use an ensemble of 1-D lunar compositional models with chemically and mineralogically distinct layers, and forward calculated physical parameters, in order to constrain the internal structure. We consider both a chemically well-mixed model with uniform bulk composition, and a chemically stratified model that includes a mantle with preserved mineralogical stratigraphy from magma ocean crystallization. Additionally, we use four different lunar temperature profiles that span the range of proposed selenotherms, giving eight separate sets of lunar models. In each set, we employed a grid search and a differential evolution genetic search algorithm to extensively explore model space, where the thickness of individual compositional layers was varied. In total, we forward calculated over one hundred thousand lunar models. It has been proposed that a dense, partially molten layer exists at the CMB to explain the lack of observed far-side deep moonquakes, the observation of reflected seismic phases from deep moonquakes, and enhanced tidal dissipation. However, subsequent models have proposed that these observables can be explained in other ways. In this study, using a variety of modeling techniques, we find that such a layer may have been formed by overturn of an ilmenite-rich layer, formed after the crystallization of a magma ocean. We therefore include a denser layer (modeled as an ilmenite-rich layer) at both the top and bottom of the lunar mantle in our models. For each set of models, we find models that explain the observed lunar mass and moment of inertia. We find that only a narrow range of core radii are consistent with the mass and moment of inertia constraints. Furthermore, in the chemically well-mixed models, we find that a dense layer is required in the upper mantle to meet the moment of inertia requirement. In no set of models is the mass of the lower dense layer well constrained. For the models that fit the observed mass and moment of inertia, we calculated 1-D seismic velocity profiles, the majority of which compare well with those determined by inverting the Apollo seismic data (Garcia et al., 2011 and Weber et al., 2011).

Surface Heat Budgets and Sea Surface Temperature in the Pacific Warm Pool During TOGA COARE

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Zhao, Wenzhong; Chou, Ming-Dah

1998-01-01

The daily mean heat and momentum fluxes at the surface derived from the SSM/I and Japan's GMS radiance measurements are used to study the temporal and spatial variability of the surface energy budgets and their relationship to the sea surface temperature during the COARE intensive observing period (IOP). For the three time legs observed during the IOP, the retrieved surface fluxes compare reasonably well with those from the IMET buoy, RV Moana Wave, and RV Wecoma. The characteristics of surface heat and momentum fluxes are very different between the southern and northern warm pool. In the southern warm pool, the net surface heat flux is dominated by solar radiation which is, in turn, modulated by the two Madden-Julian oscillations. The surface winds are generally weak, leading to a shallow ocean mixed layer. The solar radiation penetrating through the bottom of the mixed layer is significant, and the change in the sea surface temperature during the IOP does not follow the net surface heat flux. In the northern warm pool, the northeasterly trade wind is strong and undergoes strong seasonal variation. The variation of the net surface heat flux is dominated by evaporation. The two westerly wind bursts associated with the Madden-Julian oscillations seem to have little effect on the net surface heat flux. The ocean mixed layer is deep, and the solar radiation penetrating through the bottom of the mixed layer is small. As opposed to the southern warm pool, the trend of the sea surface temperature in the northern warm pool during the IOP is in agreement with the variation of the net heat flux at the surface.

Bibliography of Research on Ocean Fronts, 1964-1984

DTIC Science & Technology

1985-08-01

water masses which exhibit notable differences in temperature, salinity , chlorophyll and other properties. One example of an ocean front is the...Phil. Trans. R. Soc. Lond. A302: 617-634. Amos, A.F., M.G. Langseth and R.G. Markl. 1972. Visible oceanic saline fronts, p. 49-62. In A.L. Gordon...On the mechanism of the deep mixed layer formation during MEDOC 1969. Cahiers Oceanogr. XXII: 427-442. Anderson, F.E. 1980. The variation in

Ocean mixing in deep-sea trenches: New insights from the Challenger Deep, Mariana Trench

NASA Astrophysics Data System (ADS)

van Haren, Hans; Berndt, Christian; Klaucke, Ingo

2017-11-01

Reliable very deep shipborne SBE 911plus Conductivity Temperature Depth (CTD) data to within 60 m from the bottom and Kongsberg EM122 0.5° × 1° multibeam echosounder data are collected in the Challenger Deep, Mariana Trench. A new position and depth are given for the deepest point in the world's ocean. The data provide insight into the interplay between topography and internal waves in the ocean that lead to mixing of the lowermost water masses on Earth. Below 5000 m, the vertical density stratification is weak, with a minimum buoyancy frequency N = 1.0 ± 0.6 cpd, cycles per day, between 6500 and 8500 m. In that depth range, the average turbulence is coarsely estimated from Thorpe-overturning scales, with limited statistics to be ten times higher than the mean values of dissipation rate εT = 3 ± 2 × 10-11 m2 s-3 and eddy diffusivity KzT = 2 ± 1.5 × 10-4 m2 s-1 estimated for the depth range between 10,300 and 10,850 m, where N = 2.5 ± 0.6 cpd. Inertial and meridionally directed tidal inertio-gravity waves can propagate between the differently stratified layers. These waves are suggested to be responsible for the observed turbulence. The turbulence values are similar to those recently estimated from CTD and moored observations in the Puerto Rico Trench. Yet, in contrast to the Puerto Rico Trench, seafloor morphology in the Mariana Trench shows up to 500 m-high fault scarps on the incoming tectonic plate and a very narrow trench, suggesting that seafloor topography does not play a crucial role for mixing.

Sensitivity of High-Resolution Simulations of Hurricane Bob (1991) to Planetary Boundary Layer Parameterizations

NASA Technical Reports Server (NTRS)

Braun, Scott A.; Tao, Wei-Kuo

1999-01-01

The MM5 mesoscale model is used to simulate Hurricane Bob (1991) using grids nested to high resolution (4 km). Tests are conducted to determine the sensitivity of the simulation to the available planetary boundary layer parameterizations, including the bulk-aerodynamic, Blackadar, Medium-RanGe Forecast (MRF) model, and Burk-Thompson boundary-layer schemes. Significant sensitivity is seen, with minimum central pressures varying by up to 17 mb. The Burk-Thompson and bulk-aerodynamic boundary-layer schemes produced the strongest storms while the MRF scheme produced the weakest storm. Precipitation structure of the simulated hurricanes also varied substantially with the boundary layer parameterizations. Diagnostics of boundary-layer variables indicated that the intensity of the simulated hurricanes generally increased as the ratio of the surface exchange coefficients for heat and momentum, C(sub h)/C(sub M), although the manner in which the vertical mixing takes place was also important. Findings specific to the boundary-layer schemes include: 1) the MRF scheme produces mixing that is too deep and causes drying of the lower boundary layer in the inner-core region of the hurricane; 2) the bulk-aerodynamic scheme produces mixing that is probably too shallow, but results in a strong hurricane because of a large value of C(sub h)/C(sub M) (approximately 1.3); 3) the MRF and Blackadar schemes are weak partly because of smaller surface moisture fluxes that result in a reduced value of C(sub h)/C(sub M) (approximately 0.7); 4) the Burk-Thompson scheme produces a strong storm with C(sub h)/C(sub M) approximately 1; and 5) the formulation of the wind-speed dependence of the surface roughness parameter, z(sub 0), is important for getting appropriate values of the surface exchange coefficients in hurricanes based upon current estimates of these parameters.

Nitrate supply from deep to near-surface waters of the North Pacific subtropical gyre.

PubMed

Johnson, Kenneth S; Riser, Stephen C; Karl, David M

2010-06-24

Concentrations of dissolved inorganic carbon (DIC) decrease in the surface mixed layers during spring and summer in most of the oligotrophic ocean. Mass balance calculations require that the missing DIC is converted into particulate carbon by photosynthesis. This DIC uptake represents one of the largest components of net community production in the world ocean. However, mixed-layer waters in these regions of the ocean typically contain negligible concentrations of plant nutrients such as nitrate and phosphate. Combined nutrient supply mechanisms including nitrogen fixation, diffusive transport and vertical entrainment are believed to be insufficient to supply the required nutrients for photosynthesis. The basin-scale potential for episodic nutrient transport by eddy events is unresolved. As a result, it is not understood how biologically mediated DIC uptake can be supported in the absence of nutrients. Here we report on high-resolution measurements of nitrate (NO(3)(-)) and oxygen (O(2)) concentration made over 21 months using a profiling float deployed near the Hawaii Ocean Time-series station in the North Pacific subtropical gyre. Our measurements demonstrate that as O(2) was produced and DIC was consumed over two annual cycles, a corresponding seasonal deficit in dissolved NO(3)(-) appeared in water at depths from 100 to 250 m. The deep-water deficit in NO(3)(-) was in near-stoichiometric balance with the fixed nitrogen exported to depth. Thus, when the water column from the surface to 250 m is considered as a whole, there is near equivalence between nutrient supply and demand. Short-lived transport events (<10 days) that connect deep stocks of nitrate to nutrient-poor surface waters were clearly present in 12 of the 127 vertical profiles.

Temperature and oxygen in Missouri reservoirs

USGS Publications Warehouse

Jones, John R.; Knowlton, Matthew F.; Obrecht, Daniel V.; Graham, Jennifer L.

2011-01-01

Vertical profiles of water temperature (n = 7193) and dissolved oxygen (n = 6516) were collected from 235 Missouri reservoirs during 1989–2007; most data were collected during May–August and provide a regional summary of summer conditions. Collectively, surface water temperature ranged from a mean of ~22 C in May to 28 C in July, and individual summer maxima typically were 28–32 C. Most (~95%) reservoirs stably stratify by mid-May, but few are deep enough to have hypolimnia with near-uniform temperatures. Among stratified reservoirs, maximum effective length and maximum depth accounted for 75% of the variation in mixed depth and thermocline depth. Ephemeral, near-surface thermoclines occurred in 39% of summer profiles and were most frequent in small, turbid reservoirs. Isotherms below the mixed layer deepen during stratification, and the water column is >20 C by August in all but the deepest reservoirs. Most reservoirs showed incipient dissolved oxygen (DO) depletion by mid-May, and by August, 80% of profiles had DO minima of 50% of variation in DO below the mixed layer during summer. Warm summer temperatures and widespread low DO often limit available fish habitat in Missouri reservoirs and compress warm-water fish communities into subsurface layers that exceed their thermal preferences. This study provides a regional baseline of reservoir temperature and oxygen conditions useful for future evaluations of eutrophication and the effects of a warming climate.

Meteorological variables to aid forecasting deep slab avalanches on persistent weak layers

USGS Publications Warehouse

Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.

2015-01-01

Deep slab avalanches are particularly challenging to forecast. These avalanches are difficult to trigger, yet when they release they tend to propagate far and can result in large and destructive avalanches. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl ski area in southwest Montana to test the usefulness of meteorological variables for predicting seasons and days with deep slab avalanches. We defined deep slab avalanches as those that failed on persistent weak layers deeper than 0.9 m, and that occurred after February 1st. Previous studies often used meteorological variables from days prior to avalanches, but we also considered meteorological variables over the early months of the season. We used classification trees and random forests for our analyses. Our results showed seasons with either dry or wet deep slabs on persistent weak layers typically had less precipitation from November through January than seasons without deep slabs on persistent weak layers. Days with deep slab avalanches on persistent weak layers often had warmer minimum 24-hour air temperatures, and more precipitation over the prior seven days, than days without deep slabs on persistent weak layers. Days with deep wet slab avalanches on persistent weak layers were typically preceded by three days of above freezing air temperatures. Seasonal and daily meteorological variables were found useful to aid forecasting dry and wet deep slab avalanches on persistent weak layers, and should be used in combination with continuous observation of the snowpack and avalanche activity.

Calculated quantum yield of photosynthesis of phytoplankton in the Marine Light-Mixed Layers (59 deg N, 21 deg W)

NASA Technical Reports Server (NTRS)

Carder, K. L.; Lee, Z. P.; Marra, John; Steward, R. G.; Perry, M. J.

1995-01-01

The quantum yield of photosynthesis (mol C/mol photons) was calculated at six depths for the waters of the Marine Light-Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating phi. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of phi calculated using the nonlinear regreesion method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.

Seasonal variation of the global mixed layer depth: comparison between Argo data and FIO-ESM

NASA Astrophysics Data System (ADS)

Zhang, Yutong; Xu, Haiming; Qiao, Fangli; Dong, Changming

2018-03-01

The present study evaluates a simulation of the global ocean mixed layer depth (MLD) using the First Institute of Oceanography-Earth System Model (FIOESM). The seasonal variation of the global MLD from the FIO-ESM simulation is compared to Argo observational data. The Argo data show that the global ocean MLD has a strong seasonal variation with a deep MLD in winter and a shallow MLD in summer, while the spring and fall seasons act as transitional periods. Overall, the FIO-ESM simulation accurately captures the seasonal variation in MLD in most areas. It exhibits a better performance during summer and fall than during winter and spring. The simulated MLD in the Southern Hemisphere is much closer to observations than that in the Northern Hemisphere. In general, the simulated MLD over the South Atlantic Ocean matches the observation best among the six areas. Additionally, the model slightly underestimates the MLD in parts of the North Atlantic Ocean, and slightly overestimates the MLD over the other ocean basins.

Storm-driven Mixing and Potential Impact on the Arctic Ocean

NASA Technical Reports Server (NTRS)

Yang, Jiayan; Comiso, Josefino; Walsh, David; Krishfield, Richard; Honjo, Susumu; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Observations of the ocean, atmosphere, and ice made by Ice-Ocean Environmental Buoys (IOEBs) indicate that mixing events reaching the depth of the halocline have occurred in various regions in the Arctic Ocean. Our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites. In this study, we analyzed these mixing events in the context of storm developments that occurred in the Beaufort Sea and in the general area just north of Fram Strait, two areas with quite different hydrographic structures. The Beaufort Sea is strongly influenced by inflow of Pacific water through Bering Strait, while the area north of Fram Strait is directly affected by the inflow of warm and salty North Atlantic water. Our analyses of the basin-wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different. The buoy-observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak. This indicates the importance of stratification, although the mixing itself was mechanically driven. We also analyze the distribution of storms, both the long-term climatology as well as the patterns for each year in the last two decades. The frequency of storms is also shown to be correlated- (but not strongly) to Arctic Oscillation indices. This study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline. On the other hand, synoptic-scale storms can force mixing deep enough to the halocline and thermocline layer. Despite a very stable stratification associated with the Arctic halocline, the warm subsurface thermocline water is not always insulated from the mixed layer.

Projection decomposition algorithm for dual-energy computed tomography via deep neural network.

PubMed

Xu, Yifu; Yan, Bin; Chen, Jian; Zeng, Lei; Li, Lei

2018-03-15

Dual-energy computed tomography (DECT) has been widely used to improve identification of substances from different spectral information. Decomposition of the mixed test samples into two materials relies on a well-calibrated material decomposition function. This work aims to establish and validate a data-driven algorithm for estimation of the decomposition function. A deep neural network (DNN) consisting of two sub-nets is proposed to solve the projection decomposition problem. The compressing sub-net, substantially a stack auto-encoder (SAE), learns a compact representation of energy spectrum. The decomposing sub-net with a two-layer structure fits the nonlinear transform between energy projection and basic material thickness. The proposed DNN not only delivers image with lower standard deviation and higher quality in both simulated and real data, and also yields the best performance in cases mixed with photon noise. Moreover, DNN costs only 0.4 s to generate a decomposition solution of 360 × 512 size scale, which is about 200 times faster than the competing algorithms. The DNN model is applicable to the decomposition tasks with different dual energies. Experimental results demonstrated the strong function fitting ability of DNN. Thus, the Deep learning paradigm provides a promising approach to solve the nonlinear problem in DECT.

Iron Biogeochemistry in the High Latitude North Atlantic Ocean.

PubMed

Achterberg, Eric P; Steigenberger, Sebastian; Marsay, Chris M; LeMoigne, Frédéric A C; Painter, Stuart C; Baker, Alex R; Connelly, Douglas P; Moore, C Mark; Tagliabue, Alessandro; Tanhua, Toste

2018-01-19

Iron (Fe) is an essential micronutrient for marine microbial organisms, and low supply controls productivity in large parts of the world's ocean. The high latitude North Atlantic is seasonally Fe limited, but Fe distributions and source strengths are poorly constrained. Surface ocean dissolved Fe (DFe) concentrations were low in the study region (<0.1 nM) in summer 2010, with significant perturbations during spring 2010 in the Iceland Basin as a result of an eruption of the Eyjafjallajökull volcano (up to 2.5 nM DFe near Iceland) with biogeochemical consequences. Deep water concentrations in the vicinity of the Reykjanes Ridge system were influenced by pronounced sediment resuspension, with indications for additional inputs by hydrothermal vents, with subsequent lateral transport of Fe and manganese plumes of up to 250-300 km. Particulate Fe formed the dominant pool, as evidenced by 4-17 fold higher total dissolvable Fe compared with DFe concentrations, and a dynamic exchange between the fractions appeared to buffer deep water DFe. Here we show that Fe supply associated with deep winter mixing (up to 103 nmol m -2 d -1 ) was at least ca. 4-10 times higher than atmospheric deposition, diffusive fluxes at the base of the summer mixed layer, and horizontal surface ocean fluxes.

Atmospheric circulation and sounding-derived parameters associated with thunderstorm occurrence in Central Europe

NASA Astrophysics Data System (ADS)

Kolendowicz, Leszek; Taszarek, Mateusz; Czernecki, Bartosz

2017-07-01

The main objective of this study is to examine the influence of atmospheric circulation patterns and sounding-derived parameters on thunderstorm occurrence in Central Europe. Thunderstorm activity tends to increase as one moves from the north to the south of the research area. Maximal thunderstorm occurrence is observed in the summer months, while between October and March such activity is much lower. Thunderstorms are also more frequent in spring than in autumn. In the warm season, the occurrence of thunderstorm is associated with the presence of a trough associated with a low located over the North Sea and Scandinavia. In the cold season, the synoptic pattern indicates a strong zonal flow from the west with significantly higher horizontal pressure gradient compared to the warm season. Thunderstorms are more likely to form when the boundary layer's mixing ratios are higher than 8 g kg- 1. Deep convection is also more likely to occur when the vertical temperature lapse rates (between 800 and 500 hPa pressure layers) exceed 6 °C km- 1. During the cold season, considerably higher lapse rates are needed to produce thunderstorms. The values obtained for the convective available potential energy indicate that at least 50 J kg- 1 is needed to produce a thunderstorm during wintertime and 125 J kg- 1 during summertime. Cold season thunderstorms are formed with a lower instability but with a more dynamic wind field having an average value of deep layer shear that exceeds 20 ms- 1. The best parameter to distinguish thunderstorm from non-thunderstorm days for both winter and summer months is a combination of the square root of the convective available potential energy multiplied by the deep layer shear.

Pathologic findings in human scabies.

PubMed

Fernandez, N; Torres, A; Ackerman, A B

1977-03-01

The histologic findings in the papular, vesicular, nodular, and Norwegian variant of scabies have in common a superficial and deep perivascular mixed inflammatory cell infiltrate of lymphocytes, histiocytes, and numerous eosinophils. A spongiotic vesicle occurs in the papulovesicular type, a dense cellular infiltrate in the nodular type, and a hyperkeratotic psoriasiform dermatitis in the Norwegian type. Eggs, larvae, and adult mites are abundant in the cornified layer of Norwegian scabies, are practically never found in biopsy specimens from lesions of nodular scabies, and are discovered only episodically in papulovesicular lesions.

Near-bottom energy cascade from subinertial flows to ocean mixing in the northeastern South China Sea

NASA Astrophysics Data System (ADS)

Zhang, Y.; Liu, Z.; Zhao, Y.; Wang, W.; Li, J.; Xu, J.

2013-12-01

The motions with different scales in the bottom boundary layer are potentially important in controlling the water mass transportation. Many physical processes are involved in transferring energy from mesoscale to small-scale motions. Recent studies suggest that subinertial flows should be taken into account in the parameterization of deep-ocean mixing besides topography and tidal forcing. Here, we present the current velocity data obtained from 2 moored downward-looking ADCPs (Acoustic Doppler Current Profiler) and 1 RCM (Recording Current Meter) moored near the bottom boundary layer at a water depth of about 2000 m in the northeastern South China Sea from 2012 to 2013. Specifically, they include an ADCP 1200 kHz deployed at 30 m, an ADCP 300 kHz deployed at 110 m, and a RCM deployed at 40 m above the seafloor. Subinertial flows were calculated from the moored current velocity data by low-pass filtering with a cutoff frequency of 0.3 cycles per day (the local inertial period is about 35 hours). The horizontal subinertial flows were quite strong with average values of 2-5 cm/s. The strong downward vertical velocity with average values of 1-2 cm/s was observed during times of weak subinertial flows. The vertical propagation during both the times of weak and strong subinertial flows can also be shown by vector spectra of horizontal near-inertial current velocity. Turbulent kinetic energy production rate estimated indirectly with the variances of ADCP velocities will be compared with the subinertial kinetic energy to detect the processes of energy cascade from mesoscale motions to small-scale oscillations. The results presented in this study can provide an observational evidence for such energy cascade near the bottom boundary layer in the deep South China Sea.

Unraveling the Role of Monovalent Halides in Mixed-Halide Organic-Inorganic Perovskites.

PubMed

Deepa, Melepurath; Ramos, F Javier; Shivaprasad, S M; Ahmad, Shahzada

2016-03-16

The performance of perovskite solar cells is strongly influenced by the composition and microstructure of the perovskite. A recent approach to improve the power conversion efficiencies utilized mixed-halide perovskites, but the halide ions and their roles were not directly studied. Unraveling their precise location in the perovskite layer is of paramount importance. Here, we investigated four different perovskites by using X-ray photoelectron spectroscopy, and found that among the three studied mixed-halide perovskites, CH3 NH3 Pb(I0.74 Br0.26 )3 and CH3 NH3 PbBr3-x Clx show peaks that unambiguously demonstrate the presence of iodide and bromide in the former, and bromide and chloride in the latter. The CH3 NH3 PbI3-x Clx perovskite shows anomalous behavior, the iodide content far outweighs that of the chloride; a small proportion of chloride, in all likelihood, resides deep within the TiO2 /absorber layer. Our study reveals that there are many distinguishable structural differences between these perovskites, and that these directly impact the photovoltaic performances. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CELL SEGREGATION, MIXING, AND TISSUE PATTERN IN THE SPINAL CORD OF THE XENOPUS LAEVIS NEURULA

PubMed Central

Davidson, Lance A.; Keller, Raymond E.

2014-01-01

Background During Xenopus laevis neurulation, neural ectodermal cells of the spinal cord are patterned at the same time that they intercalate mediolaterally and radially, moving within and between two cell layers. Curious if these rearrangements disrupt early cell identities, we lineage-traced cells in each layer from neural plate stages to the closed neural tube, and used in situ hybridization to assay gene expression in the moving cells. Results Our biotin- and fluorescent labeling of deep and superficial cells reveals that mediolateral intercalation does not disrupt cell cohorts, in other words it is conservative. However, outside the midline notoplate, later radial intercalation does displace superficial cells dorsoventrally, radically disrupting cell cohorts. The tube roof is composed almost exclusively of superficial cells, including some displaced from ventral positions; gene expression in these displaced cells must now be surveyed further. Superficial cells also flank the tube’s floor, which is, itself, almost exclusively composed of deep cells. Conclusions Our data provide: 1) a fate map of superficial- and deep-cell positions within the Xenopus neural tube, 2) the paths taken to these positions, and 3) preliminary evidence of re-patterning in cells carried out of one environment and into another, during neural morphogenesis. PMID:23813905

ICF Implosions, Space-Charge Electric Fields, and Their Impact on Mix and Compression

NASA Astrophysics Data System (ADS)

Knoll, Dana; Chacon, Luis; Simakov, Andrei

2013-10-01

The single-fluid, quasi-neutral, radiation hydrodynamics codes, used to design the NIF targets, predict thermonuclear ignition for the conditions that have been achieved experimentally. A logical conclusion is that the physics model used in these codes is missing one, or more, key phenomena. Two key model-experiment inconsistencies on NIF are: 1) a lower implosion velocity than predicted by the design codes, and 2) transport of pusher material deep into the hot spot. We hypothesize that both of these model-experiment inconsistencies may be a result of a large, space-charge, electric field residing on the distinct interfaces in a NIF target. Large space-charge fields have been experimentally observed in Omega experiments. Given our hypothesis, this presentation will: 1) Develop a more complete physics picture of initiation, sustainment, and dissipation of a current-driven plasma sheath / double-layer at the Fuel-Pusher interface of an ablating plastic shell implosion on Omega, 2) Characterize the mix that can result from a double-layer field at the Fuel-Pusher interface, prior to the onset of fluid instabilities, and 3) Quantify the impact of the double-layer induced surface tension at the Fuel-Pusher interface on the peak observed implosion velocity in Omega.

Quantitative evaluation of deep and shallow tissue layers' contribution to fNIRS signal using multi-distance optodes and independent component analysis.

PubMed

Funane, Tsukasa; Atsumori, Hirokazu; Katura, Takusige; Obata, Akiko N; Sato, Hiroki; Tanikawa, Yukari; Okada, Eiji; Kiguchi, Masashi

2014-01-15

To quantify the effect of absorption changes in the deep tissue (cerebral) and shallow tissue (scalp, skin) layers on functional near-infrared spectroscopy (fNIRS) signals, a method using multi-distance (MD) optodes and independent component analysis (ICA), referred to as the MD-ICA method, is proposed. In previous studies, when the signal from the shallow tissue layer (shallow signal) needs to be eliminated, it was often assumed that the shallow signal had no correlation with the signal from the deep tissue layer (deep signal). In this study, no relationship between the waveforms of deep and shallow signals is assumed, and instead, it is assumed that both signals are linear combinations of multiple signal sources, which allows the inclusion of a "shared component" (such as systemic signals) that is contained in both layers. The method also assumes that the partial optical path length of the shallow layer does not change, whereas that of the deep layer linearly increases along with the increase of the source-detector (S-D) distance. Deep- and shallow-layer contribution ratios of each independent component (IC) are calculated using the dependence of the weight of each IC on the S-D distance. Reconstruction of deep- and shallow-layer signals are performed by the sum of ICs weighted by the deep and shallow contribution ratio. Experimental validation of the principle of this technique was conducted using a dynamic phantom with two absorbing layers. Results showed that our method is effective for evaluating deep-layer contributions even if there are high correlations between deep and shallow signals. Next, we applied the method to fNIRS signals obtained on a human head with 5-, 15-, and 30-mm S-D distances during a verbal fluency task, a verbal working memory task (prefrontal area), a finger tapping task (motor area), and a tetrametric visual checker-board task (occipital area) and then estimated the deep-layer contribution ratio. To evaluate the signal separation performance of our method, we used the correlation coefficients of a laser-Doppler flowmetry (LDF) signal and a nearest 5-mm S-D distance channel signal with the shallow signal. We demonstrated that the shallow signals have a higher temporal correlation with the LDF signals and with the 5-mm S-D distance channel than the deep signals. These results show the MD-ICA method can discriminate between deep and shallow signals. Copyright © 2013 Elsevier Inc. All rights reserved.

Observations of ozone-poor air in the tropical tropopause layer

NASA Astrophysics Data System (ADS)

Newton, Richard; Vaughan, Geraint; Hintsa, Eric; Filus, Michal T.; Pan, Laura L.; Honomichl, Shawn; Atlas, Elliot; Andrews, Stephen J.; Carpenter, Lucy J.

2018-04-01

Ozonesondes reaching the tropical tropopause layer (TTL) over the west Pacific have occasionally measured layers of very low ozone concentrations - less than 15 ppbv - raising the question of how prevalent such layers are and how they are formed. In this paper, we examine aircraft measurements from the Airborne Tropical Tropopause Experiment (ATTREX), the Coordinated Airborne Studies in the Tropics (CAST) and the Convective Transport of Active Species in the Tropics (CONTRAST) experiment campaigns based in Guam in January-March 2014 for evidence of very low ozone concentrations and their relation to deep convection. The study builds on results from the ozonesonde campaign conducted from Manus Island, Papua New Guinea, as part of CAST, where ozone concentrations as low as 12 ppbv were observed between 100 and 150 hPa downwind of a deep convective complex. TTL measurements from the Global Hawk unmanned aircraft show a marked contrast between the hemispheres, with mean ozone concentrations in profiles in the Southern Hemisphere between 100 and 150 hPa of between 10.7 and 15.2 ppbv. By contrast, the mean ozone concentrations in profiles in the Northern Hemisphere were always above 15.4 ppbv and normally above 20 ppbv at these altitudes. The CAST and CONTRAST aircraft sampled the atmosphere between the surface and 120 hPa, finding very low ozone concentrations only between the surface and 700 hPa; mixing ratios as low as 7 ppbv were regularly measured in the boundary layer, whereas in the free troposphere above 200 hPa concentrations were generally well in excess of 15 ppbv. These results are consistent with uplift of almost-unmixed boundary-layer air to the TTL in deep convection. An interhemispheric difference was found in the TTL ozone concentrations, with values < 15 ppbv measured extensively in the Southern Hemisphere but seldom in the Northern Hemisphere. This is consistent with a similar contrast in the low-level ozone between the two hemispheres found by previous measurement campaigns. Further evidence of a boundary-layer origin for the uplifted air is provided by the anticorrelation between ozone and halogenated hydrocarbons of marine origin observed by the three aircraft.

Computations in the deep vs superficial layers of the cerebral cortex.

PubMed

Rolls, Edmund T; Mills, W Patrick C

2017-11-01

A fundamental question is how the cerebral neocortex operates functionally, computationally. The cerebral neocortex with its superficial and deep layers and highly developed recurrent collateral systems that provide a basis for memory-related processing might perform somewhat different computations in the superficial and deep layers. Here we take into account the quantitative connectivity within and between laminae. Using integrate-and-fire neuronal network simulations that incorporate this connectivity, we first show that attractor networks implemented in the deep layers that are activated by the superficial layers could be partly independent in that the deep layers might have a different time course, which might because of adaptation be more transient and useful for outputs from the neocortex. In contrast the superficial layers could implement more prolonged firing, useful for slow learning and for short-term memory. Second, we show that a different type of computation could in principle be performed in the superficial and deep layers, by showing that the superficial layers could operate as a discrete attractor network useful for categorisation and feeding information forward up a cortical hierarchy, whereas the deep layers could operate as a continuous attractor network useful for providing a spatially and temporally smooth output to output systems in the brain. A key advance is that we draw attention to the functions of the recurrent collateral connections between cortical pyramidal cells, often omitted in canonical models of the neocortex, and address principles of operation of the neocortex by which the superficial and deep layers might be specialized for different types of attractor-related memory functions implemented by the recurrent collaterals. Copyright © 2017 Elsevier Inc. All rights reserved.

Deep-water kelp refugia as potential hotspots of tropical marine diversity and productivity.

PubMed

Graham, Michael H; Kinlan, Brian P; Druehl, Louis D; Garske, Lauren E; Banks, Stuart

2007-10-16

Classic marine ecological paradigms view kelp forests as inherently temperate-boreal phenomena replaced by coral reefs in tropical waters. These paradigms hinge on the notion that tropical surface waters are too warm and nutrient-depleted to support kelp productivity and survival. We present a synthetic oceanographic and ecophysiological model that accurately identifies all known kelp populations and, by using the same criteria, predicts the existence of >23,500 km(2) unexplored submerged (30- to 200-m depth) tropical kelp habitats. Predicted tropical kelp habitats were most probable in regions where bathymetry and upwelling resulted in mixed-layer shoaling above the depth of minimum annual irradiance dose for kelp survival. Using model predictions, we discovered extensive new deep-water Eisenia galapagensis populations in the Galápagos that increased in abundance with increasing depth to >60 m, complete with cold-water flora and fauna of temperate affinities. The predictability of deep-water kelp habitat and the discovery of expansive deep-water Galápagos kelp forests validate the extent of deep-water tropical kelp refugia, with potential implications for regional productivity and biodiversity, tropical food web ecology, and understanding of the resilience of tropical marine systems to climate change.

Hydrographic trends in Prince William Sound, Alaska, 1960-2016

NASA Astrophysics Data System (ADS)

Campbell, Robert W.

2018-01-01

A five-decade time series of temperature and salinity profiles within Prince William Sound (PWS) and the immediately adjacent shelf was assembled from several archives and ongoing field programs, and augmented with archived SST observations. Observations matched with recent cool (2007-2013) and warm (2013-onward) periods in the region, and also showed an overall regional warming trend ( 0.1 to 0.2 °C decade-1) that matched long-term increases in heat transport to the surface ocean. A cooling and freshening trend ( - 0.2 °C decade-1 and 0.02 respectively) occurred in the near surface waters in some portions of PWS, particularly the northwestern margin, which is also the location of most of the ice mass in the region; discharge (estimated from other studies) has increased over time, suggesting that those patterns were due to increased meltwater inputs. Increases in salinity at depth were consistent with enhanced entrainment of deep water by estuarine circulations, and by enhanced deep water renewal caused by reductions in downwelling-favorable winds. As well as local-scale effects, temperature and salinity were positively cross correlated with large scale climate and lunar indexes at long lags (years to months), indicating the longer time scales of atmospheric and transport connections with the Gulf of Alaska. Estimates of mixed layer depths show a shoaling of the seasonal mixed layer over time by several meters, which may have implications for ecosystem productivity in the region.

Ocean barrier layers' effect on tropical cyclone intensification.

PubMed

Balaguru, Karthik; Chang, Ping; Saravanan, R; Leung, L Ruby; Xu, Zhao; Li, Mingkui; Hsieh, Jen-Shan

2012-09-04

Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are "quasi-permanent" features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.

Rocks of the early lunar crust

NASA Technical Reports Server (NTRS)

James, O. B.

1980-01-01

Data are summarized which suggest a model for the early evolution of the lunar crust. According to the model, during the final stages of accretion, the outer part of the moon melted to form a magma ocean approximately 300 km deep. This ocean fractionated to form mafic and ultramafic cumulates at depth and an overlying anorthositic crust made up of ferroan anorthosites. Subsequent partial melting in the primitive mantle underlying the crystallized magma ocean produced melts which segregated, moved upward, intruded the primordial crust, and crystallized to form layered plutons consisting of Mg-rich plutonic rocks. Intense impact bombardment at the lunar surface mixed and melted the rocks of the two suites to form a thick layer of granulated debris, granulitic breccias, and impact-melt rocks.

Early MAVEN Deep Dip campaign reveals thermosphere and ionosphere variability.

PubMed

Bougher, S; Jakosky, B; Halekas, J; Grebowsky, J; Luhmann, J; Mahaffy, P; Connerney, J; Eparvier, F; Ergun, R; Larson, D; McFadden, J; Mitchell, D; Schneider, N; Zurek, R; Mazelle, C; Andersson, L; Andrews, D; Baird, D; Baker, D N; Bell, J M; Benna, M; Brain, D; Chaffin, M; Chamberlin, P; Chaufray, J-Y; Clarke, J; Collinson, G; Combi, M; Crary, F; Cravens, T; Crismani, M; Curry, S; Curtis, D; Deighan, J; Delory, G; Dewey, R; DiBraccio, G; Dong, C; Dong, Y; Dunn, P; Elrod, M; England, S; Eriksson, A; Espley, J; Evans, S; Fang, X; Fillingim, M; Fortier, K; Fowler, C M; Fox, J; Gröller, H; Guzewich, S; Hara, T; Harada, Y; Holsclaw, G; Jain, S K; Jolitz, R; Leblanc, F; Lee, C O; Lee, Y; Lefevre, F; Lillis, R; Livi, R; Lo, D; Ma, Y; Mayyasi, M; McClintock, W; McEnulty, T; Modolo, R; Montmessin, F; Morooka, M; Nagy, A; Olsen, K; Peterson, W; Rahmati, A; Ruhunusiri, S; Russell, C T; Sakai, S; Sauvaud, J-A; Seki, K; Steckiewicz, M; Stevens, M; Stewart, A I F; Stiepen, A; Stone, S; Tenishev, V; Thiemann, E; Tolson, R; Toublanc, D; Vogt, M; Weber, T; Withers, P; Woods, T; Yelle, R

2015-11-06

The Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above the well-mixed atmosphere, the layer of peak extreme ultraviolet heating and primary reservoir for atmospheric escape. In situ measurements of the upper atmosphere reveal previously unmeasured populations of neutral and charged particles, the homopause altitude at approximately 130 kilometers, and an unexpected level of variability both on an orbit-to-orbit basis and within individual orbits. These observations help constrain volatile escape processes controlled by thermosphere and ionosphere structure and variability. Copyright © 2015, American Association for the Advancement of Science.

A case study of microphysical structures and hydrometeor phase in convection using radar Doppler spectra at Darwin, Australia

NASA Astrophysics Data System (ADS)

Riihimaki, L. D.; Comstock, J. M.; Luke, E.; Thorsen, T. J.; Fu, Q.

2017-07-01

To understand the microphysical processes that impact diabatic heating and cloud lifetimes in convection, we need to characterize the spatial distribution of supercooled liquid water. To address this observational challenge, ground-based vertically pointing active sensors at the Darwin Atmospheric Radiation Measurement site are used to classify cloud phase within a deep convective cloud. The cloud cannot be fully observed by a lidar due to signal attenuation. Therefore, we developed an objective method for identifying hydrometeor classes, including mixed-phase conditions, using k-means clustering on parameters that describe the shape of the Doppler spectra from vertically pointing Ka-band cloud radar. This approach shows that multiple, overlapping mixed-phase layers exist within the cloud, rather than a single region of supercooled liquid. Diffusional growth calculations show that the conditions for the Wegener-Bergeron-Findeisen process exist within one of these mixed-phase microstructures.

Microfluidic Chips Controlled with Elastomeric Microvalve Arrays

PubMed Central

Li, Nianzhen; Sip, Chris; Folch, Albert

2007-01-01

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays. Robust flow control and precise fluidic volumes are two critical requirements for these applications. We have developed microfluidic chips featuring elastomeric polydimethylsiloxane (PDMS) microvalve arrays that: 1) need no extra energy source to close the fluidic path, hence the loaded device is highly portable; and 2) allow for microfabricating deep (up to 1 mm) channels with vertical sidewalls and resulting in very precise features. The PDMS microvalves-based devices consist of three layers: a fluidic layer containing fluidic paths and microchambers of various sizes, a control layer containing the microchannels necessary to actuate the fluidic path with microvalves, and a middle thin PDMS membrane that is bound to the control layer. Fluidic layer and control layers are made by replica molding of PDMS from SU-8 photoresist masters, and the thin PDMS membrane is made by spinning PDMS at specified heights. The control layer is bonded to the thin PDMS membrane after oxygen activation of both, and then assembled with the fluidic layer. The microvalves are closed at rest and can be opened by applying negative pressure (e.g., house vacuum). Microvalve closure and opening are automated via solenoid valves controlled by computer software. Here, we demonstrate two microvalve-based microfluidic chips for two different applications. The first chip allows for storing and mixing precise sub-nanoliter volumes of aqueous solutions at various mixing ratios. The second chip allows for computer-controlled perfusion of microfluidic cell cultures. The devices are easy to fabricate and simple to control. Due to the biocompatibility of PDMS, these microchips could have broad applications in miniaturized diagnostic assays as well as basic cell biology studies. PMID:18989408

The Vertical Profile of Ocean Mixing

NASA Astrophysics Data System (ADS)

Ferrari, R. M.; Nikurashin, M.; McDougall, T. J.; Mashayek, A.

2014-12-01

The upwelling of bottom waters through density surfaces in the deep ocean is not possible unless the sloping nature of the sea floor is taken into account. The bottom--intensified mixing arising from interaction of internal tides and geostrophic motions with bottom topography implies that mixing is a decreasing function of height in the deep ocean. This would further imply that the diapycnal motion in the deep ocean is downward, not upwards as is required by continuity. This conundrum regarding ocean mixing and upwelling in the deep ocean will be resolved by appealing to the fact that the ocean does not have vertical side walls. Implications of the conundrum for the representation of ocean mixing in climate models will be discussed.

GoAmazon2014/5 campaign points to deep-inflow approach to deep convection across scales

DOE PAGES

Schiro, Kathleen A.; Ahmed, Fiaz; Giangrande, Scott E.; ...

2018-04-17

Representations of strongly precipitating deep-convective systems in climate models are among the most important factors in their simulation. Parameterizations of these motions face the dual challenge of unclear pathways to including mesoscale organization and high sensitivity of convection to approximations of turbulent entrainment of environmental air. Ill-constrained entrainment processes can even affect global average climate sensitivity under global warming. Multiinstrument observations from the Department of Energy GoAmazon2014/5 field campaign suggest that an alternative formulation from radar-derived dominant updraft structure yields a strong relationship of precipitation to buoyancy in both mesoscale and smaller-scale convective systems. This simultaneously provides a key stepmore » toward representing the influence of mesoscale convection in climate models and sidesteps a problematic dependence on traditional entrainment rates. A substantial fraction of precipitation is associated with mesoscale convective systems (MCSs), which are currently poorly represented in climate models. Convective parameterizations are highly sensitive to the assumptions of an entraining plume model, in which high equivalent potential temperature air from the boundary layer is modified via turbulent entrainment. Here we show, using multiinstrument evidence from the Green Ocean Amazon field campaign (2014–2015; GoAmazon2014/5), that an empirically constrained weighting for inflow of environmental air based on radar wind profiler estimates of vertical velocity and mass flux yields a strong relationship between resulting buoyancy measures and precipitation statistics. This deep-inflow weighting has no free parameter for entrainment in the conventional sense, but to a leading approximation is simply a statement of the geometry of the inflow. The structure further suggests the weighting could consistently apply even for coherent inflow structures noted in field campaign studies for MCSs over tropical oceans. For radar precipitation retrievals averaged over climate model grid scales at the GoAmazon2014/5 site, the use of deep-inflow mixing yields a sharp increase in the probability and magnitude of precipitation with increasing buoyancy. Furthermore, this applies for both mesoscale and smaller-scale convection. Results from reanalysis and satellite data show that this holds more generally: Deep-inflow mixing yields a strong precipitation–buoyancy relation across the tropics. Lastly, deep-inflow mixing may thus circumvent inadequacies of current parameterizations while helping to bridge the gap toward representing mesoscale convection in climate models.« less

GoAmazon2014/5 campaign points to deep-inflow approach to deep convection across scales

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

Schiro, Kathleen A.; Ahmed, Fiaz; Giangrande, Scott E.

Representations of strongly precipitating deep-convective systems in climate models are among the most important factors in their simulation. Parameterizations of these motions face the dual challenge of unclear pathways to including mesoscale organization and high sensitivity of convection to approximations of turbulent entrainment of environmental air. Ill-constrained entrainment processes can even affect global average climate sensitivity under global warming. Multiinstrument observations from the Department of Energy GoAmazon2014/5 field campaign suggest that an alternative formulation from radar-derived dominant updraft structure yields a strong relationship of precipitation to buoyancy in both mesoscale and smaller-scale convective systems. This simultaneously provides a key stepmore » toward representing the influence of mesoscale convection in climate models and sidesteps a problematic dependence on traditional entrainment rates. A substantial fraction of precipitation is associated with mesoscale convective systems (MCSs), which are currently poorly represented in climate models. Convective parameterizations are highly sensitive to the assumptions of an entraining plume model, in which high equivalent potential temperature air from the boundary layer is modified via turbulent entrainment. Here we show, using multiinstrument evidence from the Green Ocean Amazon field campaign (2014–2015; GoAmazon2014/5), that an empirically constrained weighting for inflow of environmental air based on radar wind profiler estimates of vertical velocity and mass flux yields a strong relationship between resulting buoyancy measures and precipitation statistics. This deep-inflow weighting has no free parameter for entrainment in the conventional sense, but to a leading approximation is simply a statement of the geometry of the inflow. The structure further suggests the weighting could consistently apply even for coherent inflow structures noted in field campaign studies for MCSs over tropical oceans. For radar precipitation retrievals averaged over climate model grid scales at the GoAmazon2014/5 site, the use of deep-inflow mixing yields a sharp increase in the probability and magnitude of precipitation with increasing buoyancy. Furthermore, this applies for both mesoscale and smaller-scale convection. Results from reanalysis and satellite data show that this holds more generally: Deep-inflow mixing yields a strong precipitation–buoyancy relation across the tropics. Lastly, deep-inflow mixing may thus circumvent inadequacies of current parameterizations while helping to bridge the gap toward representing mesoscale convection in climate models.« less

Spiraling pathways of global deep waters to the surface of the Southern Ocean.

PubMed

Tamsitt, Veronica; Drake, Henri F; Morrison, Adele K; Talley, Lynne D; Dufour, Carolina O; Gray, Alison R; Griffies, Stephen M; Mazloff, Matthew R; Sarmiento, Jorge L; Wang, Jinbo; Weijer, Wilbert

2017-08-02

Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60-90 years.Deep waters of the Atlantic, Pacific and Indian Oceans upwell in the Southern Oceanbut the exact pathways are not fully characterized. Here the authors present a three dimensional view showing a spiralling southward path, with enhanced upwelling by eddy-transport at topographic hotspots.

Laminar recordings in frontal cortex suggest distinct layers for maintenance and control of working memory

PubMed Central

Bastos, André M.; Loonis, Roman; Kornblith, Simon; Lundqvist, Mikael; Miller, Earl K.

2018-01-01

All of the cerebral cortex has some degree of laminar organization. These different layers are composed of neurons with distinct connectivity patterns, embryonic origins, and molecular profiles. There are little data on the laminar specificity of cognitive functions in the frontal cortex, however. We recorded neuronal spiking/local field potentials (LFPs) using laminar probes in the frontal cortex (PMd, 8A, 8B, SMA/ACC, DLPFC, and VLPFC) of monkeys performing working memory (WM) tasks. LFP power in the gamma band (50–250 Hz) was strongest in superficial layers, and LFP power in the alpha/beta band (4–22 Hz) was strongest in deep layers. Memory delay activity, including spiking and stimulus-specific gamma bursting, was predominately in superficial layers. LFPs from superficial and deep layers were synchronized in the alpha/beta bands. This was primarily unidirectional, with alpha/beta bands in deep layers driving superficial layer activity. The phase of deep layer alpha/beta modulated superficial gamma bursting associated with WM encoding. Thus, alpha/beta rhythms in deep layers may regulate the superficial layer gamma bands and hence maintenance of the contents of WM. PMID:29339471

Laminar recordings in frontal cortex suggest distinct layers for maintenance and control of working memory.

PubMed

Bastos, André M; Loonis, Roman; Kornblith, Simon; Lundqvist, Mikael; Miller, Earl K

2018-01-30

All of the cerebral cortex has some degree of laminar organization. These different layers are composed of neurons with distinct connectivity patterns, embryonic origins, and molecular profiles. There are little data on the laminar specificity of cognitive functions in the frontal cortex, however. We recorded neuronal spiking/local field potentials (LFPs) using laminar probes in the frontal cortex (PMd, 8A, 8B, SMA/ACC, DLPFC, and VLPFC) of monkeys performing working memory (WM) tasks. LFP power in the gamma band (50-250 Hz) was strongest in superficial layers, and LFP power in the alpha/beta band (4-22 Hz) was strongest in deep layers. Memory delay activity, including spiking and stimulus-specific gamma bursting, was predominately in superficial layers. LFPs from superficial and deep layers were synchronized in the alpha/beta bands. This was primarily unidirectional, with alpha/beta bands in deep layers driving superficial layer activity. The phase of deep layer alpha/beta modulated superficial gamma bursting associated with WM encoding. Thus, alpha/beta rhythms in deep layers may regulate the superficial layer gamma bands and hence maintenance of the contents of WM. Copyright © 2018 the Author(s). Published by PNAS.

Aponeurosis of the levator palpebrae superioris in Chinese subjects

PubMed Central

Pan, Er; Nie, Yun-Fei; Wang, Zhen-Jun; Peng, Li-Xia; Wu, Yan-Hong; Li, Qin

2016-01-01

Abstract An accurate understanding of the anatomy of the levator palpebrae superioris aponeurosis (LPSA) is critical for successful blepharoplasty of aponeurotic ptosis. We investigated the macroscopic and microscopic anatomy of the LPSA. This prospective live gross anatomy study enrolled 200 adult Chinese patients with bilateral mild ptosis undergoing elective blepharoplasty. Full-thick eyelid tissues and sagittal sections from the eyelid skin to the conjunctiva were examined with Masson trichrome staining or antismooth muscle actin (SMA) immunohistochemistry. Gross anatomy showed that the space between the superficial and deep layers of the LPSA could be accessed after incising the overlying superficial fascia, by retracting the white line. Adipose layers were clearly observed in 195 out of 200 patients with bilateral mild ptosis, among which 180 cases had the superficial layer connected to the uncoated adipose. Fifteen cases had the superficial layer connected to the smoothly coated layer, and 5 cases had the superficial layer directly connected to the deep loose fiber, almost without adipose. In previously untreated patients, the LPSA space was located beneath the intact orbital septum. In those with previous surgeries, it was beneath the superficial layer of the LPSA, underlying the destructed orbital septum. Cadaveric histology showed that the deep layer of the LPSA extended into the anterior layer of the tarsal plate and the superficial layer reflexed upward in continuity with the vertical orbital septum. An occult space existed between the 2 layers of the LPSA, with a smooth lining on the deep layer. The superficial layer of the LPSA was SMA-immunonegative but the deep layer was slightly immunopositive for SMA. An occult anatomic space exists between the superficial and deep layers of the LPSA, in proximity to the superior tarsal plate margin. Recognition of the more anatomically significant LPSA deep layer may help improve the aesthetic outcome of blepharoplasty. PMID:27495084

Ozone Transport Aloft Drives Surface Ozone Maxima Across the Mojave Desert

NASA Astrophysics Data System (ADS)

VanCuren, R. A.

2014-12-01

A persistent layer of polluted air in the lower free troposphere over the Mojave Desert (California and Nevada) drives spring and summer surface ozone maxima as deep afternoon mixing delivers ozone and ozone precursors to surface measurement sites 200 km or more downwind of the mountains that separate the deserts from the heavily populated coastal areas of California. Pollutants in this elevated layer derive from California source regions (the Los Angeles megacity region and the intensive agricultural region of the San Joaquin Valley), and from long-range transport from Asia. Recognition of this poorly studied persistent layer explains and expands the significance of previously published reports of ozone and other pollutants observed in and over the Mojave Desert, resolves an apparent paradox in the timing of ozone peaks due to transport from the upwind basins, and provides a new perspective on the long-range downwind impacts of megacity pollution plumes.

Speculations on the dynamics of Jupiter's atmosphere from 1 to 100 bars

NASA Astrophysics Data System (ADS)

Ingersoll, A. P.

2017-12-01

The latitude-altitude map of ammonia mixing ratio shows an ammonia-rich zone at 0-5°N, with mixing ratios of 320-340 ppm, extending from 40-60 bars up to the ammonia cloud base at 0.7 bars. Ammonia-poor air occupies a belt from 5-20°N. We argue that downdrafts as well as updrafts are needed in the 0-5°N zone to balance the upward ammonia flux. Outside the 0-20°N region, the belt-zone signature is weaker. At latitudes out to ±40°, there is an ammonia-rich layer from cloud base down to 2 bars which we argue is caused by falling precipitation. Below, there is an ammonia-poor layer with a minimum at 6 bars. Unanswered questions include how the ammonia-poor layer is maintained, why the belt-zone structure is barely evident in the ammonia distribution outside 0-20°N, and how the internal heat is transported through the ammonia-poor layer to the ammonia cloud base. Here we speculate on possible answers, including double-diffusive convection, deep abyssal overturning, and mass loading of heavy condensates in a hydrogen/helium atmosphere. Ingersoll, A. P. et al. (2017). Implications of the ammonia distribution on Jupiter from 1 to 100 bars as measured by the Juno microwave radiometer. Geophys. Res. Lett., in press, doi: 10.1002/2017GL074277.

Characterization of double diffusive convection step and heat budget in the deep Arctic Ocean

NASA Astrophysics Data System (ADS)

Zhou, S.; Lu, Y.

2013-12-01

In this paper, we explore the hydrographic structure and heat budget in deep Canada Basin using data measured with McLane-Moored-Profilers (MMPs), bottom-pressure-recorders (BPRs), and conductivity-temperature-depth (CTD) profilers. From the bottom upward, a homogenous bottom layer and its overlaying double diffusive convection (DDC) steps are well identified at Mooring A (75oN, 150oW). We find that the deep water is in weak diapycnal mixing because the effective diffusivity of the bottom layer is ~1.8×10-5 m 2s-1 while that of the other steps is ~10-6 m 2s-1. The vertical heat flux through DDC steps is evaluated with different methods. We find that the heat flux (0.1-11 mWm-2) is much smaller than geothermal heating (~50 mWm-2), which suggests that the stack of DDC steps acts as a thermal barrier in the deep basin. Moreover, the temporal distributions of temperature and salinity differences across the interface are exponential, while those of heat flux and effective diffusivity are found to be approximately log-normal. Both are the result of strong intermittency. Between 2003 and 2011, temperature fluctuation close to the sea floor distributed asymmetrically and skewed towards positive values, which provides direct indication that geothermal heating is transferred into ocean. Both BPR and CTD data suggest that geothermal heating, not the warming of upper ocean, is the dominant mechanism responsible for the warming of deep water. As the DDC steps prevent the vertical heat transfer, geothermal heating will be unlikely to have significant effect on the middle and upper oceans.

Characterization of double diffusive convection steps and heat budget in the deep Arctic Ocean

NASA Astrophysics Data System (ADS)

Zhou, Sheng-Qi; Lu, Yuan-Zheng

2013-12-01

In this paper, we explore the hydrographic structure and heat budget in the deep Canada Basin by using data measured with McLane-Moored-Profilers (MMP), bottom pressure recorders (BPR), and conductivity-temperature-depth (CTD) profilers. Upward from the bottom, a homogeneous bottom layer and its overlaying double diffusive convection (DDC) steps are well identified at Mooring A (75°N,150°W). We find that the deep water is in weak diapycnal mixing because the effective diffusivity of the bottom layer is ˜1.8 × 10-5 m2s-1, while that of the other steps is ˜10-6 m2s-1. The vertical heat flux through the DDC steps is evaluated by using different methods. We find that the heat flux (0.1-11 mWm -2) is much smaller than geothermal heating (˜50 mWm -2). This suggests that the stack of DDC steps acts as a thermal barrier in the deep basin. Moreover, the temporal distributions of temperature and salinity differences across the interface are exponential, whereas those of heat flux and effective diffusivity are found to be approximately lognormal. Both are the result of strong intermittency. Between 2003 and 2011, temperature fluctuations close to the sea floor were distributed asymmetrically and skewed toward positive values, which provide a direct observation that geothermal heating was transferred into the ocean. Both BPR and CTD data suggest that geothermal heating and not the warming of the upper ocean is the dominant mechanism responsible for the warming of deep water. As the DDC steps prevent vertical heat transfer, geothermal heating is unlikely to have a significant effect on the middle and upper Arctic Ocean.

Intercomparison and validation of the mixed layer depth fields of global ocean syntheses

NASA Astrophysics Data System (ADS)

Toyoda, Takahiro; Fujii, Yosuke; Kuragano, Tsurane; Kamachi, Masafumi; Ishikawa, Yoichi; Masuda, Shuhei; Sato, Kanako; Awaji, Toshiyuki; Hernandez, Fabrice; Ferry, Nicolas; Guinehut, Stéphanie; Martin, Matthew J.; Peterson, K. Andrew; Good, Simon A.; Valdivieso, Maria; Haines, Keith; Storto, Andrea; Masina, Simona; Köhl, Armin; Zuo, Hao; Balmaseda, Magdalena; Yin, Yonghong; Shi, Li; Alves, Oscar; Smith, Gregory; Chang, You-Soon; Vernieres, Guillaume; Wang, Xiaochun; Forget, Gael; Heimbach, Patrick; Wang, Ou; Fukumori, Ichiro; Lee, Tong

2017-08-01

Intercomparison and evaluation of the global ocean surface mixed layer depth (MLD) fields estimated from a suite of major ocean syntheses are conducted. Compared with the reference MLDs calculated from individual profiles, MLDs calculated from monthly mean and gridded profiles show negative biases of 10-20 m in early spring related to the re-stratification process of relatively deep mixed layers. Vertical resolution of profiles also influences the MLD estimation. MLDs are underestimated by approximately 5-7 (14-16) m with the vertical resolution of 25 (50) m when the criterion of potential density exceeding the 10-m value by 0.03 kg m-3 is used for the MLD estimation. Using the larger criterion (0.125 kg m-3) generally reduces the underestimations. In addition, positive biases greater than 100 m are found in wintertime subpolar regions when MLD criteria based on temperature are used. Biases of the reanalyses are due to both model errors and errors related to differences between the assimilation methods. The result shows that these errors are partially cancelled out through the ensemble averaging. Moreover, the bias in the ensemble mean field of the reanalyses is smaller than in the observation-only analyses. This is largely attributed to comparably higher resolutions of the reanalyses. The robust reproduction of both the seasonal cycle and interannual variability by the ensemble mean of the reanalyses indicates a great potential of the ensemble mean MLD field for investigating and monitoring upper ocean processes.

Hurricane Arthur and its effect on the short-term variability of pCO2 on the Scotian Shelf, NW Atlantic

NASA Astrophysics Data System (ADS)

Lemay, Jonathan; Thomas, Helmuth; Craig, Susanne E.; Burt, William J.; Fennel, Katja; Greenan, Blair J. W.

2018-04-01

The understanding of the seasonal variability of carbon cycling on the Scotian Shelf in the NW Atlantic Ocean has improved in recent years; however, very little information is available regarding its short-term variability. In order to shed light on this aspect of carbon cycling on the Scotian Shelf we investigate the effects of Hurricane Arthur, which passed the region on 5 July 2014. The hurricane caused a substantial decline in the surface water partial pressure of CO2 (pCO2), even though the Scotian Shelf possesses CO2-rich deep waters. High-temporal-resolution data of moored autonomous instruments demonstrate that there is a distinct layer of relatively cold water with low dissolved inorganic carbon (DIC) slightly above the thermocline, presumably due to a sustained population of phytoplankton. Strong storm-related wind mixing caused this cold intermediate layer with high phytoplankton biomass to be entrained into the surface mixed layer. At the surface, phytoplankton begin to grow more rapidly due to increased light. The combination of growth and the mixing of low DIC water led to a short-term reduction in the partial pressure of CO2 until wind speeds relaxed and allowed for the restratification of the upper water column. These hurricane-related processes caused a (net) CO2 uptake by the Scotian Shelf region that is comparable to the spring bloom, thus exerting a major impact on the annual CO2 flux budget.

Impact of an intense water column mixing (0-1500 m) on prokaryotic diversity and activities during an open-ocean convection event in the NW Mediterranean Sea.

PubMed

Severin, Tatiana; Sauret, Caroline; Boutrif, Mehdi; Duhaut, Thomas; Kessouri, Fayçal; Oriol, Louise; Caparros, Jocelyne; Pujo-Pay, Mireille; Durrieu de Madron, Xavier; Garel, Marc; Tamburini, Christian; Conan, Pascal; Ghiglione, Jean-François

2016-12-01

Open-ocean convection is a fundamental process for thermohaline circulation and biogeochemical cycles that causes spectacular mixing of the water column. Here, we tested how much the depth-stratified prokaryotic communities were influenced by such an event, and also by the following re-stratification. The deep convection event (0-1500 m) that occurred in winter 2010-2011 in the NW Mediterranean Sea resulted in a homogenization of the prokaryotic communities over the entire convective cell, resulting in the predominance of typical surface Bacteria, such as Oceanospirillale and Flavobacteriales. Statistical analysis together with numerical simulation of vertical homogenization evidenced that physical turbulence only was not enough to explain the new distribution of the communities, but acted in synergy with other parameters such as exported particulate and dissolved organic matters. The convection also stimulated prokaryotic abundance (+21%) and heterotrophic production (+43%) over the 0-1500 m convective cell, and resulted in a decline of cell-specific extracellular enzymatic activities (-67%), thus suggesting an intensification of the labile organic matter turnover during the event. The rapid re-stratification of the prokaryotic diversity and activities in the intermediate layer 5 days after the intense mixing indicated a marked resilience of the communities, apart from the residual deep mixed water patch. © 2016 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.

Observations of the atmospheric boundary layer height over Abu Dhabi, United Arab Emirates: Investigating boundary layer climatology in arid regions

NASA Astrophysics Data System (ADS)

Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa

2014-05-01

Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.

Eddy-Pump: Pelagic carbon pump processes along the eddying Antarctic Polar Front in the Atlantic Sector of the Southern Ocean

NASA Astrophysics Data System (ADS)

Strass, Volker H.; Wolf-Gladrow, Dieter; Pakhomov, Evgeny A.; Klaas, Christine

2017-04-01

The Southern Ocean influences earth's climate in many ways. It hosts the largest upwelling region of the world oceans where 80% of deep waters resurface (Morrison et al., 2015). A prominent feature is the broad ring of cold water, the Antarctic Circumpolar Current (ACC), which encircles the Antarctic continent and connects all other oceans. The ACC plays a major role in the global heat and freshwater transports and ocean-wide cycles of chemical and biogenic elements, and harbours a series of unique and distinct ecosystems. Due to the upwelling of deep-water masses in the Antarctic Divergence, there is high supply of natural CO2 as well as macronutrients, leading to the worldwide highest surface nutrient concentrations. Despite the ample macronutrients supply, phytoplankton concentration is generally low, limited either by low micronutrient (iron) availability, insufficient light due to deep wind-mixed layers or grazing by zooplankton, or by the combination of all, varying temporally and regionally.

Deep Learning and Developmental Learning: Emergence of Fine-to-Coarse Conceptual Categories at Layers of Deep Belief Network.

PubMed

Sadeghi, Zahra

2016-09-01

In this paper, I investigate conceptual categories derived from developmental processing in a deep neural network. The similarity matrices of deep representation at each layer of neural network are computed and compared with their raw representation. While the clusters generated by raw representation stand at the basic level of abstraction, conceptual categories obtained from deep representation shows a bottom-up transition procedure. Results demonstrate a developmental course of learning from specific to general level of abstraction through learned layers of representations in a deep belief network. © The Author(s) 2016.

Meteorological variables associated with deep slab avalanches on persistent weak layers

USGS Publications Warehouse

Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.

2014-01-01

Deep slab avalanches are a particularly challenging avalanche forecasting problem. These avalanches are typically difficult to trigger, yet when they are triggered they tend to propagate far and result in large and destructive avalanches. For this work we define deep slab avalanches as those that fail on persistent weak layers deeper than 0.9m (3 feet), and that occur after February 1st. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl Ski Area to test the usefulness of meteorological variables for predicting deep slab avalanches. As in previous studies, we used data from the days preceding deep slab cycles, but we also considered meteorological metrics over the early months of the season. We utilized classification trees for our analyses. Our results showed warmer temperatures in the prior twenty-four hours and more loading over the seven days before days with deep slab avalanches on persistent weak layers. In line with previous research, extended periods of above freezing temperatures led to days with deep wet slab avalanches on persistent weak layers. Seasons with either dry or wet avalanches on deep persistent weak layers typically had drier early months, and often had some significant snow depth prior to those dry months. This paper provides insights for ski patrollers, guides, and avalanche forecasters who struggle to forecast deep slab avalanches on persistent weak layers late in the season.

Ocean barrier layers’ effect on tropical cyclone intensification

PubMed Central

Balaguru, Karthik; Chang, Ping; Saravanan, R.; Leung, L. Ruby; Xu, Zhao; Li, Mingkui; Hsieh, Jen-Shan

2012-01-01

Improving a tropical cyclone’s forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone’s path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are “quasi-permanent” features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity. PMID:22891298

Ocean Barrier Layers’ Effect on Tropical Cyclone Intensification

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

Balaguru, Karthik; Chang, P.; Saravanan, R.

2012-09-04

Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are 'quasi-permanent' features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropicalmore » cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.« less

Origin and Constraints on Ilmenite-rich Partial Melt in the Lunar Lower Mantle

NASA Astrophysics Data System (ADS)

Mallik, A.; Fuqua, H.; Bremner, P. M.; Panovska, S.; Diamond, M. R.; Lock, S. J.; Nishikawa, Y.; Jiménez-Pérez, H.; Shahar, A.; Panero, W. R.; Lognonne, P. H.; Faul, U.

2015-12-01

Existence of a partially molten layer at the lunar core-mantle boundary has been proposed to explain the lack of observed far-side deep moonquakes, the observation of reflected seismic phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior [1,2]. However, subsequent models explored the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers [3]. Using thermo-chemical and dynamic modeling (including models of the early lunar mantle convection), we explore the hypothesis that an ilmenite-rich layer forms below crustal anorthosite during lunar magma ocean crystallization and may sink to the base of the mantle to create a partial melt layer at the lunar core-mantle boundary. Self-consistent physical parameters (including gravity, pressure, density, VP and Vs) are forward calculated for a well-mixed mantle with uniform bulk composition versus a mantle with preserved mineralogical stratigraphy from lunar magma ocean crystallization. These parameters are compared against observed mass, moment of inertia, real and imaginary parts of the Love numbers, and seismic travel times to further limit the acceptable models for the Moon. We have performed a multi-step grid search with over twenty thousand forward calculations varying thicknesses of chemically/mineralogically distinct layers within the Moon to evaluate if a partially molten layer at the base of the lunar mantle is well-constrained by the observed data. Furthermore, dynamic mantle modeling was employed on the best-fit model versions to determine the survivability of a partially molten layer at the core-mantle boundary. This work was originally initiated at the CIDER 2014 program. [1] Weber et al. (2011). Science 331(6015), 309-12. [2] Khan et al. (2014). JGR 119. [3] Nimmo et al. (2012). JGR 117, 1-11.

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.

Deep SOMs for automated feature extraction and classification from big data streaming

NASA Astrophysics Data System (ADS)

Sakkari, Mohamed; Ejbali, Ridha; Zaied, Mourad

2017-03-01

In this paper, we proposed a deep self-organizing map model (Deep-SOMs) for automated features extracting and learning from big data streaming which we benefit from the framework Spark for real time streams and highly parallel data processing. The SOMs deep architecture is based on the notion of abstraction (patterns automatically extract from the raw data, from the less to more abstract). The proposed model consists of three hidden self-organizing layers, an input and an output layer. Each layer is made up of a multitude of SOMs, each map only focusing at local headmistress sub-region from the input image. Then, each layer trains the local information to generate more overall information in the higher layer. The proposed Deep-SOMs model is unique in terms of the layers architecture, the SOMs sampling method and learning. During the learning stage we use a set of unsupervised SOMs for feature extraction. We validate the effectiveness of our approach on large data sets such as Leukemia dataset and SRBCT. Results of comparison have shown that the Deep-SOMs model performs better than many existing algorithms for images classification.

The Magmatic Structure of Mt. Vesuvius: Isotopic and Thermal Constraints

NASA Astrophysics Data System (ADS)

Civetta, L.; D'Antonio, M.; de Lorenzo, S.; Gasparini, P.

2002-12-01

Mt. Vesuvius is an active volcano famous for the AD 79 eruption that destroyed Pompeii, Herculaneum and Stabiae. Because of the intense urbanization around and on the volcano, the risk today is very high. Therefore, the knowledge of the structure and behavior of the magmatic system is fundamental both for the interpretation of any change in the dynamics of the volcano and for prediction of eruptions. A review of available and new isotopic data on rocks from Mt. Vesuvius, together with mineralogical and geochemical data and recent geophysical results, allow us to constrain a thermal modeling that describes history and present state of Mt. Vesuvius magmatic system. This system is formed by a "deep", complex magmatic reservoir where mantle-derived magmas arrive, stagnate and differentiate. The reservoir extends discontinuously between 10 and 20 km of depth, is hosted in densely fractured crustal rocks, where magmas and crust can interact, and has been fed more than once since 400 ka. The hypothesis of crustal contamination is favored by the high temperatures reached by crustal rocks as a consequence of repetitive intrusions of magma. From the "deep" reservoir magmas of K-basaltic to K-tephritic to K-phonotephritic composition rise to shallow depths where they stagnate at 3-5 km of depth before plinian eruptions, and through crystallization and mixing processes with the residual portion of the feeding systems, generate isotopically and geochemically layered reservoirs. Alternatively, during "open conduit" conditions deep, volatile-rich magma batches rise from the "deep" reservoir to less than 1 km of depth and mix with the crystal-rich, volatile-poor resident magma, triggering eruptions.

Seasonal Dynamics of Biogeochemical Processes in the Water Column of the Northeastern Black Sea

NASA Astrophysics Data System (ADS)

Rusanov, I. I.; Lein, A. Yu.; Makkaveev, P. N.; Klyuvitkin, A. A.; Kravchishina, M. D.; Ivanov, M. V.; Flint, M. V.

2018-01-01

Integrated studies on the hydrochemistry and water column rates of microbial processes in the eastern sector of the Black Sea along a standard 100-miles transect off Gelendzhik from the coast to the central part of the sea at water depths of 100-2170 m show that a series of warm winters and the absence of intense convective winter mixing resulted in a relatively low content of suspended particulate matter (SPM), particulate organic carbon (POC), and nutrients in the water column in March 2009. The relatively high SPM concentrations and the presence of isotopically light POC at the offshore station are indicative of the supply of terrigenous material from land and low contributions of phytoplanktonic organic matter to the composition of SPM. This may explain the low rates of biogeochemical processes in the water column near the coast. The surface layer at deep-water stations is dominated by isotopically heavy phytoplanktonic organic matter. This suggests that the supply of terrigenous material from land was insufficient in offshore deep-water areas. Therefore, warm winters and insufficient nutrient supply do not prevent photosynthesis in the photic layer of the deep-water zone, which generates organic substrates for heterotrophic aquatic communities. The results of isotopic analysis of POC, measurements of the rates biogeochemical processes, and the hydrochemical characteristics of the water column can be used to determine the nature and seasonal variability of the POC composition.

Effects of thinning intensities on soil infiltration and water storage capacity in a Chinese pine-oak mixed forest.

PubMed

Chen, Lili; Yuan, Zhiyou; Shao, Hongbo; Wang, Dexiang; Mu, Xingmin

2014-01-01

Thinning is a crucial practice in the forest ecosystem management. The soil infiltration rate and water storage capacity of pine-oak mixed forest under three different thinning intensity treatments (15%, 30%, and 60%) were studied in Qinling Mountains of China. The thinning operations had a significant influence on soil infiltration rate and water storage capacity. The soil infiltration rate and water storage capacity in different thinning treatments followed the order of control (nonthinning): <60%, <15%, and <30%. It demonstrated that thinning operation with 30% intensity can substantially improve soil infiltration rate and water storage capacity of pine-oak mixed forest in Qinling Mountains. The soil initial infiltration rate, stable infiltration rate, and average infiltration rate in thinning 30% treatment were significantly increased by 21.1%, 104.6%, and 60.9%, compared with the control. The soil maximal water storage capacity and noncapillary water storage capacity in thinning 30% treatment were significantly improved by 20.1% and 34.3% in contrast to the control. The soil infiltration rate and water storage capacity were significantly higher in the surface layer (0~20 cm) than in the deep layers (20~40 cm and 40~60 cm). We found that the soil property was closely related to soil infiltration rate and water storage capacity.

Turbulence increases the average settling velocity of phytoplankton cells

PubMed Central

Ruiz, Javier; Macías, Diego; Peters, Francesc

2004-01-01

It is a well known fact that stirring keeps particles suspended in fluids. This is apparent, for instance, when shaking medicine flasks, when agitating tea deposits in a mug, or when heavy winds fill the air with dust particles. The commonplace nature of such observations makes it easy to accept that this feature will apply to any natural phenomenon as long as the flow is turbulent enough. This has been the case for phytoplankton in the surface mixed layers of lakes and oceans. The traditional view assumes that an increase in turbulence bears ecological advantages for nonmotile groups like diatoms that, otherwise, would settle in deep and unlit waters. However, this assumption has no theoretical ground, and the experimental results we present here point in the opposite direction. Phytoplankton settling velocity increases when turbulence intensifies from the low to the higher values recorded in the upper mixed layers of lakes and oceans. Consequently, turbulence does not favor phytoplankton remaining in lit waters but is rather an environmental stress that can only be avoided through morphological and/or physiological adaptations. PMID:15601780

When a Slowly Rotating Aquaplanet is Coupled to a Dynamical Ocean

NASA Astrophysics Data System (ADS)

Salameh, J.; Marotzke, J.

2017-12-01

Planets orbiting in close distance from their stars have a high probability to be detected, and are expected to be slowly rotating due to strong tidal forces. By increasing the rotation period from 1 Earth-day to 365 Earth-days, we previously found that the global-mean surface temperature of an aquaplanet with a static mixed-layer ocean decreases by up to 27 K. The cooling is attributed to an increase of the planetary albedo with the rotation period, which is associated with the different distributions of the sea ice and the deep convective clouds. However, we had there assumed a fixed mixed-layer depth and a zero oceanic heat transport in the aquaplanet configuration. The limitations of these assumptions in such exotic climates are still unclear. We therefore perform coupled atmosphere-ocean aquaplanet simulations with the general circulation model ICON for various rotation periods ranging from 1 Earth-day to 365 Earth-days. We investigate how the underlying oceanic circulation modifies the mean climate of slowly rotating aquaplanets, and whether the day-to-night oceanic heat transport reduces the surface-temperature gradients and the sea-ice extent.

Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

NASA Astrophysics Data System (ADS)

Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

2010-11-01

Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine-rejection in the local coastal polynyas. In 2005 two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for nearly two weeks at the onset of sea ice growth. One of the seals migrated north thereafter and the other headed west, possibly utilising the Antarctic Slope Front current near the continental shelf break. In 2010, after that years calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and occupied the Commonwealth Bay polynya from March through April. Here we present unique observations of the regional oceanography during the summer-fall transition, in particular (a) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (b) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (c) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth (7.5-12.5 cm s-1). Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content, heat flux and sea ice growth rates. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer-fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

Antarctic Ocean Nutrient Conditions During the Last Two Glacial Cycles

NASA Astrophysics Data System (ADS)

Studer, A.; Sigman, D. M.; Martinez-Garcia, A.; Benz, V.; Winckler, G.; Kuhn, G.; Esper, O.; Lamy, F.; Jaccard, S.; Wacker, L.; Oleynik, S.; Gersonde, R.; Haug, G. H.

2014-12-01

The high concentration of the major nutrients nitrate and phosphate in the Antarctic Zone of the Southern Ocean dictates the nature of Southern Ocean ecosystems and permits these nutrients to be carried from the deep ocean into the nutrient-limited low latitudes. Incomplete nutrient consumption in the Antarctic also allows the leakage of deeply sequestered carbon dioxide (CO2) back to the atmosphere, and changes in this leakage may have driven glacial/interglacial cycles in atmospheric CO2. In a sediment core from the Pacific sector of the Antarctic Ocean, we report diatom-bound N isotope (δ15Ndb) records for total recoverable diatoms and two assemblages of diatom species. These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ15Ndb (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Measurements in the same sediment core indicate that export production was reduced during ice ages, pointing to an ice age reduction in the supply of deep ocean-sourced nitrate to the Antarctic Ocean surface. The reduced export production of peak ice ages also implies a weaker winter-to-summer decline (i.e. reduced seasonality) in mixed layer nitrate concentration, providing a plausible explanation for an observed reduction in the inter-assemblage δ15Ndb difference during these coldest times. Despite the weak summertime productivity, the reduction in wintertime nitrate supply from deep waters left the Antarctic mixed layer with a low nitrate concentration, and this wintertime change also would have reduced the outgassing of CO2. Relief of light limitation fails to explain the intermediate degree of nitrate consumption that characterizes early glacial conditions, as improved light limitation coincident with reduced nitrate supply would drive nitrate consumption to completion. Thus, the data favor iron availability as the dominant control on annual Antarctic Ocean export production over glacial cycles.

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.

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.

Observation of oxygen ventilation into deep waters through targeted deployment of multiple Argo-O2 floats in the north-western Mediterranean Sea in 2013

NASA Astrophysics Data System (ADS)

Coppola, L.; Prieur, L.; Taupier-Letage, I.; Estournel, C.; Testor, P.; Lefevre, D.; Belamari, S.; LeReste, S.; Taillandier, V.

2017-08-01

During the winter 2013, an intense observation and monitoring was performed in the north-western Mediterranean Sea to study deep water formation process that drives thermohaline circulation and biogeochemical processes (HYMEX SOP2 and DEWEX projects). To observe intensively and continuously the impact of deep convection on oxygen (O2) ventilation, an observation strategy was based on the enhancement of the Argo-O2 floats to monitor the offshore dense water formation area (DWF) in the Gulf of Lion prior to and at the end of the convective period (December 2012 to April 2013). The intense O2 measurements performed through shipborne CTD casts and Argo-O2 floats deployment revealed an O2 inventory rapidly impacted by mixed layer (ML) deepening on the month scale. The open-sea convection in winter 2013 ventilated the deep waters from mid-February to the end of May 2013. The newly ventilated dense water volume, based on an Apparent Oxygen Utilization (AOU) threshold, was estimated to be about 1.5 × 1013 m3 during the DWF episode, increasing the deep O2 concentrations from 196 to 205 µmol kg-1 in the north-western basin.

Laminar Neural Field Model of Laterally Propagating Waves of Orientation Selectivity

PubMed Central

2015-01-01

We construct a laminar neural-field model of primary visual cortex (V1) consisting of a superficial layer of neurons that encode the spatial location and orientation of a local visual stimulus coupled to a deep layer of neurons that only encode spatial location. The spatially-structured connections in the deep layer support the propagation of a traveling front, which then drives propagating orientation-dependent activity in the superficial layer. Using a combination of mathematical analysis and numerical simulations, we establish that the existence of a coherent orientation-selective wave relies on the presence of weak, long-range connections in the superficial layer that couple cells of similar orientation preference. Moreover, the wave persists in the presence of feedback from the superficial layer to the deep layer. Our results are consistent with recent experimental studies that indicate that deep and superficial layers work in tandem to determine the patterns of cortical activity observed in vivo. PMID:26491877

Pathways of upwelling deep waters to the surface of the Southern Ocean

NASA Astrophysics Data System (ADS)

Tamsitt, Veronica; Drake, Henri; Morrison, Adele; Talley, Lynne; Dufour, Carolina; Gray, Alison; Griffies, Stephen; Mazloff, Matthew; Sarmiento, Jorge; Wang, Jinbo; Weijer, Wilbert

2017-04-01

Upwelling of Atlantic, Indian and Pacific deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of anthropogenic carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. Here we go beyond the two-dimensional view of Southern Ocean upwelling, to show detailed Southern Ocean upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution ocean and climate models. The northern deep waters enter the Antarctic Circumpolar Current (ACC) via narrow southward currents along the boundaries of the three ocean basins, before spiraling southeastward and upward through the ACC. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the southern ACC boundary, with a spatially nonuniform distribution, regionalizing warm water supply to Antarctic ice shelves and the delivery of nutrient and carbon-rich water to the sea surface. The timescale for half of the deep water to upwell from 30°S to the mixed layer is on the order of 60-90 years, which has important implications for the timescale for signals to propagate through the deep ocean. In addition, we quantify the diabatic transformation along particle trajectories, to identify where diabatic processes are important along the upwelling pathways.

Vertical Transport Processes for Inert and Scavenged Species: TRACE-A Measurements

NASA Technical Reports Server (NTRS)

Chatfield, Robert B.; Chan, K. Roland (Technical Monitor)

1997-01-01

The TRACE-A mission of the NASA DC-8 aircraft made a large-scale survey of the tropical and subtropical atmosphere in September and October of 1992. Both In-situ measurements of CO (G. Sachsen NASA Langley) and aerosol size (J. Browell group, NASA Langley) provide excellent data sets with which to constrain vertical transport by planetary boundary layer mixing and deep-cloud cumulus convection. Lidar profiles of aerosol-induced scattering and ozone (also by Bremen) are somewhat require more subtle interpretation as tracers, but the vertical information on layering largely compensates for these complexities. The reason this DC-8 dataset is so useful is that very large areas of biomass burning over Africa and South America provide surface sources of appropriate sizes with which to characterize vertical and horizontal motions; the major limitation of our source description is that biomass burning patterns move considerably every few days, and daily burning inventories are a matter of concurrent, intensive research. We use the Penn State / NCAR MM5 model in an assimilation mode on the synoptic and intercontinental scale, and assess the success it shows in vertical transport descriptions. We find that the general level of emissions suggested by the climatological approach (Will. Has, U. of Montana) appears to be approximately correct, possibly a bit low, for this October, 1992, time period. Vertical transport in planetary boundary layer mixing to 5.5 kin was observed and reproduced in our simulations. Furthermore we find evidence that Blackader "transilient" or matrix-transport scheme is needed, but may require some adaptation in our tracer model: CO seems to exhibit very high values at the top of the planetary boundary layer, a process that stretches the eddy-diffusion parameterization. We will report on progress in improving the deep convective transport of carbon monoxide: the Grail scheme as we used it at 100 kin resolution did not transport enough material to the upper troposphere. We expect to be able to attribute this to either parameterization reasons (inadequacy of this parameterization at the large 100km scale) or other reasons. Nevertheless, the qualitative nature of deep transport by clouds shows up well in the simulations. As for scavengable species, the simulations predict tens of micrograms per standard cubic meter of smoke aerosol in the boundary layer. In a straightforward illustration of our simple bulk-mass scavenging parameterization, to one or two micrograms per standard cubic meter of smoke aerosol in the free troposphere just above the source regions: very high concentrations for the free troposphere. We expect to report on comparisons of these predictions to a variety of observations.

USArray Imaging of North American Continental Crust

NASA Astrophysics Data System (ADS)

Ma, Xiaofei

The layered structure and bulk composition of continental crust contains important clues about its history of mountain-building, about its magmatic evolution, and about dynamical processes that continue to happen now. Geophysical and geological features such as gravity anomalies, surface topography, lithospheric strength and the deformation that drives the earthquake cycle are all directly related to deep crustal chemistry and the movement of materials through the crust that alter that chemistry. The North American continental crust records billions of years of history of tectonic and dynamical changes. The western U.S. is currently experiencing a diverse array of dynamical processes including modification by the Yellowstone hotspot, shortening and extension related to Pacific coast subduction and transform boundary shear, and plate interior seismicity driven by flow of the lower crust and upper mantle. The midcontinent and eastern U.S. is mostly stable but records a history of ancient continental collision and rifting. EarthScope's USArray seismic deployment has collected massive amounts of data across the entire United States that illuminates the deep continental crust, lithosphere and deeper mantle. This study uses EarthScope data to investigate the thickness and composition of the continental crust, including properties of its upper and lower layers. One-layer and two-layer models of crustal properties exhibit interesting relationships to the history of North American continental formation and recent tectonic activities that promise to significantly improve our understanding of the deep processes that shape the Earth's surface. Model results show that seismic velocity ratios are unusually low in the lower crust under the western U.S. Cordillera. Further modeling of how chemistry affects the seismic velocity ratio at temperatures and pressures found in the lower crust suggests that low seismic velocity ratios occur when water is mixed into the mineral matrix, and the combination of high temperature and water may point to small amounts of melt in the lower crust of Cordillera.

The hydrogeochemical and isotopic investigations of the two-layered Shiraz aquifer in the northwest of Maharlou saline lake, south of Iran

NASA Astrophysics Data System (ADS)

Tajabadi, Mehdi; Zare, Mohammad; Chitsazan, Manouchehr

2018-03-01

Maharlou saline lake is the outlet of Shiraz closed basin in southern Iran, surrounded by several disconnected alluvial fresh water aquifers. These aquifers in the west and northwest of the lake are recharged by karstic anticlines such as Kaftarak in the north and Barmshour in the south. Here groundwater salinity varies along the depth so that better quality water is located below brackish or saline waters. The aim of this study is to investigate the reason for the salinity anomaly and the origin of the fresher groundwater in lower depth. Hence, the change in groundwater salinity along depth has been investigated by means of a set of geoelectrical, hydrogeological, hydrogeochemical, and environmental isotopes data. The interpretation of geoelectrical profiles and hydrogeological data indicates that the aquifer in the southeast of Shiraz plain is a two-layer aquifer separated by a fine-grained (silt and clay) layer with an approximate thickness of 40 m at the depth of about 100-120 m. Hydrgeochemistry showed that the shallow aquifer is recharged by Kaftarak karstic anticline and is affected by the saline lake water. The lake water fraction varies in different parts from zero for shallow aquifer close to the karstic anticlines to ∼70 percent in the margin of the lake. The deep aquifer is protected from the intrusion of saline lake water due to the presence of the above-mentioned confining layer with lake water fraction of zero. The stable isotopes signatures also indicate that the 'fresh' groundwater belonging to the deep aquifer is not subject to severe evaporation or mixing which is typical of the karstic water of the area. It is concluded that the characteristics of the deep aquifer are similar to those of the karstic carbonate aquifer. This karstic aquifer is most probably the Barmshour carbonated anticline buried under the shallow aquifer in the southern part. It may also be the extension of the Kaftarak anticline in the northern part.

The deep layer of the tractus iliotibialis and its relevance when using the direct anterior approach in total hip arthroplasty: a cadaver study.

PubMed

Putzer, David; Haselbacher, Matthias; Hörmann, Romed; Klima, Günter; Nogler, Michael

2017-12-01

Surgical approaches through smaller incisions reveal less of the underlying anatomy, and therefore, detailed knowledge of the local anatomy and its variations is important in minimally invasive surgery. The aim of this study was to determine the location, extension, and histomorphology of the deep layer of the iliotibial band during minimally invasive hip surgery using the direct anterior approach (DAA). The morphology of the iliotibial tract was determined in this cadaver study on 40 hips with reference to the anterior superior iliac spine and the tibia. The deep layer of the tractus iliotibialis was exposed up to the hip-joint capsule and length and width measurements taken. Sections of the profound iliotibial tract were removed from the hips and the thickness of the sections was determined microscopically after staining. The superficial tractus iliotibialis had a length of 50.1 (SD 3.8) cm, while tensor fasciae latae total length was 18 (SD 2) cm [unattached 15 (SD 2.5) cm]. Length and width of the deep layer of the tractus iliotibialis were 10.4 (SD 1.3) × 3.3 (SD 0.6) cm. The deep iliotibial band always extended from the distal part of the tensor fascia latae (TFL) muscle to the lateral part of the hip capsule (mean maximum thickness 584 μm). Tractus iliotibialis deep layer morphology did not correlate to other measurements taken (body length, thigh length, and TFL length). The length of the deep layer is dependent on the TFL, since the profound part of the iliotibial band reaches from the TFL to the hip-joint capsule. The deep layer covers the hip-joint capsule, rectus, and lateral vastus muscles in the DAA interval. To access the precapsular fat pad and the hip-joint capsule, the deep layer has to be split in all approaches that use the direct anterior interval.

Impact of different parameterization schemes on simulation of mesoscale convective system over south-east India

NASA Astrophysics Data System (ADS)

Madhulatha, A.; Rajeevan, M.

2018-02-01

Main objective of the present paper is to examine the role of various parameterization schemes in simulating the evolution of mesoscale convective system (MCS) occurred over south-east India. Using the Weather Research and Forecasting (WRF) model, numerical experiments are conducted by considering various planetary boundary layer, microphysics, and cumulus parameterization schemes. Performances of different schemes are evaluated by examining boundary layer, reflectivity, and precipitation features of MCS using ground-based and satellite observations. Among various physical parameterization schemes, Mellor-Yamada-Janjic (MYJ) boundary layer scheme is able to produce deep boundary layer height by simulating warm temperatures necessary for storm initiation; Thompson (THM) microphysics scheme is capable to simulate the reflectivity by reasonable distribution of different hydrometeors during various stages of system; Betts-Miller-Janjic (BMJ) cumulus scheme is able to capture the precipitation by proper representation of convective instability associated with MCS. Present analysis suggests that MYJ, a local turbulent kinetic energy boundary layer scheme, which accounts strong vertical mixing; THM, a six-class hybrid moment microphysics scheme, which considers number concentration along with mixing ratio of rain hydrometeors; and BMJ, a closure cumulus scheme, which adjusts thermodynamic profiles based on climatological profiles might have contributed for better performance of respective model simulations. Numerical simulation carried out using the above combination of schemes is able to capture storm initiation, propagation, surface variations, thermodynamic structure, and precipitation features reasonably well. This study clearly demonstrates that the simulation of MCS characteristics is highly sensitive to the choice of parameterization schemes.

Vertical nutrient fluxes, turbulence and the distribution of chlorophyll a in the north-eastern North Sea

NASA Astrophysics Data System (ADS)

Bendtsen, Jørgen; Richardson, Katherine

2017-04-01

During summer the northern North Sea is characterized by nutrient rich bottom water masses and nutrient poor surface layers. This explains the distribution of chlorophyll a in the water column where a subsurface maximum, referred to as the deep chlorophyll maximum (DCM), often is present during the growth season. Vertical transport of nutrients between bottom water masses and the well lit surface layer stimulates phytoplankton growth and this generally explains the location of the DCM. However, a more specific understanding of the interplay between vertical transports, nutrient fluxes and phytoplankton abundance is required for identifying the nature of the vertical transport processes, e.g the role of advection versus vertical turbulent diffusion or the role of localized mixing associated with mesoscale eddies. We present results from the VERMIX study in the north-eastern North Sea where nutrients, chlorophyll a and turbulence profiles were measured along five north-south directed transects in July 2016. A high-resolution sampling program, with horizontal distances of 1-10 km between CTD-stations, resolved the horizontal gradients of chlorophyll a across the steep bottom slope from the relatively shallow central North Sea ( 50-80 m) towards the deep Norwegian Trench (>700 m). Low oxygen concentrations in the bottom water masses above the slope indicated enhanced biological production where vertical mixing would stimulate phytoplankton growth around the DCM. Measurements of variable fluorescence (Fv/Fm) showed elevated values in the DCM which demonstrates a higher potential for electron transport in the Photosystem II in the phytoplankton cells, i.e. an indication of nutrient-rich conditions favorable for phytoplankton production. Profiles of the vertical shear and microstructure of temperature and salinity were measured by a VMP-250 turbulence profiler and the vertical diffusion of nutrients was calculated from the estimated vertical turbulent diffusivity and the distributions of nutrients. Results from the five transects and two time-series stations, where vertical profiles were made at hourly intervals, showed that vertical mixing processes above the slope increased the vertical transport of nutrients significantly and mixing above the slope can explain the hydrographic features and the distribution of the DCM in the area.

Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry.

PubMed

Zhong, Jian; Cai, Xiao-Ming; Bloss, William James

2017-05-01

A large eddy simulation (LES) model coupled with O 3 -NO x -VOC chemistry is implemented to simulate the coupled effects of emissions, mixing and chemical pre-processing within an idealised deep (aspect ratio = 2) urban street canyon under a weak wind condition. Reactive pollutants exhibit significant spatial variations in the presence of two vertically aligned unsteady vortices formed in the canyon. Comparison of the LES results from two chemical schemes (simple NO x -O 3 chemistry and a more comprehensive Reduced Chemical Scheme (RCS) chemical mechanism) shows that the concentrations of NO 2 and O x inside the street canyon are enhanced by approximately 30-40% via OH/HO 2 chemistry. NO, NO x , O 3 , OH and HO 2 are chemically consumed, while NO 2 and O x (total oxidant) are chemically produced within the canyon environment. Within-canyon pre-processing increases oxidant fluxes from the canyon to the overlying boundary layer, and this effect is greater for deeper street canyons (as found in many traditional European urban centres) than shallower (lower aspect ratio) streets. There is clear evidence of distinct behaviours for emitted chemical species and entrained chemical species, and positive (or negative) values of intensities of segregations are found between pairs of species with similar (or opposite) behaviour. The simplified two-box model underestimated NO and O 3 levels, but overestimated NO 2 levels for both the lower and upper canyon compared with the more realistic LES-chemistry model. This suggests that the segregation effect due to incomplete mixing reduces the chemical conversion rate of NO to NO 2 . This study reveals the impacts of nonlinear O 3 -NO x -VOC photochemical processes in the incomplete mixing environment and provides a better understanding of the pre-processing of emissions within canyons, prior to their release to the urban boundary layer, through the coupling of street canyon dynamics and chemistry. Copyright © 2017 Elsevier Ltd. All rights reserved.

On the origin of mixed-layered clay minerals from the San Andreas Fault at 2.5-3 km vertical depth (SAFOD drillhole at Parkfield, California)

NASA Astrophysics Data System (ADS)

Schleicher, A. M.; Warr, L. N.; van der Pluijm, B. A.

2009-02-01

A detailed mineralogical study is presented of the matrix of mudrocks sampled from spot coring at three key locations along the San Andreas Fault Observatory at depth (SAFOD) drill hole. The characteristics of authigenic illite-smectite (I-S) and chlorite-smectite (C-S) mixed-layer mineral clays indicate a deep diagenetic origin. A randomly ordered I-S mineral with ca. 20-25% smectite layers is one of the dominant authigenic clay species across the San Andreas Fault zone (sampled at 3,066 and 3,436 m measured depths/MD), whereas an authigenic illite with ca. 2-5% smectite layers is the dominant phase beneath the fault (sampled at 3,992 m MD). The most smectite-rich mixed-layered assemblage with the highest water content occurs in the actively deforming creep zone at ca. 3,300-3,353 m (true vertical depth of ca. 2.7 km), with I-S (70:30) and C-S (50:50). The matrix of all mudrock samples show extensive quartz and feldspar (both plagioclase and K-feldspar) dissolution associated with the crystallization of pore-filling clay minerals. However, the effect of rock deformation in the matrix appears only minor, with weak flattening fabrics defined largely by kinked and fractured mica grains. Adopting available kinetic models for the crystallization of I-S in burial sedimentary environments and the current borehole depths and thermal structure, the conditions and timing of I-S growth can be evaluated. Assuming a typical K+ concentration of 100-200 ppm for sedimentary brines, a present-day geothermal gradient of 35°C/km and a borehole temperature of ca. 112°C for the sampled depths, most of the I-S minerals can be predicted to have formed over the last 4-11 Ma and are probably still in equilibrium with circulating fluids. The exception to this simple burial pattern is the occurrence of the mixed layered phases with higher smectite content than predicted by the burial model. These minerals, which characterize the actively creeping section of the fault and local thin film clay coating on polished brittle slip surfaces, can be explained by the influence of either cooler fluids circulating along this segment of the fault or the flow of K+-depleted brines.

Determination of nitrogen to carbon abundance ratios from transition layer emission lines

NASA Technical Reports Server (NTRS)

Boehm-Vitense, Erika

1992-01-01

We have finished studying the nitrogen to carbon abundance ratios for stars with different effective temperatures T(sub eff) and luminosities using transition layer emission lines and using spectra available in the IUE archives. The N/C abundance ratio determinations using transition layer emission lines are as accurate as the photospheric abundance determinations as found by comparison of results obtained by both methods for the same stars. Our measurements confirm photospheric abundance determinations in regions of the HR diagram where they can be obtained. Our studies have extended the temperature range to higher temperatures. They have shown the exact positions in the HR diagram where the mixing due to the outer convection zones reaches deep enough to bring nuclear processed material to the surface. This occurs at effective temperatures which are higher by delta log T(sub eff) approximately 0.04 or roughly 400 K than expected theoretically. Since the depth of the convection zone increases rapidly with decreasing T(sub eff) this may indicate considerable overshoot beyond the lower boundary of the convection zone. Our N/C abundance ratio determinations from transition layer emission lines have confirmed that the actual enrichment observed for some cool giants is larger than expected theoretically, again indicating a larger degree of mixing in several stars either from below or from above. For the supergiants it probably indicates overshoot above the convective core in the progenitor main sequence stars. For the more massive giants this may also be the case, though we did not find a correlation between delta log N/C and the absolute magnitudes, but these are rather uncertain. As byproducts of these studies we also found anomalies in Si/C and N/C abundance ratios for F giants which can be understood as the relict of surface abundance changes for their main sequence progenitors due to diffusion. This anomaly disappears for G giants, for which the depths of the convection zones are apparently deep enough to wipe out these element separations (Bohm-Vitense 1992).

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.

Hurricane Arthur and its effect on the short term variation of pCO2

NASA Astrophysics Data System (ADS)

Lemay, Jonathan; Thomas, Helmuth; Craig, Susanne; Greenan, Blair; Fennel, Katja

2016-04-01

Seasonal changes in carbon cycling over the years have become better understood on the Scotian Shelf, however little is resolved in short term variation. Hourly measurements were collected from an autonomous moored instrument (CARIOCA) stationed at Halifax Line 2 (HL2), roughly 30km off the coast of Halifax for the 2014 year. Data from the 2007 deployment of the SeaHorse vertical sampling mooring at HL2 was also collected. Focusing on the storm event, Hurricane Arthur, July 5th 2014 reveals a significant drop in pCO2. With the shelf having carbon rich deep water, a reduction of pCO2 due to mixing went against current understanding. It was revealed that slightly above the mixed layer there is a sustained population of phytoplankton. When wind mixing from storms occurs, this population moves to the surface allowing greater light and nutrients for short term growth. This growth then reduces pCO2 for a short period of time until wind speeds slow down reducing mixing of the water column.

Counterintuitive effect of fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Fawcett, S. E.; Lomas, M. W.; Ward, B. B.; Sigman, D. M.

2012-12-01

The Sargasso Sea is characterized by a short period of deep vertical mixing in the late winter and early spring, followed by strong thermal stratification during the summer. Stratification persists into the fall, impeding the upward flux of nitrate from depth so that recycled forms of nitrogen (N) such as ammonium are thought to support most primary production. We collected particles from surface waters during March, July, October, and December, used flow cytometry to separate the prokaryotic and eukaryotic phytoplankton, and analyzed their respective 15N/14N. In all months, the 15N/14N of the prokaryotic genera, Prochlorococcus and Synechococcus, was low, indicative of reliance on recycled N throughout the year. In July, the 15N/14N of eukaryotic phytoplankton was variable but consistently higher than that of the prokaryotes, reflecting eukaryotic consumption of subsurface nitrate. Two eukaryotic profiles from October and December were similar to those from July. In three other fall profiles, the eukaryotes had a 15N/14N similar to that of the prokaryotes, suggesting a switch toward greater reliance on recycled N. This change in the dominant N source supporting eukaryotic production appears to be driven by the density structure of the upper water column. The very shallow low-density surface "mixed layer" (≤20 m) that develops in early-to-mid summer does not contribute to stratification at the base of the euphotic zone, and subsurface nitrate can mix up into the lower euphotic zone, facilitating continued production. The deepening of the mixed layer into the fall, typically taken as an indication of weaker overall stratification, actually strengthens the isolation of the euphotic zone as a whole, reducing the upward supply of nitrate to the photosynthetically active layer. The same counterintuitive dynamic explains the latitudinal patterns in a set of three October depth profiles. Two northern stations (32°N and 27°N) were characterized by a thick, low-density surface layer, and the 15N/14N of all phytoplankton was low, consistent with assimilation of recycled N. The southernmost station (23°N) had a shallower mixed layer, and eukaryote 15N/14N reflects growth on nitrate. In the subtropics, evidence for the direct supply of nitrate into surface waters in the face of the strong upper ocean stratification has long been sought. Our N isotope results suggest a mechanism by which subsurface nitrate is imported into shallow waters. This interpretation offers a new perspective on the relationship between euphotic zone stratification and nitrate assimilation, implying that significant new production occurs under conditions previously assumed to drive oligotrophy.

Surface atmosphere exchange in dry and a wet regime over the Ganges valley: a comprehensive investigation with direct observations and numerical simulations

NASA Astrophysics Data System (ADS)

Sathyanadh, Anusha; Prabhakaran, Thara; Karipot, Anandakumar

2017-04-01

Land atmosphere interactions in the Ganges Valley basin is a topic of significant importance as it is most vulnerable region due to extreme weather, air pollution, etc. The complete energy balance observations over this region was conducted as part of the CAIPEEX-IGOC (Cloud Aerosol Interaction and Precipitation Enhancement Experiment - Integrated Ground based Observational Campaign) experiment for an entire year. These observations give first insight into the partitioning of energy in this vulnerable environment during the dry and wet regimes, which are typically part of the intraseasonal oscillations during the Indian monsoon season. These transitions wet-dry and dry-wet are poorly represented in GCMs and is the motivation for the detailed investigation here. Observations conducted with micrometeorological tower instrumented with eddy covariance sensors, radiation balance, soil heat flux measurements, microwave radiometer, sodar, radiosonde data are used in the present study. A set of numerical investigations of different Planetary Boundary Layer (PBL) schemes is also carried out to investigate features of the diurnal cycle during the wet and dry regimes. General behaviour of both local and nonlocal PBL schemes found from the investigation is to accomplish enhanced mixing, leading to a deeper PBL in the valley. However, observations give clear evidence of residual boundary layer characterised by a weak stratification, playing a key role in the exchange of PBL air mass with that of free atmosphere. Impact of changes in parameterization and controlling factors on the PBL height are investigated. Case studies for a dry phase during the incidence of a heat wave and a wet phase during a land depression are presented. Observed diurnal features of the surface meteorological parameters including the surface energy budget components were well captured by local and nonlocal PBL schemes during both the cases. Vertical profiles of temperature, mixing ratio and winds from microwave radiometer, radiosonde sounding and SODAR measurements compared well with the model vertical profiles. All the schemes are able to capture the development of a drying phase, its persistence and revival after the drying, similar to observation. The characteristic features of the drying such as decrease in mixing ratio, PBL warming, enhanced PBL growth, variations in wind speed, etc were reproduced by the model simulations. Results indicate that model is simulating a drier and deeper surface and mixed layer, compared to the observations, which is assisted by enhanced mixing through deep updrafts rooted from the surface layer and downdrafts associated with the subsiding air reaching down to the surface. Two issues are identified with model as a) relating to enhanced mixing also assisted by the subsiding air at top of the boundary layer and b) the energy partitioning at the surface with significantly excess energy partitioned in to sensible heat flux, thus warming the model surface layer. A few aircraft observations are used to investigate entrainment issue and results from these analysis and inferences will be presented. The surface layer eddy covariance measurements of sensible and latent heat fluxes and surface layer relationships are used to tune the surface layer exchanges.

Preliminary Geophysical Characterization of a CO2-Driven Geyser in the Rio Grande Rift, New Mexico

NASA Astrophysics Data System (ADS)

Feucht, D. W.; Jensen, K. J.; Kelly, C.; Ryan, J. C.; Ferriz, H.; Kanjorski, N.; Ferguson, J. F.; McPhee, D. K.; Pellerin, L.

2009-12-01

As part of the Summer of Applied Geophysical Experience (SAGE) a preliminary geophysical investigation was conducted in the vicinity of a cold CO2-driven geyser located at Chimayó, NM, along the eastern margin of the Rio Grand Rift. This geyser is of interest as a possible analog for CO2 leakage from deep saline-aquifer carbon sequestration projects. Observed water chemistry variations can be explained by mixing of a CO2-rich, high salinity brine rising into, and mixing with a shallow freshwater aquifer. Several large, basin bounding faults and numerous smaller normal faults cut the area of the well and may constitute the necessary conduit for the deep water. Geophysical methods were used to characterize the subsurface properties at the Chimayó geyser as well as regional structures that may influence groundwater flow in the area. Shallow transient electromagnetic (TEM) data and capactively-coupled resistivity (CCR) data were acquired in close proximity to the geyser. The CCR shows a near-surface resistive feature, possibly hematite-cemented Tesuque formation sediment, in close proximity to the geyser. A shallow, highly conductive layer delineated through modeling of the TEM data is postulated to be a fluid consistent with high levels of Total Dissolved Solid (TDS) content. The well is located almost directly on the Roberts fault, which is antithetic to the basin bounding Chimayó fault 1.5 km to the east. Previously published hydrogeochemical studies associate this fault with high CO2 and TDS water along its strike. Deeper sounding TEM and audiomagnetotelluric (AMT) data were acquired along the Alamo Arroyo, 3 km to the southwest of the well. The Kelley Federal #1 Well located in this arroyo provides deep stratigraphic control to Pennsylvanian carbonate basement at 740 m. Tesuque formation conglomeritic alluvial fan deposits occur between 230 and 708 m and are overlain by finer grained basin floor deposits. The deep, coarse grained unit is thought to be a good, freshwater aquifer. A 2-D model of the AMT data indicates a resistive layer at about 200 m depth, which may correspond to the aquifer. High conductivity observed in the TEM and AMT data likely reflects saline fluids. Gravity data were collected at approximately 500 m station spacing along transects in Arroyo Alamo and Arroyo Seco 2 km to the south, and throughout the Chimayó Valley. The new data, combined with previously collected data, were used to create regional complete Bouguer anomaly and depth to basement maps. Two-dimensional forward models were constructed to provide a geohydrologic framework consistent with migration of CO2 rich brine up the Chimayó fault to mix with freshwater in the conglomeritic aquifer. The shallow, mixed groundwater emerges at the surface along the Roberts fault and drives the geyser at the Roberts well.

A case study of microphysical structures and hydrometeor phase in convection using radar Doppler spectra at Darwin, Australia

DOE PAGES

Riihimaki, Laura D.; Comstock, J. M.; Luke, E.; ...

2017-07-12

To understand the microphysical processes that impact diabatic heating and cloud lifetimes in convection, we need to characterize the spatial distribution of supercooled liquid water. To address this observational challenge, ground-based vertically pointing active sensors at the Darwin Atmospheric Radiation Measurement site are used to classify cloud phase within a deep convective cloud. The cloud cannot be fully observed by a lidar due to signal attenuation. Therefore, we developed an objective method for identifying hydrometeor classes, including mixed-phase conditions, using k-means clustering on parameters that describe the shape of the Doppler spectra from vertically pointing Ka-band cloud radar. Furthermore, thismore » approach shows that multiple, overlapping mixed-phase layers exist within the cloud, rather than a single region of supercooled liquid. Diffusional growth calculations show that the conditions for the Wegener-Bergeron-Findeisen process exist within one of these mixed-phase microstructures.« less

A case study of microphysical structures and hydrometeor phase in convection using radar Doppler spectra at Darwin, Australia

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

Riihimaki, Laura D.; Comstock, J. M.; Luke, E.

To understand the microphysical processes that impact diabatic heating and cloud lifetimes in convection, we need to characterize the spatial distribution of supercooled liquid water. To address this observational challenge, ground-based vertically pointing active sensors at the Darwin Atmospheric Radiation Measurement site are used to classify cloud phase within a deep convective cloud. The cloud cannot be fully observed by a lidar due to signal attenuation. Therefore, we developed an objective method for identifying hydrometeor classes, including mixed-phase conditions, using k-means clustering on parameters that describe the shape of the Doppler spectra from vertically pointing Ka-band cloud radar. Furthermore, thismore » approach shows that multiple, overlapping mixed-phase layers exist within the cloud, rather than a single region of supercooled liquid. Diffusional growth calculations show that the conditions for the Wegener-Bergeron-Findeisen process exist within one of these mixed-phase microstructures.« less

Prefrontal bore mixing

NASA Astrophysics Data System (ADS)

van Haren, Hans; Duineveld, Gerard; de Stigter, Henko

2017-09-01

Rainbow Ridge, a 1950 m deep upthrusted ultramafic block along the axis of the Mid-Atlantic Ridge, has an active hydrothermal vent system at 2400 m on its western slope. However, within 1 km from the vent excessive temperatures are barely measurable, probably due to strong turbulent mixing. This mixing is studied here using a 400 m long high-resolution temperature sensor array moored with a 600 m ranging 75 kHz acoustic Doppler current profiler. Rich internal wave turbulence was recorded, characterized by 100-200 m upshoots and >200 m large overturning in particular near the end of the warming phase of the up and down moving tide. These highly nonlinear internal waves of tides interacting with buoyancy frequency waves extend up to 400 m above the sloping bottom of the ridge. While a turbulent "bottom boundary layer" could barely be defined, the more intense turbulence higher up in the water column is suggested to lead to the strong dispersion of the hydrothermal plume.

One year of Seaglider dissolved oxygen concentration profiles at the PAP site

NASA Astrophysics Data System (ADS)

Binetti, Umberto; Kaiser, Jan; Heywood, Karen; Damerell, Gillian; Rumyantseva, Anna

2015-04-01

Oxygen is one of the most important variables measured in oceanography, influenced both by physical and biological factors. During the OSMOSIS project, 7 Seagliders were used in 3 subsequent missions to measure a multidisciplinary suite of parameters at high frequency in the top 1000 m of the water column for one year, from September 2012 to September 2013. The gliders were deployed at the PAP time series station (nominally at 49° N 16.5° W) and surveyed the area following a butterfly-shaped path. Oxygen concentration was measured by Aanderaa optodes and calibrated using ship CTD O2 profiles during 5 deployment and recovery cruises, which were in turn calibrated by Winkler titration of discrete samples. The oxygen-rich mixed layer deepens in fall and winter and gets richer in oxygen when the temperature decreases. The spring bloom did not happen as expected, but instead the presence of a series of small blooms was measured throughout spring and early summer. During the summer the mixed layer become very shallow and oxygen concentrations decreased. A Deep Oxygen Maximum (DOM) developed along with a deep chlorophyll maximum during the summer and was located just below the mixed layer . At this depth, phytoplankton had favourable light and nutrient conditions to grow and produce oxygen, which was not subject to immediate outgassing. The oxygen concentration in the DOM was not constant, but decreased, then increased again until the end of the mission. Intrusions of oxygen rich water are also visible throughout the mission. These are probably due to mesoscale events through the horizontal transport of oxygen and/or nutrients that can enhance productivity, particularly at the edge of the fronts. We calculate net community production (NCP) by analysing the variation in oxygen with time. Two methods have been proposed. The classical oxygen budget method assumes that changes in oxygen are due to the sum of air-sea flux, isopycnal advection, diapycnal mixing and NCP. ERA-Interim provides climatological data to calculate air-sea gas exchange fluxes based on wind-speed parameterisations of the gas exchange coefficient. The second method exploits the high frequency of the measurements to determine the increment of oxygen over time during daylight hours to measure NCP. Together with the O2 concentration decrease during the night (due to community respiration), this method also allows us to derive gross oxygen production rates. The results of these two methods are compared.

Biological Productivity from an Oxygen Mass Balance in the subarctic North Pacific

NASA Astrophysics Data System (ADS)

Giesbrecht, K. E.; Hamme, R. C.

2008-12-01

Biological productivity is an important process controlling the export of carbon into the deep ocean and thus influencing the earth's climate. An O2 mass balance of the upper ocean can estimate this export of organic carbon if the physical processes affecting the O2 concentrations are accounted for. This can be accomplished by measuring the dissolved O2/Ar ratio, because their similar physical properties allow us to consider Ar an 'abiotic' O2 analogue. Here we present a two-year data set of O2/N2/Ar ratio measurements collected at Station Papa and along Line P in 2007/08. Line P, situated in the subarctic North Pacific, is a series of oceanographic stations running from the southwest tip of Vancouver Island to Station Papa (50°N, 145°W), one of the oldest deep-ocean time series in existence which is located in the High-Nutrient/Low-Chlorophyll (HNLC) region of the subarctic gyre. Current cruises along Line P run three times per year, typically in February, June and August. The dissolved gas ratios are measured using a stable isotope mass spectrometer and oxygen concentrations by titration. In a simple steady state, we equate biological O2 production to diffusive gas exchange, using the O2/Ar ratio to normalize the physical component of the oxygen signal and calculate the net biological oxygen production. Diffusive gas exchange is calculated using a wind speed parameterization. Preliminary estimates of the net biological production in the mixed layer at Station Papa for 2007 are calculated at 30.9 and 14.0 mmol C m-2 d- 1 for June and August respectively, both exhibiting mixed layer O2/Ar supersaturations. The O2/Ar undersaturation in the mixed layer for February 2007 suggests net respiration at that time. The wind speed parameterization of diffusive gas exchange is the major source of error for this method. We plan to refine our productivity calculation to account for vertical mixing and also by measuring rates of production using a number of different methods, so that we may determine if the values obtained converge on a result. Future investigations to obtain a better-constrained estimate of the biological carbon export in this region by measuring Nitrogen and Carbon uptake rates in the euphotic zone using dual, stable isotope tracer 15N/13C incubations in addition to the oxygen mass balance will be discussed.

Ventilation of the Subtropical North Atlantic: Locations and Times of Last Ventilation Estimated Using Tracer Constraints From GEOTRACES Section GA03

NASA Astrophysics Data System (ADS)

Holzer, Mark; Smethie, William M.; Ting, Yu-Heng

2018-04-01

The ventilation of the subtropical North Atlantic along GEOTRACES section GA03 is quantified in terms of where and how long ago water was last in the mixed layer. Measurements of T, S, PO4∗, CFC-11, CFC-12, SF6, and estimates of prebomb 14C are deconvolved for the boundary propagator G using a maximum-entropy approach. From G, we calculate the fractions of water last ventilated in specified surface regions Ωw. We estimate that (56 ± 13)% of the water deeper than 1,000 m was ventilated in northern high latitudes, (15 ± 5)% in the Mediterranean, and (27 ± 12)% in the Southern Ocean. Below the thermocline and outside the deep western boundary current, mean ages of Ωw-ventilated water exceed a century. Consequently, memory of where last ventilation occurred tends to get lost and the deep mean-age patterns of Ωw-ventilated water are broadly similar for all Ωw. The mean ventilation ages, averaged over the section with Ωw-fraction weights, are roughly 200 years for all deep water masses except for water last ventilated south of the Antarctic divergence, which is about twice as old. The uncertainties in the section-mean profiles of the Ωw fractions and their mean ages are ˜50% and ˜20%, respectively. The Ωw fractions have vertically diffuse overlapping patterns suggesting significant diapycnal mixing, consistent with century-scale mean ages. We quantify the seasonal cycle of ventilation and find that in both hemispheres peak ventilation occurs during late winter and early spring, but Northern Hemisphere ventilated deep waters have a more pronounced seasonal cycle with nearly zero summertime ventilation.

Nutritive value and fermentation characteristics of alfalfa-mixed grass forage wrapped with minimal stretch film layers and stored for different lengths of time.

PubMed

Coblentz, W K; Ogden, R K; Akins, M S; Chow, E A

2017-07-01

A key aspect of managing baled silages is to quickly achieve and then rigorously maintain anaerobic conditions within the silage mass. The concept of inserting an O 2 -limiting barrier (OB) into plastic commercial silage wraps has been evaluated previously, yielding mixed or inconclusive results. Our objective for this study was to maximize the challenge to a commercial polyethylene bale wrap, or the identical wrap containing an OB, by using minimal plastic (4 layers), and then extending storage periods as long as 357 d. Forty-eight 1.2 × 1.2-m large-round bales of alfalfa (Medicago sativa L.) and mixed grass forage (66.3 ± 8.66% alfalfa; DM basis) were made at 2 moisture concentrations [47.5 (ideal) or 36.1% (dry)], wrapped with 4 layers of plastic containing an OB or no OB, and then stored for 99, 243, or 357 d. After storage, yeast counts within the 0.15-m deep surface layer were not affected by treatment (mean = 5.85 log 10 cfu/g); mold counts could not be analyzed statistically because 26 bales were nondetectable at a 3.00 log 10 cfu/g detection limit, but means among detectable counts were numerically similar for OB (4.74 log 10 cfu/g) and no OB (4.77 log 10 cfu/g). Fermentation characteristics were most affected by initial bale moisture, resulting in a more acidic final pH for ideal compared with dry bales (5.52 vs. 6.00). This was facilitated by greater concentrations of total fermentation acids (3.80 vs. 1.45% of dry matter), lactic acid (2.24 vs. 0.71% of dry matter), and acetic acid (1.07 vs. 0.64% of dry matter) within ideal compared with dry silages. Plastic wrap type had no effect on final concentrations of any fermentation product. During fermentation and storage, we noted greater change in concentrations of fiber components and whole-plant ash within the 0.15-m deep surface layer than in the bale core, and these changes always differed statistically from 0 (no change) based on pre-ensiled baseline concentrations. Overall, concentrations of water-soluble carbohydrates were reduced (mean = 2.3 percentage units) during fermentation and storage, which resulted (indirectly) in increased concentrations of fiber components and crude protein, as well as an overall energy cost of 2.2 percentage units of total digestible nutrient. It remains unclear under what conditions an OB plastic wrap will consistently benefit the fermentation and preservation of baled silages. Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Anatomy of the subcutaneous tissue of the trunk and lower extremity.

PubMed

Markman, B; Barton, F E

1987-08-01

Dissections on 8 fresh and 10 embalmed cadavers were used to determine the anatomy of the subcutaneous adipose tissue in the trunk and extremities. These dissections, along with CT scans, confirmed Gray's original description of the subcutaneous tissue consisting of a superficial and deep adipose layer. The superficial adipose layer is contained within organized, compact fascial septa. The deep adipose layer demonstrated regional variations with respect to its fascial framework, but was contained within a relatively loose, less organized, and more widely spaced fascial septa. We observed that the adipose layers are partitioned by a discrete subcutaneous fascia which fuses with the underlying muscle fascia at particular anatomic locations. The deep layer is thus contained by the subcutaneous fascia above and the muscle fascia below to form what we termed the deep adipose compartments. The deep adipose compartments contributed significantly to overall adipose thickness, are bilateral, and are found in the abdomen and paralumbar and gluteal-thigh regions.

Comparison of frailty of primary neurons, embryonic, and aging mouse cortical layers.

PubMed

Fugistier, Patrick; Vallet, Philippe G; Leuba, Geneviève; Piotton, Françoise; Marin, Pascale; Bouras, Constantin; Savioz, Armand

2014-02-01

Superficial layers I to III of the human cerebral cortex are more vulnerable toward Aβ peptides than deep layers V to VI in aging. Three models of layers were used to investigate this pattern of frailty. First, primary neurons from E14 and E17 embryonic murine cortices, corresponding respectively to future deep and superficial layers, were treated either with Aβ(1-42), okadaic acid, or kainic acid. Second, whole E14 and E17 embryonic cortices, and third, in vitro separated deep and superficial layers of young and old C57BL/6J mice, were treated identically. We observed that E14 and E17 neurons in culture were prone to death after the Aβ and particularly the kainic acid treatment. This was also the case for the superficial layers of the aged cortex, but not for the embryonic, the young cortex, and the deep layers of the aged cortex. Thus, the aged superficial layers appeared to be preferentially vulnerable against Aβ and kainic acid. This pattern of vulnerability corresponds to enhanced accumulation of senile plaques in the superficial cortical layers with aging and Alzheimer's disease. Copyright © 2014 Elsevier Inc. All rights reserved.

Deep Sea Drilling Project Site 612 bolide event: New evidence of a late Eocene impact-wave deposit and a possible impact site, US east coast

USGS Publications Warehouse

Wei, W.; Poag, C. Wylie; Poppe, Lawrence J.; Folger, David W.; Powars, David S.; Mixon, Robert B.; Edwards, Lucy E.; Bruce, Scott

1992-01-01

A remarkable >60-m-thick, upward-fining, polymictic, marine boulder bed is distributed over >15 000 km2 beneath Chesapeake Bay and the surrounding Middle Atlantic Coastal Plain and inner continental shelf. The wide varieties of clast lithologies and microfossil assemblages were derived from at least seven known Cretaceous, Paleocene, and Eocene stratigraphic units. The supporting pebbly matrix contains variably mixed assemblages of microfossils along with trace quantities of impact ejecta. The youngest microfossils in the boulder bed are of early-late Eocene age. On the basis of its unusual characteristics and its stratigraphic equivalent to a layer of impact ejecta at Deep Sea Drilling Project (DSDP) Site 612. It is postulated that this boulder bed was formed by a powerful bolide-generated wave train that scoured the ancient inner shelf and coastal plain of southeastern Virginia. 

North Atlantic Deep Water and the World Ocean

NASA Technical Reports Server (NTRS)

Gordon, A. L.

1984-01-01

North Atlantic Deep Water (NADW) by being warmer and more saline than the average abyssal water parcel introduces heat and salt into the abyssal ocean. The source of these properties is upper layer or thermocline water considered to occupy the ocean less dense than sigma-theta of 27.6. That NADW convects even though it's warmer than the abyssal ocean is obviously due to the high salinity. In this way, NADW formation may be viewed as saline convection. The counter force removing heat and salinity (or introducing fresh water) is usually considered to to take place in the Southern Ocean where upwelling deep water is converted to cold fresher Antarctic water masses. The Southern ocean convective process is driven by low temperatures and hence may be considered as thermal convection. A significant fresh water source may also occur in the North Pacific where the northward flowing of abyssal water from the Southern circumpolar belt is saltier and denser than the southward flowing, return abyssal water. The source of the low salinity input may be vertical mixing of the low salinity surface water or the low salinity intermediate water.

High Energy Benthic Boundary Layer Experiment (HEBBLE): Preliminary program plan and conceptual design

NASA Technical Reports Server (NTRS)

Frewing, K.

1980-01-01

Deep sea processes of flow-sediment interaction, particularly the role of high energy ocean bottom current events in forming the seafloor topography, transporting material, and mixing the bottom of the water column are examined. A series of observations at and near the sea bottom, in water depths of 4 to 5 km, in areas of the western North Atlantic where high energy current events occur, include site surveys and physical reconnaissance to identify suitable areas and positions, and one or more six month experiments to investigate temporal and spatial variations of high energy events within the boundary layer and their interaction with the seabed. Descriptions of proposed HEBBLE activities are included, with emphasis on technology transfer to the oceanographic community through design, fabrication, testing, and operation of an instrumented ocean bottom lander.

Crustal characteristic variation in the central Yamato Basin, Japan Sea back-arc basin, deduced from seismic survey results

NASA Astrophysics Data System (ADS)

Sato, Takeshi; No, Tetsuo; Miura, Seiichi; Kodaira, Shuichi

2018-02-01

The crustal structure of the Yamato Bank, the central Yamato Basin, and the continental shelf in the southern Japan Sea back-arc basin is obtained based on a seismic survey using ocean bottom seismographs and seismic shot to elucidate the back-arc basin formation processes. The central Yamato Basin can be divided into three domains based on the crustal structure: the deep basin, the seamount, and the transition domains. In the deep basin domain, the crust without the sedimentary layer is about 12-13 km thick. Very few units have P-wave velocity of 5.4-6.0 km/s, which corresponds to the continental upper crust. In the seamount and transition domains, the crust without the sedimentary layer is about 12-16 km thick. The P-wave velocities of the upper and lower crusts differs among the deep basin, the seamount, and the transition domains. These results indicate that the central Yamato Basin displays crustal variability in different domains. The crust of the deep basin domain is oceanic in nature and suggests advanced back-arc basin development. The seamount domain might have been affected by volcanic activity after basin opening. In the transition domain, the crust comprises mixed characters of continental and oceanic crust. This crustal variation might represent the influence of different processes in the central Yamato Basin, suggesting that crustal development was influenced not only by back-arc opening processes but also by later volcanic activity. In the Yamato Bank and continental shelf, the upper crust has thickness of about 17-18 km and P-wave velocities of 3.3-4.1 to 6.6 km/s. The Yamato Bank and the continental shelf suggest a continental crustal character.

Late Quaternary palaeoenvironmental reconstruction of sediment drift accumulation in the Malta Graben (central Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Ferraro, Serena; Sulli, Attilio; Di Stefano, Enrico; Giaramita, Luigi; Incarbona, Alessandro; Graham Mortyn, P.; Sprovieri, Mario; Sprovieri, Rodolfo; Tonielli, Renato; Vallefuoco, Mattia; Zizzo, Elisabetta; Tranchida, Giorgio

2018-06-01

The Malta Graben is a deep tectonic depression in the Sicily Channel, bounded by NW-SE normal faults and filled by thick Pliocene-Quaternary deposits. A previous analysis of a giant piston core (LC09) from the Malta Graben had revealed a wide range of sedimentary features (carbonate turbidites, bioturbated mud and scours), although the chronostratigraphic constraint of the stacking pattern has remained elusive. After establishing a reliable chronological framework based on seven radiocarbon dates for a shorter core from the Malta Graben (ANSIC03-735), a down-core analysis of planktonic foraminifer and coccolith abundance, stable isotopes and sediment grain size was carried out. Since the last glacial maximum, palaeoenvironmental conditions (surface fertility and deep chlorophyll maximum during the last glacial and the Younger Dryas; warm and oligotrophic water masses, with a deep nutricline and intense winter mixing during the Holocene) as well as selected calcareous plankton taxa trends and peaks seem to be similar to those reported for other central and western Mediterranean sites, possibly in spite of a unique response of these areas to late Quaternary climatic fluctuations. Four distinct layers, each tens of centimetres thick, are barren of foraminifers but not of coccoliths. Morphobathymetric data as well as new high-resolution and high-penetration seismic profiles show that prolonged contouritic activity has persisted on the western side of the Malta Graben. It is thus likely that layers barren of foraminifers are due to the overflow of fine-grained (clayey) material beyond drift channel dikes.

Late Quaternary palaeoenvironmental reconstruction of sediment drift accumulation in the Malta Graben (central Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Ferraro, Serena; Sulli, Attilio; Di Stefano, Enrico; Giaramita, Luigi; Incarbona, Alessandro; Graham Mortyn, P.; Sprovieri, Mario; Sprovieri, Rodolfo; Tonielli, Renato; Vallefuoco, Mattia; Zizzo, Elisabetta; Tranchida, Giorgio

2018-03-01

The Malta Graben is a deep tectonic depression in the Sicily Channel, bounded by NW-SE normal faults and filled by thick Pliocene-Quaternary deposits. A previous analysis of a giant piston core (LC09) from the Malta Graben had revealed a wide range of sedimentary features (carbonate turbidites, bioturbated mud and scours), although the chronostratigraphic constraint of the stacking pattern has remained elusive. After establishing a reliable chronological framework based on seven radiocarbon dates for a shorter core from the Malta Graben (ANSIC03-735), a down-core analysis of planktonic foraminifer and coccolith abundance, stable isotopes and sediment grain size was carried out. Since the last glacial maximum, palaeoenvironmental conditions (surface fertility and deep chlorophyll maximum during the last glacial and the Younger Dryas; warm and oligotrophic water masses, with a deep nutricline and intense winter mixing during the Holocene) as well as selected calcareous plankton taxa trends and peaks seem to be similar to those reported for other central and western Mediterranean sites, possibly in spite of a unique response of these areas to late Quaternary climatic fluctuations. Four distinct layers, each tens of centimetres thick, are barren of foraminifers but not of coccoliths. Morphobathymetric data as well as new high-resolution and high-penetration seismic profiles show that prolonged contouritic activity has persisted on the western side of the Malta Graben. It is thus likely that layers barren of foraminifers are due to the overflow of fine-grained (clayey) material beyond drift channel dikes.

Effects of Thinning Intensities on Soil Infiltration and Water Storage Capacity in a Chinese Pine-Oak Mixed Forest

PubMed Central

Chen, Lili; Yuan, Zhiyou; Shao, Hongbo; Wang, Dexiang; Mu, Xingmin

2014-01-01

Thinning is a crucial practice in the forest ecosystem management. The soil infiltration rate and water storage capacity of pine-oak mixed forest under three different thinning intensity treatments (15%, 30%, and 60%) were studied in Qinling Mountains of China. The thinning operations had a significant influence on soil infiltration rate and water storage capacity. The soil infiltration rate and water storage capacity in different thinning treatments followed the order of control (nonthinning): <60%, <15%, and <30%. It demonstrated that thinning operation with 30% intensity can substantially improve soil infiltration rate and water storage capacity of pine-oak mixed forest in Qinling Mountains. The soil initial infiltration rate, stable infiltration rate, and average infiltration rate in thinning 30% treatment were significantly increased by 21.1%, 104.6%, and 60.9%, compared with the control. The soil maximal water storage capacity and noncapillary water storage capacity in thinning 30% treatment were significantly improved by 20.1% and 34.3% in contrast to the control. The soil infiltration rate and water storage capacity were significantly higher in the surface layer (0~20 cm) than in the deep layers (20~40 cm and 40~60 cm). We found that the soil property was closely related to soil infiltration rate and water storage capacity. PMID:24883372

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.

Intensified diapycnal mixing in the midlatitude western boundary currents.

PubMed

Jing, Zhao; Wu, Lixin

2014-12-10

The wind work on oceanic near-inertial motions is suggested to play an important role in furnishing the diapycnal mixing in the deep ocean which affects the uptake of heat and carbon by the ocean as well as climate changes. However, it remains a puzzle where and through which route the near-inertial energy penetrates into the deep ocean. Using the measurements collected in the Kuroshio extension region during January 2005, we demonstrate that the diapycnal mixing in the thermocline and deep ocean is tightly related to the shear variance of wind-generated near-inertial internal waves with the diapycnal diffusivity 6 × 10(-5) m(2)s(-1) almost an order stronger than that observed in the circulation gyre. It is estimated that 45%-62% of the local near-inertial wind work 4.5 × 10(-3) Wm(-2) radiates into the thermocline and deep ocean and accounts for 42%-58% of the energy required to furnish mixing there. The elevated mixing is suggested to be maintained by the energetic near-inertial wind work and strong eddy activities causing enhanced downward near-inertial energy flux than earlier findings. The western boundary current turns out to be a key region for the penetration of near-inertial energy into the deep ocean and a hotspot for the diapycnal mixing in winter.

Convectively-driven cold layer and its influences on moisture in the UTLS

NASA Astrophysics Data System (ADS)

Kim, J.; Randel, W. J.; Birner, T.

2016-12-01

Characteristics of the cold anomaly in the tropical tropopause layer (TTL) that is commonly observed with deep convection are examined using CloudSat and Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS radio occultation measurements. Deep convection is sampled based on the cloud top height (>17 km) from CloudSat 2B-CLDCLASS, and then temperature profiles from COSMIC are composited around the deep convection. The composite temperature shows anomalously warm troposphere (up to 14 km) and a significantly cold layer near the tropopause (at 16-18 km) in the regions of deep convection. Generally in the tropics, the cold layer has very large horizontal scale (2,000 - 6,000 km) compared to that of mesoscale convective cluster, and it lasts one or two weeks with minimum temperature anomaly of - 2K. The cold layer shows slight but clear eastward-tilted vertical structure in the deep tropics indicating a large-scale Kelvin wave response. Further analyses on circulation patterns suggest that the anomaly can be explained as a part of Gill-type response in the TTL to deep convective heating in the troposphere. Response of moisture to the cold layer is also examined in the upper troposphere and lower stratosphere using microwave limb sounder (MLS) measurements. The water vapor anomalies show coherent structures with the temperature and circulation anomalies. A clear dry anomaly is found in the cold layer and its outflow region, implying a large-scale dehydration process due to the convectively driven cold layer in the upper TTL.

How ocean lateral mixing changes Southern Ocean variability in coupled climate models

NASA Astrophysics Data System (ADS)

Pradal, M. A. S.; Gnanadesikan, A.; Thomas, J. L.

2016-02-01

The lateral mixing of tracers represents a major uncertainty in the formulation of coupled climate models. The mixing of tracers along density surfaces in the interior and horizontally within the mixed layer is often parameterized using a mixing coefficient ARedi. The models used in the Coupled Model Intercomparison Project 5 exhibit more than an order of magnitude range in the values of this coefficient used within the Southern Ocean. The impacts of such uncertainty on Southern Ocean variability have remained unclear, even as recent work has shown that this variability differs between different models. In this poster, we change the lateral mixing coefficient within GFDL ESM2Mc, a coarse-resolution Earth System model that nonetheless has a reasonable circulation within the Southern Ocean. As the coefficient varies from 400 to 2400 m2/s the amplitude of the variability varies significantly. The low-mixing case shows strong decadal variability with an annual mean RMS temperature variability exceeding 1C in the Circumpolar Current. The highest-mixing case shows a very similar spatial pattern of variability, but with amplitudes only about 60% as large. The suppression of mixing is larger in the Atlantic Sector of the Southern Ocean relatively to the Pacific sector. We examine the salinity budgets of convective regions, paying particular attention to the extent to which high mixing prevents the buildup of low-saline waters that are capable of shutting off deep convection entirely.

Gas Classification Using Deep Convolutional Neural Networks.

PubMed

Peng, Pai; Zhao, Xiaojin; Pan, Xiaofang; Ye, Wenbin

2018-01-08

In this work, we propose a novel Deep Convolutional Neural Network (DCNN) tailored for gas classification. Inspired by the great success of DCNN in the field of computer vision, we designed a DCNN with up to 38 layers. In general, the proposed gas neural network, named GasNet, consists of: six convolutional blocks, each block consist of six layers; a pooling layer; and a fully-connected layer. Together, these various layers make up a powerful deep model for gas classification. Experimental results show that the proposed DCNN method is an effective technique for classifying electronic nose data. We also demonstrate that the DCNN method can provide higher classification accuracy than comparable Support Vector Machine (SVM) methods and Multiple Layer Perceptron (MLP).

Gas Classification Using Deep Convolutional Neural Networks

PubMed Central

Peng, Pai; Zhao, Xiaojin; Pan, Xiaofang; Ye, Wenbin

2018-01-01

In this work, we propose a novel Deep Convolutional Neural Network (DCNN) tailored for gas classification. Inspired by the great success of DCNN in the field of computer vision, we designed a DCNN with up to 38 layers. In general, the proposed gas neural network, named GasNet, consists of: six convolutional blocks, each block consist of six layers; a pooling layer; and a fully-connected layer. Together, these various layers make up a powerful deep model for gas classification. Experimental results show that the proposed DCNN method is an effective technique for classifying electronic nose data. We also demonstrate that the DCNN method can provide higher classification accuracy than comparable Support Vector Machine (SVM) methods and Multiple Layer Perceptron (MLP). PMID:29316723

Alkyl nitrate (C1-C3) depth profiles in the tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Dahl, E. E.; Yvon-Lewis, S. A.; Saltzman, E. S.

2007-01-01

This paper reports the first depth profile measurements of methyl, ethyl, isopropyl and n-propyl nitrates in the tropical Pacific Ocean. Depth profile measurements were made at 22 stations during the Project Halocarbon Air Sea Exchange cruise, in warm pool, equatorial, subequatorial, and gyre waters. The highest concentrations, up to several hundred pM of methyl nitrate, were observed in the central Pacific within 8 degrees of the equator. In general, alkyl nitrate levels were highest in the surface mixed layer, and decreased with depth below the mixed layer. The spatial distribution of the alkyl nitrates suggests that there is a strong source associated with biologically productive ocean regions, that is characterized by high ratios of methyl:ethyl nitrate. However, the data do not allow discrimination between direct biological emissions and photochemistry as production mechanisms. Alkyl nitrates were consistently detectable at several hundred meters depth. On the basis of the estimated chemical loss rate of these compounds, we conclude that deep water alkyl nitrates must be produced in situ. Possible sources include free radical processes initiated by radioactive decay or cosmic rays, enzymatically mediated reactions involving bacteria, or unidentified chemical mechanisms involving dissolved organic matter.

Interannual Variations in Global Net Carbon Production in the Absence of Fixed Nitrogen: Implication of New Production Supported by Dinitrogen Fixing Microorganisms

NASA Astrophysics Data System (ADS)

Lee, K.; Ko, Y. H.

2016-12-01

In the ocean without the measurable levels of nitrate, new production, i.e. the amount of carbon transported from the sunlit upper water to deep water, was estimated by summing the seasonal reduction in the total dissolved inorganic carbon (NCT = CT x 35/S) concentration in the surface mixed layer. Total reduction in the mixed layer NCT inventory in each 4o latitude by 5o longitude was calculated using an annual cycle of NCT, which was deduced from global monthly records of partial pressure of CO2 (based on more than 6.5 million data) and total alkalinity fields using thermodynamic models. The estimation of total NCT reduction for each pixel was then corrected for small changes caused by atmospheric nitrogen deposition and net air-sea CO2 exchange. This novel method yields 0.8 ± 0.3 petagrams of global new production per year (Pg C yr, Pg = 1015 grams), which is likely to be mediated exclusively by dinitrogen (N2) fixing microorganisms. These organisms utilize the inexhaustible pool of dissolved N2 and thereby circumvent nitrate limitation, particularly in the oligotrophic tropical and subtropical ocean.

An IR Sounding-Based Analysis of the Saharan Air Layer in North Africa

NASA Technical Reports Server (NTRS)

Nicholls, Stephen D.; Mohr, Karen I.

2018-01-01

Intense daytime surface heating over barren-to-sparsely vegetated surfaces results in dry convective mixing. In the absence of external forcing such as mountain waves, the dry convection can produce a deep, well-mixed, nearly isentropic boundary layer that becomes a well-mixed residual layer in the evening. These well-mixed layers (WML) retain their unique mid-tropospheric thermal and humidity structure for several days. To detect the SAL and characterize its properties, AIRS Level 2 Ver. 6 temperature and humidity products (2003-Present) are evaluated against rawinsondes and compared to model analysis at each of the 55 rawinsonde stations in northern Africa. To distinguish WML from Saharan air layers (WMLs of Saharan origin), the detection involved a two-step process: 1) algorithm-based detection of WMLs in dry environments (less than 7 g per kilogram mixing ratio) 2) identification of Sahara air layers (SAL) by applying Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) back trajectories to determine the history of each WML. WML occurrence rates from AIRS closely resemble that from rawinsondes, yet rates from model analysis were up to 30% higher than observations in the Sahara due to model errors. Despite the overly frequent occurrence of WMLs from model analysis, HYSPLIT trajectory analysis showed that SAL occurrence rates (given a WML exists) from rawinsondes, AIRS, and model analysis were nearly identical. Although the number of WMLs varied among the data sources, the proportion of WMLs which were classified as SAL was nearly the same. The analysis of SAL bulk properties showed that AIRS and model analysis exhibited a slight warm and moist bias relative to rawinsondes in non-Saharan locations, but model analysis was notably warmer than rawinsondes and AIRS within the Sahara. The latter result is likely associated with the dearth of available data assimilated by model analysis in the Sahara. The variability of SAL thicknesses was reasonably captured by both AIRS and model analysis, but the former favor layers than are thinner than observations. Finally, further analysis of HYSPLIT trajectories revealed that fewer than 10% and 33% of all SAL back trajectories passed through regions with notable precipitation (>100 mm accumulated along the trajectory path) or Aerosol Optical Depth (AOD greater than 0.4, 75th percentile of AOD) on average, respectively. Trajectory analysis indicated that only 57% of Saharan and 24% of non-Saharan WMLs are definitively of Saharan origin (Saharan requirement: Two consecutive days in Sahara and 24 or more of those hours within 72 hours of detection). Non-SAL WMLs either originate from local-to-regionally generated residual layers or from mid-latitude air streams that do not linger over the Sahara for a sufficient time period. Initial analysis shows these non-SAL WMLs tend to be both notably cooler and slightly moister than their SAL counter parts. Continuing analysis will address what role Saharan and non-Saharan air masses characteristics may play on local and regional environmental conditions.

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.

The Weddell-Scotia Confluence in midwinter

NASA Astrophysics Data System (ADS)

Muench, Robin D.; Gunn, John T.; Husby, David M.

1990-10-01

The southern central Scotia Sea, site of the Weddell-Scotia Confluence where outflowing Weddell Sea waters converge with the eastward flowing waters of the Scotia Sea, was sampled during June-August (austral winter) 1988 with respect to temperature and salinity. Both drogued and ice-mounted drifters, tracked by Argos, were deployed in the region and yielded Lagrangian drift tracks of ice and water motion. The data substantiate past accounts of the region, based upon summer field research, as dominated by eastward flow upon which a complex array of mesoscale features is superimposed. Weddell-Scotia Confluence Water, documented by past summer work in the region and characterized by decreased static stability, was not detected, and the Scotia Front was not well defined. The region was one of intense mixing activity and primarily anticyclonic mesoscale features. Two such features, one an eddy and the other either an eddy or a meander in the Scotia Front, dominated the mesoscale field. With warm cores and containing Polar Front Water, they may have been advected eastward from Drake Passage or may have formed as detached eddies from a sharp northward bend in the Polar Front which typically lies just west of the study region. Several smaller eddies, primarily anticyclonic and some having warm cores, were also detected. There was no evidence of the deep convective mixing which has been hypothesized, on the basis of past summer data, to occur in winter, and vigorous vertical mixing was limited to a 100-m-thick upper mixed layer. Vertical stability in the upper layers was enhanced by low-salinity water derived from melting ice. Temperature-salinity analyses show that winter water in the study region can be derived through isopycnal mixing between waters from the Scotia Sea and waters from the northwestern Weddell Sea. This is in apparent contrast with summer conditions, wherein conditioning of water either through vertical mixing or via lateral mixing on continental margins has been invoked to arrive at the water mass characteristics which typify the Weddell-Scotia Confluence.

Noble gas as tracers for CO2 deep input in petroleum reservoirs

NASA Astrophysics Data System (ADS)

Pujol, Magali; Stuart, Finlay; Gilfillan, Stuart; Montel, François; Masini, Emmanuel

2016-04-01

The sub-salt hydrocarbon reservoirs in the deep offshore part of the Atlantic Ocean passive margins are a new key target for frontier oil and gas exploration. Type I source rocks locally rich in TOC (Total Organic Carbon) combined with an important secondary connected porosity of carbonate reservoirs overlain by an impermeable salt layer gives rise to reservoirs with high petroleum potential. However, some target structures have been found to be mainly filled with CO2 rich fluids. δ13C of the CO2 is generally between -9 and -4 permil, compatible with a deep source (metamorphic or mantle). Understanding the origin of the CO2 and the relative timing of its input into reservoir layers in regard to the geodynamic context appears to be a key issue for CO2 risk evaluation. The inertness and ubiquity of noble gases in crustal fluids make them powerful tools to trace the origin and migration of mixed fluids (Ballentine and Burnard 2002). The isotopic signature of He, Ne and Ar and the elemental pattern (He to Xe) of reservoir fluid from pressurized bottom hole samples provide an insight into fluid source influences at each reservoir depth. Three main end-members can be mixed into reservoir fluids (e.g. Gilfillan et al., 2008): atmospheric signature due to aquifer recharge, radiogenic component from organic fluid ± metamorphic influence, and mantle input. Their relative fractionation provides insights into the nature of fluid transport (Burnard et al., 2012)and its relative migration timing. In the studied offshore passive margin reservoirs, from both sides of South Atlantic margin, a strong MORB-like magmatic CO2 influence is clear. Hence, CO2 charge must have occurred during or after lithospheric break-up. CO2 charge(s) history appears to be complex, and in some cases requires several inputs to generate the observed noble gas pattern. Combining the knowledge obtained from noble gas (origin, relative timing, number of charges) with organic geochemical and thermodynamic understanding of the fluid, in regards with the geodynamical context, helps us to unravel the complex fluid history of these deep environments. Ballentine C.J. and Burnard P.G. (2002). Rev. Mineral. Geochem., vol. 47, pp 481-538. Burnard P et al. (2012) EPSL 341, pp 68-78. Gilfillan, S.M.V. et al. (2008) GCA, vol. 72, pp 1174-1198.

The role of horizontal exchanges on ventilation of the benthic boundary layer on the Black Sea shelf

NASA Astrophysics Data System (ADS)

Shapiro, Georgy; Wobus, Fred

2010-05-01

The state of the benthic component of the shelf ecosystem is strongly influenced by availability of dissolved oxygen. The chemical structure of the Black Sea waters is largely determined by the location and the strength of the pycnocline. Due to similarity in the mechanisms of vertical exchanges the oxycline and the chemocline occur at the same depth intervals as the halocline and pycnocline (Özsoy and Ünlüata, 1997). As the data for dissolved oxygen on the shelf is relatively sparse we assume that much abundant data on physical parameters (temperature and salinity) can be used as proxy in determining the location of the oxycline and hence the spatial extent of near-bottom waters depleted in oxygen. When the waters of the benthic boundary layers below the pycnocline are ‘locked' i.e. unable to mix vertically with surface then the biological pump and supply of oxygen are suppressed. However, the locked water can, in principle, move ‘horizontally', predominantly along the constant density levels and get ventilated via isopycnal exchanges. The isopycnals in the Black Sea have generally a dome-like structure, so that the isopycnal movements across the shelf break can ventilate bottom shelf waters with water masses from upper parts of the water column in the deep sea. We use the intra- and inter-annual variations in the near-bottom temperature as indicators for variability of physical conditions in the benthic boundary layer on the shelf. The physical reason for this is that interannual variations in the near-bottom temperature are directly related with the volume of cold waters (Ivanov et al., 2000) which are formed on the shelf and then exported into the deep sea, so that variations in temperature may indicate changes in the intensity of horizontal exchanges. In this paper we identified areas on the Black Sea margin where bottom waters can not be mixed vertically (‘locked' waters) during the winter months and locations to which the locked waters can move ‘horizontally'. The potential energy approach was used to identify the spatial and temporal variability of the areas and volumes occupied by the locked waters. This approach allows to assess a relative strength of the ability of locked waters to mix vertically with oxygen rich surface waters as compared to ‘horizontal' exchanges with the deep sea along isopycnic surfaces. Analysis of interannual variability of temperature showed that the period 1965-1983 was a warm period when the ‘summer' season ( May to November) temperatures of the benthic waters were higher than the average; to the contrary the period 1983-2001 (i.e. up to end of available data sets) was a cold period. Correlations between various time series of hydrographical and meteorological parameters were calculated to establish the relative importance of vertical versus horizontal exchanges in ventilation of the locked water masses. A low correlation (R=0.24) was obtained between the variation of the winter sea surface temperature on the shelf and the ‘summer' temperatures of locked waters. A higher correlation (R=0.56) was found between the summer temperatures of the Cold Intermediate Waters below the seasonal pycnocline in the deep sea (density range sigma-theta= 14.2-14.8) and the ‘summer' temperatures of the ‘locked' waters in the benthic boundary layer on the shelf. Analysis shows that the isopycnic exchanges with the deep sea are more important for ventilation of the benthic boundary layer on the shelf than winter convection on the shelf itself. This work was made possible via support from EU FP6 SESAME and EU FP7 MyOcean projects and NERC PhD studentship. References Özsoy, E. and Ünlüata, Ü., 1997. Oceanography of the Black Sea: a review of some recent results. Earth-Sci. Rev., 42(4): 231-272. Ivanov, L.I., Belokopytov, V.N., Özsoy, E. and Samodurov, A., 2000. Ventilation of the Black Sea pycnocline on seasonal and interannual time scales. Mediterr. Mar. Sci., 1/2: 61-74.

Upper Ocean Evolution Across the Beaufort Sea Marginal Ice Zone from Autonomous Gliders

NASA Astrophysics Data System (ADS)

Lee, Craig; Rainville, Luc; Perry, Mary Jane

2016-04-01

The observed reduction of Arctic summertime sea ice extent and expansion of the marginal ice zone (MIZ) have profound impacts on the balance of processes controlling sea ice evolution, including the introduction of several positive feedback mechanisms that may act to accelerate melting. Examples of such feedbacks include increased upper ocean warming though absorption of solar radiation, elevated internal wave energy and mixing that may entrain heat stored in subsurface watermasses (e.g., the relatively warm Pacific Summer (PSW) and Atlantic (AW) waters), and elevated surface wave energy that acts to deform and fracture sea ice. Spatial and temporal variability in ice properties and open water fraction impact these processes. To investigate how upper ocean structure varies with changing ice cover, and how the balance of processes shift as a function of ice fraction and distance from open water, four long-endurance autonomous Seagliders occupied sections that extended from open water, through the marginal ice zone, deep into the pack during summer 2014 in the Beaufort Sea. Sections reveal strong fronts where cold, ice-covered waters meet waters that have been exposed to solar warming, and O(10 km) scale eddies near the ice edge. In the pack, Pacific Summer Water and a deep chlorophyll maximum form distinct layers at roughly 60 m and 80 m, respectively, which become increasingly diffuse as they progress through the MIZ and into open water. The isopynal layer between 1023 and 1024 kgm-3, just above the PSW, consistently thickens near the ice edge, likely due to mixing or energetic vertical exchange associated with strong lateral gradients in this region. This presentation will discuss the upper ocean variability, its relationship to sea ice extent, and evolution over the summer to the start of freeze up.

Upper Ocean Evolution Across the Beaufort Sea Marginal Ice Zone from Autonomous Gliders

NASA Astrophysics Data System (ADS)

Lee, C.; Rainville, L.; Perry, M. J.

2016-02-01

The observed reduction of Arctic summertime sea ice extent and expansion of the marginal ice zone (MIZ) have profound impacts on the balance of processes controlling sea ice evolution, including the introduction of several positive feedback mechanisms that may act to accelerate melting. Examples of such feedbacks include increased upper ocean warming though absorption of solar radiation, elevated internal wave energy and mixing that may entrain heat stored in subsurface watermasses (e.g., the relatively warm Pacific Summer (PSW) and Atlantic (AW) waters), and elevated surface wave energy that acts to deform and fracture sea ice. Spatial and temporal variability in ice properties and open water fraction impact these processes. To investigate how upper ocean structure varies with changing ice cover, and how the balance of processes shift as a function of ice fraction and distance from open water, four long-endurance autonomous Seagliders occupied sections that extended from open water, through the marginal ice zone, deep into the pack during summer 2014 in the Beaufort Sea. Sections reveal strong fronts where cold, ice-covered waters meet waters that have been exposed to solar warming, and O(10 km) scale eddies near the ice edge. In the pack, Pacific Summer Water and a deep chlorophyll maximum form distinct layers at roughly 60 m and 80 m, respectively, which become increasingly diffuse as they progress through the MIZ and into open water. The isopynal layer between 1023 and 1024 kg m-3, just above the PSW, consistently thickens near the ice edge, likely due to mixing or energetic vertical exchange associated with strong lateral gradients in this region. This presentation will discuss the upper ocean variability, its relationship to sea ice extent, and evolution over the summer to the start of freeze up.

Provenance and accommodation pathways of late Quaternary sediments in the deep-water northern Ionian Basin, southern Italy

NASA Astrophysics Data System (ADS)

Perri, Francesco; Critelli, Salvatore; Dominici, Rocco; Muto, Francesco; Tripodi, Vincenzo; Ceramicola, Silvia

2012-12-01

The northern Calabria along the southeastern coast of Italy provides a favorable setting in which to study complete transects from continental to deep-marine environments. The present northern Ionian Calabrian Basin is a wedge-top basin within the modern foreland-basin system of southern Italy. The Ionian margin of northern Calabria consists of a moderately developed fluvial systems, the Crati and Neto rivers, and diverse smaller coastal drainages draining both the Calabria continental block (i.e., Sila Massif) and the southern Apennines thrust belt (i.e., Pollino Massif). The main-channel sand of the Crati and Neto rivers is quartzofeldspathic with abundant metamorphic and plutonic lithic fragments (granodiorite, granite, gneiss, phyllite and sedimentary lithic fragments). Sedimentary lithic fragments were derived from Jurassic sedimentary successions of the Longobucco Group. The mud samples contain mostly phyllosilicates, quartz, calcite, feldspars and dolomite. Traces of gypsum are present in some samples. The I-S mixed layers, 10 Å-minerals (illite and micas), chlorite and kaolinite are the most abundant phyllosilicates, whereas smectite and chlorite/smectite mixed layers are in small amounts. The geochemical signatures of the muds reflect a provenance characterized by both felsic and mafic rocks with a significant input from carbonate rocks. Furthermore, the degree of source-area weathering was most probably of low intensity rather than moderately intense because CIA values for the studied mud samples are low. Extrapolation of the mean erosion budget from 1 to 25 Ma suggests that at least 5 to 8 km of crust have been removed from the Calabrian orogenic belt and deposited in the marine basins. The Calabrian microplate played an important role in the dynamic evolution of southern Italian fossil and modern basins, representing the key tectonic element of the entire orogenic belt.

Structure and Optical Properties of the Atmospheric Boundary Layer over Dusty Hot Deserts

NASA Astrophysics Data System (ADS)

Chalermthai, B.; Al Marzooqi, M.; Basha, G.; Ouarda, T.; Armstrong, P.; Molini, A.

2014-12-01

Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature of the atmospheric boundary layer (ABL) over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main common features however, desert boundary layers present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as transport and deposition of dust and pollutants, local wind fields, turbulent fluxes and their impacts on the sustainable development, human health and solar energy harvesting in these regions. In this study, we explore the potential of the joint usage of Lidar Ceilometer backscattering profiles and sun-photometer optical depth retrievals to quantitatively determine the vertical aerosol profile over dusty hot desert regions. Toward this goal, we analyze a continuous record of observations of the atmospheric boundary layer height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4425N 54.6163E, Abu Dhabi, United Arab Emirates), starting March 2013, and the concurrent measurements of aerosol optical depth derived independently from the Masdar Institute AERONET sun-photometer. The main features of the desert ABL are obtained from the ceilometer range corrected backscattering profiles through bi-dimensional clustering technique we developed as a modification of the recently proposed single-profile clustering method, and therefore "directly" and "indirectly" calibrated to obtain a full diurnal cycle climatology of the aerosol optical depth and aerosol profiles. The challenges and the advantages of applying a similar methodology to the monitoring of aerosols and dust over hyper-arid regions are also discussed, together with the issues related to the sensitivity of commercial ceilometers to changes in the solar background.

Injection in the lower stratosphere of biomass fire emissions followed by long-range transport: a MOZAIC case study

NASA Astrophysics Data System (ADS)

Cammas, J.-P.; Brioude, J.; Chaboureau, J.-P.; Duron, J.; Mari, C.; Mascart, P.; Nédélec, P.; Smit, H.; Pätz, H.-W.; Volz-Thomas, A.; Stohl, A.; Fromm, M.

2008-12-01

This paper analyses a stratospheric injection by deep convection of biomass fire emissions over North America (Alaska, Yukon and Northwest Territories) on 24 June 2004 and its long-range transport over the eastern coast of the United States and the eastern Atlantic. The case study is done using MOZAIC observations of ozone, carbon monoxide, nitrogen oxides (NOx+PAN) and water vapour during the crossing of the southernmost tip of an upper level trough over the Eastern Atlantic on 30 June 03:00 UTC and 10:00 UTC and in a vertical profile over Washington DC on 30 June 17:00 UTC, and by lidar observations of aerosol backscattering at Madison (University of Wisconsin) on 28 June. Attribution of the plumes to the boreal fires is achieved by backward simulations with a Lagrangian particle dispersion model (FLEXPART). A simulation with the Meso-NH model for the source region shows that a boundary layer tracer, mimicking the boreal forest fire smoke, is lofted into the lowermost stratosphere (2-5 pvu layer) during the diurnal convective cycle. The isentropic levels (above 335 K) correspond to those of the downstream MOZAIC observations. The parameterized convective detrainment flux is intense enough to fill the volume of a model mesh (20 km horizontal, 500 m vertical) above the tropopause with pure boundary layer air in a time period compatible with the convective diurnal cycle, i.e. about 5 h. The maximum instantaneous detrainment fluxes deposited about 15-20% of the initial boundary layer tracer concentration at 335 K, which according to the 275-ppbv carbon monoxide maximum mixing ratio observed by MOZAIC over eastern Atlantic, would be associated with a 1.4-1.8 ppmv carbon monoxide mixing ratio in the boundary layer over the source region.

Vertical wind shear characteristics that promote supercell-to-MCS transitions

NASA Astrophysics Data System (ADS)

Peters, J. M.

2017-12-01

What causes supercells to transition into MCSs in some situations, but not others? To explore this question, I first examined observed environmental characteristics of supercell events when MCSs formed, and compared them to the analogous environmental characteristics of supercell events when MCSs did not form. During events when MCS growth occurred, 0-1 km (low-level) vertical wind shear was stronger and 0-10 km (deep-layer) vertical wind shear was weaker than the wind shear during events when MCS growth did not occur. Next, I used idealized simulations of supercell thunderstorms to understand the connections between low-level and deep-layer shear and MCS growth. Compared to simulations with strong deep-layer shear, the simulations with weak deep-layer shear had rain in the storm's forward-flank downdraft (FFD) that fell closer to the updraft, fell through storm-moistened air and evaporated less, and produced a more intense FFD. Compared to simulations with weak low-level shear, the simulations with stronger low-level shear showed enhanced northward low-level hydrometeor transport into the FFD. Environments with strong low-level shear and weak deep-layer shear therefore conspired to produce a storm with a more intense FFD cold pool, when compared to environments with weak low-level shear and/or strong deep-layer shear. This strong FFD periodically disrupted the supercells' mesocyclones, and favorably interacted with westerly wind shear to produce widespread linear convection initiation, which drove MCS growth. These results suggest that increasing low-level wind shear after dark - while commonly assumed to enhance tornado potential - may in fact drive MCS growth and reduce tornado potential, unless it is combined with sufficiently strong deep layer shear.

Understanding wetland sub-surface hydrology using geologic and isotopic signatures

NASA Astrophysics Data System (ADS)

Sikdar, P. K.; Sahu, P.

2009-07-01

This paper attempts to utilize hydrogeology and isotope composition of groundwater to understand the present hydrological processes prevalent in a freshwater wetland, source of wetland groundwater, surface water/groundwater interaction and mixing of groundwater of various depth zones in the aquifer. This study considers East Calcutta Wetlands (ECW) - a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems, developed by local people through ages, using wastewater of the city. Geological investigations reveal that the sub-surface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades and sand mixed with occasional gravels and thin intercalations of silty clay. At few places the top silty clay layer is absent due to scouring action of past channels. In these areas sand is present throughout the geological column and the areas are vulnerable to groundwater pollution. Groundwater mainly flows from east to west and is being over-extracted to the tune of 65×103 m3/day. δ18O and δD values of shallow and deep groundwater are similar indicating resemblance in hydrostratigraphy and climate of the recharge areas. Groundwater originates mainly from monsoonal rain with some evaporation prior to or during infiltration and partly from bottom of ponds, canals and infiltration of groundwater withdrawn for irrigation. Relatively high tritium content of the shallow groundwater indicates local recharge, while the deep groundwater with very low tritium is recharged mainly from distant areas. At places the deep aquifer has relatively high tritium, indicating mixing of groundwater of shallow and deep aquifers. Metals such as copper, lead, arsenic, cadmium, aluminium, nickel and chromium are also present in groundwater of various depths. Therefore, aquifers of wetland and surrounding urban areas which are heavily dependent on groundwater are vulnerable to pollution. In the area south of ECW isotope data indicates no interaction between shallow and deep aquifer and hence this area may be a better location to treat sewage water than within ECW. To reduce the threat of pollution in ECW's aquifer, surface water-groundwater interaction should be minimized by regulating tubewell operation time, introducing treated surface water supply system and artificial recharging of the aquifer.

Mesoscale and high-frequency variability of macroscopic particles (> 100 μm) in the Ross Sea and its relevance for late-season particulate carbon export

NASA Astrophysics Data System (ADS)

Bochdansky, Alexander B.; Clouse, Melissa A.; Hansell, Dennis A.

2017-02-01

The Ross Sea plays a major role in the transfer of organic carbon from the surface into the deep sea due to the combination of high seasonal productivity and Antarctic bottom water formation. Here we present a particle inventory of the Ross Sea based on a combined deployment of a video particle profiler (VPP) and a high-resolution digital holographic microscope (DIHM). Long-distance (100 s of kilometers) and short-distance (10 s of kilometers) sections showed high variability of particle distributions that co-varied with the density structure of the water column. Particle export was apparent at sites of locally weakened pycnoclines, likely an indirect effect of nutrient mixing into the surface layer and local blooms that lead to export. Particle volume abundances at 200-300 m depth were highly correlated with particle volume abundances in the upper mixed layer (< 60 m), consistent with particles at depth primarily the result of export rather than lateral advection. Phaeocystis antarctica (Haptophyta) colonies that were initially retained in the mixed layer sank below the euphotic zone within a period of two weeks. Fine-scale analysis at a resolution < 1 m revealed a significantly overdispersed (i.e., highly patchy) environment in all casts. Patchiness, as determined by the Lloyd index of patchiness and the Index of Aggregation, increased in and below the pycnocline presumably due to aggregation of particles while accumulating on density gradients. In contrast, particles in the upper mixed layer and in the nepheloid layers were more randomly distributed. In 40 of the 84 VPP depth profiles, a periodicity of particle peaks ranged from 10 to 90 m with a mode of 30 m, which can be regarded as the "relevant scale" or "characteristic patch size" of the vertical distribution of particles. While chlorophyll fluorescence and particle mass determined by VPP were significantly correlated at higher particle abundances, the relationship changed from cast to cast, reflecting changes in the relative contribution of fresh phytoplankton to total particle mass. Particles that sank below the main pycnocline were composed of phytoplankton, marine snow with and without embedded phytoplankton, crustacean plankton, and a surprisingly high percentage of heterotrophic (and perhaps mixotrophic) protists, such as acantharians and tintinnids.

Mechanisms controlling primary and new production in a global ecosystem model - Part I: Validation of the biological simulation

NASA Astrophysics Data System (ADS)

Popova, E. E.; Coward, A. C.; Nurser, G. A.; de Cuevas, B.; Fasham, M. J. R.; Anderson, T. R.

2006-12-01

A global general circulation model coupled to a simple six-compartment ecosystem model is used to study the extent to which global variability in primary and export production can be realistically predicted on the basis of advanced parameterizations of upper mixed layer physics, without recourse to introducing extra complexity in model biology. The "K profile parameterization" (KPP) scheme employed, combined with 6-hourly external forcing, is able to capture short-term periodic and episodic events such as diurnal cycling and storm-induced deepening. The model realistically reproduces various features of global ecosystem dynamics that have been problematic in previous global modelling studies, using a single generic parameter set. The realistic simulation of deep convection in the North Atlantic, and lack of it in the North Pacific and Southern Oceans, leads to good predictions of chlorophyll and primary production in these contrasting areas. Realistic levels of primary production are predicted in the oligotrophic gyres due to high frequency external forcing of the upper mixed layer (accompanying paper Popova et al., 2006) and novel parameterizations of zooplankton excretion. Good agreement is shown between model and observations at various JGOFS time series sites: BATS, KERFIX, Papa and HOT. One exception is the northern North Atlantic where lower grazing rates are needed, perhaps related to the dominance of mesozooplankton there. The model is therefore not globally robust in the sense that additional parameterizations are needed to realistically simulate ecosystem dynamics in the North Atlantic. Nevertheless, the work emphasises the need to pay particular attention to the parameterization of mixed layer physics in global ocean ecosystem modelling as a prerequisite to increasing the complexity of ecosystem models.

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.

Glacial - interglacial changes of northwest Pacific stratification, inferred from deep and shallow living radiolarians

NASA Astrophysics Data System (ADS)

Hays, J. D.

2009-12-01

Shallow (0-200m) and deep (200 to1000m) living radiolarian flux is used to measure past production from within discrete intervals of the ocean’s water column. Deep-living faunas can also be used as proxies for export production, for they remineralize it and respond geographically and temporally to varying export. Few members of the mesopelagic community leave a fossil record, but of those that do, radiolarians are the most abundant and diverse group. In northwest Pacific late Pleistocene (glacial) sediments, deep-living radiolarian flux dominates over shallow-living flux, but the reverse is true in Holocene sediments, with the dramatic dominance change occurring across the Pleistocene-Holocene boundary. Changing primary productivity can’t cause these flux changes, for shallow-living faunas have access to the same carbon flux as do deep-living faunas, but rather they signal a major reorganization of the radiolarian fauna within the water column and suggest greater glacial than Holocene carbon export. In the Holocene world-ocean, the only region where deep-living radiolarian flux dominates over shallow-living flux is in the Sea of Okhotsk, suggesting environmental similarities between this sea and the northwest Pacific. In winter, cold Siberian air chills the upper hundred meters of the Sea of Okhotsk, promoting the spread of vast sea ice fields. High productivity in a thin (10-15m) summer mixed layer depletes nutrients Between 15 and about 150m exists a layer of cold (-1 to 0 degrees C.) intermediate water, within which radiolarian concentrations are low, but these concentrations increase between 200 and 500m in warmer intermediate water (Nimmergut and Abelmann, 2002). This radiolarian stratification results in greater deep- than shallow-living radiolarian flux to the sea floor. A similar water structure in the glacial northwest Pacific is the probable cause of similar flux patterns between the glacial northwest Pacific and Holocene Sea of Okhotsk. If so then cold glacial northwest Pacific intermediate water promoted the southward spread of sea ice. This inference is supported by the near coincidence of the southern limit of deep-living species dominated glacial sediments and extensive ice rafting. It also explains nutrient depleted glacial northwest Pacific surface waters inferred from isotopic data.

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.

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.

Physical determinants of phytoplankton production, algal stoichiometry, and vertical nutrient fluxes.

PubMed

Jäger, Christoph G; Diehl, Sebastian; Emans, Maximilian

2010-04-01

Most phytoplankters face opposing vertical gradients in light versus nutrient supplies but have limited capacities for vertical habitat choice. We therefore explored a dynamical model of negatively buoyant algae inhabiting a one-dimensional water column to ask how water column depth and turbulence constrain total (areal) phytoplankton biomass. We show that the population persistence boundaries in water column depth-turbulence space are set by sinking losses and light limitation but that nutrients are most limiting to total biomass in water columns that are neither too shallow or too weakly mixed (where sinking losses prevail) nor too deep and turbulent (where light limitation prevails). In shallow waters, the most strongly limiting process is nutrient influx to the bottom of the water column (e.g., from sediments). In deep waters, the most strongly limiting process is turbulent upward transport of nutrients to the photic zone. Consequently, the highest total biomasses are attained in turbulent waters at intermediate water column depths and in deep waters at intermediate turbulences. These patterns are insensitive to the assumption of fixed versus flexible algal carbon-to-nutrient stoichiometry, and they arise irrespective of whether the water column is a surface layer above a deep water compartment or has direct contact with sediments.

Linking deep convection and phytoplankton blooms in the northern Labrador Sea in a changing climate

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

Balaguru, Karthik; Doney, Scott C.; Bianucci, Laura

Wintertime convective mixing plays a pivotal role in the sub-polar North Atlantic spring phytoplankton blooms by favoring phytoplankton survival in the competition between light-dependent production and losses due to grazing and gravitational settling. We use satellite and ocean reanalyses to show that the area-averaged maximum winter mixed layer depth is positively correlated with April chlorophyll concentration in the northern Labrador Sea. A simple theoretical framework is developed to understand the relative roles of winter/spring convection and gravitational sedimentation in spring blooms in this region. Combining climate model simulations that project a weakening of wintertime Labrador Sea convection from Arctic seamore » ice melt with our framework suggests a potentially significant reduction in the initial fall phytoplankton population that survive the winter to seed the region's spring bloom by the end of the 21st century.« less

Convective instabilities in SN 1987A

NASA Technical Reports Server (NTRS)

Benz, Willy; Thielemann, Friedrich-Karl

1990-01-01

Following Bandiera (1984), it is shown that the relevant criterion to determine the stability of a blast wave, propagating through the layers of a massive star in a supernova explosion, is the Schwarzschild (or Ledoux) criterion rather than the Rayleigh-Taylor criterion. Both criteria coincide only in the incompressible limit. Results of a linear stability analysis are presented for a one-dimensional (spherical) explosion in a realistic model for the progenitor of SN 1987A. When applying the Schwarzschild criterion, unstable regions get extended considerably. Convection is found to develop behind the shock, with a characteristic growth rate corresponding to a time scale much smaller than the shock traversal time. This ensures that efficient mixing will take place. Since the entire ejected mass is found to be convectively unstable, Ni can be transported outward, even into the hydrogen envelope, while hydrogen can be mixed deep into the helium core.

Linking deep convection and phytoplankton blooms in the northern Labrador Sea in a changing climate

PubMed Central

Doney, Scott C.; Bianucci, Laura; Rasch, Philip J.; Leung, L. Ruby; Yoon, Jin-Ho; Lima, Ivan D.

2018-01-01

Wintertime convective mixing plays a pivotal role in the sub-polar North Atlantic spring phytoplankton blooms by favoring phytoplankton survival in the competition between light-dependent production and losses due to grazing and gravitational settling. We use satellite and ocean reanalyses to show that the area-averaged maximum winter mixed layer depth is positively correlated with April chlorophyll concentration in the northern Labrador Sea. A simple theoretical framework is developed to understand the relative roles of winter/spring convection and gravitational sedimentation in spring blooms in this region. Combining climate model simulations that project a weakening of wintertime Labrador Sea convection from Arctic sea ice melt with our framework suggests a potentially significant reduction in the initial fall phytoplankton population that survive the winter to seed the region’s spring bloom by the end of the 21st century. PMID:29370224

Linking deep convection and phytoplankton blooms in the northern Labrador Sea in a changing climate.

PubMed

Balaguru, Karthik; Doney, Scott C; Bianucci, Laura; Rasch, Philip J; Leung, L Ruby; Yoon, Jin-Ho; Lima, Ivan D

2018-01-01

Wintertime convective mixing plays a pivotal role in the sub-polar North Atlantic spring phytoplankton blooms by favoring phytoplankton survival in the competition between light-dependent production and losses due to grazing and gravitational settling. We use satellite and ocean reanalyses to show that the area-averaged maximum winter mixed layer depth is positively correlated with April chlorophyll concentration in the northern Labrador Sea. A simple theoretical framework is developed to understand the relative roles of winter/spring convection and gravitational sedimentation in spring blooms in this region. Combining climate model simulations that project a weakening of wintertime Labrador Sea convection from Arctic sea ice melt with our framework suggests a potentially significant reduction in the initial fall phytoplankton population that survive the winter to seed the region's spring bloom by the end of the 21st century.

Hydrothermal plumes over spreading-center axes: Global distributions and geological inferences

NASA Astrophysics Data System (ADS)

Baker, Edward T.; German, Christopher R.; Elderfield, Henry

Seafloor hydrothermal circulation is the principal agent of energy and mass exchange between the ocean and the earth's crust. Discharging fluids cool hot rock, construct mineral deposits, nurture biological communities, alter deep-sea mixing and circulation patterns, and profoundly influence ocean chemistry and biology. Although the active discharge orifices themselves cover only a minuscule percentage of the ridge-axis seafloor, the investigation and quantification of their effects is enhanced as a consequence of the mixing process that forms hydrothermal plumes. Hydrothermal fluids discharged from vents are rapidly diluted with ambient seawater by factors of 104-105 [Lupton et al., 1985]. During dilution, the mixture rises tens to hundreds of meters to a level of neutral buoyancy, eventually spreading laterally as a distinct hydrographic and chemical layer with a spatial scale of tens to thousands of kilometers [e.g., Lupton and Craig, 1981; Baker and Massoth, 1987; Speer and Rona, 1989].

Plate and Plume Flux: Constraints for paleomagnetic reference frames and interpretation of deep mantle seismic heterogeneity. (Invited)

NASA Astrophysics Data System (ADS)

Bunge, H.; Schuberth, B. S.; Shephard, G. E.; Müller, D.

2010-12-01

Plate and plume flow are dominant modes of mantle convection, as pointed out by Geoff Davies early on. Driven, respectively, from a cold upper and a hot lower thermal boundary layer these modes are now sufficiently well imaged by seismic tomographers to exploit the thermal boundary layer concept as an effective tool in exploring two long standing geodynamic problems. One relates to the choice of an absolute reference frame in plate tectonic reconstructions. Several absolute reference frames have been proposed over the last decade, including those based on hotspot tracks displaying age progression and assuming either fixity or motion, as well as palaeomagnetically-based reference frames, a subduction reference frame and hybrid versions. Each reference frame implies a particular history of the location of subduction zones through time and thus the evolution of mantle heterogeneity via mixing of subducted slab material in the mantle. Here we compare five alternative absolute plate motion models in terms of their consequences for deep mantle structure. Taking global paleo-plate boundaries and plate velocities back to 140 Ma derived from the new plate tectonic reconstruction software GPlates and assimilating them into vigorous 3-D spherical mantle circulation models, we infer geodynamic mantle heterogeneity and compare it to seismic tomography for each absolute rotation model. We also focus on the challenging problem of interpreting deep mantle seismic heterogeneity in terms of thermal and compositional variations. Using published thermodynamically self-consistent mantle mineralogy models in the pyrolite composition, we find strong plume flux from the CMB, with a high temperature contrast (on the order of 1000 K) across the lower thermal boundary layer is entirely sufficient to explain elastic heterogeneity in the deep mantle for a number of quantitative measures. A high excess temperatures of +1000--1500 K for plumes in the lowermost mantle is particularly important in understanding the strong seismic velocity reduction mapped by tomography in low-velocity bodies of the deep mantle, as this produces significant negative anomalies of shear wave velocity of up to -4%. We note, however, that our results do not account for the curious observation of seismic anti-correlation, which appears difficult to explain in any case. Our results provide important constraints for the integration of plate tectonics and mantle dynamics and their use in forward and inverse geodynamic mantle models.

Beyond Retinal Layers: A Deep Voting Model for Automated Geographic Atrophy Segmentation in SD-OCT Images

PubMed Central

Ji, Zexuan; Chen, Qiang; Niu, Sijie; Leng, Theodore; Rubin, Daniel L.

2018-01-01

Purpose To automatically and accurately segment geographic atrophy (GA) in spectral-domain optical coherence tomography (SD-OCT) images by constructing a voting system with deep neural networks without the use of retinal layer segmentation. Methods An automatic GA segmentation method for SD-OCT images based on the deep network was constructed. The structure of the deep network was composed of five layers, including one input layer, three hidden layers, and one output layer. During the training phase, the labeled A-scans with 1024 features were directly fed into the network as the input layer to obtain the deep representations. Then a soft-max classifier was trained to determine the label of each individual pixel. Finally, a voting decision strategy was used to refine the segmentation results among 10 trained models. Results Two image data sets with GA were used to evaluate the model. For the first dataset, our algorithm obtained a mean overlap ratio (OR) 86.94% ± 8.75%, absolute area difference (AAD) 11.49% ± 11.50%, and correlation coefficients (CC) 0.9857; for the second dataset, the mean OR, AAD, and CC of the proposed method were 81.66% ± 10.93%, 8.30% ± 9.09%, and 0.9952, respectively. The proposed algorithm was capable of improving over 5% and 10% segmentation accuracy, respectively, when compared with several state-of-the-art algorithms on two data sets. Conclusions Without retinal layer segmentation, the proposed algorithm could produce higher segmentation accuracy and was more stable when compared with state-of-the-art methods that relied on retinal layer segmentation results. Our model may provide reliable GA segmentations from SD-OCT images and be useful in the clinical diagnosis of advanced nonexudative AMD. Translational Relevance Based on the deep neural networks, this study presents an accurate GA segmentation method for SD-OCT images without using any retinal layer segmentation results, and may contribute to improved understanding of advanced nonexudative AMD. PMID:29302382

Beyond Retinal Layers: A Deep Voting Model for Automated Geographic Atrophy Segmentation in SD-OCT Images.

PubMed

Ji, Zexuan; Chen, Qiang; Niu, Sijie; Leng, Theodore; Rubin, Daniel L

2018-01-01

To automatically and accurately segment geographic atrophy (GA) in spectral-domain optical coherence tomography (SD-OCT) images by constructing a voting system with deep neural networks without the use of retinal layer segmentation. An automatic GA segmentation method for SD-OCT images based on the deep network was constructed. The structure of the deep network was composed of five layers, including one input layer, three hidden layers, and one output layer. During the training phase, the labeled A-scans with 1024 features were directly fed into the network as the input layer to obtain the deep representations. Then a soft-max classifier was trained to determine the label of each individual pixel. Finally, a voting decision strategy was used to refine the segmentation results among 10 trained models. Two image data sets with GA were used to evaluate the model. For the first dataset, our algorithm obtained a mean overlap ratio (OR) 86.94% ± 8.75%, absolute area difference (AAD) 11.49% ± 11.50%, and correlation coefficients (CC) 0.9857; for the second dataset, the mean OR, AAD, and CC of the proposed method were 81.66% ± 10.93%, 8.30% ± 9.09%, and 0.9952, respectively. The proposed algorithm was capable of improving over 5% and 10% segmentation accuracy, respectively, when compared with several state-of-the-art algorithms on two data sets. Without retinal layer segmentation, the proposed algorithm could produce higher segmentation accuracy and was more stable when compared with state-of-the-art methods that relied on retinal layer segmentation results. Our model may provide reliable GA segmentations from SD-OCT images and be useful in the clinical diagnosis of advanced nonexudative AMD. Based on the deep neural networks, this study presents an accurate GA segmentation method for SD-OCT images without using any retinal layer segmentation results, and may contribute to improved understanding of advanced nonexudative AMD.

The role of Southern Ocean mixing and upwelling in glacial-interglacial atmospheric CO2 change

NASA Astrophysics Data System (ADS)

Watson, Andrew J.; Naveira Garabato, Alberto C.

2006-02-01

Decreased ventilation of the Southern Ocean in glacial time is implicated in most explanations of lower glacial atmospheric CO2. Today, the deep (>2000 m) ocean south of the Polar Front is rapidly ventilated from below, with the interaction of deep currents with topography driving high mixing rates well up into the water column. We show from a buoyancy budget that mixing rates are high in all the deep waters of the Southern Ocean. Between the surface and ~2000 m depth, water is upwelled by a residual meridional overturning that is directly linked to buoyancy fluxes through the ocean surface. Combined with the rapid deep mixing, this upwelling serves to return deep water to the surface on a short time scale. We propose two new mechanisms by which, in glacial time, the deep Southern Ocean may have been more isolated from the surface. Firstly, the deep ocean appears to have been more stratified because of denser bottom water resulting from intense sea ice formation near Antarctica. The greater stratification would have slowed the deep mixing. Secondly, subzero atmospheric temperatures may have meant that the present-day buoyancy flux from the atmosphere to the ocean surface was reduced or reversed. This in turn would have reduced or eliminated the upwelling (contrary to a common assumption, upwelling is not solely a function of the wind stress but is coupled to the air-sea buoyancy flux too). The observed very close link between Antarctic temperatures and atmospheric CO2 could then be explained as a natural consequence of the connection between the air-sea buoyancy flux and upwelling in the Southern Ocean, if slower ventilation of the Southern Ocean led to lower atmospheric CO2. Here we use a box model, similar to those of previous authors, to show that weaker mixing and reduced upwelling in the Southern Ocean can explain the low glacial atmospheric CO2 in such a formulation.

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.

Intensified Diapycnal Mixing in the Midlatitude Western Boundary Currents

PubMed Central

Jing, Zhao; Wu, Lixin

2014-01-01

The wind work on oceanic near-inertial motions is suggested to play an important role in furnishing the diapycnal mixing in the deep ocean which affects the uptake of heat and carbon by the ocean as well as climate changes. However, it remains a puzzle where and through which route the near-inertial energy penetrates into the deep ocean. Using the measurements collected in the Kuroshio extension region during January 2005, we demonstrate that the diapycnal mixing in the thermocline and deep ocean is tightly related to the shear variance of wind-generated near-inertial internal waves with the diapycnal diffusivity 6 × 10−5 m2s−1 almost an order stronger than that observed in the circulation gyre. It is estimated that 45%–62% of the local near-inertial wind work 4.5 × 10−3 Wm−2 radiates into the thermocline and deep ocean and accounts for 42%–58% of the energy required to furnish mixing there. The elevated mixing is suggested to be maintained by the energetic near-inertial wind work and strong eddy activities causing enhanced downward near-inertial energy flux than earlier findings. The western boundary current turns out to be a key region for the penetration of near-inertial energy into the deep ocean and a hotspot for the diapycnal mixing in winter. PMID:25491363

Soil Physical Constraints on Intrinsic Biodegradation of Petroleum Vapors in a Layered Subsurface

PubMed Central

Kristensen, Andreas H.; Henriksen, Kaj; Mortensen, Lars; Scow, Kate M.; Moldrup, Per

2011-01-01

Naturally occurring biodegradation of petroleum hydrocarbons in the vadose zone depends on the physical soil environment influencing field-scale gas exchange and pore-scale microbial metabolism. In this study, we evaluated the effect of soil physical heterogeneity on biodegradation of petroleum vapors in a 16-m-deep, layered vadose zone. Soil slurry experiments (soil/water ratio 10:30 w/w, 25°C) on benzene biodegradation under aerobic and well-mixed conditions indicated that the biodegradation potential in different textured soil samples was related to soil type rather than depth, in the order: sandy loam > fine sand > limestone. Similarly, O2 consumption rates during in situ respiration tests performed at the site were higher in the sandy loam than in the fine sand, although the difference was less significant than in the slurries. Laboratory and field data generally agreed well and suggested a significant potential for aerobic biodegradation, even with nutrient-poor and deep subsurface conditions. In slurries of the sandy loam, the biodegradation potential declined with increasing in situ water saturation (i.e., decreasing air-filled porosity in the field). This showed a relation between antecedent undisturbed field conditions and the slurry biodegradation potential, and suggested airfilled porosity to be a key factor for the intrinsic biodegradation potential in the field. PMID:21617737

Simulation of Shallow Cumuli and Their Transition to Deep Convective Clouds by Cloud-resolving Models with Different Third-order Turbulence Closures

NASA Technical Reports Server (NTRS)

Cheng, Anning; Xu, Kuan-Man

2006-01-01

The abilities of cloud-resolving models (CRMs) with the double-Gaussian based and the single-Gaussian based third-order closures (TOCs) to simulate the shallow cumuli and their transition to deep convective clouds are compared in this study. The single-Gaussian based TOC is fully prognostic (FP), while the double-Gaussian based TOC is partially prognostic (PP). The latter only predicts three important third-order moments while the former predicts all the thirdorder moments. A shallow cumulus case is simulated by single-column versions of the FP and PP TOC models. The PP TOC improves the simulation of shallow cumulus greatly over the FP TOC by producing more realistic cloud structures. Large differences between the FP and PP TOC simulations appear in the cloud layer of the second- and third-order moments, which are related mainly to the underestimate of the cloud height in the FP TOC simulation. Sensitivity experiments and analysis of probability density functions (PDFs) used in the TOCs show that both the turbulence-scale condensation and higher-order moments are important to realistic simulations of the boundary-layer shallow cumuli. A shallow to deep convective cloud transition case is also simulated by the 2-D versions of the FP and PP TOC models. Both CRMs can capture the transition from the shallow cumuli to deep convective clouds. The PP simulations produce more and deeper shallow cumuli than the FP simulations, but the FP simulations produce larger and wider convective clouds than the PP simulations. The temporal evolutions of cloud and precipitation are closely related to the turbulent transport, the cold pool and the cloud-scale circulation. The large amount of turbulent mixing associated with the shallow cumuli slows down the increase of the convective available potential energy and inhibits the early transition to deep convective clouds in the PP simulation. When the deep convective clouds fully develop and the precipitation is produced, the cold pools produced by the evaporation of the precipitation are not favorable to the formation of shallow cumuli.

Abyssal Upwelling and Downwelling and the role of boundary layers

NASA Astrophysics Data System (ADS)

McDougall, T. J.; Ferrari, R. M.

2016-02-01

The bottom-intensified mixing activity arising from the interaction of internal tides with bottom topography implies that the dianeutral advection in the ocean interior is downwards, rather than upwards as is required by continuity. The upwelling of Bottom Water through density surfaces in the deep ocean is however possible because of the sloping nature of the sea floor. A budget study of the abyss (deeper than 2000m) will be described that shows that while the upwelling of Bottom Water might be 25 Sv, this is achieved by very strong upwelling in the bottom turbulent boundary layer (of thickness 50m) of 100 Sv and strong downwelling in the ocean interior of 75 Sv. This downwelling occurs within 10 degrees of longitude of the continental boundaries. This near-boundary confined strong upwelling and downwelling clearly has implications for the Stommel-Arons circulation.

Three-Dimensional Effects of Artificial Mixing in a Shallow Drinking-Water Reservoir

NASA Astrophysics Data System (ADS)

Chen, Shengyang; Little, John C.; Carey, Cayelan C.; McClure, Ryan P.; Lofton, Mary E.; Lei, Chengwang

2018-01-01

Studies that examine the effects of artificial mixing for water-quality mitigation in lakes and reservoirs often view a water column with a one-dimensional (1-D) perspective (e.g., homogenized epilimnetic and hypolimnetic layers). Artificial mixing in natural water bodies, however, is inherently three dimensional (3-D). Using a 3-D approach experimentally and numerically, the present study visualizes thermal structure and analyzes constituent transport under the influence of artificial mixing in a shallow drinking-water reservoir. The purpose is to improve the understanding of artificial mixing, which may help to better design and operate mixing systems. In this reservoir, a side-stream supersaturation (SSS) hypolimnetic oxygenation system and an epilimnetic bubble-plume mixing (EM) system were concurrently deployed in the deep region. The present study found that, while the mixing induced by the SSS system does not have a distinct 3-D effect on the thermal structure, epilimnetic mixing by the EM system causes 3-D heterogeneity. In the experiments, epilimnetic mixing deepened the lower metalimnetic boundary near the diffuser by about 1 m, with 55% reduction of the deepening rate at 120 m upstream of the diffuser. In a tracer study using a 3-D hydrodynamic model, the operational flow rate of the EM system is found to be an important short-term driver of constituent transport in the reservoir, whereas the duration of the EM system operation is the dominant long-term driver. The results suggest that artificial mixing substantially alters both 3-D thermal structure and constituent transport, and thus needs to be taken into account for reservoir management.

Optical Characterization of an Eddy-induced Diatom Bloom West of the Island of Hawaii

NASA Astrophysics Data System (ADS)

Nencioli, F.; Chang, G.; Twardowski, M.; Dickey, T. D.

2010-01-01

Optical properties were collected along a transect across cyclonic eddy Opal in the lee of Hawaii during the E-Flux III field experiment (10-27 March 2005). The eddy was characterized by an intense doming of isopycnal surfaces, and by an enhanced Deep Chlorophyll Maximum Layer (DCML) within its core. The phytoplankton bloom was diatom dominated, evidencing an eddy-induced shift in ecological community. Four distinct regions were identified throughout the water column at Opal's core: a surface mixed layer dominated by small phytoplankton; a layer dominated by "senescent" diatoms between the bottom of the upper mixed layer and the DCML; the DCML; and a deep layer characterized by decreasing phytoplankton activity. We focused on two parameters, the ratio of chlorophyll concentration to particulate beam attenuation coefficient, [chl]/cp, and the backscattering ratio (the particle backscattering to particle scattering ratio), b~bp, and tested their sensitivity to the changes in particle composition observed through the water column at the eddy center. Our results show that [chl]/cp is not a good indicator. Despite the shift in ecological community, the ratio remains controlled primarily by the variation in chlorophyll concentration per cell with depth (photoadaptation), so that its values increase throughout the DCML. Steeper increase of [chl]/cp below the DCML suggest that remineralization might be another important controlling factor. On the other hand, b~bp clearly indicates a shift from a small phytoplankton to a diatom dominated community. Below an upper layer characterized by constant values, the b~bp showed a rapid decrease to a broad minimum within the DCML. The higher values below the DCML are consistent with enhanced remineralization below the eddy-induced bloom. Both the "senescent" and the "healthy" diatom layers are characterized by similar optical properties, indicating some possible limitations in using optical measurements to fully characterize the composition of suspended material in the water column. The inverse relationship between b~bp, reported by others for Case II waters, is observed neither for the background conditions, nor in the presence of the eddy-induced diatom bloom. Between the two parameters, only the backscattering ratio showed the potential to be a successful indicator for changes in particle composition in Case I waters.