Lateral Gradients Research Articles

A new structural and kinematic framework for the Alborán Domain (Betic–Rif arc, western Mediterranean orogenic system)

The processes that drastically thinned and rapidly exhumed the Alborán Domain in southern Spain are poorly understood. Geological maps, cross-sections and a synthesis of previous work in the Alpujárride Complex provide a new structural framework for the Alborán Domain, with major revision of the previously defined lithotectonic units. Alborán continental lithosphere was buried and thickened in the Paleogene (D 1 ) and subsequently thinned during late-orogenic extension in the early Miocene. Regional patterns of stretching lineations and late recumbent folds record important spatiotemporal changes in the kinematics of extension. East-directed shear (D 2 ) is preserved in deep orogenic levels and thinned the crustal sequence during rapid exhumation and high-temperature metamorphism. North-directed shear (D 3 /D 4 ) is preserved in upper orogenic levels and reworked earlier structures during the later stages of exhumation and cooling. This large-scale switch in the direction of finite stretching resulted from the interaction between components of orogen-parallel (D 2 ) and orogen-perpendicular (D 3 /D 4 ) extension, and associated vertical and lateral gradients in strain. We provide a novel kinematic model for gravity-driven extensional collapse of the Alborán Domain, compatible with both westward motion of the Alborán Domain relative to the Iberian margin and subsequent northward extensional flow and emplacement of Alborán lithosphere onto the Iberian margin. Supplementary material: A list of sample names, coordinates and descriptions, plus a Google Earth .kmz file of sample locations is available at https://doi.org/10.6084/m9.figshare.5508643 . A geological sketch map of the Sierra de las Estancias, indicating the trend of stretching lineations in the Alpujárride Complex and location of major geological boundaries is available at https://doi.org/10.6084/m9.figshare.5513398 .

Lateral heterogeneity of soil physicochemical properties in riparian zones after agricultural abandonment

The study aimed to identify the lateral heterogeneity of soil physicochemical properties in riparian zones, and its underlying drivers during natural restoration after agricultural abandonment. Abandoned farmlands, after 5-year natural restoration, within 500 m from the edges on both sides of Liaohe River were selected as the study area. Soil physicochemical properties of four lateral buffers (<10 m, 10~100 m, 100~300 m, and >300 m from river edge, respectively) along riparian zones were measured. The results showed that riparian soils were characterized by high sand content (78.88%~96.52%) and poor soil nutrients. Soil silt content, organic carbon (OC), cation exchange capacity (CEC), total nitrogen (TN), and available nitrogen (AN) increased laterally with increasing distance from river edge, while soil sand content decreased. Total phosphorus (TP) and available phosphorus (AP) are not spatially autocorrelated. Soil OC, TN, AN, and CEC along upstream and midstream reaches showed negative spatial autocorrelation along the lateral gradients, and positive along downstream reach. Altitude, distance from river edge and distance from nearest farmland were the pronounced factors affecting soil physicochemical properties in this study.

Longitudinal variation in lateral trapping of fine sediment in tidal estuaries: observations and a 3D exploratory model

This study investigates the longitudinal variation of lateral entrapment of suspended sediment, as is observed in some tidal estuaries. In particular, field data from the Yangtze Estuary are analysed, which reveal that in one cross-section, two maxima of suspended sediment concentration (SSC) occur close to the south and north sides, while in a cross-section 2 km down-estuary, only one SSC maximum on the south side is present. This pattern is found during both spring tide and neap tide, which are characterised by different intensities of turbulence. To understand longitudinal variation in lateral trapping of sediment, results of a new three-dimensional exploratory model are analysed. The hydrodynamic part contains residual flow due to fresh water input, density gradients and Coriolis force and due to channel curvature-induced leakage. Moreover, the model includes a spatially varying eddy viscosity that accounts for variation of intensity of turbulence over the spring-neap cycle. By imposing morphodynamic equilibrium, the two-dimensional distribution of sediment in the domain is obtained analytically by a novel procedure. Results reveal that the occurrence of the SSC maxima near the south side of both cross-sections is due to sediment entrapment by lateral density gradients, while the second SSC maximum near the north side of the first cross-section is by sediment transport due to curvature-induced leakage. Coriolis deflection of longitudinal flow also contributes the trapping of sediment near the north side. This mechanism is important in the upper estuary, where the flow due to lateral density gradients is weak.

Double-Diffusive Convection at Low Prandtl Number

This work reviews present knowledge of double-diffusive convection at low Prandtl number obtained using direct numerical simulations, in both the fingering regime and the oscillatory regime. Particular emphasis is given to modeling the induced turbulent mixing and its impact in various astrophysical applications. The nonlinear saturation of fingering convection at low Prandtl number usually drives small-scale turbulent motions whose transport properties can be predicted reasonably accurately using a simple semi-analytical model. In some instances, large-scale internal gravity waves can be excited by a collective instability and eventually cause layering. The nonlinear saturation of oscillatory double-diffusive convection exhibits much more complex behavior. Weakly stratified systems always spontaneously transition into layered convection associated with very efficient mixing. More strongly stratified systems remain dominated by weak wave turbulence unless they are initialized into a layered state. The effects of rotation, shear, lateral gradients, and magnetic fields are briefly discussed.

The Potential for Metamorphic Thermal Pulses to Develop During Compaction‐Driven Fluid Flow

AbstractCompaction‐driven fluid flow below the brittle‐ductile transition may be a means of transporting fluids during metamorphism. In particular, when a decompaction weakening mechanism is introduced to account for the rock viscosity reduction due to fluid overpressures, channeling instabilities evolve into high‐porosity/permeability fluid conduits that focus mass and energy transfer. In this study, we consider a crustal rheology that accounts simultaneously for upward‐increasing viscosity and decompaction weakening to examine the nucleation and evolution of fluid channelization in two dimensions (2‐D). The model shows that plume‐shaped flow patterns can develop on time scales as short as 104 years, during which the plume tails act as fluid conduits and the plume heads act as fluid dispersion zones near the brittle‐ductile transition. Collection of fluids into conduits is accomplished by a basal fluid catchment zone characterized by strong lateral fluid pressure gradients but low porosity/permeability. Relatively narrow ranges of viscous activation energy (∼100 kJ mol−1) and decompaction weakening factor (∼10−4) are constrained if the fluid conduits are of kilometer scale in width. Significant thermal excursions (∼65 °C) can be induced if a high flow rate, potentially from rapid intermittent dehydration, is realized within channels. Moreover, if the focused fluids emanate from external anomalously hot sources (e.g., magma intrusion), thermal pulses (&gt;100°C), and steep lateral temperature gradients (&gt;50°C km−1) can be generated. Given the focusing efficiency estimated from our 2‐D compaction model, simple 3‐D modeling further shows that tubular conduits have the potential to cause thermal pulses &gt;200°C within 104 years.

Shallow flow over a bed with a lateral change of roughness

River beds frequently exhibit a lateral variation of roughness. For example, in the case of an overflowing river, the main channel has a smoother topography compared to the adjacent floodplains where vegetation and land occupation yield an important hydraulic roughness. The lateral difference in roughness can induce a high lateral velocity gradient within the river cross- section that gives birth to a mixing layer. This mixing layer leads to fluid and momentum transfers between the two adjacent beds. To understand such mix- ing processes in rivers is important for predicting stage-discharge relationships and the velocity distribution within the cross-section. In order to address these issues in the context of a shallow water flow with a water depth h of the same order as the roughness elements of the bed, experiments were undertaken in a 26 m long and 1.1 m wide glass-walled open-channel flume. One half-side of the bed was covered with an array of cubes of height k arranged in a square configuration, the other side with smooth glass. Three different levels of cube submergence h/k were examined (h/k = 0.8, 1.5 and 2). The experiments and measurements were designed to yield the flow in the complete volume of the interstices across the cube array. To achieve this, 2C-3D linear-scanning PIV measurements with zero-parallax optics were developed and set up. The mea- surements revealed the complexity of the flow structure around the interface between the rough and smooth beds. The results show that the ability of the mixing layer to exchange momentum is highly dependent on the level of the cube submergence h/k.

Turbulence-Induced Anti-Stokes Flow and the Resulting Limitations of Large-Eddy Simulation

AbstractThis study shows that the presence of Stokes drift us in the turbulent upper ocean induces a near-surface Eulerian current that opposes the Stokes drift. This current is distinct from previously studied anti-Stokes currents because it does not rely on the presence of planetary rotation or mean lateral gradients. Instead, the anti-Stokes flow arises from an interaction between the Stokes drift and turbulence. The new anti-Stokes flow is antiparallel to us near the ocean surface, is parallel to us at depth, and integrates to zero over the depth of the boundary layer. The presence of Stokes drift in large-eddy simulations (LES) is shown to induce artificial energy production caused by a combination of the new anti-Stokes flow and LES numerics. As a result, care must be taken when designing and interpreting simulations of realistic wave forcing, particularly as rotation becomes weak and/or us becomes perpendicular to the surface wind stress. The mechanism of the artificial energy production is demonstrated for a generalized LES subgrid scheme.

A High Aspect Ratio Micropattern in Freestanding Bulk Pyroelectric Cells

AbstractPyroelectric‐based energy harvesting with the Olsen cycle offers high energy‐transformation efficiency. The pyroelectric effect offers the opportunity to convert temporal temperature fluctuations into usable electrical energy for exploiting abundantly available waste heat. A thinner pyroelectric cell is profitable with regard to generating a higher induced current and a higher charge within a smaller working period owing to a higher temperature variation rate and a smaller thermal capacity. Nevertheless, a thicker pyroelectric cell is advantageous for generating a higher induced voltage over a longer working period owing to a smaller equivalent capacitance and a larger thermal capacity. The use of a high aspect ratio micropattern in a thicker bulk pyroelectric cell is attempted herein to improve the heat transfer and pyroelectric energy transformation by adopting a lower equivalent capacitance to enhance the induced voltage, whereas lateral temperature gradients are introduced to increase the temperature variation rate, the induced charge, and the current. Furthermore, a low‐cost sandblast etching apparatus is adopted to fabricate a high aspect ratio micropattern in thicker bulk lead zirconate titanate (PZT) pyroelectric cells. Within an integral measurement coupled thermal and electrical system, it is demonstrated that relative to a fully covered electrode cell, the high aspect ratio micropattern with an electrode area coverage of 60 % is able to significantly enhance the induced voltage by a factor of 9.3, to increase the induced current by a factor of 5.2, to increase the charge per period by a factor of 3.3, and to increase the stored voltage by a factor of 6.3.

Thermal characterisation with modelling for a microgravity experiment into polycrystalline equiaxed dendritic solidification with in-situ observation

The Multiple Equiaxed Dendrite Interaction (MEDI) experiment was launched on the MASER-13 sounding rocket campaign to investigate polycrystalline equiaxed solidification in the transparent phase change material Neopentylgycol-30wt.%(d)Camphor. This material is of interest as an energy-storage material and as a transparent analogue system of solidification in hypoeutectic metal alloys with a Face Centred Cubic lattice. The liquid sample was cooled under a controlled rate of 0.75 K/min with sufficient time to allow semi-solid conditions to develop under microgravity conditions with the absence of gravity-driven convection. This manuscript provides details on the experimental apparatus and procedures. In addition, the experimental method has been augmented with a numerical model to assist with the characterisation of the essential thermal aspects of the experiment. The model followed a volume-averaging, continuum approach for mushy-zone development. A fast algorithm for computing non-isothermal crystallisation kinetics was applied to the case of binary alloy solidification. To build confidence, a formal numerical verification procedure was performed. The model converged sufficiently with second order accuracy as expected. Application of the model gave close agreement between experimental thermocouple readings and numerical simulation data with a Root Mean Square of 0.2 K for the error. A 2D thermal model is sufficient with a suitable heat loss coefficient at the sample-viewing window boundary. Thermal gradients within the sample and along the growth direction were uniform and approximately 0.3 K/mm. Lateral thermal gradients in the sample ranged from zero at the median plane to 0.3 K/mm at the boundary with the containing structure. However, temperature variation in the lateral direction was predicted to be less than 0.22 K.

Modeling lateral circulation and its influence on the along-channel flow in a branched estuary

A numerical modeling study of the influence of the lateral flow on the estuarine exchange flow was conducted in the north passage of the Changjiang estuary. The lateral flows show substantial variabilities within a flood-ebb tidal cycle. The strong lateral flow occurring during flood tide is caused primarily by the unique cross-shoal flow that induces a strong northward (looking upstream) barotropic force near the surface and advects saltier water toward the northern part of the channel, resulting in a southward baroclinic force caused by the lateral density gradient. Thus, a two-layer structure of lateral flows is produced during the flood tide. The lateral flows are vigorous near the flood slack and the magnitude can exceed that of the along-channel tidal flow during that period. The strong vertical shear of the lateral flows and the salinity gradient in lateral direction generate lateral tidal straining, which are out of phase with the along-channel tidal straining. Consequently, stratification is enhanced at the early stage of the ebb tide. In contrast, strong along-channel straining is apparent during the late ebb tide. The vertical mixing disrupts the vertical density gradient, thus suppressing stratification. The impact of lateral straining on stratification during spring tide is more pronounced than that of along-channel straining during late flood and early ebb tides. The momentum balance along the estuary suggests that lateral flow can augment the residual exchange flow. The advection of lateral flows brings low-energy water from the shoal to the deep channel during the flood tide, whereas the energetic water is moved to the shoal via lateral advection during the ebb tide. The impact of lateral flow on estuarine circulation of this multiple-channel estuary is different from single-channel estuary. A model simulation by blocking the cross-shoal flow shows that the magnitudes of lateral flows and tidal straining are reduced. Moreover, the reduced lateral tidal straining results in a decrease in vertical stratification from the late flood to early ebb tides during the spring tide. By contrast, the along-channel tidal straining becomes dominant. The model results illustrate the important dynamic linkage between lateral flows and estuarine dynamics in the Changjiang estuary.

Exhumed lateral margins and increasing flow confinement of a submarine landslide complex

AbstractSubmarine landslides, including the basal shear surfaces along which they fail, and their subsequent infill, are commonly observed in modern seabed and seismic reflection data sets; their resultant relief impacts sediment routing and storage patterns on continental margins. Here, three stacked submarine landslides are documented from the Permian Ecca Group, Laingsburg depocentre, Karoo Basin, South Africa, including two superimposed lateral margins. The stratigraphic framework includes measured sections and correlated surfaces along a 3 km long, 150 m high outcrop. Two stacked 2·0 to 4·5 km wide and 90 m and 60 m deep erosion surfaces are recognized, with lateral gradients of 8° and 4°, respectively. The aim of this study was to understand the evolution of a submarine landslide complex, including: evolution of basal shear surfaces/zones; variation of infill confinement; and location of the submarine landslides in the context of basin‐scale sedimentation and degradation rates. Three stages of formation are identified: (i) failure of submarine landslide 1, with deposition of unconfined remobilized deposits; (ii) failure of submarine landslide 2, forming basal shear surface/zone 1, with infill of remobilized deposits and weakly confined turbidites; and (iii) failure of submarine landslide 3, forming basal shear surface/zone 2, with infill of remobilized deposits and confined turbidites, transitioning stratigraphically to unconfined deposits. The expression of basal shear varies laterally, from metres thick zones in silt‐rich strata to sharp stepped surfaces in sand‐rich strata. Faulting and rotation of overlying bedding suggest that the shear surfaces/zones were dynamic. Stacking of landslides resulted from multi‐phase slope failure, increasing down‐dip topography and confinement of infilling deposits. The failure slope was probably a low supply tilted basin margin evidenced by megaclast entrainment from underlying basin‐floor successions and the lack of channel systems. This study develops a generic model of landslide infill, as a function of sedimentation and degradation rates, which can be applied globally.

Velocity structure of the western North China basement from high-resolution wide-angle reflection/refraction profiles

Two 1420 km-long, high-resolution wide-angle reflection/refraction profiles were produced for the western part of the North China Craton. Twenty-one shots were fired along the two profiles and seismic data was collected by 700 portable three-component digital seismographers. The crust-mantle structure was investigated in different regions, including the Ordos Block, Haiyuan arcuate tectonic region, Alashan Block, and Yinchuan Basin. First-arrival Pg waves were analyzed using the finite-difference method of first-arrival traveltime tomography to construct the 2D interface morphology and velocity structure of the crystalline basement. The study identified the location and shape of major faults, and notable variations in basement depth and velocity structure in different regions. The crystalline basement in the Ordos Block is typically stable with a depth of 4.5–5.5 km and exhibits only minor fluctuations in the lateral velocity gradient. This is evidenced by Pg wave features, including stable travel time, long tracing distance and high velocity. Between the Helan Mountains and the Yinchuan Basin, notable variations in topography, basement depth, and velocity structure were identified, indicating strong divergence in vertical movement and deformation. In the Yinchuan Basin, the Pg wave traveltime curve revealed the complex structure of the crystalline basement and variations in the velocity gradient. Since the Cenozoic Era, the western North China Craton has experienced strong and frequent tectonic activity causing strong deformation on the periphery of the Alashan Block. The presence of small, low-velocity, near-surface basins, and variations in the crystalline basement interface and velocity isolines provides evidence of strong tectonic deformation of the basement near Bayan Ura Hill, on the eastern margin of the Alashan Block. The Haiyuan arcuate tectonic region is complex and interacts with the Qilian Mountains, Alashan Block, and Ordos Block. Basement depth extends to 6.0 km and varies considerably from the adjacent uplift zone, which has a depth of 2.0 km. The highly deformed and unstable basement structure at the northeastern margin of the Tibetan Plateau is probably related to the collision and squeezing of the Indian Plate and the Eurasian Plate. Seismology data indicates differences between the crystalline basement interface and the velocity structure, as well as strong transverse inhomogeneity. Differences in basement depth in the Ordos Block, together with significant lateral heterogeneity, compressional fold deformation, and the presence of fault zones in the marginal basement, block the continuous compressive movement of the Tibetan Plateau in a northeast direction.

Dynamical links between small- and large-scale mantle heterogeneity: Seismological evidence

We identify PKP•PKP scattered waves (also known as P′•P′) from earthquakes recorded at small-aperture seismic arrays at distances less than 65°. P′•P′ energy travels as a PKP wave through the core, up into the mantle, then scatters back down through the core to the receiver as a second PKP. P′•P′ waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged. We use array-processing methods to amplify low amplitude, coherent scattered energy signals and resolve their incoming direction. We deterministically map scattering heterogeneity locations from the core–mantle boundary to the surface. We use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible, representing a significant increase in our understanding of small-scale structure within the mantle. Our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally. Scattering is most abundant in the uppermost and lowermost mantle, and a minimum in the mid-mantle, resembling the radial distribution of tomographically derived whole-mantle velocity heterogeneity. We investigate the spatial correlation of scattering heterogeneities with large-scale tomographic velocities, lateral velocity gradients, the locations of deep-seated hotspots and subducted slabs. In the lowermost 1500 km of the mantle, small-scale heterogeneities correlate with regions of low seismic velocity, high lateral seismic gradient, and proximity to hotspots. In the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs. Between 600 and 900 km depth, scattering heterogeneities are more common in the regions most remote from slabs, and close to hotspots. Scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the mantle. The similarity between the distribution of large-scale and small-scale mantle structures suggests a dynamic connection across scales, whereby mantle heterogeneities of all sizes may be directed in similar ways by large-scale convective currents.

Combinatorial study of low-refractive Mg–F–Si–O nano-composites deposited by magnetron co-sputtering from compound targets

Deposition of nano-composite Mg–F–Si–O films on optical grade silica glass was studied employing RF magnetron co-sputtering from magnesium fluoride (MgF2) and fused silica (SiO2) targets. The aim was to obtain a stable and reliable sputtering process for optical coatings exhibiting a refractive index lower than the one of quartz glass (1.46 at 550nm) without adding gaseous fluorine to the deposition process. The two magnetrons were installed in a confocal way at 45° off-axis with respect to a static substrate, thus creating a lateral gradient in the thin-film composition. The deposited Mg–F–Si–O coatings were structurally analysed by electron dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The obtained films consist of MgF2 nanocrystals embedded in a SiO2-rich amorphous matrix. Spectroscopic ellipsometry and spectrophotometry measurements showed that they are highly transparent exhibiting a very-low extinction coefficient k and a refractive index n in the desired range between the one of MgF2 (1.38) and SiO2 (1.46). Films with n=1.424 and 1.435 at 550nm were accomplished with absorption below the detection threshold.

Microfluidic device as a facile in vitro tool to generate and investigate lipid gradients

This work describes a method that utilizes a microfluidic gradient generator to develop lateral lipid gradients in supported lipid bilayers (SLB). The new methodology provides freedom of choice with respect to the lipid composition of the SLB. In addition, the device has the ability to create a protein or bivalent cation gradient in the aqueous phase above the lipid bilayer which can elicit a gradient specific response in the SLB. To highlight these features we demonstrate that we can create a phosphoinositide gradient on various length scales, ranging from 2mm to 50μm. We further show that a Ca2+ gradient in the aqueous phase above the SLB causes anionic lipid clustering mirroring the cation gradient. We demonstrate this effect for mixed phosphatidylcholine/phosphatidylinositol-4,5-bisphosphate bilayers and fora mixed phosphatidylcholine/phosphatidylserine bilayers. The biomimetic platform can be combined with a Total Internal Reflection Fluorescence (TIRF) microscopy setup, which allows for the convenient observation of the time evolution of the gradient and the interaction of ligands with the lipid bilayer. The method provides unprecedented access to study the dynamics and mechanics of protein-lipid interactions on membranes with micron level gradients, mimicking plasma membrane gradients observed in organisms such as Dictyostelium discodeum and neutrophils.

Internal flow and external jet characteristics of double serpentine nozzle with different aspect ratio

In order to increase the survivability of the fighter aircraft, the serpentine nozzle has been applied in series of stealth bombers and unmanned aerial vehicles due to its excellent potentiality of evidently suppressing the infrared radiation signatures and radar cross section emitted by engine exhausts. Among the geometric parameters of the serpentine nozzle, the aspect ratio (AR) at the nozzle exit is one of the most critical parameters for the nozzle design as the infrared suppression effect could be greatly enhanced with the increment of AR by strengthening the mixing between the exhaust plume and atmosphere; the aim of this paper is to study the influence of the AR on the flow characteristics of the double serpentine nozzle. The flow features of six double serpentine convergent nozzles, i.e. AR = 3, 5, 7, 9, 11, 15 respectively, were numerically simulated with the shear stress transport κ–ω turbulent model adopted, which had been validated by the experimental data. The characteristics of internal flow and external jet, and the aerodynamic performances of these six nozzles were compared. Results show that the Ma contours at the symmetric plane are different due to the distinct flow accelerations caused by the change of the curvature and the duct height for diverse AR, and the surface pressure and the shock wave features are different correspondingly. The lateral divergence and the lateral convergence characteristics of the nozzle configuration lead to opposite lateral flow under diverse AR, and the change of lateral width induced different lateral pressure gradient, then lead to various lateral vortex distributions. The length of potential core is the contribution of the comprehensive effects of geometry parameters, and it is decreased with the increase of AR due to the dominated effect of the increased mixing area; however, the declining rate is slowed down. The AR of 5 should be chosen for the best aerodynamic performance of the double serpentine nozzle under the qualifications to completely shield the high-temperature turbine.

Analysis of Thermal Structure of Arctic Lakes at Local and Regional Scales Using in Situ and Multidate Landsat‐8 Data

AbstractThe Arctic coastal plain is covered with numerous thermokarst lakes. These lakes are closely linked to climate and environmental change through their heat and water budgets. We examined the intralake thermal structure at the local scale and investigated the water temperature pattern of lakes at the regional scale by utilizing extensive in situ measurements and multidate Landsat‐8 remote sensing data. Our analysis indicates that the lake skin temperatures derived from satellite thermal sensors during most of the ice‐free summer period effectively represent the lake bulk temperature because the lakes are typically well‐mixed and without significant vertical stratification. With the relatively high‐resolution Landsat‐8 thermal data, we were able to quantitatively examine intralake lateral temperature differences and gradients in relation to geographical location, topography, meteorological factors, and lake morphometry for the first time. Our results suggest that wind speed and direction not only control the vertical stratification but also influences lateral differences and gradients of lake surface temperature. Wind can considerably reduce the intralake temperature gradient. Interestingly, we found that geographical location (latitude, longitude, distance to the ocean) and lake morphometry (surface size, depth, volume) not only control lake temperature regionally but also affect the lateral temperature gradient and homogeneity level within each individual lake. For the Arctic coastal plain, at regional scales, inland and southern lakes tend to have larger horizontal temperature differences and gradients compared to coastal and northern lakes. At local scales, large and shallow lakes tend to have large lateral temperature differences relative to small and deep lakes.

Micromagnetic Simulations of Magnetization Spatial Distribution in Ultrathin Cobalt Layers With Gradient Magnetic Anisotropy

Spatial distribution of magnetization in an ultrathin ferromagnetic Co layer with a lateral gradient of magnetic anisotropy, while approaching spin reorientation transition (SRT) (from perpendicular to in-plane magnetization alignment), has been investigated by means of micromagnetic simulations in the 2-D mode, using OOMMF software. The geometry of the out-of-plane-magnetized domains (parallel stripes, labyrinth, and bubbles) has been found to be dependent on both the initial distribution of magnetization and the direction of the applied magnetic field. A fast decrease in the domain size has been observed while moving toward SRT. In the experiment, Pt/Co/Pt layers with initial in-plane magnetization orientation have been irreversibly modified by femtosecond laser pulses. In the irradiated spot, rings with induced perpendicular magnetic anisotropy have been formed, resulting in an appearance of several local SRTs. Magnetic domain structure in the SRT regions has been visualized using magnetic force microscopy. The experimental observations are qualitatively explained by the results of the micromagnetic simulations.

Contribution of topographically generated submesoscale turbulence to Southern Ocean overturning

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.

Within-field advection enhances evaporation and transpiration in a vineyard in an arid environment

Advection of hot air from a warmer to a cooler surface is known to enhance evaporation through additional supply of energy, provided that water is readily available. This study investigated advection in an isolated irrigated vineyard in the Negev desert, over a period of several months under changing plant cover and environmental conditions, and for different degrees of water availability. Field, canopy, and soil energy balance fluxes were assessed, as well as likely indicators of advection such as wind speed, VPD, vertical temperature gradients between the soil, the canopy air space, and the air, and lateral temperature gradients between the vineyard and the surrounding desert. It was found that for a period from May to July, advection enhanced transpiration by 8%, where diurnal patterns suggested that most of the advection originated from within the field. At times, soil-to-canopy advection enhanced transpiration by as much as 30–40%. Wet irrigated strips likewise experienced soil-to-soil advection from drier soil, but to a much lesser degree. A surprisingly large difference was observed in the contribution of advection to transpiration between June (2%) and July (11%), which had almost identical environmental conditions. This indicates that small changes in the agro-system such as row-width and leaf area could have a large impact on within-field advection, and that row crops could potentially be managed to reduce or enhance advection.