Mesoscale Shear Research Articles

Role of Crack Interaction on Shear Localization in Porous Granular Rocks Deformed in the Brittle and Ductile Fields

AbstractCrack interactions leading to shear localization were quantified using microstructural analysis for brittle faults and high‐temperature ductile faults formed during experiments on quartz sandstone. In both faulting regimes, the nucleation of macroscopic faults results from the interactions of microfractures at two length scales in ensemble. Brittle faults nucleate when the longest mesoscale shear fractures and transgranular tensile cracks critically interact. In contrast, ductile faults nucleate when the longest mesoscale shear fractures and multi‐grain scale intergranular shear cracks critically interact. For both faulting regimes, we conclude the interaction and coalescence of the longest mesoscale shear fractures is the fundamental process responsible for fault nucleation. Hence, mesoscale shear fractures, which accommodate the majority of axial strain prior to shear localization in both faulting regimes, also serve as the nucleus of macroscopic faults. Locally, the growth of the mesoscale shear fractures is promoted by the interaction and coalescence of the multi‐grain scale cracks in both faulting regimes. We hypothesize that attainment of a critical microstructure for shear localization (i.e., local clustering of the longest microfractures) requires a characteristic amount of plastic axial strain, which depends on deformation conditions. In brittle faulting, distributed microfracturing is confined within limited regions of the rock volume, which expedites crack clustering and fault nucleation at low characteristic strains. In ductile faulting, distributed microfracturing occurs more uniformly throughout the rock volume, delaying shear localization to high characteristic strains. Accurate prediction of shear localization requires models that describe crack interactions of the largest flaws that account for crack clustering.

Comparative Analysis of Different Heavy Rainstorm Periods Lasting for Two Consecutive Days in the Qinba Region under the Influence of the Southwest Vortex

In recent years, heavy rainfall events have occurred frequently in the Qinba region. Forecasting and predicting heavy rainfall in the Qinba region is difficult due to the unique underlying terrain and complicated mechanisms involved. One significant weather system that might bring significant rainfall to the region is the southwest vortex (SWV); however, its different positions, intensities, and interaction with other weather systems might result in precipitation with different intensities and distributions. In this study, ERA-5 reanalysis data, FY-4A satellite data, and conventional observation data were used to examine heavy rainstorms that occurred in the Qinba region in the periods of 3–4 September 2021 (referred to as Stage I) and 4–5 September 2021 (referred to as Stage II), while the SWV was in effect. During Stage I, the northwest vortex (NWV) and SWV generated a mesoscale shear line and mesoscale convective complex (MCC) in the Qinba region. This led to a considerable area of heavy rainfall, with a maximum hourly precipitation of 129 mm and heavy precipitation at 15 stations. During Stage II, a mesoscale convective system (MCS) influenced by the SWV was initiated by a low-level jet, resulting in a localized heavy downpour with a maximum hourly precipitation of 72 mm. Significant topography-forced uplift was found in both Stages I and II in the high-altitude Qinba region. Furthermore, the rainfall was stronger during Stage I due to the secondary circulation that developed in the middle and lower levels. These findings will improve our capability to predict rainstorms and prevent disasters in the Qinba region.

A Hall-Petch-like relationship linking nanoscale heterogeneity to yield stress of heterogeneous metallic glasses

Metallic glasses (MGs) undergo plastic deformation through shear transformation zones (STZs) at small deformations and shear banding at large deformations. The STZ mechanism is linked to microstructural heterogeneities, including nano-heterogeneities associated with atom clustering and their spatial distribution. Shear banding occurs due to the coalescence of STZs. In this study, we investigate the yielding behavior of heterogeneous MGs by varying the spatial correlation and standard deviation of local shear moduli associated with clustering atoms on the nanoscale. Using a mesoscale shear transformation zone (STZ) dynamics model, we compute the yielding strength and observe deformation behaviors associated with the formation and propagation of STZs. We propose a Hall-Petch-like relationship where the yield stress of the MG scales inversely with the square root of the spatial correlation length. Our results show that the yielding of MGs corresponds to the percolation of STZs from soft to hard regions. Prior to macroscopic yielding, the activated STZs tend to accumulate inside soft regions, forming a Super-STZ array, which is similar to the formation of dislocation pile-up at grain boundaries. We derive the stress concentration in the front of the Super-STZ using the Eshelby inclusion model and formulate a Hall-Petch-like equation to quantify the yield of MGs with the spatial correlation length and standard deviation of the nanoscale heterogeneity. Our results provide insights into the structure-property relationship of MGs and have important implications for the design of nanoscale MGs with tunable properties.

The Strain Rate Sensitivity of Heterogeneous Thin Film Metallic Glasses: Interplay Between Nanoscale Heterogeneity and Dynamic Plasticity

The dynamic mechanical properties of metallic glasses (MGs) are crucial to capturing the deformation signatures as well as for structural and functional applications. In this work, we investigate the influence of nanoscale structural heterogeneity of MGs on dynamic plasticity, focusing on the variation in strain rate sensitivity and the transition of deformation mechanisms, using a combined experimental and simulation approach. The Cu50Zr50 thin-film MGs with different nanoscale heterogeneities are synthesized using magnetron sputtering and further characterized using dynamic force microscopy and nanoindentation. All the films exhibit a strain rate hardening effect, but a transition in strain rate sensitivity as the indentation rate increases has been found in the MG with a higher heterogeneity. To understand the underlying mechanisms, mesoscale shear transformation zone dynamics simulations are performed on model Cu50Zr50 MGs. The simulation results are able to capture the experimental trend. Notably, the transition in strain rate sensitivity for a heterogenous MG stems from a change in deformation mechanisms: from structure-dictated strain localization at a lower strain rate to stress-dictated strain percolation into a shear band at a higher strain rate. The observed strain rate sensitivity and the corresponding mechanisms are summarized in a deformation mechanism map where nanoscale structural heterogeneity and strain rate are varied. We envision our study not only providing insights into the structure and property relationship of MGs on the nanoscale but also will facilitate the design of heterogeneous MGs for dynamic applications.

Study on the constitutive model of the whole process of macroscale and mesoscale shear damage of prestressed anchored jointed rock

Study on the constitutive model of the whole process of macroscale and mesoscale shear damage of prestressed anchored jointed rock

Observational analyses of topographic effects on convective systems in an extreme rainfall event in Northern China

An extreme rainfall event occurred in northern China between 18 and 21 July 2016, with the strongest precipitation of 783.4 mm occurring within the rainfall zone of Taihang Mountain. In this study, mesoscale convective systems (MCSs) resulting in heavy rainfall are studied using high-resolution surface observations, soundings and radar data. The topographic effect in addition to shear zone cyclonic circulation is mainly responsible for the heavy rainfall. The synoptic low-pressure environmental circulation promotes mesocyclone and convection development in northern China, where a strong and moist low-level jet is observed. The interaction between the mesocyclone and mesoscale topography produces two strong, separate precipitation centers, which are clearly the direct results of three MCSs. Orographic blocking plays a crucial role in the development of MCSs. Diabatic cooling due to raindrop evaporation in association with MCS1 forms a cold pool on the plain east of the central Taihang Mountain area. Convective cell initiation and development in MCS2 is due to the impingement of southeasterly flow near the surface of the hills east of Linzhou basin. Convective cells that are successively generated and shifted along a mesoscale shear line comprise the MCS2 linear distribution and a northwestward rain belt. The northern extreme rainfall center is caused by MCS3 along the southern slopes of an eastward-opening valley. Convective cells are triggered along a shear line, which is affected by a combination of topography, a cold pool in the boundary layer and mesocyclone outer flow. Together, the orographic forcing and cold pool enhance the Taihang Mountain precipitation event.

Femtosecond laser rejuvenation of nanocrystalline metals

Nanocrystalline metals are distinct from traditional engineering materials due to their high concentration of grain boundaries and corresponding structural disorder at grain boundaries. The effect of local disorder in nanocrystalline materials manifests in ways reminiscent of fully amorphous materials, such as mesoscale shear localization and pressure-dependent yielding, owing to the high concentration of grain boundaries and their predominance in governing plasticity. Relaxation processes in nanocrystalline materials that facilitate reconfigurations of grain boundaries and lower their energy, such as low temperature annealing, have been shown to enhance mechanical strength. However, processes that raise the energy of a nanocrystalline metal have not been observed, limiting the tunability of properties and the prospect for suppressing shear localization. Here, we use femtosecond laser processing as a unique non-equilibrium process that can generate complex stress states due to ultrafast electronic excitation and subsequent relaxation events. Experiments on nanocrystalline Al-O and Cu-Zr alloys indicate that sub-ablation femtosecond laser pulses cause up to an 87% reduction in hardness with no change in grain size, which can be ascribed to grain boundary-mediated processes. Parallels between our results and rejuvenation processes in glassy systems will be discussed in the context of controlling metastable structural configurations through novel processing routes.

Spatial correlation of elastic heterogeneity tunes the deformation behavior of metallic glasses

Metallic glasses (MGs) possess remarkably high strength but often display only minimal tensile ductility due to the formation of catastrophic shear bands. Purposely enhancing the inherent heterogeneity to promote distributed flow offers new possibilities in improving the ductility of monolithic MGs. Here, we report the effect of the spatial heterogeneity of elasticity, resulting from the inherently inhomogeneous amorphous structures, on the deformation behavior of MGs, specifically focusing on the ductility using multiscale modeling methods. A highly heterogeneous, Gaussian-type shear modulus distribution at the nanoscale is revealed by atomistic simulations in Cu64Zr36 MGs, in which the soft population of the distribution exhibits a marked propensity to undergo the inelastic shear transformation. By employing a mesoscale shear transformation zone dynamics model, we find that the organization of such nanometer-scale shear transformation events into shear-band patterns is dependent on the spatial heterogeneity of the local shear moduli. A critical spatial correlation length of elastic heterogeneity is identified for the simulated MGs to achieve the best tensile ductility, which is associated with a transition of shear-band formation mechanisms, from stress-dictated nucleation and growth to structure-dictated strain percolation, as well as a saturation of elastically soft sites participating in the plastic flow. This discovery is important for the fundamental understanding of the role of spatial heterogeneity in influencing the deformation behavior of MGs. We believe that this can facilitate the design and development of new ductile monolithic MGs by a process of tuning the inherent heterogeneity to achieve enhanced ductility in these high-strength metallic alloys.

A NUMERICAL STUDY OF THE MICROSCALE PLASTIC STRAIN LOCALIZATION IN FRICTION STIR WELD ZONES

A crystal plasticity approach was used to study the effects of grain shape and texture on the deformation behavior of friction stir weld (FSW) microregions. The explicit stress-strain analysis was performed for two representative grain structures with equiaxed and extended grains. Grain orientations were assigned to simulate no texture or a weak or strong cubic texture. Calculations have shown that the texture gave rise to earlier plastic strain localization on a larger scale. The highest stresses were found to develop in a non-textured specimen with equiaxed grains where the grain boundaries served as a barrier to dislocation motion. In both equiaxed and extended grain structures with a strong cubic texture no pronounced strain localization was seen on the grain scale but mesoscale shear bands appeared early in the deformation process. The calculations have shown that the microstructure-based simulation is a reasonable tool to study the deformation behavior of FSW materials, which is difficult to be predicted within macroscopic models alone.

Phase equilibria modelling constraints on P–T conditions during fluid catalysed conversion of granulite to eclogite in the Bergen Arcs, Norway

AbstractExhumed eclogitic crust is rare and exposures that preserve both protoliths and altered domains are limited around the world. Nominally anhydrous Neoproterozoic anorthositic granulites exposed on the island of Holsnøy, in the Bergen Arcs in western Norway, preserve different stages of progressive prograde deformation, together with the corresponding fluid‐assisted metamorphism, which record the conversion to eclogite during the Ordovician–Silurian Caledonian Orogeny. Four stages of deformation can be identified: (1) brittle deformation resulting in the formation of fractures and the generation of pseudotachylites in the granulite; (2) development of mesoscale shear zones associated with increased fluid–rock interaction; (3) the complete large‐scale replacement of granulite by hydrous eclogite with blocks of granulite sitting in an eclogitic “matrix”; and (4) the break‐up of completely eclogitized granulite by continued fluid influx, resulting in the formation of coarse‐grained phengite‐dominated mineral assemblages. P–T constraints derived from phase equilibria forward modelling of mineral assemblages of the early and later stages of the conversion to eclogite document burial and partial exhumation path with peak metamorphic conditions of ~21–22 kbar and 670–690°C. The P–T models, in combination with existing T–t constraints, imply that the Lindås Nappe underwent extremely rapid retrogressive pressure change. Fluid infiltration began on the prograde burial path and continued throughout the recorded P–T evolution, implying a fluid source that underwent progressive dehydration during subduction of the granulites. However, in places limited fluid availability on the prograde path resulted in assemblages largely consuming the available fluid, essentially freezing in snapshots of the prograde evolution. These were carried metastably deeper into the mantle with strain and metamorphic recrystallization partitioned into areas where ongoing fluid infiltration was concentrated.

Winter meso-scale shear front in the Yellow Sea and its sedimentary effects

In this paper, the authors explored the presence of shear fronts between the Yellow Sea Coastal Current (YSCC) and the monsoon-strengthened Yellow Sea Warm Current (YSWC) in winter and their sedimentary effects within the shear zone based on a fully validated numerical model. This work added the wind force to a tidal model during simulating the winter baroclinic circulation in the Yellow Sea. The results indicate that the YSWC is significantly strengthened by wind-driven compensation due to a northeast monsoon during winter time. When this warm current encounters the North Shandong-South Yellow Sea coastal current, there is a strong reverse shear action between the two current systems, forming a reverse-S-shaped shear front that begins near 34°N in the south and extends to approximately 38°N, with an overall length of over 600 km. The main driving force for the formation of this shear front derives from the circulation system with the reverse flow. In the shear zone, temperature and salinity gradients increase, flow velocities are relatively small and the flow direction on one side of the shear zone is opposite to that on the other side. The vertical circulation structure is complicated, consisting of a series of meso- and small-scale anti-clockwise eddies. Particularly, this shear effect significantly hinders the horizontal exchange of coastal sediments carried by warm currents, resulting in fine sediments deposition due to the weak hydrodynamic regime.

Experimental Study of Shear Zones Formed at Sand/Steel Interfaces in Axial and Torsional Axisymmetric Tests

The interface shear behavior of granular materials is central to many engineering applications, including the performance of structures like deep foundations, landfills, and retaining walls. Consequently, it is paramount to understand the behavior of construction material-soil interfaces involved in these applications. Furthermore, it has been shown that the study of interface behavior, in the laboratory and in-situ, can provide robust information about the soil's properties and engineering performance. This paper presented laboratory evaluations of micro and meso-scale shear deformation of medium-sized sands aimed at developing an improved fundamental understanding of granular-continuum stress-strain behavior. A comparison of interface testing results from two different shear directions—axial and torsional—demonstrated that the evolution and progression of shear zone formation was affected differently by changes in the interface surface roughness and particle angularity. In particular, it was observed that torsional shear is a more dilative process that induces a larger degree of soil shearing and is greatly affected by particle angularity. Studies of shear-induced volume changes also revealed that the influence zone for torsional shearing is larger than that for axial shearing, with soil dilation occurring inside the shear zone in contact with the material counterface and soil contraction in a surrounding outer zone. Fundamental micromechanical processes that aim to explain the differences between the behavior of axial and torsional tests are proposed.

Magnetic fabric evolution in ductile shear zones: examples in metagranites of the Aar Massif (Swiss Central Alps)

AbstractThe Aar Massif forms part of the polycyclic basement of the External Crystalline Massifs in central Switzerland. Strong heterogeneous Alpine deformation produced a network of broad, anastomosing shear zones, with deformation strongly localized in mylonitic domains. This study investigates the combined effects of high‐strain deformation and synkinematic metamorphism on magnetic fabric evolution in Tertiary shear zones of the Aar granite and Grimsel granodiorite. In transects across several mesoscale shear zones with large strain gradients, magnetic fabric orientations are in excellent agreement with principal strain orientations determined from outcrop fabrics and strain markers. However, the magnitude and shape of the magnetic anisotropy do not change systematically with increasing finite strain, likely as a result of recrystallization and metamorphism. The overall pattern of steeply dipping fabrics is consistent with the main shortening stage of regional Alpine kinematics, while some mylonite structures reflect a local component of dextral shearing.

The influence of phase and grain size distribution on the dynamics of strain localization in polymineralic rocks

Deformation microstructures of a quartzo-feldspathic pegmatite deformed at mid-crustal levels allow the study of the dynamics of strain localization in polymineralic rocks. Strain localization results from (i) difference in grain sizes between phases, both original and obtained during fluid present reactions and (ii) initial compositional banding. Due to original difference in grain size stress concentrates in the initially finer-grained phases resulting in their intense grain size reduction via subgrain rotation recrystallization (SGR). When the grain size is sufficiently reduced through either deformation or interphase coupled dissolution–precipitation replacement of the coarse grained feldspar, aggregates start to deform by dominantly diffusion accommodated grain boundary sliding (GBS). Phase mixing inhibits grain growth and sustains a grain size allowing GBS. Consequently, discontinuous microscale shear zones form locally within initially coarse grained areas. At the same time difference in strain rate between feldspar-rich and quartz-rich domains needs to be accommodated at domain boundaries. This results in the formation of continuous mesoscale shear zones deformed by GBS. Once these are formed, deformation in the coarse grained parts is arrested and strain is mainly accommodated in the mesoscale shear zones resulting in “superplastic” behaviour consistent with diffusion creep.

Nonlinear evolution of a baroclinic wave and imbalanced dissipation

AbstractWe consider the nonlinear evolution of an unstable baroclinic wave in a regime of rotating stratified flow that is of relevance to interior circulation in the oceans and in the atmosphere: a regime characterized by small large-scale Rossby and Froude numbers, a small vertical to horizontal aspect ratio and no bounding horizontal surfaces. Using high-resolution simulations of the non-hydrostatic Boussinesq equations and companion integrations of the balanced quasi-geostrophic (QG) equations, we present evidence for a local route to dissipation of balanced energy directly through interior turbulent cascades. That is, analysis of simulations presented in this study suggest that a developing baroclinic instability can lead to secondary instabilities that can cascade a small fraction of the energy forward to unbalanced scales whereas the bulk of the energy is confined to large balanced scales. Mesoscale shear and strain resulting from the hydrostatic geostrophic baroclinic instability drive frontogenesis. The fronts in turn support ageostrophic secondary circulation and instabilities. These two processes acting together lead to a quick rise in dissipation rate which then reaches a peak and begins to fall slowly when frontogenesis slows down; eventually balanced and imbalanced modes decouple. A measurement of the dissipation of balanced energy by imbalanced processes reveals that it scales exponentially with Rossby number of the base flow. We expect that this scaling will hold more generally than for the specific set-up we consider given the fundamental nature of the dynamics involved. In other results, (a) a break is seen in the total energy (TE) spectrum at small scales: while a steep $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}k^{-3}$ geostrophic scaling (where $k$ is the three-dimensional wavenumber) is seen at intermediate scales, the smaller scales display a shallower $k^{-5/3}$ scaling, reminiscent of the atmospheric spectra of Nastrom & Gage and (b) at the higher of the Rossby numbers considered a minimum is seen in the vertical shear spectrum, reminiscent of similar spectra obtained using in situ measurements.

The plastic shear channeling effect and the nonlinear waves of localized plastic deformation and fracture

Approaches adopted in physical mesomechanics and nonequilibrium thermodynamics are combined in an integrated framework to examine the mechanisms involved in generation of nonlinear waves of localized plastic deformation and fracture in a loaded solid treated as a multiscale system. It has been found that in a loaded solid, local structural transformation fluxes develop at the nanoscale level and undergo channeling at the mesoscale level, whereas accommodation kink bands form at the macroscale level. Generation of the nonlinear waves of localized plastic flow is shown to be due to self-organization of the three processes in question. In the case where work hardening takes place at deformation, traveling waves of localized plastic flow are eventually transformed into steady-state phase failure waves localized at the macroscale level. In a hierarchy of mesoscale levels, propagation of channeled local structural transformations in a heterogeneous medium gives rise to strain-induced defects, such as dislocations, mesoscale shear bands, etc. These deformation mechanisms define the dissipative components of the overall plastic flow process developing in solid bodies under loading. A theory of nonlinear waves of localized plastic flow in a deformed material is proposed. The theoretical predictions made conform with experimental data known from the available literature.

Detailed 2-D imaging of the Mediterranean outflow and meddies off W Iberia from multichannel seismic data

Reprocessing of a 326-km long multichannel seismic line acquired in the Tagus Abyssal Plain off W Iberia in 1991 allowed detailed imaging of the thermohaline structure of several mesoscale features within the water column. The interpretation was supported by subsurface float measurements, Sea Level Anomaly (SLA) maps and Sea Surface Temperature (SST) images contemporaneous with the acquisition of the seismic data. Clear images were obtained of the reflective patterns associated with one previously known and one newly discovered meddy, one cyclone, the upper and lower cores of the Mediterranean Undercurrent, and the interface of the high-salinity tongue of the Mediterranean Water with the North Atlantic Central Water. These reveal a complexity and a detail of the lateral variations of the thermohaline structure not easily observed by conventional physical oceanography tools. The mesoscale structures were imaged via reflections from oceanic fine structures of scale 30 m or less. We compare the characteristics of observed reflections with known mechanisms of fine-structure production. Most of the observed reflections are consistent with internal waves and thermohaline intrusions as previously hypothesized. We postulate a new mechanism to explain the formation of the steeply sloping reflections that outline the meddy and other features, involving frontogenetic isopycnal advection, formation of thermohaline intrusions, and tilting of the intrusive layers by mesoscale shear flows. The imaging technique therefore shows the relationship between mesoscale features and the fine-scale oceanographic phenomena associated with mixing, including steeply-sloped structures that would otherwise not be tracked using CTD profiles alone.

Measurement of meso-scale shear deformations for modelling textile composites

Textile preforms undergo complex in-plane and out-of-plane deformations during forming processes. In-plane shear is the most significant mode of deformation during draping or forming around double-curvature surfaces. This paper reports an improved method for measuring the constitutive shear properties of textile preforms—a wide strip bias extension test has been found to give significantly better results in comparison to conventional narrow strip bias test. Shear angles, computed directly from global strains, were in close agreement to those measured using an optical method. Constitutive shear stress–strain relation, computed from the bias extension test data, was in good agreement with KES (Kawabata Evaluation System) test results. Meso-scale tow deformations have been measured using two techniques: an inexpensive flatbed scanner-based full-field strain measurement technique for measuring in-plane tow deformations and a strain-freezing technique for measuring through-thickness tow deformations. With this data, a 3D Representative Volume Element (RVE) can be constructed for each stage of shear deformation. Beyond the geometric shear limit, tow deformations during bias extension appear to be somewhat different from those normally expected from pure shear—a reduction in tow thickness and tow cross-sectional area and a corresponding increase in packing factor.

Shear-induced structure in polymer–clay nanocomposite solutions

The equilibrium structure and shear response of model polymer–clay nanocomposite gels are measured using X-ray scattering, light scattering, optical microscopy, and rheometry. The suspensions form physical gels via the “bridging” of neighboring colloidal clay platelets by the polymer, with reversible adsorption of polymer segments onto the clay surface providing a short-range attractive force. As the flow disrupts this transient network, coupling between composition and stress leads to the formation of a macroscopic domain pattern, while the clay platelets orient with their surface normal parallel to the direction of vorticity. We discuss the shear-induced structure, steady-shear rheology, and oscillatory-shear response of these dynamic networks, and we offer a physical explanation for the mesoscale shear response. In contrast to flow-induced “banding” transitions, no stress plateau is observed in the region where macroscopic phase separation occurs. The observed platelet orientation is different from that reported for polymer–melt clay nanocomposites, which we attribute to effects associated with macroscopic phase separation under shear flow.

The Kinematics of a Midlatitude, Continental Mesoscale Convective System and Its Mesoscale Vortex

The authors present a unique, scale-discriminating study of the environment-relative circulations within a mesoscale convective system (MCS) and mesoscale convective vortex (MCV). The MCS, a leading convective line and trailing stratiform region that became asymmetric, passed through the National Oceanic and Atmospheric Administration (NOAA) Profiler Network (NPN) in Kansas and Oklahoma on 1 August 1996. The MCV appeared in the MCS’s stratiform region just prior to the system’s mature stage and grew to a depth of over 12 km as the MCS dissipated. The MCV did not apparently survive to the next day. A spatial bandpass filter was used to divide observed wind into a component that was predominantly synoptic background wind and a component that was predominantly a mesoscale perturbation on that background wind. A mesoscale updraft, mesoscale downdraft, and divergent outflows in the lower and upper troposphere were evident after the synoptic background wind was removed, so these four circulations were internal and fundamental to the MCS. The mesoscale perturbation in wind in the middle troposphere extended farther behind the MCS than ahead of it, consistent with analytic studies and numerical simulations of gravity waves generated by heat sources characteristic of MCSs with leading convective lines and trailing stratiform regions. Deepening of the MCV appeared to be reflected in the vertical wind shear at the vortex’s center: as the MCV strengthened, the mesoscale shear through its lower part decreased, perhaps as wind became more vortical at increasing altitudes. Mesoscale and synoptic vertical shears were of similar magnitude, so an average of environmental soundings outside an MCS probably does not accurately represent the shear that affects an MCV. This suggests the need to reevaluate how the kinematical settings of MCVs are diagnosed.