Vorticity Filaments Research Articles

Cancellation exponents in isotropic turbulence and magnetohydrodynamic turbulence.

Small-scale characteristics of turbulence such as velocity gradients and vorticity fluctuate rapidly in magnitude and oscillate in sign. Much work exists on the characterization of magnitude variations, but far less on sign oscillations. While in homogeneous turbulence averages performed on large scales tend to zero because of the oscillatory character, those performed on increasingly smaller scales will vary with the averaging scale in some characteristic way. This characteristic variation at high Reynolds numbers is captured by the so-called cancellation exponent, which measures how local averages tend to cancel out as the averaging scale increases, in space or time. Past experimental work suggests that the exponents in turbulence depend on whether one considers quantities in full three-dimensional (3D) space or uses their one- or two-dimensional cuts. We compute cancellation exponents of vorticity and longitudinal as well as transverse velocity gradients in isotropic turbulence at Taylor-scale Reynolds numbers up to 1300 on 8192^{3} grids. The 2D cuts yield the same exponents as those for full 3D, while the 1D cuts yield smaller numbers, suggesting that the results in higher dimensions are more reliable. We make the case that the presence of vortical filaments in isotropic turbulence leads to this conclusion. This effect is particularly conspicuous in magnetohydrodynamic turbulence, where an increased degree of spatial coherence develops along the direction of an imposed magnetic field.

Mesoscale-submesoscale interactions in the Gulf of Mexico: From oil dispersion to climate

In the ocean, forcing acts at planetary scales and dissipation at the microscales. In between are the mesoscales, in a lot of respects akin to nearly two-dimensional, quasi-geostrophically, balanced turbulence. Eddies and fronts, extending from ten to hundred kilometers, represent their best-known dynamical expression. At the ocean boundary layers, near the surface and at the bottom, smaller ageostrophic, coherent flow structures may appear in the form of vorticity filaments, density fronts or coherent vortices, with typical scales of hundreds of meters to few kilometers and a lifespan of few days. These so-called submesoscale circulations provide a pathway for energy transfer towards smaller scales, contribute to the global overturning budget, and impact substantially lateral and diapycnal mixing. They develop in presence of density gradients in the turbulent boundary layers, and their statistics are not well known in a global sense, but are likely to change in the future due to projected changes in near surface stratification.This perspective presents an overview of recent studies illustrating physical and biogeochemical interactions across mesoscale and submesoscale flows focusing on the Gulf of Mexico, where much modeling and observational work has been taking place following the 2010 Deepwater Horizon blow-out. The physical interpretation of several biogeochemical data-sets illustrates how mesoscale and submesoscale circulations impact the dispersion of biologically and climatically relevant tracers, from coral larvae to carbon.The ultimate goal is present the reader with examples of spatial and temporal multiscale interactions in a complex, chaotic system such as the ocean that is key to the future evolution of the climate system with its enormous storage capacity of heat and carbon.

Spectral and dynamical analysis of a single vortex ring in anisotropic harmonically trapped three-dimensional Bose-Einstein condensates

In the present work, motivated by numerous recent experimental developments we revisit the dynamics of a single vortex ring in anisotropic harmonic traps. At the theoretical level, we start from a general Lagrangian dynamically capturing the evolution of a vortex ring and not only consider its spectrum of linearized excitations, but also explore the full nonlinear dynamical evolution of the ring as a vortical filament. The theory predicts that the ring is stable for $1 \leq \lambda \leq 2$, where $\lambda=\omega_z/\omega_r$ is the ratio of the trapping frequencies along the $z$ and $r$ axes, i.e., for spherical to slightly oblate condensates. We compare this prediction with direct numerical simulations of the full 3D Gross-Pitaevskii equation (GPE) capturing the linearization spectrum of the ring for different values of the chemical potential and as a function of the anisotropy parameter $\lambda$. We identify this result as being only asymptotically valid as the chemical potential $\mu \rightarrow \infty$, revealing how the stability interval narrows and, in particular, its upper bound decreases for finite $\mu$. Finally, we compare at the dynamical level the results of the GPE with the ones effectively capturing the ring dynamics, revealing the unstable evolution for different values of $\lambda$, as well as the good agreement between the two.

Interaction of Superinertial Waves with Submesoscale Cyclonic Filaments in the North Wall of the Gulf Stream

AbstractHigh-resolution, nearly Lagrangian observations of velocity and density made in the North Wall of the Gulf Stream reveal banded shear structures characteristic of near-inertial waves (NIWs). Here, the current follows submesoscale dynamics, with Rossby and Richardson numbers near one, and the vertical vorticity is positive. This allows for a unique analysis of the interaction of NIWs with a submesoscale current dominated by cyclonic as opposed to anticyclonic vorticity. Rotary spectra reveal that the vertical shear vector rotates primarily clockwise with depth and with time at frequencies near and above the local Coriolis frequency f. At some depths, more than half of the measured shear variance is explained by clockwise rotary motions with frequencies between f and 1.7f. The dominant superinertial frequencies are consistent with those inferred from a dispersion relation for NIWs in submesoscale currents that depends on the observed aspect ratio of the wave shear as well as the vertical vorticity, baroclinicity, and stratification of the balanced flow. These observations motivate a ray tracing calculation of superinertial wave propagation in the North Wall, where multiple filaments of strong cyclonic vorticity strongly modify wave propagation. The calculation shows that the minimum permissible frequency for inertia–gravity waves is mostly greater than the Coriolis frequency, and superinertial waves can be trapped and amplified at slantwise critical layers between cyclonic vortex filaments, providing a new plausible explanation for why the observed shear variance is dominated by superinertial waves.

The Record Los Angeles Heat Event of September 2010: 1. Synoptic‐Scale‐Meso‐β‐Scale Analyses of Interactive Planetary Wave Breaking, Terrain‐ and Coastal‐Induced Circulations

AbstractOn 27 September 2010 the Los Angeles Civic Center reached its all‐time record maximum temperature of 45°C before 1330 local daylight time with several other regional stations observing all‐time record breaking heat early in that afternoon. This record event is associated with a general circulation pattern predisposed to hemispheric wave breaking. Three days before the event, wave breaking organizes complex terrain‐ and coastal‐induced processes that lead to isentropic surface folding into the Los Angeles Basin. The first wave break occurs over the western two thirds of North America leading to trough elongation across the southwestern U.S. Collocated with this trough is an isentropic potential vorticity filament that is the locus of a thermally indirect circulation central to warming and associated thickness increases and ridging westward across the Great Basin. In response to this circulation, two subsynoptic wave breaks are triggered along the Pacific coast. The isentropic potential vorticity filament is coupled to the breaking waves and the interaction produces a subsynoptic low‐pressure center and a deep vortex aloft over the southeastern California desert. This coupling leads to advection of an elevated mixed layer over Point Conception the night before the record‐breaking heat that creates a coastally trapped low‐pressure area southwest of Los Angeles. The two low‐pressure centers create a low‐level pressure gradient and east‐southeasterly jet directed offshore over the Los Angeles Basin by sunrise on 27 September. This allows the advection of low‐level warm air from the inland terrain toward the coastally trapped disturbance and descending circulation resulting in record heating.

Using Splitters to Control Secondary Flow

This article elaborates the concept of splitter vanes in controlling secondary flow. Secondary flow vortices are formed by the rotation of vorticity filaments, located in the endwall boundary layers, as the filaments move through the passage. The connection between the number of stators and the secondary kinetic energy suggests that the only way to significantly reduce the mixing loss is to increase the number of blades in the row. The designs evaluated were produced with fast turn-around computational fluid dynamics (10 minutes per solution) and automated optimization techniques. Experimental tests showed that the theory was correct, and that by increasing vane count, the secondary kinetic energy was reduced by up to 80%.

Regional turbulence patterns driven by meso- and submesoscale processes in the Caribbean Sea

The surface ocean circulation in the Caribbean Sea is characterized by the interaction between anticyclonic eddies and the Caribbean Upwelling System (CUS). These interactions lead to instabilities that modulate the transfer of kinetic energy up- or down-cascade. The interaction of North Brazil Current rings with the islands leads to the formation of submesoscale vorticity filaments leeward of the Lesser Antilles, thus transferring kinetic energy from large to small scales. Within the Caribbean, the upper ocean dynamic ranges from large-scale currents to coastal upwelling filaments and allow the vertical exchange of physical properties and supply KE to larger scales. In this study, we use a regional model with different spatial resolutions (6, 3, and 1 km), focusing on the Guajira Peninsula and the Lesser Antilles in the Caribbean Sea, in order to evaluate the impact of submesoscale processes on the regional KE energy cascade. Ageostrophic velocities emerge as the Rossby number becomes O(1). As model resolution is increased submesoscale motions are more energetic, as seen by the flatter KE spectra when compared to the lower resolution run. KE injection at the large scales is greater in the Guajira region than in the others regions, being more effectively transferred to smaller scales, thus showing that submesoscale dynamics is key in modulating eddy kinetic energy and the energy cascade within the Caribbean Sea.

Detection of vortex coherent structures in superfluid turbulence

Filamentary regions of high vorticity irregularly form and disappear in the turbulent flows of classical fluids. We report an experimental comparative study of these so-called “coherent structures” in a classical vs. quantum fluid, using liquid helium with a superfluid fraction varied from 0% up to 83%. The low-pressure core of the vorticity filaments is detected by pressure probes located on the sidewall of a 78-cm-diameter von Kármán cell driven up to record turbulent intensity . The statistics of occurrence, magnitude and relative distribution of the filaments in a classical fluid are found indistinguishable from their superfluid counterpart, namely the bundles of quantized vortex lines. This suggests that the internal structure of vortex filaments, as well as their dissipative properties have a negligible impact on their macroscopic dynamics, such as lifetime and intermittent properties.

Vorticity filaments beneath regular turbulent flow

Two-dimensional vorticity flow fields created in the wake of a plunging breaker were investigated for regular turbulent flow at a Reynolds number of 30 000. Velocity flow fields obtained from an earlier study that had employed digital particle image velocimetry, were analysed to determine vorticity shedding patterns and the interactions between the vorticity filaments as flow progressed. Central difference approximations were applied to the velocity fields to determine vorticity at each point in the field. Most of the strong instantaneous vorticity observed in the flow field was in the form of filaments. A hierarchy of filaments of different lengths were observed, with the longest being as long as the height of the wave used. During the early phases of the flow, instantaneous vorticity tended to organise into thin filaments of counter-rotating pairs. Eventually, the co-rotating vorticity filaments coalesced and ultimately merged in the turbulent flow as flow progressed, while counter-rotating vorticity filaments were cancelled by viscous dissipation. The results suggested that filaments travel more slowly than the wave velocity and drifted towards the bed as they became elongated, and the number of filaments remaining in the flow were observed to decrease as flow progressed. Whereas phase-resolved instantaneous vorticity results showed pairs of counter-rotating vorticity filaments near the crest, the phase-averaged vorticity description of flow fields showed a dominant primary positive vorticity filament around the shear boundary layer.

Experimental study of free-stream turbulence induced transition in an adverse pressure gradient

Results from Particle Image Velocimetry (PIV) investigations have been discussed in order to characterize the dynamics driving the transition process in a strong adverse pressure gradient condition exposed to high Free Stream Turbulence Intensity (FSTI) level. Measurements have been carried out in the suction side boundary layer of a low pressure turbine cascade. Two orthogonal planes are analyzed in order to study both lift-up mechanisms of low speed streaks (in the wall-normal plane) as well as instability mechanisms (in the wall-parallel plane) leading to the breakdown of streaks, thus transition. Proper Orthogonal Decomposition (POD) has been used to provide the reconstruction of the PIV data highlighting the instability motions as well as the occurrence of wall-normal oriented vortical filaments growing on the flanks of the streaks during their breakdown process. The dynamics characterizing the transition process in this strong adverse pressure gradient condition has been discussed in detail and analogies with recent models developed for flat plate are highlighted. The main streak dimensions (e.g. the spacing and wavelength during breakdown) are also compared with flat plate data reported in the literature. Once made dimensionless with the local boundary layer displacement thickness, the streak dimensions observed in the present case agree well with flat plate ones, making evident the self-similarity properties of the streaky structures irrespective of the strong adverse pressure gradient condition.

On the link between martian total ozone and potential vorticity

We demonstrate for the first time that total ozone in the martian atmosphere is highly correlated with the dynamical tracer, potential vorticity, under certain conditions. The degree of correlation is investigated using a Mars global circulation model including a photochemical model. Potential vorticity is the quantity of choice to explore the dynamical nature of polar vortices because it contains information on winds and temperature in a single scalar variable. The correlation is found to display a distinct seasonal variation, with a strong positive correlation in both northern and southern winter at poleward latitudes in the northern and southern hemisphere respectively.The identified strong correlation implies variations in polar total ozone during winter are predominantly controlled by dynamical processes in these spatio-temporal regions. The weak correlation in northern and southern summer is due to the dominance of photochemical reactions resulting from extended exposure to sunlight. The total ozone/potential vorticity correlation is slightly weaker in southern winter due to topographical variations and the preference for ozone to accumulate in Hellas basin. In northern winter, total ozone can be used to track the polar vortex edge.The ozone/potential vorticity ratio is calculated for both northern and southern winter on Mars for the first time. Using the strong correlation in total ozone and potential vorticity in northern winter inside the polar vortex, it is shown that potential vorticity can be used as a proxy to deduce the distribution of total ozone where satellites cannot observe for the majority of northern winter. Where total ozone observations are available on the fringes of northern winter at poleward latitudes, the strong relationship of total ozone and potential vorticity implies that total ozone anomalies in the surf zone of the northern polar vortex can potentially be used to determine the origin of potential vorticity filaments.

Characterizing storm water dispersion and dilution from small coastal streams

AbstractCharacterizing the dispersion and dilution of storm water from small coastal creeks is important for understanding the importance of land‐derived subsidies to nearby ecosystems and the management of anthropogenic pollutants. In Southern California, creek runoff is episodic, intense, and short‐lived while the plumes are buoyant, all of which make the field sampling of freshwater plumes challenging. Numerical modeling offers a viable way to characterize these systems. The dilution and dispersion of freshwater from two creeks that discharge into the Santa Barbara Channel, California is investigated using Regional Ocean Modeling System (ROMS) simulations with a horizontal resolution of 100 m. Tight coupling is found among precipitation, hydrologic discharge, wind forcing, and submesoscale flow structures which all contribute to plume evolution. During flooding, plumes are narrow and attached to the coast, due to downwelling/onshore wind forcing and intense vorticity filaments lying parallel to the shelf. As the storm passes, the winds typically shift to offshore/upwelling favorable conditions and the plume is advected offshore which enhances its dilution. Plumes reach the bottom nearshore while they form thin layers a few meters thick offshore. Dilution field of passive tracers released with the runoff is strongly anisotropic with stronger cross‐shelf gradients than along‐shelf. Dispersion analysis of statistical moments of the passive tracer distribution results in scale‐dependent diffusivities consistent with the particle‐pair analysis of Romero et al. (). Model validation, the roles of submesoscale processes, and wind forcing on plume evolution and application to ecological issues and marine resource management are discussed.

Fast descent routes from within or near the stratosphere to the surface at Fukuoka, Japan, studied using <sup>7</sup>Be measurements and trajectory calculations

Abstract. By using high concentrations of 7Be as an indicator, we clarify fast descent routes from within or near the stratosphere to Earth's surface, with the study site being in Fukuoka, Japan. Most routes arise from high latitudes through the following processes. First, the descent associated with a tropopause fold occurs, followed by southward movement with slow descent at the rear side of a strong trough. Because this motion occurs along an isentropic surface, the descending air parcels nearly conserve the potential temperature. As an extension, a strong descent associated with a sharp drop in the isentropic-surface height occurs at the southern edge of the trough; this transports air parcels to low altitudes. This process involves irreversible phenomena such as filamentation and cutoff of potential vorticity. Finally, upon meeting appropriate near-surface disturbances, parcels at low altitudes are transported to Earth's surface.In some cases, parcels descend within midlatitudes. In such routes, because the potential temperature is much higher at high altitudes than at low altitudes, descent with conservation of the potential temperature is impossible, and the potential temperature decreases along the trajectories through mixing.The prevalence of the high-latitude route is explained as follows. In the midlatitude route, because parcels at high and relatively low altitudes mix, the high concentrations of 7Be included in high-altitude parcels are difficult to maintain. Therefore, for parcels to arrive at low altitudes in the midlatitude while maintaining high concentrations of 7Be, i.e., conserving the potential temperature, their area of origin should be high altitudes in high latitudes where the potential temperature is almost the same as that in the arrival area.In spring, tropopause folds are frequent in high latitudes, disturbances in the southward transport of parcels are strong, and disturbances occur by which parcels descend to the surface. Therefore, high concentrations of 7Be occur most frequently in spring.

Submesoscale currents in the northern Gulf of Mexico: Deep phenomena and dispersion over the continental slope

This study examines the mesoscale and submesoscale circulations along the continental slope in the northern Gulf of Mexico at depths greater than 1000m. The investigation is performed using a regional model run at two horizontal grid resolutions, 5km and 1.6km, over a 3year period, from January 2010 to December 2012.Ageostrophic submesoscale eddies and vorticity filaments populate the continental slope, and they are stronger and more abundant in the simulation at higher resolution, as to be expected. They are formed from horizontal shear layers at the edges of highly intermittent, bottom-intensified, along-slope boundary currents and in the cores of those currents where they are confined to steep slopes. Two different flow regimes are identified. The first applies to the De Soto Canyon that is characterized by weak mean currents and, in the high-resolution run, by intense but few submesoscale eddies that form near preferentially along the Florida continental slope. The second is found in the remainder of the domain, where the mean currents are stronger and the circulation is highly variable in both space and time, and the vorticity field is populated, in the high-resolution case, by numerous vorticity filaments and short-lived eddies.Lagrangian tracers are deployed at different times along the continental shelf below 1000m depth to quantify the impact of the submesoscale currents on transport and mixing. The modeled absolute dispersion is, on average, independent of horizontal resolution, while mixing, quantified by finite-size Lyapunov exponents and vertical relative dispersion, increases when submesoscale processes are present. Dispersion in the De Soto Canyon is smaller than in the rest of the model domain and less affected by resolution. This is further confirmed comparing the evolution of passive dye fields deployed in De Soto Canyon near the Macondo Prospect, where the Deepwater Horizon rig exploded in 2010, and at the largest known natural hydrocarbon seep in the northern Gulf, known as GC600, located a few hundred kilometers to the west of the rig wellhead.

External turbulence-induced axial flow and instability in a vortex

External turbulence-induced axial flow in an incompressible, normal-mode stable Lamb–Oseen (two-dimensional) vortex column is studied via direct numerical simulations of the Navier–Stokes equations. Azimuthally oriented vorticity filaments, formed from external turbulence, advect radially towards or away from the vortex axis (depending on the filament’s swirl direction), resulting in a net induced axial flow in the vortex core; axial flow increases with increasing vortex Reynolds number ($Re=$ vortex circulation/viscosity). This contrasts the viscous mechanism for axial flow generation downstream of a lifting body, wherein an axial pressure gradient is produced by viscous diffusion of the swirl (Batchelor, J. Fluid Mech., vol. 20, 1964, pp. 645–658). Analysis of the self-induced motion of an arbitrarily curved external filament shows that any non-axisymmetric filament undergoes radial advection. We then studied the evolution of a vortex column starting with an imposed optimal transient growth perturbation. For a range of Re values, axial flow develops and initially grows as (time)$^{5/2}$ before decreasing after two turnover times; for $Re=10\,000$ – the highest computationally achievable – axial flow at late times becomes sufficiently strong to induce vortex instability. Contrary to a prior claim of a parent–offspring mechanism at the outer edge of the core, vorticity tilting within the core by axial flow is the underlying mechanism producing energy growth. Thus, external perturbations in practical flows (at $Re\sim 10^{7}$) produce destabilizing axial flow, possibly leading to the sought-after vortex breakup.

$$1/f^{\alpha }$$ 1 / f α Low Frequency Fluctuations in Turbulent Flows

We report the experimental observation of low frequency fluctuations with a spectrum varying as \(1/f^{\alpha }\) in three different turbulent flow configurations: the large scale velocity driven by a two-dimensional turbulent flow, the magnetic field generated by a turbulent swirling flow of liquid sodium and the pressure fluctuations due to vorticity filaments in a swirling flow. For these three systems, \(1/f^{\alpha }\) noise is shown to result from the dynamics of coherent structures that display transitions between a small number of states. The interevent duration is distributed as a power law. The exponent of this power law and the nature of the dynamics (transition between symmetric states or asymmetric ones) select the exponent \(\alpha \) of the \(1/f^{\alpha }\) fluctuations.

Examining the Roles of the Easterly Wave Critical Layer and Vorticity Accretion during the Tropical Cyclogenesis of Hurricane Sandy*

Abstract The tropical cyclogenesis sequence of Hurricane Sandy is examined. It is shown that genesis occurs within a recirculating Kelvin cat’s-eye flow of a westward-propagating tropical wave. The cat’s-eye flow is able to provide a protective environment for the mesoscale vortex to grow and is characterized by gradual column moistening and increased areal coverage of deep cumulus convection. These findings are generally consistent with a recently proposed tropical cyclogenesis sequence referred to as the “marsupial paradigm.” Sandy’s cyclogenesis provides a useful illustration of the marsupial paradigm within a partially open recirculating region, with the opening located south of the pouch center. It is suggested that the opening acts to enhance the genesis process because it is adjacent to an environment characterized by warm, moist air, conditions favorable for tropical cyclogenesis. From a dynamical perspective, accretion of low-level cyclonic vorticity filaments into the developing vortex from several sources (the South American convergence zone, an easterly wave located west of the pre-Sandy wave, and cyclonic vorticity generated along Hispaniola) is documented. Organization and growth of the nascent storm is enhanced by this accretion of cyclonic vorticity. A Lagrangian trajectory analysis is used to assess potential contributions to Sandy’s spinup from a Caribbean gyre and the easterly wave that formed Hurricane Tony. This analysis indicates that these features are outside of the Lagrangian flow boundaries that define the pre-Sandy wave and do not directly contribute to spinup of the vortex. Finally, the effectiveness of forecasts from the U.S. and European operational numerical weather prediction models is discussed for this case.

Experimental study on the role of spanwise vorticity and vortex filaments in the outer region of open-channel flow

ABSTRACTThe dynamic importance of spanwise vorticity and vortex filaments has been assessed in steady, uniform open-channel flows by means of particle image velocimetry. By expressing the net force due to Reynolds’ turbulent shear stress, , in terms of two velocity–vorticity correlations, and , the results show that both spanwise vorticity and the portion of it that is due to spanwise filaments make important contributions to the net force and hence the shape of the mean flow profile. Using the swirling strength to identify spanwise vortex filaments, it is found that they account for about 45% of , the remainder coming from non-filamentary spanwise vorticity, i.e. shear. The mechanism underlying this contribution is the movement of vortex filaments away from the wall. The contribution of spanwise vortex filaments to the Reynolds stress is small because they occupy a small fraction of the flow. The contribution of the induced motion of the spanwise vortex filaments is significant.

A hidden life of Peregrine's soliton: Rouge waves in the oceanic depths

Although the Peregrine-type solutions of the nonlinear Schrödinger (NLS) equation have long been associated mainly with the infamous "rouge waves" on the surface of the ocean, they might have a much more interesting role in the oceanic depths; in this paper we show that these solutions play an important role in the evolution of the intrathermocline eddies, also known as the "oceanic lenses". In particular, we show that the collapse of a lens is determined by the particular generalization of the Peregrine soliton — the so-called exultons — of the NLS equation. In addition, we introduce a new mathematical method of construction of a vortical filament (a frontal zone of a lens) from a known one by the Darboux transformation.

Large fluctuations of the nonlinearities in isotropic turbulence. Anisotropic filtering analysis

Using a Navier–Stokes isotropic turbulent field numerically simulated in a box with a discretization of 10243 (Biferale et al., 2005), we show that the probability of having a stretching–tilting larger than a few times the local enstrophy is low. By using an anisotropic kind of filter in the Fourier space, where wavenumbers that have at least one component below a threshold or inside a range are removed, we analyze these survival statistics when the large, the small inertial or the small inertial and dissipation scales are filtered out. By considering a flow obtained by randomizing the phases of the Fourier modes, and applying our filtering techniques, we identified clearly the properties attributable to turbulence.It can be observed that, in the unfiltered isotropic Navier–Stokes field, the probability of the ratio (|ω⋅∇U|/|ω|2) being higher than a given threshold is higher than in the fields where the large scales were filtered out. At the same time, it is lower than in the fields where the small inertial and dissipation range of scales is filtered out. This is basically due to the suppression of compact structures in the ranges that have been filtered in different ways. The partial removal of the background of filaments and sheets does not have a first order effect on these statistics. These results are discussed in the light of a hypothesized relation between vortical filaments, sheets and blobs in physical space and in Fourier space. The study in fact can be viewed as a kind of test for this idea and tries to highlight its limits. We conclude that a qualitative relation in physical space and in Fourier space can be supposed to exist for blobs only. That is for the near isotropic structures which are sufficiently described by a single spatial scale and do not suffer from the disambiguation problem as filaments and sheets do.Information is also given on the filtering effect on statistics concerning the inclination of the strain rate tensor eigenvectors with respect to vorticity. In all filtered ranges, eigenvector 2 reduces its alignment, while eigenvector 3 reduces its misalignment. All filters increase the gap between the most extensional eigenvalue 〈λ1〉 and the intermediate one 〈λ2〉 and the gap between this last 〈λ2〉 and the contractile eigenvalue 〈λ3〉. When the large scales are missing, the modulus of the eigenvalue 1 becomes nearly equal to that of the eigenvalue 3, similarly to the modulus of the associated components of the enstrophy production.