22) Augmented Four-Dimensional Mesosphere and Lower Thermosphere Wind Field Reconstruction via the Physics-Informed Machine Learning Approach HYPER
J.M. Urco, F. Feraco, J.L. Chau, R. Marino
JGR: Machine Learning and Computation, Vol. 1(3), August 2024
The mesosphere and lower thermosphere (MLT) is a fluid framework whose multiscale dynamics is determined by a superposition of non-linear processes and by the interplay of gravity waves and turbulent motions. A thorough comprehension of this atmospheric region requires substantial observational infrastructure, needed to resolve and disentangle its complex dynamics. State-of-the-art observational methods struggle to accurately capture mesoscale dynamics due to the inherent difficulty to perform observations at MLT altitudes. A majority of the observational methods rely on assumptions such as homogeneity, smoothness of the prognostic fields, or zero vertical wind velocities, which may not hold in the upper atmosphere at the mesoscales. In this study, we introduce a novel machine learning-based approach HYPER (HYdrodynamic Point-wise Environment Reconstructor), designed to characterize MLT dynamics. HYPER utilizes a physics-informed neural network to project sparse Doppler meteor detections into four-dimensional time-series arrays containing the Cartesian components of the velocity field. This method combines meteor radar observations with the physics prescribed by the Navier-Stokes equations. The validation of HYPER was conducted through a series of benchmarks on numerical data and the application of our algorithm on actual meteor radar observations, all of which yielded realistic approximations of the reconstructed physical fields. This innovative approach represents a significant step toward an accurate characterization of the MLT dynamics, overcoming the limitations of existing methods, and providing valuable insights into the behavior of this poorly accessible region of the atmosphere.
21) Lagrangian Irreversibility and Energy Exchanges in Rotating-Stratified Turbulent Flows
S. Gallon, A. Sozza, F. Feraco, R. Marino, A. Pumir
Physical Review Letters, 133 024101, July 2024
Turbulence in stratified and rotating turbulent flows is characterized by an interplay between waves and eddies, resulting in continuous exchanges between potential and kinetic energy. Here, we study how these processes affect the turbulent energy cascade from large to small scales, which manifests itself by an irreversible evolution of the relative kinetic energy between two tracer particles. We find that when \(𝑟_0\), the separation between particles, is below a characteristic length ℓ𝑡, potential energy is on average transferred to kinetic energy, reducing time irreversibility, and conversely when \(𝑟_0>ℓ_𝑡\). Our Letter reveals that the scale \(ℓ_𝑡\) coincides with the buoyancy length scale \(𝐿_𝐵\) over a broad range of configurations until a transition to a wave-dominated regime is reached.
20) Our Vision for JGR: Machine Learning and Computation
E. Camporeale, R. Marino, the Editorial Board
JGR: Machine Learning and Computation, e2024JH000184, April 2024
This editorial introduces the inaugural issue of the Journal of Geophysical Research: Machine Learning and Computation to the scientific community, elucidating the motivations and vision behind its establishment. The landscape of computational tools for geoscientists has undergone a rapid transformation in the last decade, akin to a new scientific revolution challenging the traditional scientific method. The paradigm shift emphasizes the integration of data‐driven methods and the possibility of predicting and/or reproducing the evolution of natural phenomena with computers as the fourth pillar of scientific discovery, sparking debates on trustworthiness, and ethical implications. The data science revolution is fueled by the convergence of advancements, including the big‐data revolution, GPU market expansion, and significant investments in Artificial Intelligence and high performance computing by both institutional and private players. This transformation has given rise to a trans‐disciplinary community that has investigated a wide range of questions under the lens of machine learning (ML) approaches and has generally advanced the field of computational methods within the broader geosciences community, the core of the American Geophysical Union (AGU) membership. Responding to an unmet demand in the existing worldwide editorial offer, the Journal of Geophysical Research: Machine Learning and Computation aims to serve as an intellectual crucible, fostering collaborations across multiple geophysical disciplines and data scientists. The journal welcomes papers with strong methodological developments that allow for geoscience advancements grounded in specific computational and data‐driven methods, leveraging ML as well as innovative computational strategies, and leading to breakthrough discoveries and original scientific outcomes. Authors are encouraged to balance succinctness in introducing methods with a thorough exploration of the novelty of the work proposed and its future applications placing special emphasis on the connection between the data science approach and the scientific outcome, considering a broad readership. Emphasis on result reproducibility aligns with AGU guidance, inviting active participation from the community in shaping geophysical research in the era of machine learning and computation.
19) Nonlocal contributions to the turbulent cascade in magnetohydrodynamic plasmas
J. Friedrich, M. Wilbert, R. Marino
Phys. Review E., 109, 045208, April 2024
We present evidence for nonlocal contributions to the turbulent energy cascade in magnetohydrodynamic (MHD) plasmas. Therefore, we revisit a well-known result derived directly from the MHD equations, i.e., the Politano & Pouquet (P&P) law for the transfer of kinetic and magnetic energy in scale. We propose adding a term that accounts for nonlocal transfer and represents the influence of fluctuations from large scales due to the Alfv’en effect. Supported by direct numerical simulations of homogeneous and isotropic MHD turbulence, we verify that in some plasma configurations, neglecting the additional nonlocal term might consistently overestimate energy dissipation rates and, thus, the contributions of turbulent energy dissipation potentially affecting solar wind heating; a central puzzle in space plasma physics that motivates the present work.
18) Large-scale self-organization in dry turbulent atmospheres
A. Alexakis, R. Marino, P.D. Mininni, A. Van Kan, R. Foldes, F. Feraco
Science Vol. 383, Issue 6686, 1105-1109, March 2024
How turbulent convective fluctuations organize to form larger-scale structures in planetary atmospheres remains a question that eludes quantitative answers. The assumption that this process is the result of an inverse cascade was suggested half a century ago in two-dimensional fluids, but its applicability to atmospheric and oceanic flows remains heavily debated, hampering our understanding of the energy balance in planetary systems. We show using direct numerical simulations with spatial resolutions of 122882 × 384 points that rotating and stratified flows can support a bidirectional cascade of energy, in three dimensions, with a ratio of Rossby to Froude numbers comparable to that of Earth’s atmosphere. Our results establish that, in dry atmospheres, spontaneous order can arise through an inverse cascade to the largest spatial scales.
17) Low-dimensional Representation of Intermittent Geophysical Turbulence with High-order Statistics-informed Neural Networks (H-SiNN)
R. Foldes, E. Camporeale, R. Marino
Physics of Fluids 36, 026607, February 2024
We present a novel machine learning approach to reduce the dimensionality of state variables in stratified turbulent flows governed by the Navier-Stokes equations in the Boussinesq approximation. The aim of the new method is to perform an accurate reconstruction of the temperature and the three-dimensional velocity of geophysical turbulent flows developing non-homogeneities, starting from a low-dimensional representation in latent space, yet conserving important information about non-Gaussian structures captured by high-order moments of distributions. To achieve this goal we modify the standard Convolutional Autoencoder (CAE) by implementing a customized loss function that enforces the accuracy of the reconstructed high order statistical moments. We present results for compression coefficients up to 16 demonstrating how the proposed method is more efficient than a standard CAE in performing dimensionality reduction of simulations of stratified geophysical flows characterized by intermittent phenomena, as observed in the atmosphere and the oceans.
16) Intermittency Scaling for Mixing and Dissipation in Rotating Stratified Turbulence at the Edge of Instability
A. Pouquet, D. Rosenberg, R. Marino, P.D. Mininni
Atmosphere 14(9), 1375
Many issues pioneered by Jackson Herring deal with how nonlinear interactions shape atmospheric dynamics. In this context, we analyze new direct numerical simulations of rotating stratified flows with a large-scale forcing, which is either random or quasi-geostrophic (QG). Runs were performed at a moderate Reynolds number \(Re\) and up to 1646 turn-over times in one case. We found intermittent fluctuations of the vertical velocity w and temperature \( \theta \) in a narrow domain of parameters as for decaying flows. Preliminary results indicate that parabolic relations between normalized third- and fourth-order moments of the buoyancy flux \(\propto \langle w\theta \rangle \) and of the energy dissipation emerge in this domain, including for passive and active scalars, with or without rotation. These are reminiscent of (but not identical to) previous findings for other variables and systems such as oceanic and atmospheric flows, climate re-analysis data, fusion plasmas, the Solar Wind, or galaxies. For QG forcing, sharp scaling transitions take place once the Ozmidov length scale \(\ell_{Oz}\) is resolved—\(\ell_{Oz}\) being the scale after which a turbulent Kolmogorov energy spectrum likely recovers at high \(Re\).
15) Helios 2 observations of solar wind turbulence decay in the inner heliosphere
L. Sorriso-Valvo, R. Marino, R. Foldes, E. Lévêque, R. D’Amicis, R. Bruno, D. Telloni, E. Yordanova
Astronomy & Astrophysics, Vol. 672, A13 (2023)
Aims. A linear scaling of the mixed third-order moment of the magnetohydrodynamic (MHD) fluctuations is used to estimate the energy transfer rate of the turbulent cascade in the expanding solar wind.
Methods. In 1976, the Helios 2 spacecraft measured three samples of fast solar wind originating from the same coronal hole, at different distances from the Sun. Along with the adjacent slow solar wind streams, these intervals represent a unique database for studying the radial evolution of turbulence in samples of undisturbed solar wind. A set of direct numerical simulations of the MHD equations performed with the Lattice-Boltzmann code FLAME was also used for interpretation.
Results. We show that the turbulence energy transfer rate decays approximately as a power law of the distance and that both the amplitude and decay law correspond to the observed radial temperature profile in the fast wind case. Results from MHD numerical simulations of decaying MHD turbulence show a similar trend for the total dissipation, suggesting an interpretation of the observed dynamics in terms of decaying turbulence and that multi-spacecraft studies of the solar wind radial evolution may help clarify the nature of the evolution of the turbulent fluctuations in the ecliptic solar wind.
14) Efficient kinetic Lattice Boltzmann simulation of three-dimensional Hall-MHD turbulence
R. Foldes, E. Lévêque, R. Marino, E. Pietroapolo, A. De Rosis, D. Telloni, F. Feraco
Journal of Plasma Physics, Vol. 89 (4) (2023)
Simulating plasmas in the Hall-magnetohydrodynamics (Hall-MHD) regime represents a valuable approach for the investigation of complex nonlinear dynamics developing in astrophysical frameworks and fusion machines. The Hall electric field is computationally very challenging as it involves the integration of an additional term, proportional to 𝛁×((𝛁×𝐵)×𝐵), in Faraday’s induction law. The latter feeds back on the magnetic field 𝐵 at small scales (between the ion and electron inertial scales), requiring very high resolutions in both space and time to properly describe its dynamics. The computational advantage provided by the kinetic lattice Boltzmann (LB) approach is exploited here to develop a new code, the fast lattice-Boltzmann algorithm for MHD experiments (FLAME). The flame code integrates the plasma dynamics in lattice units coupling two kinetic schemes, one for the fluid protons (including the Lorentz force), the other to solve the induction equation describing the evolution of the magnetic field. Here, the newly developed algorithm is tested against an analytical wave-solution of the dissipative Hall-MHD equations, pointing out its stability and second-order convergence, over a wide range of the control parameters. Spectral properties of the simulated plasma are finally compared with those obtained from numerical solutions from the well-established pseudo-spectral code ghost. Furthermore, the LB simulations we present, varying the Hall parameter, highlight the transition from the MHD to the Hall-MHD regime, in excellent agreement with the magnetic field spectra measured in the solar wind.
13) Scaling laws for the energy transfer in space plasma turbulence
R. Marino, L. Sorriso-Valvo
Physics Reports, Vol. 1006, pp.1-144 (2023)
One characteristic trait of space plasmas is the multi-scale dynamics resulting from non-linear transfers and conversions of various forms of energy. Routinely evidenced in a range from the large-scale solar structures down to the characteristic scales of ions and electrons, turbulence is a major cross-scale energy transfer mechanism in space plasmas. At intermediate scales, the fate of the energy in the outer space is mainly determined by the interplay of turbulent motions and propagating waves. More mechanisms are advocated to account for the transfer and conversion of energy, including magnetic reconnection, emission of radiation and particle energization, all contributing to make the dynamical state of solar and heliospheric plasmas difficult to predict. The characterization of the energy transfer in space plasmas benefited from numerous robotic missions. However, together with breakthrough technologies, novel theoretical developments and methodologies for the analysis of data played a crucial role in advancing our understanding of how energy is transferred across the scales in the space. In recent decades, several scaling laws were obtained providing effective ways to model the energy flux in turbulent plasmas. Under certain assumptions, these relations enabled to utilize reduced knowledge (in terms of degrees of freedom) of the fields from spacecraft observations to obtain direct estimates of the energy transfer rates (and not only) in the interplanetary space, also in the proximity of the Sun and planets. Starting from the first third-order exact law for the magnetohydrodynamics by Politano and Pouquet (1998), we present a detailed review of the main scaling laws for the energy transfer in plasma turbulence and their application, presenting theoretical, numerical and observational milestones of what has become one of the main approaches for the characterization of turbulent dynamics and energetics in space plasmas.
12) Effect of rotation on mixing efficiency in homogeneous stratified turbulence using unforced direct numerical simulations
M. Klema, S.K. Venayagamoorthy, A. Pouquet, D. Rosenberg, R. Marino
Environmental Fluid Mechanics, May 2022
Diapycnal (irreversible) mixing is analyzed using thirty direct numerical simulations (at \(1024^3\) resolution) of homogeneous rotating stratified turbulence (RST) in the absence of imposed shear or forcing. The influence of varied rotation and stratification rates on the energetics (in particular the dissipation rates of kinetic and potential energies) is presented. Data is also analyzed within a new parametric framework, using the turbulent Froude and Rossby numbers \(Fr_t = 𝜖∕Nk\), \(Ro_t = 𝜖∕fk\) , where k is the turbulent kinetic energy, 𝜖 its rate of dissipation, N the buoyancy frequency and f the Coriolis parameter. This framework is used to illustrate relative magnitudes of the stratification and rotation in geophysical flows and provide a useful tool for explicating the relationship between \(Fr_t\) and Rot as relevant dynamic parameters in the geophysical setting. Results indicate that unforced rotation does not impact the magnitude of the irreversible mixing coefficient ( \(Γ = 𝜖_p∕𝜖\) ) when compared to results without rotation, where \(𝜖_p\) is the rate of potential energy dissipation. Moreover, it is shown that the recent scaling laws for mixing efficiency in stably stratified turbulence in the absence of rotation, as exemplified in Garanaik & Venayagamoorthy (J. Fluid Mech. 867, 2019, pp. 323-333), are applicable as well for homogeneous and decaying RST. Results also highlight the ambiguity of the ratio N/f as a control parameter for the classification of small-scale RST, and thus for evaluating diapycnal mixing.
11) Direct Observational Evidence of an Oceanic Dual Kinetic Energy Cascade
D. Balwada, J.H. Xie, R. Marino, F. Feraco
Science Advances Vol. 8 (41)
The Ocean’s turbulent energy cycle has a paradox; large-scale eddies under the control of Earth’s rotation primarily transfer kinetic energy (KE) to larger scales via an inverse cascade, while a transfer to smaller scales is needed to accomplish dissipation. It has been argued, using numerical simulations, that fronts, waves and other turbulent structures can produce a forward cascade of KE toward dissipation scales. However, this forward cascade and its coexistence with known inverse cascade were not confirmed in observations. Here we present the first evidence of a dual KE cascade in the Ocean by analyzing velocity measurements from surface drifters released in the Gulf of Mexico. Our results show that KE is injected at two dominant scales and transferred to both large and small scales, with the downscale flux dominating at scales smaller than ~1-10km. The cascade rates are modulated seasonally, with stronger KE injection and forward transfer during winter.
10) Frequency spectra of horizontal winds in the mesosphere and lower thermosphere region from multistatic specular meteor radar observations during the SIMONe 2018 campaign
H. Charuvil Asokan, J. L. Chau, R. Marino, J. Vierinen, F. Vargas, J. M. Urco, M. Clahsen, C. Jacobi
, Vol. 74(1), May 2022
In recent years, multistatic specular meteor radars (SMRs) have been introduced to study the Mesosphere and Lower Thermosphere (MLT) dynamics with increasing spatial and temporal resolution. In this paper, frequency spectra of MLT horizontal winds are explored through observations from a campaign using the SIMONe (Spread-spectrum Interferometric Multistatic meteor radar Observing Network) approach conducted in northern Germany in 2018 (hereafter SIMONe 2018). The seven-day SIMONe 2018 comprised of fourteen multistatic SMR links and allows to build a substantial database of specular meteor trail events, collecting more than one hundred thousand detections per day within a geographic area of \(\sim\) 500 km \(\times\) 500 km. We have implemented two methods to obtain the frequency spectra of the horizontal wind components: (1) Mean Wind Estimation (MWE) and (2) Wind field Correlation Function Inversion (WCFI), which utilizes the mean and the covariances of the line of sight velocities, respectively. Monte Carlo simulations of a gravity wave spectral model were implemented to validate and compare both methods. The simulation analyses suggest that the WCFI helps to capture the energy of smaller-scale wind fluctuations than those capture with MWE. Characterization of the spectral slope of the horizontal wind at different MLT altitudes has been conducted on the SIMONe 2018, and it provides evidence that gravity waves with periods smaller than seven hours and greater than two hours dominate with horizontal structures significantly larger than 500 km. These waves might be associated with secondary gravity waves during this observational campaign. In the future, these analyses can be extended to understand the significance of small-scale fluctuations in the MLT, which were not possible with conventional MWE methods.
9) Sudden Depletion of Alfvénic Turbulence in the Rarefaction Region of Corotating Solar Wind High Speed Streams at 1 AU: Possible Solar Origin?
G. Carnevale, R. Bruno, R. Marino, E. Pietropaolo, J.M. Raines
Astronomy & Astrophysics, Vol. 661, A64 (2022)
A canonical description of a corotating solar wind high speed stream, in terms of velocity profile, would indicate three main regions:a stream interface or corotating interaction region characterized by a rapid flow speed increase and by compressive phenomena due to dynamical interaction between the fast wind flow and the slower ambient plasma;a fast wind plateau characterized by weak compressive phenomena and large amplitude fluctuations with a dominant Alfvénic character;a rarefaction region characterized by a decreasing trend of the flow speed and wind fluctuations dramatically reduced in amplitude and Alfvénic character, followed by the slow ambient wind. Interesting enough, in some cases the region where the severe reduction of these fluctuations takes place is remarkably short in time, of the order of minutes, and located at the flow velocity knee separating the fast wind plateau from the rarefaction region. The aim of this work is to investigate which are the physical mechanisms that might be at the origin of this phenomenon. We firstly looked for the presence of any tangential discontinuity which might inhibit the propagation of Alfvénic fluctuations from fast wind region to rarefaction region. The absence of a clear evidence for the presence of this discontinuity between these two regions led us to proceed with ion composition analysis for the corresponding solar wind, looking for any abrupt variation in minor ions parameters (as tracers of the source region) which might be linked to the phenomenon observed in the wind fluctuations. In the lack of a positive feedback from this analysis, we finally propose a mechanism based on interchange reconnection experienced by the field lines at the base of the corona, within the region separating the open field lines of the coronal hole, source of the fast wind, from the surrounding regions mainly characterized by closed field lines.
8) Turbulence Generation by Large-Scale Extreme Vertical Drafts and the Modulation of Local Energy Dissipation in Stably Stratified Geophysical Flows
R. Marino, F. Feraco, L. Primavera, A. Pumir, A. Pouquet, D. Rosenberg, P. Mininni
Physical Review Fluids, Vol. 7 (3), p. 033801 (2022)
We observe the emergence of strong vertical drafts in direct numerical simulations of the Boussinesq equations in a range of parameters of geophysical interest. These structures, which appear intermittently in space and time, generate turbulence and enhance kinetic and potential energy dissipation, providing an explanation for the observed variability of the local energy dissipation in the ocean and the modulation of its probability distribution function. We show how, due to the extreme drafts, in runs with Froude numbers observable in oceans, roughly 10% of the domain flow can account for up to 50% of the total volume dissipation, consistently with recent estimates based on oceanic models.
7) Validation of Multi-Static Meteor Radar Analysis using Modelled Mesospheric Dynamics: An Assessement of the Reliability of Gradients and Vertical Velocities
H. Charuvil Asokan, J. L. Chau, M. F. Larsen, J. F, Conte, R. Marino, J. Vierinen, G. Baumgarten, S. Borchert
Vol. 127(5), February 2022
A virtual meteor radar system based on the upper-atmosphere extension of the high-resolution ICOsahedral Non-hydrostatic general circulation model is constructed to validate multistatic specular meteor radar (SMR) analyses. The virtual radar system examines the validity of mean winds and gradients estimation techniques used in multistatic SMRs. The study is motivated by unexpected mean values and tide-like features recently observed in the vertical velocities estimated from multistatic SMRs at different latitudes in the mesosphere and lower thermosphere. The proposed analysis confirms multistatic SMR systems’ excellent capability to measure the horizontal mean wind components and gradient terms. It is also found that multistatic SMRs can estimate mean vertical winds if they have an amplitude greater than ±2 m/s. Due to the smoothing inherent to the model results, these results should be treated as lower bounds to the error incurred using real data. Hourly variability in vertical velocity estimates up to ±1–2 m/s in the observed vertical winds are due to contamination by small-scale horizontal structures in the horizontal winds.
6) Connecting Large-Scale Velocity and Temperature Bursts with Small-Scale Intermittency in Stratified Turbulence
F. Feraco, R. Marino, L. Primavera, A. Pumir, P.D. Mininni, D. Rosenberg, A. Pouquet, R. Foldes, E. Lévêque, E. Camporeale, S. Cerri, H. Charuvil Asokan, J.L. Chau, J.P. Bertoglio, P. Salizzoni, M. Marro
, September 2021
Non-Gaussian statistics of large-scale fields are routinely observed in data from atmospheric and oceanic campaigns and global models. Recent direct numerical simulations (DNSs) showed that large-scale intermittency in stably stratified flows is due to the emergence of sporadic, extreme events in the form of bursts in the vertical velocity and the temperature. This phenomenon results from the interplay between waves and turbulent motions, affecting mixing. We provide evidence of the enhancement of the classical small-scale (or internal) intermittency due to the emergence of large-scale drafts, connecting large- and small-scale bursts. To this aim we analyze a large set of DNSs of the stably stratified Boussinesq equations over a wide range of values of the Froude number (\(Fr\approx0.1-1\)). The variation of the buoyancy field kurtosis with \(Fr\) is similar to (though with smaller values than) the kurtosis of the vertical velocity, both showing a non-monotonic trend. We present a mechanism for the generation of extreme vertical drafts and vorticity enhancements which follows from the exact equations for field gradients.
5) Scalar Mixing in Homogeneous Isotropic Turbulence: A Numerical Study
M. Orsi, L. Soulhac, F. Feraco, M. Marro, D. Rosenberg, R. Marino, M. Boffadossi, P. Salizzoni
, March 2021
The understanding of the mechanics of turbulent dispersion is of primary importance in estimating the effects of mixing processes involved in a variety of events playing a significant role in our daily life. This motivates research on the characterization of statistics and the complex temporal evolution of passive scalars in turbulent flows. A key aspect of these studies is the modeling of the probability density function (PDF) of the passive scalar concentration and the identification of its link with the mixing properties. In order to investigate the dynamics of passive scalars as observed in nature and in laboratory experiments, we perform here direct numerical simulations of a passive tracer injected in the stationary phase of homogeneous isotropic turbulence flows in a setup mimicking the evolution of a fluid volume in the reference frame of the mean flow. In particular, we show how the gamma distribution proves to be a suitable model for the PDF of the passive scalar concentration and its temporal evolution in a turbulent flow throughout the different phases of the mixing process. Then, assuming a gamma distribution, we develop a simple mixing model by which we can estimate a mixing timescale, which regulates the decay rate of the intensity of the concentration fluctuations.
4) Radar Observation of Extreme Vertical Drafts in the Polar Summer Mesosphere
J.L. Chau, R. Marino, F. Feraco, J.M. Urco, G. Baumgarten, F.-J. Lübken, W.K. Hocking, C. Shult, T. Renkwitz, R. Latteck
Geophysical Research Letters Vol. 48(16), August 2021
The polar summer mesosphere is the Earth’s coldest region, allowing the formation of mesospheric ice clouds. These ice clouds produce strong polar mesospheric summer echoes (PMSE) that are used as tracers of mesospheric dynamics. Here, we report the first observations of extreme vertical drafts (\(\pm\)50 \(ms^{-1}\)) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles a solitary wave in a varicose mode, narrow along propagation (3–4 km) and elongated (> 10 km) transverse to propagation direction, with a relatively large vertical extent (~ 13 km). These spatial features are similar to previously observed mesospheric bores, but we observe only one crest with much larger vertical extent and higher vertical velocities.
3) Comparing turbulence in a Kelvin-Helmholtz instability region across the terrestrial magnetopause
P. Quijia, F. Fraternale, J.E. Stawarz, C.L. Vásconez, S. Perri, R. Marino, E. Yordanova, L. Sorriso-Valvo
Monthly Notices of the Royal Astronomical Society, Vol. 503 (4), p.4815 (2021)
The properties of turbulence observed within the plasma originating from the magnetosheath and the magnetospheric boundary layer, which have been entrained within vortices driven by the Kelvin–Helmholtz Instability (KHI), are compared. The goal of such a study is to determine similarities and differences between the two different regions. In particular, we study spectra, intermittency and the third-order moment scaling, as well as the distribution of a local energy transfer rate proxy. The analysis is performed using the Magnetospheric Multiscale data from a single satellite that crosses longitudinally the KHI. Two sets of regions, one set containing predominantly magnetosheath plasma and the other containing predominantly magnetospheric plasma, are analysed separately, thus allowing us to explore turbulence properties in two portions of very different plasma samples. Results show that the dynamics in the two regions is different, with the boundary layer plasma presenting a shallower spectra and larger energy transfer rate, indicating an early stage of turbulence. In both regions, the effect of the KHI is evidenced.
2) Local and Global Properties of Energy Transfer in Models of Plasma Turbulence
C.L. Vásconez, D. Perrone, R. Marino, D. Laveder, F. Valentini, S. Servidio, P. Mininni, L. Sorriso-Valvo
Journal of Plasma Physics Vol. 87(1), January 2021
The nature of the turbulent energy transfer rate is studied using direct numerical simulations of weakly collisional space plasmas. This is done comparing results obtained from hybrid Vlasov–Maxwell simulations of collisionless plasmas, Hall magnetohydrodynamics and Landau fluid models reproducing low-frequency kinetic effects, such as the Landau damping. In this turbulent scenario, estimates of the local and global scaling properties of different energy channels are obtained using a proxy of the local energy transfer. This approach provides information on the structure of energy fluxes, under the assumption that the turbulent cascade transfers most of the energy that is then dissipated at small scales by various kinetic processes in these kinds of plasmas.
1) Correlation between Buoyancy Flux, Dissipation and Potential Vorticity in Rotating Stratified Turbulence
D. Rosenberg, A. Pouquet, R. Marino
Atmosphere Vol. 12(2), January 2021
We study in this paper the correlation between the buoyancy flux, the efficiency of energy dissipation and the linear and nonlinear components of potential vorticity, PV, a point-wise invariant of the Boussinesq equations, contrasting the three identified regimes of rotating stratified turbulence, namely wave-dominated, wave–eddy interactions and eddy-dominated. After recalling some of the main novel features of these flows compared to homogeneous isotropic turbulence, we specifically analyze three direct numerical simulations in the absence of forcing and performed on grids of \(1024^3\) points, one in each of these physical regimes. We focus in particular on the link between the point-wise buoyancy flux and the amount of kinetic energy dissipation and of linear and nonlinear PV. For flows dominated by waves, we find that the highest joint probability is for minimal kinetic energy dissipation (compared to the buoyancy flux), low dissipation efficiency and low nonlinear PV, whereas for flows dominated by nonlinear eddies, the highest correlation between dissipation and buoyancy flux occurs for weak flux and high localized nonlinear PV. We also show that the nonlinear potential vorticity is strongly correlated with high dissipation efficiency in the turbulent regime, corresponding to intermittent events, as observed in the atmosphere and oceans.