Von Karman correlation similarity in solar wind magnetohydrodynamic turbulence

A major development underlying hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth, here extended empirically to plasma turbulence in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here, we analyze an ensemble of Elsässer autocorrelation functions computed from Advanced Composition Explorer data at 1 astronomical unit (AU), and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman's hypothesis applied to weakly compressive magnetohydrodynamic turbulence. This provides a firm empirical basis for employing the similarity decay hypothesis to the Elsässer correlations that represent the incompressive turbulence cascade. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.Fil: Roy, Sohom. University Of Delaware; Estados UnidosFil: Chhiber, R.. University Of Delaware; Estados UnidosFil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Ruiz, Maria Emilia. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Matthaeus, W .H.. University Of Delaware; Estados Unido

Statistics of Energy Dissipation rate at reconnection sites

Magnetic reconnection is considered to play a central role in dissipating turbulent energy in plasmas. Traditionally, the Ohmic dissipation measure ($\mathbf{j}.\mathbf{E}$) has been used to identify the dissipation region and calculate the dissipation rates in reconnection sites. However, recent works have shown that the pressure-strain rate may be a more appropriate measure of dissipation. We consider large-scale reconnection in the Earth\u27s magnetopause, small-scale reconnection in the Earth\u27s magnetosheath, and the electron-only reconnection sites recently observed by MMS in the magnetosheath. We carry out a statistical survey of the pressure-strain rates and the Ohmic dissipation measure at these different reconnection sites, in order to better understand the nature of energy conversion in reconnection

Quantifying gyrotropy of proton-electron heating in turbulent plasmas

An important aspect of energy dissipation in weakly collisional plasmas is that of energy partitioning between different species. Instead of identifying specific models for this preferential heating, here we adopt pressure-strain interaction to quantify the fraction of isotropic compressive, gyrotropic and nongyrotropic heating for each species. Analysis of kinetic turbulence simulations is complemented by analogous observational results from the Magnetosphere Multiscale mission. In assessing how the two species (i.e., ions and electrons) respond to different parts of the pressure-strain interaction, we find that the local compressive heating for electrons is stronger than that for ions. Concerning the incompressive heating, the gyrotropic contribution for electrons is dominant over the nongyrotropic contribution, while for ions the nongyrotropic-to-gyrotropic heating is enhanced. These characterizations apply also to the level of gyrotropy of the respective velocity distribution functions

Von Karman Correlation Similarity of the Turbulent Interplanetary Magnetic Field

A major development underlying much of hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth here extended empirically to magnetic field fluctuations in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here we analyze an ensemble of magnetic correlation functions computed from Advanced Composition Explorer data at 1 au, and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman's hypothesis. This provides for the first time a firm empirical basis for employing the similarity decay hypothesis to the magnetic field, one of the primitive variables of magnetohydrodynamics, and one frequently more accessible from spacecraft instruments. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.Fil: Roy, Sohom. University of Delaware; Estados UnidosFil: Chhiber, R.. University of Delaware; Estados UnidosFil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Ruiz, Maria Emilia. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Matthaeus, W. H.. University of Delaware; Estados Unido

Smart Prediction of Water Quality System for Aquaculture using Machine Learning Algorithms

This article focuses on the importance of the continuous collection of water parameters data from the sensors and also the prediction of water quality using the latest different Machine learning algorithms like Logistic Regression, Random Forest, Support Vector Machine, Decision Tree, K-nearest Neighbour, XGBoost, Gradient Boosting and Naive Bayes. These Machine learning models are implemented and tested to validate and achieve a satisfactory result of water quality prediction in terms of different attributes like pH, hardness, Solids, Chloramines, Sulfate, Conductivity, organic carbon, trihalomethanes, Turbidity and potability.</p

Energy transfer and proton-electron heating in turbulent plasmas

Despite decades of study of high-temperature weakly-collisional plasmas, a complete understanding of how energy is transferred between particles and fields remains elusive. Two major questions in this regard are how fluid-scale energy transfer rates, associated with turbulence, connect with kinetic-scale dissipation, and what controls the fraction of dissipation on different charged species. Although the rate of cascade has long been recognized as a limiting factor in the heating rate at kinetic scale, no study has reported direct evidence correlating the heating rate with MHD-scale cascade rates. Using kinetic simulations and in-situ spacecraft data, we show the connection between the fluid-scale energy flux and the total energy dissipated at kinetic scales. The proton versus electron heating is controlled by the ratio of non-linear time scale to the proton-cyclotron time and increases with the total dissipation rate. These results advance a key step toward understanding dissipation of turbulent energy in collisionless plasmas

Relaxation of the Turbulent Magnetosheath

The large-scale phenomena that involve plasmas can be adequately described by using magnetohydrodynamics equations. Such a set of equations consists of several nonlinear terms that are responsible for driving the energy contained in the large-scale eddies to small scales through the so-called energy cascade. A turbulent state is a state in which the nonlinear terms are of the order of (or greater) than the linear terms. It has been shown that space plasma turbulence (e.g., described by three-dimensional magnetohydrodynamics) tends to relax toward equilibrium states that minimize the energy; these states, in principle, are considered global. However, turbulence can locally relax toward such equilibrium states, creating patches where the magnitude of the nonlinear terms is reduced and the energy cascade impaired. Boundaries between such patches are expected to have a stronger unimpaired cascade. We argue that this “cellularization” of turbulence can happen in strongly turbulent environments (large fluctuations\u27 amplitude) such as the Earth\u27s magnetosheath, as we demonstrate here by analysis of MMS observations

Magnetic-field Line Curvature Observed by Magnetospheric Multiscale

We examine the probability density function (PDF) of magnetic-field line curvature for a variety of solar wind and magnetosheath intervals of burst data from the Magnetospheric Multiscale Mission. Existing theories, based on isotropic magnetic fields, are able to predict the behavior of the curvature distribution for small and large values. We still lack a universal description of curvature in the case in which a mean magnetic field is present, i.e., in the case of anisotropic magnetic fields. Here we examine the effect of magnetic field fluctuations amplitude on the curvature distribution and predict a steeper PDF tail at large curvature value for small magnetic-field fluctuations. While existing theories apply to the case of isotropic magnetic fields, when a mean magnetic field is present, the plane perpendicular can be considered isotropic (i.e., gyrotropic). Therefore, we examine the components of magnetic field curvature in the directions parallel and perpendicular to the mean field. We find that the perpendicular curvature is responsible for the behavior of the PDF in the small curvature limit, whereas the parallel curvature’s contribution depends heavily on the strength of the mean magnetic field. This assessment of magnetic curvature examines the effects of varied parameters that can impact particle energization processes in a turbulence context