Turbulence-generated proton-scale structures in the terrestrial magnetosheath

Recent results of numerical magnetohydrodynamic simulations suggest that in collisionless space plasmas turbulence can spontaneously generate thin current sheets. These coherent structures can partially explain intermittency and the non-homogenous distribution of localized plasma heating in turbulence. In this Letter Cluster multi-point observations are used to investigate the distribution of magnetic field discontinuities and the associated small-scale current sheets in the terrestrial magnetosheath downstream of a quasi-parallel bow shock. It is shown experimentally, for the first time, that the strongest turbulence generated current sheets occupy the long tails of probability distribution functions (PDFs) associated with extremal values of magnetic field partial derivatives. During the analyzed one hour long time interval, about a hundred strong discontinuities, possibly proton-scale current sheets were observed.Comment: 10 pages, 5 figures in The Astrophysical Journal Letters, Volume 819, Number 1, 201

Turbulence, intermittency and cross-scale energy transfer in an interplanetary coronal mass ejection

Solar wind measurements carried out by NASA's Wind spacecraft before, during and after the passing of an interplanetary coronal mass ejection (ICME) detected on 12-14 September 2014 have been used in order to examine several properties of magnetohydrodynamic (MHD) turbulence. Spectral indices and flatness scaling exponents of magnetic field, velocity and proton density measurements were obtained, and provided a standard description of the characteristics of turbulence within different sub-regions of the ICME and its surroundings. This analysis was followed by the validation of the third-order moment scaling law for isotropic, incompressible MHD turbulence in the same sub-regions, which confirmed the fully developed nature of turbulence in the ICME plasma. The energy transfer rate was also estimated in each ICME sub-region and in the surrounding solar wind. An exceptionally high value was found within the ICME sheath, accompanied by enhanced intermittency, possibly related to the powerful energy injection associated with the arrival of the ICME

Procalcitonin - a specific marker for the diagnosis of infection and guide to antibiotic decisions

Съществуват редица ограничения при използването на конвенционални диагностични маркери за пациенти с клинично подозрение за инфекция. Вследствие на това ненужната и продължителна употреба на антимикробни средства оказва неблагоприятно въздействие върху резултатите на пациентите, докато неправилната антибиотична терапия увеличава устойчивостта към антибиотици. Все повече лабора-торни проучвания подкрепят използването на този вид диагностичен тест в ежедневната диагностика. Контролирани проучвания показват полза от използването на прокалцитонин (РСТ) алгоритми за насочване на решенията за започване и/или преустановяване на антибиотичната терапия. Статията разглежда многобройни изследвания от различни литературни източници и има за цел да обобщи настоящите данни за PCT при различни инфекции, както и да обсъди надеждността на този маркер.There are a number of limitations to using conventional diagnostic markers for patients with clinical suspicion of infection. As a consequence, unnecessary and prolonged exposure to antimicrobial agents adversely affects patient outcomes, while inappropriate antibiotic therapy increases antibiotic resistance. Laboratory studies support the use of this type of diagnostic test. Controlled trials have shown a benefit of using procalcitonin (PCT) algorithms to guide decisions about initiation and/or discontinuation of antibiotic therapy. For some other types of infections, observational studies have shown promising first results, but further intervention studies are needed before the routine use of PCT in clinical practice can be recommended. The aim of this review is to summarize the current evidence for PCT in different infections and clinical settings, and discuss the reliability of this marker when used with validated diagnostic algorithms

Kramers-Moyal analysis of interplanetary magnetic field fluctuations at sub-ion scales

In the framework of statistical time series analysis of complex dynamics we present a multiscale characterization of solar wind turbulence in the near-Earth environment. The data analysis, based on the Markov-process theory, is meant to estimate the Kramers-Moyal coefficients associated with the measured magnetic field fluctuations. In fact, when the scale-to-scale dynamics can be successfully described as a Markov process, first- and second-order Kramers-Moyal coefficients provide a complete description of the dynamics in terms of Langevin stochastic process. The analysis is carried out by using high-resolution magnetic field measurements gathered by Cluster during a fast solar wind period on January 20, 2007. This analysis extends recent findings in the near-Sun environment with the aim of testing the universality of the Markovian nature of the magnetic field fluctuations in the sub-ion/kinetic domain

A Possible Link between Turbulence and Plasma Heating

Erratum: A Possible Link between Turbulence and Plasma Heating (Astrophysical Journal (2021) 921 (65) DOI: 10.3847/1538-4357/ac1942). Astrophysical Journal, Volume 923, Issue 2, 20 December 2021, Article number 282.Numerical simulations and experimental results have shown that the formation of current sheets in space plasmas can be associated with enhanced vorticity. Also, in simulations the generation of such structures is associated with strong plasma heating. Here, we compare four-point measurements in the terrestrial magnetosheath turbulence from the Magnetospheric Multiscale mission of the flow vorticity and the magnetic field curlometer versus their corresponding one-point proxies PVI(V) and PVI(B) based on the Partial Variance of Increments (PVI) method. We show that the one-point proxies are sufficiently precise in identifying not only the generic features of the current sheets and vortices statistically, but also their appearance in groups associated with plasma heating. The method has been further applied to the region of the turbulent sheath of an interplanetary coronal mass ejection (ICME) observed at L1 by the WIND spacecraft. We observe current sheets and vorticity associated heating in larger groups (blobs), which so far have not been considered in the literature on turbulent data analysis. The blobs represent extended spatial regions of activity with enhanced regional correlations between the occurrence of conditioned currents and vorticity, which at the same time are also correlated with enhanced temperatures. This heating mechanism is substantially different from the plasma heating in the vicinity of the ICME shock, where plasma beta is strongly fluctuating and there is no vorticity. The proposed method describes a new pathway for linking the plasma heating and plasma turbulence, and it is relevant to in situ observations when only single spacecraft measurements are available.Peer reviewe

Helios 2 observations of solar wind turbulence decay in the inner heliosphere

The linear scaling of the mixed third-order moment of the magnetohydrodynamic fluctuations is used to estimate the energy transfer rate of the turbulent cascade in the expanding solar wind. In 1976 the Helios 2 spacecraft measured three samples of fast solar wind originating from the same coronal hole, at different distance from the sun. Along with the adjacent slow solar wind streams, these 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 is also used for interpretation. 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 magnetohydrodynamic numerical simulations of decaying magnetohydrodynamic 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 clarifying the nature of the evolution of the turbulent fluctuations in the ecliptic solar wind.Comment: In press on Astron. Astrophy

Magnetic field fluctuation properties of coronal mass ejection-driven sheath regions in the near-Earth solar wind

In this work, we investigate magnetic field fluctuations in three coronal mass ejection (CME)-driven sheath regions at 1 AU, with their speeds ranging from slow to fast. The data set we use consists primarily of high-resolution (0.092 s) magnetic field measurements from the Wind spacecraft. We analyse magnetic field fluctuation amplitudes, compressibility, and spectral properties of fluctuations. We also analyse intermittency using various approaches; we apply the partial variance of increments (PVIs) method, investigate probability distribution functions of fluctuations, including their skewness and kurtosis, and perform a structure function analysis. Our analysis is conducted separately for three different subregions within the sheath and one in the solar wind ahead of it, each 1 h in duration. We find that, for all cases, the transition from the solar wind ahead to the sheath generates new fluctuations, and the intermittency and compressibility increase, while the region closest to the ejecta leading edge resembled the solar wind ahead. The spectral indices exhibit large variability in different parts of the sheath but are typically steeper than Kolmogorov's in the inertial range. The structure function analysis produced generally the best fit with the extended p model, suggesting that turbulence is not fully developed in CME sheaths near Earth's orbit. Both Kraichnan-Iroshinikov and Kolmogorov's forms yielded high intermittency but different spectral slopes, thus questioning how well these models can describe turbulence in sheaths. At the smallest timescales investigated, the spectral indices indicate shallower than expected slopes in the dissipation range (between 2 and 2 :5), suggesting that, in CME-driven sheaths at 1 AU, the energy cascade from larger to smaller scales could still be ongoing through the ion scale. Many turbulent properties of sheaths (e.g. spectral indices and compressibility) resemble those of the slow wind rather than the fast. They are also partly similar to properties reported in the terrestrial magnetosheath, in particular regarding their intermittency, compressibility, and absence of Kolmogorov's type turbulence. Our study also reveals that turbulent properties can vary considerably within the sheath. This was particularly the case for the fast sheath behind the strong and quasi-parallel shock, including a small, coherent structure embedded close to its midpoint. Our results support the view of the complex formation of the sheath and different physical mechanisms playing a role in generating fluctuations in them.Peer reviewe

Sign Singularity of the Local Energy Transfer in Space Plasma Turbulence

In weakly collisional space plasmas, the turbulent cascade provides most of the energy that is dissipated at small scales by various kinetic processes. Understanding the characteristics of such dissipative mechanisms requires the accurate knowledge of the fluctuations that make energy available for conversion at small scales, as different dissipation processes are triggered by fluctuations of a different nature. The scaling properties of different energy channels are estimated here using a proxy of the local energy transfer, based on the third-order moment scaling law for magnetohydrodynamic turbulence. In particular, the sign-singularity analysis was used to explore the scaling properties of the alternating positive-negative energy fluxes, thus providing information on the structure and topology of such fluxes for each of the different type of fluctuations. The results show the highly complex geometrical nature of the flux, and that the local contributions associated with energy and cross-helicity non-linear transfer have similar scaling properties. Consequently, the fractal properties of current and vorticity structures are similar to those of the Alfvenic fluctuations

Current Sheet Statistics in the Magnetosheath

The magnetosheath (MSH) plasma turbulence depends on the structure and properties of the bow shock (BS). Under quasi-parallel (Q(||)) and quasi-perpendicular (Q(perpendicular to)) BS configurations the electromagnetic field and plasma quantities possess quite distinct behavior, e.g., being highly variable and structured in the Q(||) case. Previous studies have reported abundance of thin current sheets (with typical scales of the order of the plasma kinetic scales) in the Q(||) MSH, associated with magnetic reconnection, plasma heating, and acceleration. Here we use multipoint observations from Magnetospheric MultiScale (MMS) mission, where for the first time a comparative study of discontinuities and current sheets in both MSH geometries at very small spacecraft separation (of the order of the ion inertial length) is performed. In Q(||) MSH the current density distribution is characterized by a heavy tail, populated by strong currents. There is high correlation between these currents and the discontinuities associated with large magnetic shears. Whilst, this seems not to be the case in Q(perpendicular to) MSH, where current sheets are virtually absent. We also investigate the effect of the discontinuities on the scaling of electromagnetic fluctuations in the MHD range and in the beginning of the kinetic range. There are two (one) orders of magnitude higher power in the magnetic (electric) field fluctuations in the Q(||) MSH, as well as different spectral scaling, in comparison to the Q(perpendicular to) MSH configuration. This is an indication that the incoming solar wind turbulence is completely locally reorganized behind Q(perpendicular to) BS while even though modified by Q(||) BS geometry, the downstream turbulence properties are still reminiscent to the ones upstream, the latter confirming previous observations. We show also that the two geometries are associated with different temperature anisotropies, plasma beta, and compressibility, where the Q(perpendicular to) MSH is unstable to mostly mirror mode plasma instability, while the Q(||) MSH is unstable also to oblique and parallel fire-hose, and ion-cyclotron instabilities