Frontiers in Physics | Space Physics section | New and Recent Articles
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RSS Feed for Space Physics section in the Frontiers in Physics journal | New and Recent Articlesen-usFrontiers Feed Generator,version:12020-03-30T11:34:47.9928938+00:0060https://www.frontiersin.org/articles/10.3389/fphy.2020.00045
https://www.frontiersin.org/articles/10.3389/fphy.2020.00045
Space Weather Related to Solar Eruptions With the ASO-S Mission2020-03-11T00:00:00ZLi FengWeiqun GanSiqing LiuHuaning WangHui LiLong XuWeiguo ZongXiaoxing ZhangYaguang ZhuHaiyan WuAnqin ChenYanmei CuiXinghua DaiJuan GuoHan HeXin HuangLei LuQiao SongJingjing WangQiuzhen ZhongLing ChenZhanle DuXingliang GuoYu HuangHu LiYing LiSenlin XiongShenggao YangBeili YingThe Advanced Space-based Solar Observatory (ASO-S) is a mission aiming at exploring solar flares, coronal mass ejections (CMEs), solar magnetic field and their relationships. To fulfill its major scientific objectives, ASO-S has three elaborately-designed payloads onboard: the Full-disk vector MagnetoGraph (FMG), the Lyman-alpha Solar Telescope (LST), and the Hard X-ray Imager (HXI) dedicated to observe vector magnetic fields, CMEs, and flares, respectively. Beside the scientific objectives, we have an operational objective to observe solar eruptions and magnetic field for making related space weather forecasts. More specifically, we have set a priority for the downlink of CME data observed by LST, and will distribute those data to different space weather prediction centers in China within 2 h once the Science Operation and Data Center (SODC) of ASO-S receive the data. After data downlink and archiving, different automatic detection, tracking, and cataloging procedures are planned to run for the most critical solar eruptive features. On the other hand, based on the distributed and downloaded data, different space weather prediction centers are to activate their forecast systems for the ASO-S observed solar eruption events. Our particular interests are currently focused on nowcast of different eruption events, prediction of CME arrivals, forecast of solar flares and the onset of solar eruptions. We are also working on further forecast potentials using the ASO-S data to make contributions to other possible important issues of space weather.]]>https://www.frontiersin.org/articles/10.3389/fphy.2019.00184
https://www.frontiersin.org/articles/10.3389/fphy.2019.00184
Anisotropy of the Spectral Index in Ion Scale Compressible Turbulence: MMS Observations in the Magnetosheath2019-11-20T00:00:00ZOwen Wyn RobertsYasuhito NaritaRumi NakamuraZoltán VörösDaniel GershmanTurbulence in the Earth's magnetosheath at ion kinetic scales is investigated with the Magnetospheric MultiScale (MMS) spacecraft. The multi-point measurements allow the three dimensional power spectra in wave-vector space to be determined. Previously the three dimensional structure of fluctuations in the magnetic field and density (using spacecraft potential as a proxy) were possible with Cluster. However, using the excellent time resolution data set provided from both the Fluxgate Magnetometer (FGM) and the Fast Plasma Investigation (FPI) on MMS the spectra can be determined for a number of different parameters such as ion velocity, and ion temperatures parallel and perpendicular to the mean magnetic field directions. The spectra for different fluctuations show similar features to one another such as a strong power anisotropy with respect to the mean magnetic field direction, such that the energy decays faster in the direction parallel to the mean magnetic field than the perpendicular direction. A weak non-gyrotropy is also seen in the direction of the bulk velocity similar to what has been seen in magnetic field fluctuations with Cluster at ion kinetic scales in the solar wind. Velocity fluctuations are shown to be the most anisotropic. The density and temperature fluctuations exhibit similar anisotropies but are much weaker in comparison.]]>https://www.frontiersin.org/articles/10.3389/fphy.2019.00151
https://www.frontiersin.org/articles/10.3389/fphy.2019.00151
Coalescence of Magnetic Flux Ropes Within Interplanetary Coronal Mass Ejections: Multi-cases Studies2019-10-04T00:00:00ZYan ZhaoHengqiang FengQiang LiuGuoqing ZhaoCoronal mass ejections (CMEs) are intense solar explosive eruptions and have significant impact on geomagnetic activities. It is important to understand how CMEs evolve as they propagate in the solar-terrestrial space. In this paper, we studied the coalescence of magnetic flux ropes embedded in five interplanetary coronal mass ejections (ICMEs) observed by both ACE and Wind spacecraft. The analyses show that coalescence of magnetic flux ropes could persist for hours and operate in scale of hundreds of earth radii. The two merging flux ropes could be very different in the axial orientation and the plasma density and temperature, which should complicate the progress of coalescence and have impact on the merged structures. The study indicates that coalescence of magnetic flux ropes should be an important factor in changing the magnetic topology of ICMEs.]]>https://www.frontiersin.org/articles/10.3389/fphy.2019.00108
https://www.frontiersin.org/articles/10.3389/fphy.2019.00108
Sign Singularity of the Local Energy Transfer in Space Plasma Turbulence2019-08-20T00:00:00ZLuca Sorriso-ValvoGaetano De VitaFederico FraternaleAlexandre GurchumeliaSilvia PerriGiuseppina NigroFilomena CatapanoAlessandro RetinòChristopher H. K. ChenEmiliya YordanovaOreste PezziKhatuna ChargaziaOleg KharshiladzeDiana KvaratskheliaChristian L. VásconezRaffaele MarinoOlivier Le ContelBarbara GilesThomas E. MooreRoy B. TorbertJames L. BurchIn 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 Alfvénic fluctuations.]]>https://www.frontiersin.org/articles/10.3389/fphy.2019.00114
https://www.frontiersin.org/articles/10.3389/fphy.2019.00114
Kinematic Collisionless Relaxation of Ions in Supercritical Shocks2019-08-14T00:00:00ZMichael GedalinWe show that kinematic collisionless relaxation in the macroscopic electric and magnetic fields plays the main role in the formation of the downstream ion distributions in a super-critical shock with ion reflection present. It is done by comparison of a theoretically predicted magnetic profile with the magnetic profile of a shocks observed by MMS mission. It is shown that pressure balance remains the main constraint for the shock stability.]]>https://www.frontiersin.org/articles/10.3389/fphy.2019.00063
https://www.frontiersin.org/articles/10.3389/fphy.2019.00063
A First Assessment of a Regression-Based Interpretation of Langmuir Probe Measurements2019-05-03T00:00:00ZJonathan ChalaturnykRichard MarchandA new approach is presented for interpreting low level Langmuir probe measurements in terms of physical plasma parameters such as density or temperature. Instead of relying on analytic expressions as in most analyses, the method uses regressions combined with a suitably prepared solution library consisting of precomputed probe characteristics for selected plasma parameters. In machine learning language, this amounts to generating a training data set, constructing and training a model, and validating it over a domain of physical parameters of interest. This study aims at establishing the feasibility and limits of the method by using synthetic data sets that can be generated quickly from analytic approximations. The ultimate goal is to use this approach with model training on data sets constructed with detailed kinetic simulations capable of accounting for more physical processes, and more realistic geometry, than are possible with analytic models.]]>https://www.frontiersin.org/articles/10.3389/fphy.2019.00008
https://www.frontiersin.org/articles/10.3389/fphy.2019.00008
A Note on Capon's Minimum Variance Projection for Multi-Spacecraft Data Analysis2019-02-01T00:00:00ZYasuhito NaritaCapon's minimum variance projection for the multi-point measurements is revisited using the method of likelihood function to derive the minimum variance projection and a simplified error estimate analytically. Theoretical construction of the minimum variance projection assumes a Gaussian form of the likelihood function and also regards the data covariance as a proxy of the noise covariance. The minimum variance projection is extended to the problem of two-spacecraft mode decomposition in the Mercury magnetosphere in which the magnetic field is a superposition of the constant field from the current sheet and the dipolar field from the planet. The extension of the Capon estimator (the data-variance projection) can identify the signal amplitudes of the different fields with a sufficient accuracy when the statistical averaging is properly done. The Capon estimator serves as a powerful analysis tool when the spatial resolution is limited to only a few points.]]>https://www.frontiersin.org/articles/10.3389/fphy.2018.00144
https://www.frontiersin.org/articles/10.3389/fphy.2018.00144
History of Los Alamos Participation in Active Experiments in Space2018-12-18T00:00:00ZMorris B. PongratzLos Alamos has a long history of participation in active experiments in space beginning with the Teak nuclear test in 1958. Above-ground nuclear testing stopped in 1962 because of the Partial Test Ban Treaty, and a program of non-nuclear chemical release experiments began in 1968. Los Alamos has participated in nearly 100 non-nuclear experiments in space, the last being the NASA-sponsored strontium and europium doped barium thermite releases in the Arecibo beam in July of 1992. The rationale for these experiments ranged from studying basic plasma processes such as gradient- driven structuring and velocity-space instabilities to illuminating the convection of plasmas in the ionosphere and polar cap to ionospheric depletion experiments to the B.E.A.R. 1-MeV neutral particle beam (NPB) test in 1989. This report reviews the objectives, techniques and diagnostics of Los Alamos participation in active experiments in space.]]>https://www.frontiersin.org/articles/10.3389/fphy.2018.00050
https://www.frontiersin.org/articles/10.3389/fphy.2018.00050
Determination of Polar Cap Boundary for the Substorm Event of 8 March 20082018-05-28T00:00:00ZChi WangJiangyan WangRamon LopezHui LiJiaojiao ZhangBinbin TangThe polar cap boundary (PCB) is a fundamental indicator of magnetospheric activities especially during a substorm cycle. Taking a period on 8 March 2008 as an example, we investigate the location of PCB and its dynamics during a substorm event. The PCB location is determined from the Piecewise Parabolic Method with a Lagrangian Remap (PPMLR) -Magnetohydrodynamic (MHD) simulation data and Defense Meteorological Satellite Program (DMSP) observations, respectively. Model-observation comparison indicates that the PPMLR-MHD model gives a reliable estimate of PCB location during a complex substorm sequence. We further analyze the evolution of PCB in that period. The polar cap expands under southward interplanetary magnetic field (IMF), since the low-latitude dayside reconnection produces new open magnetic flux. Meanwhile, more solar wind energy enters and stores in the magnetosphere with the decreasing SML (SuperMAG Auroral Lower) index. After the substorm expansion onset, the polar cap contracts for a while due to the explosive increase of nightside reconnection. When the IMF direction turns northward, the polar cap contracts continuously, since the dayside reconnection ceases and no more open magnetic flux are supplied, and the storage energy in the magnetosphere releases with the increasing SML index. The model results are in good accord with the features from observations.]]>https://www.frontiersin.org/articles/10.3389/fphy.2017.00008
https://www.frontiersin.org/articles/10.3389/fphy.2017.00008
Ion-Scale Sideband Waves and Filament Formation: Alfvénic Impact on Heliospheric Plasma Turbulence2017-02-23T03:46:41ZYasuhito NaritaUwe MotschmannA mini-review is given about two recent discoveries in the solar wind turbulence research on ion-kinetic scales: the existence of sideband waves (or breakdown of the linear mode wave picture) and the wavevector anisotropy leading to a persistent filament formation in a wide range of plasma beta.]]>https://www.frontiersin.org/articles/10.3389/fphy.2016.00029
https://www.frontiersin.org/articles/10.3389/fphy.2016.00029
On Electron Adiabaticity in Collisionless Shocks2016-07-22T00:00:00ZHoria Comişelhttps://www.frontiersin.org/articles/10.3389/fphy.2015.00040
https://www.frontiersin.org/articles/10.3389/fphy.2015.00040
Broad current sheets, current bifurcation, and collisionless reconnection—An Opinion on “Onset of fast magnetic reconnection via subcritical bifurcation” by Z. Guo and X. Wang2015-06-08T00:00:00ZRudolf A. TreumannWolfgang Baumjohannhttps://www.frontiersin.org/articles/10.3389/fphy.2015.00034
https://www.frontiersin.org/articles/10.3389/fphy.2015.00034
Information kinetics—an extension2015-05-19T00:00:00ZRudolf A. TreumannWolfgang BaumjohannWe present an operator formalism for the recently developed kinetic information theory, construct Poisson brackets between the Liouville and information operators in μ space, proposing its quantum version. Making use of the universal quantum of time, the Planck time τ_{p}, a pseudo-energy-time uncertainty relation is constructed. It suggests that tiny amounts of information production may cause large variations in energy. The Hubble time τ_{H} sets an upper bound on information in the universe.]]>https://www.frontiersin.org/articles/10.3389/fphy.2015.00022
https://www.frontiersin.org/articles/10.3389/fphy.2015.00022
Ideal MHD turbulence: the inertial range spectrum with collisionless dissipation2015-04-09T00:00:00ZRudolf A. TreumannWolfgang BaumjohannYasuhito NaritaThe inertial range spectrum of ideal (collisionless/dissipationless) MHD turbulence is analyzed in view of the transition from the large-scale Iroshnikov-Kraichnan-like (IK) to the meso-scale Kolmogorov (K) range under the assumption that the ultimate dissipation which terminates the Kolmogorov range is provided by collisionless reconnection in thin turbulence-generated current sheets. Kolmogorov's dissipation scale is identified with the electron inertial scale, as suggested by collisionless particle-in-cell simulations of reconnection. Transition between the IK- and K-ranges occurs at the ion inertial length allowing determination of the IK-coefficient. With the electron inertial scale the K-dissipation scale, stationarity of the spectrum implies a relation between the energy injection and dissipation rates. Application to solar wind is critically discussed.]]>https://www.frontiersin.org/articles/10.3389/fphy.2015.00019
https://www.frontiersin.org/articles/10.3389/fphy.2015.00019
Kinetic theory of information—the dynamics of information2015-03-30T00:00:00ZRudolf A. TreumannWolfgang BaumjohannA kinetic approach to the notion of information is proposed, based on Liouville kinetic theory. The general kinetic equation for the evolution of the N-particle information _{N} in a Hamiltonian system of large particle number N ≫ 1 is obtained. It is shown that the N-particle information is strictly conserved. Defining reduced particle number information densities in phase space should be possible to obtain a kinetic equation for the ordinary one-particle information _{1} ≡ following the Bogoliubov prescription. The kinetic equation for is a kind of generalized Boltzmann equation with interaction term depending on the hierarchy of reduced informations. This term in its general form is the most general expression for the Kolmogorov entropy rate of evolution of the information.]]>https://www.frontiersin.org/articles/10.3389/fphy.2014.00076
https://www.frontiersin.org/articles/10.3389/fphy.2014.00076
Lessons on collisionless reconnection from quantum fluids2014-12-15T00:00:00ZYasuhito NaritaWolfgang BaumjohannMagnetic reconnection in space plasmas remains a challenge in physics in that the phenomenon is associated with the breakdown of frozen-in magnetic field in a collisionless medium. Such a topology change can also be found in superfluidity, known as the quantum vortex reconnection. We give a plasma physicists' view of superfluidity to obtain insights on essential processes in collisionless reconnection, including discussion of the kinetic and fluid pictures, wave dynamics, and time reversal asymmetry. The most important lesson from the quantum fluid is the scenario that reconnection is controlled by the physics of topological defects on the microscopic scale, and by the physics of turbulence on the macroscopic scale. Quantum vortex reconnection is accompanied by wave emission in the form of Kelvin waves and sound waves, which imprints the time reversal asymmetry.]]>https://www.frontiersin.org/articles/10.3389/fphy.2014.00059
https://www.frontiersin.org/articles/10.3389/fphy.2014.00059
The strongest magnetic fields in the universe: how strong can they become?2014-10-16T00:00:00ZRudolf A. TreumannWolfgang BaumjohannAndré BaloghMagnetic fields in the universe are in general weak, of the order of μGauss only. However, in compact objects they assume extraordinarily large values. These are produced by gravitational collapse of massive magnetized objects. Clearly, fields in the massive progenitor are energetically limited by the available energy which can be fed into the generation of currents and magnetic fields. However, when collapsing down to small scales magnetic fields become superstrong exceeding any limits which can be reached in the laboratory. A brief review and discussion is given on the absolute limitation to the magnetic field strengths which can be obtained during such collapses.]]>https://www.frontiersin.org/articles/10.3389/fphy.2014.00049
https://www.frontiersin.org/articles/10.3389/fphy.2014.00049
Beyond Gibbs-Boltzmann-Shannon: general entropies—the Gibbs-Lorentzian example2014-08-14T00:00:00ZRudolf A. TreumannWolfgang BaumjohannWe propose a generalization of Gibbs' statistical mechanics into the domain of non-negligible phase space correlations. Derived are the probability distribution and entropy as a generalized ensemble average, replacing Gibbs-Boltzmann-Shannon's entropy definition enabling construction of new forms of statistical mechanics. The general entropy may also be of importance in information theory and data analysis. Application to generalized Lorentzian phase space elements yields the Gibbs-Lorentzian power law probability distribution and statistical mechanics. The corresponding Boltzmann, Fermi and Bose-Einstein distributions are found. They apply only to finite temperature states including correlations. As a by-product any negative absolute temperatures are categorically excluded, supporting a recent “no-negative T” claim.]]>https://www.frontiersin.org/articles/10.3389/fphy.2014.00047
https://www.frontiersin.org/articles/10.3389/fphy.2014.00047
Alfvén wave characteristics of equatorial plasma irregularities in the ionosphere derived from CHAMP observations2014-08-11T00:00:00ZHermann LührJaeheung ParkChao XiongJan RaubergWe report magnetic field observations of the components transverse to the main field in the frequency range 1–25 Hz from times of equatorial plasma irregularity crossings. These field variations are interpreted as Alfvénic signatures accompanying intermediate-scale (150 m–4 km) plasma density depletions. Data utilized are the high-resolution CHAMP magnetic field measurements sampled at 50 Hz along the north-south satellite track. The recorded signals do not reflect the temporal variation but the spatial distribution of Alfvénic signatures. This is the first comprehensive study of Alfvénic signatures related to equatorial plasma bubbles that covers the whole solar cycle from 2000 to 2010. A detailed picture of the wave characteristics can be drawn due to the large number (almost 9000) of events considered. Some important findings are: Alfvénic features are a common feature of intermediate-scale plasma structures. The zonal and meridional magnetic components are generally well correlated suggesting skewed current sheets. The sheets have an orientation that is on average deflect by about 32° away from magnetic east toward upward or downward depending on the hemisphere. We have estimated the Poynting flux flowing into the E region. Typical values are distributed over the range 10^{−8}–10^{−6} W/m^{2}. Large Poynting fluxes are related to steep spectra of the Alfvénic signal, which imply passages through regularly varying electron density structures. No dependence of the Poynting flux level on solar activity has been found. But below a certain solar flux value (F10.7 < 100 sfu) practically no events are detected. There is a clear tendency that large Poynting flux events occur preferably at early hours after sunset (e.g., 20:00 local time). Toward later times the occurrence peak shifts successively toward lower energy levels. Finally we compare our observations with the recently published results of the high-resolution 3-D model simulations by Dao et al. [1].]]>https://www.frontiersin.org/articles/10.3389/fphy.2014.00029
https://www.frontiersin.org/articles/10.3389/fphy.2014.00029
Fractional Laplace transforms—a perspective2014-06-10T00:00:00ZRudolf A. TreumannWolfgang BaumjohannA new form of the Laplace transform is reviewed as a paradigm for an entire class of fractional functional transforms. Various of its properties are discussed. Such transformations should be useful in application to differential/integral equations or problems in non-extensive statistical mechanics.]]>