scholarly journals On the magnetic field fluctuations during magnetospheric tail current disruption: A statistical approach

2005 ◽  
Vol 110 (A7) ◽  
Author(s):  
Giuseppe Consolini
Keyword(s):  
Magnetic Field ◽  
Statistical Approach ◽  
Tail Current ◽  
Current Disruption ◽  
Field Fluctuations ◽  
Magnetospheric Tail ◽  
The Magnetic Field

scholarly journals Multi-point observations of intermittency in the cusp regions

2007 ◽  
Vol 14 (4) ◽  
pp. 525-534 ◽  
Author(s):  
M. M. Echim ◽  
H. Lamy ◽  
T. Chang
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Haar Wavelet ◽  
Distribution Functions ◽  
Statistical Properties ◽  
Coarse Grained ◽  
Haar Wavelet Transform ◽  
Intermittent Behavior ◽  
Field Fluctuations ◽  
The Magnetic Field

Abstract. In this paper we investigate the statistical properties of magnetic field fluctuations measured by the four Cluster spacecraft in the cusp and close to the interface with the magnetospheric lobes, magnetopause and magnetosheath. At lower altitudes along the outbound orbit of 26 February 2001, the magnetic field fluctuations recorded by all four spacecraft are random and their Probability Distribution Functions (PDFs) are Gaussian at all scales. The flatness parameter, F – related to the kurtosis of the time series, is equal to 3. At higher altitudes, in the cusp and its vicinity, closer to the interface with the magnetopause and magnetosheath, the PDFs from all Cluster satellites are non-Gaussian and show a clear intermittent behavior at scales smaller than τG≈ 61 s (or 170 km). The flatness parameter increases to values greater than 3 for scales smaller than τG. A Haar wavelet transform enables the identification of the "events" that produce sudden variations of the magnetic field and of the scales that have most of the power. The LIM parameter (i.e. normalized wavelet power) indicates that events for scales below 65 s are non-uniformly distributed throughout the cusp passage. PDFs, flatness and wavelet analysis show that at coarse-grained scales larger than τG the intermittency is absent in the cusp. Fluctuations of the magnetic energy observed during the same orbit in the magnetosheath show PDFs that tend toward a Gaussian at scales smaller than τG found in the cusp. The flatness analysis confirms the decreasing of τG from cusp to magnetosheath. Our analysis reveals the turbulent cusp as a transition region from a non-intermittent turbulent state inside the magnetosphere to an intermittent turbulent state in the magnetosheath that has statistical properties resembling the solar wind turbulence. The observed turbulent fluctuations in the cusp suggests a phenomenon of nonlinear interactions of plasma coherent structures as in contemporary models of space plasma turbulence.

scholarly journals Distortions of the magnetic field by storm-time current systems in Earth's magnetosphere

2010 ◽  
Vol 28 (1) ◽  
pp. 123-140 ◽  
Author(s):  
N. Yu. Ganushkina ◽  
M. W. Liemohn ◽  
M. V. Kubyshkina ◽  
R. Ilie ◽  
H. J. Singer
Keyword(s):  
Magnetic Field ◽  
Ring Current ◽  
Geostationary Orbit ◽  
Modeling Framework ◽  
Inner Magnetosphere ◽  
Tail Current ◽  
Modeling Approaches ◽  
Intense Storm ◽  
The Magnetic Field ◽  
Moderate Storm

Abstract. Magnetic field and current system changes in Earth's inner magnetosphere during storm times are studied using two principally different modeling approaches: on one hand, the event-oriented empirical magnetic field model, and, on the other, the Space Weather Modeling Framework (SWMF) built around a global MHD simulation. Two storm events, one moderate storm on 6–7 November 1997 with Dst minimum about −120 nT and one intense storm on 21–23 October 1999 with Dst minimum about −250 nT were modeled. Both modeling approaches predicted a large ring current (first partial, later symmetric) contribution to the magnetic field perturbation for the intense storm. For the moderate storm, the tail current plays a dominant role in the event-oriented model results, while the SWMF results showed no strong tail current in the main phase, which resulted in a poorly timed storm peak relative to the observations. These results imply that the the development of a ring current depends on a strong force to inject the particles deep into the inner magnetosphere, and that the tail current is an important external source for the distortions of the inner magnetospheric magnetic field for both storms. Neither modeling approach was able to reproduce all the variations in the Bx and By components observed at geostationary orbit by GOES satellites during these two storms: the magnetopause current intensifications are inadequate, and the field-aligned currents are not sufficiently represented. While the event-oriented model reproduces rather well the Bz component at geostationary orbit, including the substorm-associated changes, the SWMF field is too dipolar at these locations. The empirical model is a useful tool for validation of the first-principle based models such as the SWMF.

Multi-point observations of a reconnection outflow associated with interacting flux ropes in the solar wind

2020 ◽  
Author(s):  
Zoltan Vörös ◽  
Emiliya Yordanova ◽  
Owen Roberts ◽  
Yasuhito Narita
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Flow Shear ◽  
Magnetic Flux Ropes ◽  
Interplanetary Coronal Mass Ejection ◽  
Flux Ropes ◽  
Magnetic Field Magnitude ◽  
Field Fluctuations ◽  
Mass Ejection ◽  
The Magnetic Field

<p>Twisted magnetic flux ropes embedded in an interplanetary coronal mass ejection (ICME) often contain oppositely oriented magnetic fields and potentially reconnecting current sheets. Reconnection outflows in the solar wind can be identified through magnetic field and plasma signatures, for example, through decreasing magnetic field magnitude, enhanced bulk velocity, temperature and (anti)correlated rotations of the magnetic field and plasma velocity. We investigate a reconnection outflow observed by ACE, WIND and Geotail spacecraft within the interaction region of two flux ropes embedded into an ICME. The SOHO spacecraft, located 15 RE upstream, 120 RE in GSE Y and 5 RE in GSE Z direction from the ACE spacecraft, does not see any plasma signatures of the reconnection outflow. At the same time the other spacecraft, also separated by more than 200 RE in X and Y GSE directions, observe strong plasma and magnetic field fluctuations at the border of the exhaust.  The fluctuations could be associated with Kelvin-Helmholtz (KH) instability at the border of the reconnection outflow with strong flow shear.  It is speculated that the KH instability driven fluctuations and dissipation is responsible for stopping the reconnection outflow which is therefore not seen by SOHO.</p>

scholarly journals Effect of Ergodic and Non-Ergodic Fluctuations on a Charge Diffusing in a Stochastic Magnetic Field

Entropy ◽  
2021 ◽  
Vol 23 (6) ◽  
pp. 781
Author(s):  
Gerardo Aquino ◽  
Kristopher J. Chandía ◽  
Mauro Bologna
Keyword(s):  
Magnetic Field ◽  
Basic Problem ◽  
Waiting Time Distribution ◽  
Field Fluctuations ◽  
Ergodic Fluctuations ◽  
A Charge ◽  
Ergodicity Breaking ◽  
Mean Time ◽  
Stochastic Magnetic Field ◽  
The Magnetic Field

In this paper, we study the basic problem of a charged particle in a stochastic magnetic field. We consider dichotomous fluctuations of the magnetic field where the sojourn time in one of the two states are distributed according to a given waiting-time distribution either with Poisson or non-Poisson statistics, including as well the case of distributions with diverging mean time between changes of the field, corresponding to an ergodicity breaking condition. We provide analytical and numerical results for all cases evaluating the average and the second moment of the position and velocity of the particle. We show that the field fluctuations induce diffusion of the charge with either normal or anomalous properties, depending on the statistics of the fluctuations, with distinct regimes from those observed, e.g., in standard Continuous-Time Random Walk models.

Strong B-Field Fluctuations Caused by the Electromagnetic LHDI and their Impact on 3D Reconnection

2021 ◽  
Author(s):  
Florian Allmann-Rahn ◽  
Simon Lautenbach ◽  
Richard Sydora ◽  
Rainer Grauer
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Moderate Level ◽  
Lower Hybrid ◽  
Particle In Cell ◽  
Strong Current ◽  
Field Fluctuations ◽  
Drift Instability ◽  
The Impact ◽  
The Magnetic Field

<p>The electromagnetic branch of the lower-hybrid drift instability (LHDI) can lead to kinking of current sheets and fluctuations in the magnetic field and is present for example in Earth’s magnetosphere. Previous particle-in-cell studies suggested that the electromagnetic LHDI’s saturation is at a moderate level and that strong current sheet kinking is only caused by slower kink-type modes. Here, we present kinetic continuum simulations that show strong kinking and high saturation levels of the B-field fluctuations. Has the impact of the electromagnetic LHDI been underestimated? The capability of the LHDI to produce x-lines and turbulence in 3D reconnection is discussed at the example of ten-moment multi-fluid simulations.</p>

Spatial coherence of interplanetary coronal mass ejection-driven sheaths at 1 AU

2020 ◽  
Author(s):  
Matti Ala-Lahti ◽  
Julia Ruohotie ◽  
Simon Good ◽  
Emilia Kilpua ◽  
Noé Lugaz
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Spatial Coherence ◽  
Field Measurements ◽  
Interplanetary Coronal Mass Ejections ◽  
Magnetic Structures ◽  
Interplanetary Coronal Mass Ejection ◽  
Field Fluctuations ◽  
Mass Ejection ◽  
The Magnetic Field

<p><span>We report on the longitudinal coherence of sheath regions driven by interplanetary coronal mass ejections (ICMEs). ICME sheaths are significant drivers of geomagnetic activity at the Earth, with a considerable fraction of ICME-driven storms being either entirely or primarily induced by the sheath. Similarly to Lugaz et al. (2018; doi:10.3847/2041-8213/aad9f4</span><span>), we have analyzed two-point magnetic field measurements made by the ACE and <em>Wind </em>spacecraft in 29 ICME sheaths to estimate the coherence scale lengths, defined as the spatial scale at which correlation between measurements falls to zero, of the field magnitude and components. Scale lengths for the sheath are found to be mostly smaller than the corresponding values in the ICME driver, an expected result given that ICME sheaths are characterized by highly fluctuating, variable magnetic fields, in contrast to the often more coherent ejecta. A relatively large scale length for the magnetic field component in the GSE <em>y</em>-direction was found. We discuss how magnetic field line draping around the ejecta and the alignment of pre-existing magnetic structures by the preceding shock may explain the observed results. In addition, we consider the existence of longitudinally extended and possibly geoeffective magnetic field fluctuations within ICME sheaths, the full understanding of which requires further multi-spacecraft analysis.</span></p>

Relations of velocity and magnetic field fluctuations in the minimum variance frames

2020 ◽  
Author(s):  
Jana Šafránková ◽  
Zdeněk Němeček ◽  
František Němec ◽  
Daniel Verscharen ◽  
Tereza Ďurovcová ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Minimum Variance ◽  
Velocity Fluctuations ◽  
Field Fluctuations ◽  
High Beta ◽  
The Magnetic Field ◽  
Scale Length

<p>The analysis of magnetic field and velocity fluctuations in corresponding minimum variance frames revealed that: (1) Minimum variance and mean magnetic field directions would be similar but these two directions are often perpendicular, especially in the high-beta environment, and a number of perpendicular cases decreases with the scale length; (2) Compressibility computed in the minimum variance frame generally increases with frequency but the increase is not monotonic; it exhibits two breaks observed for the magnetic field as well as for velocity fluctuations with approximately the same break frequencies. (3) We suggest that the first break can be connected with a change of pure Alfven to kinetic Alfven modes and the second break approximately coincides with the transition from the inertial to kinetic scales.</p>

Simple magnetohydrodynamic waves

1995 ◽  
Vol 53 (1) ◽  
pp. 109-125 ◽  
Author(s):  
G. Mann
Keyword(s):  
Magnetic Field ◽  
Large Amplitude ◽  
Wave Theory ◽  
Mhd Waves ◽  
Linear Wave ◽  
Magnetohydrodynamic Waves ◽  
Earth’S Bow Shock ◽  
Field Fluctuations ◽  
Arbitrary Amplitude ◽  
The Magnetic Field

Large-amplitude magnetic field fluctuations often accompanied by density variations are frequently observed in front of the earth's bow shock and in the vicinity of comets by extraterrestrial in situ measurements. They are identified as a manifestation of magnetohydrodynainic (MHD) waves in space plasmas. Because of their large amplitudes (i.e. because the magnetic field amplitude is of the order of the ambient magnetic field, for instance), these fluctuations cannot be satisfactorily described by linear wave theory. In this paper the properties of one-dimensional MHD waves of arbitrary amplitude, i.e. so-called simple MHD waves, are investigated, and a relationship is derived between the enhancement of the magnetic field and the density as well as the propagation velocity. Fast large-amplitude magnetosonic waves exhibit wave steepening. Here the dependence of the steepening time on the wave amplitude is derived and illustrated numerically.

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