scholarly journals Magnetic turbulence and particle dynamics in the Earth’s magnetotail

2003 ◽  
Vol 21 (9) ◽  
pp. 1947-1953 ◽  
Author(s):  
G. Zimbardo ◽  
A. Greco ◽  
A. L. Taktakishvili ◽  
P. Veltri ◽  
L. M. Zelenyi
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Sheet Thickness ◽  
Particle Dynamics ◽  
Particle Simulation ◽  
Mhd Waves ◽  
Magnetic Fluctuations ◽  
Magnetic Turbulence ◽  
Magnetospheric Configuration And Dynamics ◽  
Interplanetary Physics

Abstract. The influence of magnetic turbulence in the near-Earth magnetotail on ion motion is investigated by numerical simulation. The magnetotail current sheet is modelled as a magnetic field reversal with a normal magnetic field com-ponent Bn , plus a three-dimensional spectrum of magnetic fluctuations dB which represents the observed magnetic turbulence. The dawn-dusk electric field Ey is also considered. A test particle simulation is performed using different values of Bn and of the fluctuation level dB/B0. We show that when the magnetic fluctuations are taken into account, the particle dynamics is deeply affected, giving rise to an increase in the cross tail transport, ion heating, and current sheet thickness. For strong enough turbulence, the current splits in two layers, in agreement with recent Cluster observations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics) – Interplanetary physics (MHD waves and turbulence) – Electromagnetics (numerical methods)

scholarly journals The penetration of ions into the magnetosphere through the magnetopause turbulent current sheet

2003 ◽  
Vol 21 (9) ◽  
pp. 1965-1973 ◽  
Author(s):  
A. Taktakishvili ◽  
A. Greco ◽  
G. Zimbardo ◽  
P. Veltri ◽  
G. Cimino ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Magnetic Fluctuations ◽  
Ion Motion ◽  
Magnetospheric Configuration And Dynamics ◽  
Shear Parameter ◽  
Magnetic Field Turbulence ◽  
The Magnetic Field ◽  
Very High ◽  
Number Of Particles

Abstract. This paper reports the results of numerical modeling of magnetosheath ion motion in the magnetopause current sheet (MCS) in the presence of magnetic fluctuations. Our model of magnetic field turbulence has a power law spectrum in the wave vector space, reaches maximum intensity in the center of MCS, and decreases towards the magnetosheath and magnetosphere boundaries. We calculated the density profile across the MCS. We also calculated the number of particles entering the magnetosphere, reflected from the magnetopause and escaping from the flanks, as a function of the fluctuation level of the turbulence and magnetic field shear parameter. All of these quantities appeared to be strongly dependent on the fluctuation level, but not on the magnetic field shear parameter. For the highest fluctuation levels the number of particles entering the magnetosphere does not exceed 15% of the total number of particles launched from the magnetosheath side of the MCS; the modeling also reproduced the effective reflection of the magnetosheath flow from very high levels of magnetic fluctuations.Key words. Magnetospheric physics (magnetosheath; magnetospheric configuration and dynamics; turbulence)

scholarly journals Electric fields and double layers in plasmas

1987 ◽  
Vol 5 (2) ◽  
pp. 233-255 ◽  
Author(s):  
Nagendra Singh ◽  
H. Thiemann ◽  
R. W. Schunk
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Electric Fields ◽  
Sheet Thickness ◽  
High Density ◽  
Effective Length ◽  
Double Layers ◽  
Low Density ◽  
Ambient Magnetic Field ◽  
Cold Plasmas

Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamic features of the double layers are discussed. These features, as seen in simulations, laboratory experiments and theory, indicate that double layers and the currents through them undergo slow oscillations, which are determined by the ion transit time across an effective length of the system in which the double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations have been considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields (parallel to an ambient magnetic field) and double layers in an expanding plasma are discussed.

scholarly journals Compressive fluctuations in high-latitude solar wind

2004 ◽  
Vol 22 (2) ◽  
pp. 689-696 ◽  
Author(s):  
B. Bavassano ◽  
E. Pietropaolo ◽  
R. Bruno
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Latitude ◽  
Correlation Coefficients ◽  
Field Measurements ◽  
Solar Wind Plasma ◽  
Ecliptic Plane ◽  
Mhd Waves ◽  
Polar Wind ◽  
Interplanetary Physics

Abstract. Solar wind compressive fluctuations at MHD scales have been extensively studied in the past using data from spacecraft on the ecliptic plane. In the present study, based on plasma and magnetic field measurements by Ulysses, a statistical analysis of the compressive fluctuations observed in the high-latitude solar wind is performed. Data are from the first out-of-ecliptic orbit of Ulysses, when the Sun's activity is low and the high-latitude heliosphere is characterized by the presence of a fast and relatively steady solar wind, the polar wind. Our analysis is based on the computation of hourly-scale correlation coefficients for several pairs of solar wind parameters such as velocity, density, temperature, magnetic field magnitude, and plasma pressures (thermal, magnetic, and total). The behaviour of the fluctuations in terms of their amplitude has been examined, too, and comparisons with the predictions of existing models have been performed. The results support the view that the compressive fluctuations in the polar solar wind are mainly a superposition of MHD compressive modes and of pressure-balanced structures. Nearly-incompressible effects do not seem to play a relevant role. In conclusion, our results about compressive fluctuations in the polar wind do not appear as a break with respect to previous low-latitude observations. However, our study clearly indicates that in a homogeneous environment, as the polar wind, the pressure-balanced fluctuations tend to play a major role. Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma) – Space plasma physics (turbulence)

scholarly journals Multi-scale analysis of compressible fluctuations in the solar wind

2018 ◽  
Vol 36 (1) ◽  
pp. 47-52 ◽  
Author(s):  
Owen W. Roberts ◽  
Yasuhito Narita ◽  
C.-Philippe Escoubet
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electron Density ◽  
Field Measurements ◽  
Slow Waves ◽  
Alfven Wave ◽  
Magnetic Helicity ◽  
Mhd Waves ◽  
Multi Scale ◽  
Interplanetary Physics

Abstract. Compressible plasma turbulence is investigated in the fast solar wind at proton kinetic scales by the combined use of electron density and magnetic field measurements. Both the scale-dependent cross-correlation (CC) and the reduced magnetic helicity (σm) are used in tandem to determine the properties of the compressible fluctuations at proton kinetic scales. At inertial scales the turbulence is hypothesised to contain a mixture of Alfvénic and slow waves, characterised by weak magnetic helicity and anti-correlation between magnetic field strength B and electron density ne. At proton kinetic scales the observations suggest that the fluctuations have stronger positive magnetic helicities as well as strong anti-correlations within the frequency range studied. These results are interpreted as being characteristic of either counter-propagating kinetic Alfvén wave packets or a mixture of anti-sunward kinetic Alfvén waves along with a component of kinetic slow waves. Keywords. Interplanetary physics (MHD waves and turbulence)

scholarly journals The global heliospheric magnetic field polarity distribution as seen at Ulysses

2003 ◽  
Vol 21 (6) ◽  
pp. 1377-1382 ◽  
Author(s):  
G. H. Jones ◽  
A. Balogh
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Magnetic Fields ◽  
Current Sheet ◽  
Heliospheric Current Sheet ◽  
Field Polarity ◽  
Heliospheric Magnetic Field ◽  
Interplanetary Magnetic Fields ◽  
Interplanetary Physics

Abstract. The Ulysses spacecraft is in a near-polar solar orbit with a period of 6.2 years. The heliospheric magnetic field polarity detected by Ulysses from its 1992 Jupiter encounter to the current time is presented, following ballistic mapping of the polarity information to the solar wind source surface, at approximately 2.5 solar radii. The spacecraft’s first foray to polar latitudes and first rapid heliolatitude scan occurred in 1994–1995, near a minimum in solar activity. The heliospheric current sheet during this period was confined to low heliolatitudes. In 2000–2001, Ulysses returned in situ data from the same region of its orbit as in 1994–1995, but near to the maximum in solar activity. Unlike at solar minimum, heliospheric current sheet crossings were detected at the spacecraft over a wide heliolatitude range, which is consistent with the reversal of the solar magnetic dipole occurring during solar maximum. Despite complexity in the solar wind parameters during the latest fast latitude scan (McComas et al., 2002), the underlying magnetic field structure appears consistent with a simple dipole inclined at a large angle to the solar rotational axis. The most recent data show the heliospheric current sheet returning to lower heliolatitudes, indicating that the dipole and rotational axes are realigning, with the Sun’s magnetic polarity having reversed.Key words. Interplanetary physics (interplanetary magnetic fields; sources of the solar wind) – Solar physics, astrophysics and astronomy (magnetic fields)

Magnetic field transport and kinematic dynamo effect: a Lagrangian interpretation

2005 ◽  
Vol 462 (2065) ◽  
pp. 137-147 ◽  
Author(s):  
A Celani ◽  
A Mazzino ◽  
D Vincenzi
Keyword(s):  
Magnetic Field ◽  
Conservation Laws ◽  
Power Laws ◽  
Particle Dynamics ◽  
Inertial Range ◽  
Magnetic Fluctuations ◽  
Time Behaviour ◽  
Lagrangian Dynamics ◽  
Dynamo Effect ◽  
Tangent Vectors

The growth of magnetic fluctuations in the inertial range of turbulence is investigated in terms of fluid particle dynamics. The existence of dynamo effect is related to the time behaviour of the correlations between tangent vectors evolving along Lagrangian trajectories. In the presence of dynamo effect, the correlations between tangent vectors grow exponentially in time; in the absence of dynamo effect they decay as power laws. The above behaviours are intimately related to statistical conservation laws for the Lagrangian dynamics.

Effect of high-frequency magnetic fluctuations on MHD waves

1994 ◽  
Vol 52 (1) ◽  
pp. 43-53
Author(s):  
Tadas K. Nakamura ◽  
C. F. Kennel
Keyword(s):  
Magnetic Field ◽  
Energy Transfer ◽  
High Frequency ◽  
Cyclotron Resonance ◽  
Mode Coupling ◽  
Energy Exchange ◽  
Wave Dispersion ◽  
Mhd Waves ◽  
Magnetic Fluctuations ◽  
Resonant Effect

We have shown earlier that compressional magnetic fluctuations modify the properties of MHD waves. The modifications can be large even when the fluctuation level is much smaller than the ambient magnetic field. There are two kinds of effects: resonant and non-resonant. The former is a result of the so- called parametric cyclotron resonance, and enables energy transfer from the wave to particle Larmor motion. This transfer causes the damping of waves even when their frequency is so small that ordinary cyclotron damping is negligible. The non-resonant effect does not cause energy exchange, but it does modify wave dispersion and causes mode coupling between the shear Alfvén mode and magnetosonic modes.

scholarly journals Proton isotropy boundaries as measured on mid- and low-altitude satellites

2005 ◽  
Vol 23 (5) ◽  
pp. 1839-1847 ◽  
Author(s):  
N. Yu. Ganushkina ◽  
T. I. Pulkkinen ◽  
M. V. Kubyshkina ◽  
V. A. Sergeev ◽  
E. A. Lvova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Pitch Angle ◽  
Large Field ◽  
Tail Region ◽  
Isotropic Distribution ◽  
Distribution Boundary ◽  
Magnetospheric Configuration And Dynamics ◽  
Low Altitude ◽  
The Difference

Abstract. Polar CAMMICE MICS proton pitch angle distributions with energies of 31-80 keV were analyzed to determine the locations where anisotropic pitch angle distributions (perpendicular flux dominating) change to isotropic distributions. We compared the positions of these mid-altitude isotropic distribution boundaries (IDB) for different activity conditions with low-altitude isotropic boundaries (IB) observed by NOAA 12. Although the obtained statistical properties of IDBs were quite similar to those of IBs, a small difference in latitudes, most pronounced on the nightside and dayside, was found. We selected several events during which simultaneous observations in the same local time sector were available from Polar at mid-altitudes, and NOAA or DMSP at low-altitudes. Magnetic field mapping using the Tsyganenko T01 model with the observed solar wind input parameters showed that the low- and mid-altitude isotropization boundaries were closely located, which leads us to suggest that the Polar IDB and low-altitude IBs are related. Furthermore, we introduced a procedure to control the difference between the observed and model magnetic field to reduce the large scatter in the mapping. We showed that the isotropic distribution boundary (IDB) lies in the region where Rc/ρ~6, that is at the boundary of the region where the non-adiabatic pitch angle scattering is strong enough. We therefore conclude that the scattering in the large field line curvature regions in the nightside current sheet is the main mechanism producing isotropization for the main portion of proton population in the tail current sheet. This mechanism controls the observed positions of both IB and IDB boundaries. Thus, this tail region can be probed, in its turn, with observations of these isotropy boundaries. Keywords. Magnetospheric physics (Energetic particles, Precipitating; Magnetospheric configuration and dynamics; Magnetotail)

scholarly journals Cluster as current sheet surveyor in the magnetotail

2013 ◽  
Vol 31 (9) ◽  
pp. 1605-1610 ◽  
Author(s):  
Y. Narita ◽  
R. Nakamura ◽  
W. Baumjohann
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Time Series Data ◽  
Sheet Thickness ◽  
Dynamical Evolution ◽  
Field Measurements ◽  
Three Dimensions ◽  
Series Data ◽  
Time Step ◽  
Analysis Technique

Abstract. A novel analysis technique is presented to estimate the current sheet thickness unambiguously and directly, without associating time series data with spatial structure. The technique is a combination of eigenvalue analysis and minimum variance estimator adapted to Harris current sheet geometry, and needs one-time, four-point magnetic field data as provided by the Cluster spacecraft. Two current sheet parameters, thickness and distance to the spacecraft, can be determined at each time step of the magnetic field measurements. An example is shown from a Cluster magnetotail crossing under quiet magnetospheric conditions, yielding the result that the current sheet thickness is on the scale of the proton gyroradius. The analysis technique can also be used to track the dynamical evolution of the current sheet structure in three dimensions.

scholarly journals The Cluster Magnetic Field Investigation: overview of in-flight performance and initial results

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1207-1217 ◽  
Author(s):  
A. Balogh ◽  
C. M. Carr ◽  
M. H. Acuña ◽  
M. W. Dunlop ◽  
T. J. Beek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Accurate Determination ◽  
Space Plasma ◽  
Active Role ◽  
Field Investigation ◽  
Primary Objective ◽  
Small Scale ◽  
Magnetospheric Configuration And Dynamics ◽  
Interplanetary Physics ◽  
The Magnetic Field

Abstract. The accurate measurement of the magnetic field along the orbits of the four Cluster spacecraft is a primary objective of the mission. The magnetic field is a key constituent of the plasma in and around the magnetosphere, and it plays an active role in all physical processes that define the structure and dynamics of magnetospheric phenomena on all scales. With the four-point measurements on Cluster, it has become possible to study the three-dimensional aspects of space plasma phenomena on scales commeasurable with the size of the spacecraft constellation, and to distinguish temporal and spatial dependences of small-scale processes. We present an overview of the instrumentation used to measure the magnetic field on the four Cluster spacecraft and an overview the performance of the operational modes used in flight. We also report on the results of the preliminary in-orbit calibration of the magnetometers; these results show that all components of the magnetic field are measured with an accuracy approaching 0.1 nT. Further data analysis is expected to bring an even more accurate determination of the calibration parameters. Several examples of the capabilities of the investigation are presented from the commissioning phase of the mission, and from the different regions visited by the spacecraft to date: the tail current sheet, the dusk side magnetopause and magnetosheath, the bow shock and the cusp. We also describe the data processing flow and the implementation of data distribution to other Cluster investigations and to the scientific community in general.Key words. Interplanetary physics (instruments and techniques) – magnetospheric physics (magnetospheric configuration and dynamics) – space plasma physics (shock waves)

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