scholarly journals Quasi-static MHD processes in Earth's magnetosphere

1988 ◽  
Vol 6 (3) ◽  
pp. 525-537 ◽  
Author(s):  
Gerd-Hannes Voigt
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Plasma Sheet ◽  
Equilibrium Theory ◽  
Flux Tubes ◽  
Earth’S Magnetosphere ◽  
Magnetospheric Convection ◽  
Mhd Equilibrium ◽  
Earth's Magnetosphere ◽  
Flow Velocities

The purpose of this paper is to demonstrate how the MHD equilibrium theory can be used to describe the global magnetic field configuration of Earth's magnetosphere and its time evolution under the influence of magnetospheric convection. The MHD equilibrium theory represents magneto-hydrodynamics in the slow-flow approximation. In this approximation time scales are long compared to typical Alfvén wave travel times, and plasma flow velocities are small compared to the Alfvén speed. Under those conditions, the inertial term ρ(dv/dt) in the MHD equation of motion is a small second order term which can be neglected. The MHD equilibrium theory is not a static theory, though, because time derivatives and flow velocities remain first order quantities in the continuity equation, in the thermodynamic equation of state, and in the induction equation. Therefore one can compute slowly time-dependent processes, such as magnetospheric convection, in terms of series of static equilibrium states. However, those series are not arbitrary; they are constrained by thermodynamic conditions according to which the magnetosphere evolves in time.It is an interesting question, whether or not the magnetosphere, driven by slow, lossless, adiabatic, earthward convection of magnetotail flux tubes, can reach a steady state. There exist magnetospheric equilibria in which magnetotail flux tubes satisfy the steady-state condition d/dt (Pρ−γ) = 0. Those configurations exhibit a deep magnetic field minimum in the equatorial plane, near the inner edge of the tail plasma sheet. The magnetosphere becomes tearing-mode unstable in the neighborhood of such a minimum, thus leading to periodic onsets of substorms in the inner plasma sheet. This explains why distinct magnetic field minima have not been observed in this region. Magnetic substorms seem to be an inevitable element of the global convection cycle which inhibit the establishment of an ultimate steady state.MHD equilibria discussed in this paper result from linear and non-linear solutions to the two-dimensional Grad-Shafranov equation for isotropic thermal plasma pressure.

scholarly journals Absence of a long-lived lunar paleomagnetosphere

2021 ◽  
Vol 7 (32) ◽  
pp. eabi7647
Author(s):  
John A. Tarduno ◽  
Rory D. Cottrell ◽  
Kristin Lawrence ◽  
Richard K. Bono ◽  
Wentao Huang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Lunar Regolith ◽  
The Moon ◽  
Earth’S Magnetosphere ◽  
Solar Winds ◽  
Planetary Bodies ◽  
Earth's Magnetosphere ◽  
Impact Glass ◽  
Magnetic Inclusions

Determining the presence or absence of a past long-lived lunar magnetic field is crucial for understanding how the Moon’s interior and surface evolved. Here, we show that Apollo impact glass associated with a young 2 million–year–old crater records a strong Earth-like magnetization, providing evidence that impacts can impart intense signals to samples recovered from the Moon and other planetary bodies. Moreover, we show that silicate crystals bearing magnetic inclusions from Apollo samples formed at ∼3.9, 3.6, 3.3, and 3.2 billion years ago are capable of recording strong core dynamo–like fields but do not. Together, these data indicate that the Moon did not have a long-lived core dynamo. As a result, the Moon was not sheltered by a sustained paleomagnetosphere, and the lunar regolith should hold buried 3He, water, and other volatile resources acquired from solar winds and Earth’s magnetosphere over some 4 billion years.

A UNIFYING THEORY OF HIGH-LATITUDE GEOPHYSICAL PHENOMENA AND GEOMAGNETIC STORMS

1961 ◽  
Vol 39 (10) ◽  
pp. 1433-1464 ◽  
Author(s):  
W. I. Axford ◽  
C. O. Hines
Keyword(s):  
Solar Wind ◽  
Steady State ◽  
High Latitude ◽  
Geomagnetic Storms ◽  
High Latitudes ◽  
Full Understanding ◽  
Earth’S Magnetosphere ◽  
Trapped Particles ◽  
Outer Portion ◽  
Earth's Magnetosphere

This paper is concerned with the occurrence at high latitudes of a large number of geophysical phenomena, including geomagnetic agitation and bay disturbances, aurorae, and various irregular distributions of ionospheric electrons. It shows that these may all be related in a simple way to a single causal agency, namely, a certain convection system in the outer portion of the earth's magnetosphere. The source of this convection is taken to be a viscous-like interaction between the magnetosphere and an assumed solar wind, though other sources of an equivalent nature may also be available. The model is capable of accounting for many aspects of the phenomena concerned, including the morphology of auroral forms and the occurrence of 'spiral' patterns in the loci of maximum intensities of several features. It also bears directly on the steady state of the magnetosphere, and in particular on the production of trapped particles in the outer Van Allen belt. In short, it provides a new basis on which a full understanding of these several phenomena may in time be built.

scholarly journals Solar wind interaction with the Earth's magnetosphere: the role of reconnection in the presence of a large scale sheared flow

2009 ◽  
Vol 16 (1) ◽  
pp. 1-10 ◽  
Author(s):  
F. Califano ◽  
M. Faganello ◽  
F. Pegoraro ◽  
F. Valentini
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Large Scale ◽  
Initial Conditions ◽  
Magnetic Layer ◽  
Magnetic Islands ◽  
Solar Wind Interaction ◽  
Earth’S Magnetosphere ◽  
Earth's Magnetosphere

Abstract. The Earth's magnetosphere and solar wind environment is a laboratory of excellence for the study of the physics of collisionless magnetic reconnection. At low latitude magnetopause, magnetic reconnection develops as a secondary instability due to the stretching of magnetic field lines advected by large scale Kelvin-Helmholtz vortices. In particular, reconnection takes place in the sheared magnetic layer that forms between adjacent vortices during vortex pairing. The process generates magnetic islands with typical size of the order of the ion inertial length, much smaller than the MHD scale of the vortices and much larger than the electron inertial length. The process of reconnection and island formation sets up spontaneously, without any need for special boundary conditions or initial conditions, and independently of the initial in-plane magnetic field topology, whether homogeneous or sheared.

The Earth's plasma sheet as a laboratory for flow turbulence in high-β MHD

1997 ◽  
Vol 57 (1) ◽  
pp. 1-34 ◽  
Author(s):  
JOSEPH E. BOROVSKY ◽  
RICHARD C. ELPHIC ◽  
HERBERT O. FUNSTEN ◽  
MICHELLE F. THOMSEN
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Plasma Sheet ◽  
Sheet Material ◽  
Single Point ◽  
Power Laws ◽  
Fluxgate Magnetometer ◽  
Flow Measurements ◽  
Field Fluctuations ◽  
Flow Velocities

The bulk flows and magnetic-field fluctuations of the plasma sheet are investigated using single-point measurements from the ISEE-2 Fast Plasma Experiment and fluxgate magnetometer. Ten several-hour-long intervals of continuous data (with 3 s and 12 s time resolution) are analysed. The plasma-sheet flow appears to be strongly ‘turbulent’ (i.e. the flow is dominated by fluctuations that are unpredictable, with rms velocities[Gt ]mean velocities and with field fluctuations≈mean fields). The flow velocities are typically sub-Alfvénic. The flow-velocity probability distribution P(v) is constructed, and is found to be well fitted by exponential functions. Autocorrelation functions [Ascr ](τ) are constructed, and the autocorrelation times τcorr for the flow velocities are found to be about 2 min. From the flow measurements, an estimate of the mixing length in the plasma sheet is produced, yielding Lmix≈2 Earth radii; correspondingly, the plasma-sheet material appears to be well mixed in density and temperature. An eddy viscosity for the plasma sheet is also estimated. Power spectra, which are constructed from the v(t) and B(t) time series, have portions that are power laws with spectral indices that are near the range of those expected for turbulence theories. The plasma sheet may provide a laboratory for the study of turbulence in parameter regimes different from that of solar-wind turbulence: the plasma sheet is a β[Gt ]1, hot-ion plasma, and the turbulence may be strongly driven rather than well developed. The turbulent nature of the flow and the disordered nature of the magnetic field have implications for the transport of plasma-sheet material, for the penetration of the solar-wind electric field into the plasma sheet, and for the calculation of particle orbits in the magnetotail.

scholarly journals Large-scale fluctuations of PSBL magnetic flux tubes induced by the field-aligned motion of highly accelerated ions

2010 ◽  
Vol 28 (6) ◽  
pp. 1273-1288 ◽  
Author(s):  
E. E. Grigorenko ◽  
T. M. Burinskaya ◽  
M. Shevelev ◽  
J.-A. Sauvaud ◽  
L. M. Zelenyi
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Plasma Sheet ◽  
Large Scale ◽  
Low Frequency ◽  
Main Magnetic Field ◽  
Sudden Increase ◽  
Data Set ◽  
Flux Tubes ◽  
Magnetic Flux Tubes

Abstract. We present a comprehensive analysis of magnetic field and plasma data measured in the course of 170 crossings of the lobeward edge of Plasma Sheet Boundary Layer (PSBL) in the Earth's magnetotail by Cluster spacecraft. We found that large-scale fluctuations of the magnetic flux tubes have been registered during intervals of propagation of high velocity field-aligned ions. The observed kink-like oscillations propagate earthward along the main magnetic field with phase velocities of the order of local Alfvén velocity and have typical wavelengths ~5–20 RE, and frequencies of the order of 0.004–0.02 Hz. The oscillations of PSBL magnetic flux tubes are manifested also in a sudden increase of drift velocity of cold lobe ions streaming tailward. Since in the majority of PSBL crossings in our data set, the densities of currents corresponding to electron-ion relative drift have been low, the investigation of Kelvin-Helmholtz (K-H) instability in a bounded flow sandwiched between the plasma sheet and the lobe has been performed to analyze its relevance to generation of the observed ultra-low frequency oscillations with wavelengths much larger than the flow width. The calculations have shown that, when plasma conditions are favorable for the excitation of K-H instability at least at one of the flow boundaries, kink-like ultra-low frequency waves, resembling the experimentally observed ones, could become unstable and efficiently develop in the system.

scholarly journals Average characteristics of the midtail plasma sheet in different dynamic regimes of the magnetosphere

2004 ◽  
Vol 22 (6) ◽  
pp. 2107-2113 ◽  
Author(s):  
N. P. Dmitrieva ◽  
V. A. Sergeev ◽  
M. A. Shukhtina
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Growth Phase ◽  
Plasma Sheet ◽  
Transfer Rate ◽  
Flux Transport ◽  
Data Set ◽  
Magnetospheric Convection ◽  
Flux Transfer ◽  
Night Flux

Abstract. We study average characteristics of plasma sheet convection in the middle tail during different magnetospheric states (Steady Magnetospheric Convection, SMC, and substorms) using simultaneous magnetotail (Geotail, 15-35 RE downtail) and solar wind (Wind spacecraft) observations during 3.5 years. (1) A large data set allowed us to obtain the average values of the plasma sheet magnetic flux transfer rate (Ey and directly compare it with the dayside transfer rate (Emod for different magnetospheric states. The results confirm the magnetic flux imbalance model suggested by Russell and McPherron (1973), namely: during SMC periods the day-to-night flux transport rate equals the global Earthward plasma sheet convection; during the substorm growth phase the plasma sheet convection is suppressed on the average by 40%, whereas during the substorm expansion phase it twice exceeds the day-to-night global flux transfer rate. (2) Different types of substorms were revealed. About 1/3 of all substorms considered displayed very weak growth in the tail lobe magnetic field before the onset. For these events the plasma sheet transport was found to be in a balance with the day-to-night flux transfer, as in the SMC events. However, the lobe magnetic field value in these cases was as large as that in the substorms with a classic growth phase just before the onset (both values exceed the average level of the lobe field during the SMC). Also, in both groups similar configurational changes (magnetic field stretching and plasma sheet thinning) were observed before the substorm onset. (3) Superimposed epoch analysis showed that the plasma sheet during the late substorm recovery phase has the characteristics similar to those found during SMC events, the SMC could be a natural magnetospheric state following the substorm.

scholarly journals Calculations of the integral invariant coordinates <i>I</i> and <i>L</i><sup>*</sup> in the magnetosphere and mapping of the regions where <i>I</i> is conserved

2014 ◽  
Vol 7 (5) ◽  
pp. 6413-6437
Author(s):  
K. Konstantinidis ◽  
T. Sarris
Keyword(s):  
Magnetic Field ◽  
Particle Motion ◽  
Pitch Angle ◽  
National Laboratory ◽  
Space Environment ◽  
Integral Invariant ◽  
Earth’S Magnetosphere ◽  
Starting Position ◽  
Geocentric Distance ◽  
Earth's Magnetosphere

Abstract. The integral invariant coordinate I and Roederer's L or L* are proxies for the second and third adiabatic invariants respectively, that characterize charged particle motion in a magnetic field. Their usefulness lies in the fact that they are expressed in more instructive ways than their counterparts: I is equivalent to the path length of the particle motion between two mirror points, whereas L*, although dimensionless, is roughly equivalent to the distance from the center of the Earth to the equatorial point of a given field line, in units of Earth radii, in the simplified case of a dipole magnetic field. However, care should be taken when calculating the above invariants, as the assumption of their adiabaticity is not valid everywhere in the Earth's magnetosphere. This is not clearly stated in state-of-the-art models that are widely used for the calculation of these invariants. In this paper, we compare the values of I and L* as calculated using LANLstar, an artificial neural network developed at the Los Alamos National Laboratory, SPENVIS, a space environment related online tool, IRBEM, a source code library dedicated to radiation belt modelling, and a 3-D particle tracing code that was developed for this purpose. We then attempt to quantify the variations between the calculations of I and L* of those models. The deviation between the results given by the models depends on particle starting position geocentric distance, pitch angle and magnetospheric conditions. Using the 3-D tracer we attempt to map the areas in the Earth's magnetosphere where I and L* can be assumed to be conserved by monitoring the constancy of I for energetic proton propagating forwards and backwards in time. These areas are found to be centered on the noon area and their size also depends on particle starting position geocentric distance, pitch angle and magnetospheric conditions.

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