Fast Dust in the Heliosphere

The dynamics of dust particles in the solar system is dominated by solar gravity, by solar radiation pressure, or by electromagnetic interaction of charged dust grains with the interplanetary magnetic field. For micron-sized or bigger dust particles solar gravity leads to speeds of about 30 to 40 km s^–1 at the Earths distance. Smaller particles that are generated close to the Sun and for which radiation pressure is dominant (the ratio of radiation pressure force over gravity F _rad/F _grav is generally termed ) are driven out of the solar system on hyperbolic orbits. Such a flow of -meteoroids has been observed by the Pioneer 8, 9 and Ulysses spaceprobes. Dust particles in interplanetary space are electrically charged to typically +5 V by the photo effect from solar UV radiation. The dust detector on Cassini for the first time measured the dust charge directly. The dynamics of dust particles smaller than about 0.1 m is dominated by the electromagnetic interaction with the ambient magnetic field. Effects of the solar wind magnetic field on interstellar grains passing through the solar system have been observed. Nanometer sized dust stream particles have been found which were accelerated by Jupiters magnetic field to speeds of about 300 km s^–1.     

Hydra — A 3-dimensional electron and ion hot plasma instrument for the POLAR spacecraft of the GGS mission

HYDRA is an experimental hot plasma investigation for the POLAR spacecraft of the GGS program. A consortium of institutions has designed a suite of particle analyzers that sample the velocity space of electron and ions between 2 keV/q – 35 keV/q in three dimensions, with a routine time resolution of 0.5 s. Routine coverage of velocity space will be accomplished with an angular homogeneity assumption of 16°, appropriate for subsonic plasmas, but with special 1.5° resolution for electrons with energies between 100 eV and 10 keV along and opposed to the local magnetic field. This instrument produces 4.9 kilobits s^–1 to the telemetry, consumes on average 14 W and requires 18.7 kg for deployment including its internal shielding. The scientific objectives for the polar magnetosphere fall into four broad categories: (1) those to define the ambient kinetic regimes of ions and electrons; (2) those to elucidate the magnetohydrodynamic responses in these regimes; (3) those to assess the particle populations with high time resolution; and (4) those to determine the global topology of the magnetic field. In thefirst group are issues of identifying the origins of particles at high magnetic latitudes, their energization, the altitude dependence of the forces, including parallel electric fields they have traversed. In thesecond group are the physics of the fluid flows, regimes of current, and plasma depletion zones during quiescent and disturbed magnetic conditions. In thethird group is the exploration of the processes that accompany the rapid time variations known to occur in the auroral zone, cusp and entry layers as they affect the flow of mass, momentum and energy in the auroral region. In thefourth class of objectives are studies in conjunction with the SWE measurements of the Strahl in the solar wind that exploit the small gyroradius of thermal electrons to detect those magnetic field lines that penetrate the auroral region that are directly open to interplanetary space where, for example, the Polar Rain is observed.     

Simulation of three-dimensional solar wind disturbances and resulting geomagnetic storms

A kinematic method of representing the three-dimensional solar wind flow is devised by taking into account qualitatively the stream-stream interaction which leads to the formation of a shock pair. Solar wind particles move radially away from the Sun, satisfying the frozen-magnetic field condition. The uniqueness of the present approach is that one can incorporate both theoretical and observational results by adjusting the parameters involved and that a self-consistent data set can be simulated. One can then infer the three-dimensional structure of the solar wind which is vital in understanding the interaction between the solar wind and the magnetosphere, and it is for this reason that the present kinematic method is devised. In the first part of this paper, the present kinematic method is described in detail by demonstrating that the following solar wind features can be simulated: (i) Variations of the solar wind quantities (such as the solar wind speed, the density and the IMF vector), associated with the solar rotation, at the Earth; (ii) the solar wind flow pattern in the meridian planes; (iii) the three-dimensional structure of the corotating interaction region (CIR); and (iv) the three-dimensional structure of the warped solar current sheet.In Section 2, the three-dimensional structure of solar wind disturbances are studied by introducing a flare-generated high speed stream into the two-stream model of the solar wind developed in Section 1. The treatment of the stream-stream interaction is generalized to deal with a flare-generated high speed stream, yielding a shock pair. The shock pair causes three-dimensional distortion of the solar current sheet as it propagates outward from the Sun. It is shown that a set of characteristic time variations of the solar wind speed, density, the interplanetary magnetic field magnitude B and angles (theta) and gf (phi) result at the time of the passage at the location of the Earth for a given set of flare conditions. These quantities allow us to compute the solar wind-magnetosphere energy coupling function . Time variations of the two geomagnetic indices AE and Dst are then estimated from . The simulated geomagnetic storms are compared with observed ones.In the third part, it is shown that recurrent geomagnetic storms can reasonably be reproduced, if fluctuating components of the interplanetary magnetic field (IMF) are superposed on the kinematic model of the solar wind developed in the first part. As an example, we simulate the fluctuating components by linearly polarized Alfvén waves and by random variations of the IMF angle (theta). Characteristics of the simulated and observed geomagnetic storms are discussed in terms of the simulated and observed AE and Dst indices. If the fluctuating components of the IMF can generally be identified as hydromagnetic waves, they may be an important cause for individual magnetospheric substorms, while the IMF magnitude B and the solar wind speed V modulate partially the intensity of magnetospheric substorms and storms.     

Finite Larmor radius effects in the magnetosphere

This article reviews theories and observations related to effects produced by finite (and large) Larmor radii of charged particles in the magnetosphere. The FLR effects depend on =r _H /L, wherer _H is the Larmor radius andL is the spatial scale for field/plasma inhomogeneity. The parameter is a basic expansion parameter for most equations describing plasma dynamics in the magnetosphere. The FLR effects enter naturally the drift approximation for particle motion and represent also non-ideal MHD terms in the fluid formalism. The linear and higher order terms in lead to charge separation, energization of particles, and produce viscosity without collisions. The FLR effects introduce also important corrections to the dispersion relations for MHD waves and drift instabilities. Expansion of plasma into magnetic field leads to filamentation of the plasma boundary and to creation of structures with thickness less than an ion gyroradius. Large Larmor radius effects (1) in curved magnetic field geometry lead to stochastic behaviour of particle trajectories and to deterministic chaos. The tiny scale of the electron and ion gyroradii does not necessarily mean that FLR/LLR phenomena have negligible effect on the macroscopic dynamics and energetics of the whole magnetosphere. On the contrary, the small scale gyro-effects may provide the physical mechanism for gyroviscous coupling between the solar wind and the magnetosphere, the mechanism for triggering disruption of the magnetotail current layer, and the mechanism for parallel electric field that accelerate auroral particles.     

The importance of anisotropic interstellar turbulence and molecular-cloud magnetic mirrors for galactic cosmic-ray propagation

Recent studies suggest that when magnetohydrodynamic (MHD) turbulence is excited by stirring a plasma at large scales, the cascade of energy from large to small scales is anisotropic, in the sense that small-scale fluctuations satisfy the inequality k k , where k and k are, respectively, the components of a fluctuations wave vector and to the background magnetic field. Such anisotropic fluctuations are very inefficient at scattering cosmic rays. Results based on the quasilinear approximation for scattering of cosmic rays by anisotropic MHD turbulence are presented and explained. The important role played by molecular-cloud magnetic mirrors in confining and isotropizing cosmic rays when scattering is weak is also discussed.     

High energy cosmic ray observations during August 1972

A series of spectacular cosmic ray events which included two relativistic solar particle enhancements and three major Forbush decreases were registered by ground-based cosmic ray monitoring stations beginning 4 August, 1972. These were associated with four major proton flare events on the Sun and with large interplanetary magnetic field disturbances and high velocity shock waves. This review attempts to discuss and interpret the high energy cosmic ray phenomena observed during this period in the light of the known behaviour of low energy particulate flux, interplanetary plasma and field observations and other associated solar and terrestrial effects recorded during this period.The first Forbush decrease event FD-1 occurred in the early hours of 4 August, exhibiting very strong north-south and east-west anisotropies. Immediately following the onset of FD-1, the first ground level solar particle enhancement occurred. This event, which had its onset almost 6 h after the flare event on 4 August, had a very steep rigidity spectrum. The major Forbush event of the series which had its onset at 2200 UT on 4 August, exhibited extremely interesting and complex behaviour, the prominent features of which are a precursory increase prior to the onset (PI-1), a large decrease (FD-2), the largest observed to date, followed immediately by an abrupt square wave like enhancement (PI-2). Interplanetary space during this entire period was highly disturbed by the presence of large low energy particulate fluxes and shock waves, at least one of which had a velocity exceeding 2000 km s^-1. Large north-south and east-west anisotropies existed throughout the event. Both FD-2 and PI-2 were characterized by almost the same rigidity spectrum, with a power law index of -1.2 ± 0.2, and a predominant anisotropy along the sunward direction. The square wave-like spike PI-2 during the recovery of FD-2 was associated with a similar abrupt change in low energy particle flux in space, as well as an abrupt decrease in the interplanetary magnetic field value from 50 to 10 .Based on the available particle, field and plasma observations, an unified model is presented to explain the Forbush event in terms of a transient modulating region associated with the passage of a narrow magnetic shock front. In this model, the reflection of particles from the approaching shock front account for the precursory increase PI-1. The main Forbush event is caused when the magnetic barrier at the shock front sweeps past the Earth. The square wave increase is due to the enhanced flux contained in the magnetic well just behind the shock front and bounded by magnetic discontinuities, which is explained as due to the transverse diffusion of particles into this region from the interplanetary space which have easy access to this region. In situ plasma, field and low energy particle observations are reviewed to support the model.Also Professor at Physical Research Laboratory, Ahmedabad 380009, India.     

Modelling of the interstellar hydrogen distribution in the heliosphere

The detailed knowledge of the distribution of neutral interstellar hydrogen in the interplanetary space is necessary for a reliable interpretation of optical and H⁺ pickup ions observations. In the paper, we review the status of the modelling efforts with the emphasis on recent improvements in that field. We discuss in particular the role of the nonstationary, solar cycle-related effects and the consequences of hydrogen filtration through the heliospheric interface region for its distribution in the inner Solar System. We demonstrate also that the use of the simple cold model, neglecting the thermal character of the hydrogen gas (T 8000 K), is generally incorrect for the whole region of the inner heliosphere (R < 5 AU) since it leads to a substantial underestimation of the local hydrogen density and thus influences the derivation of the H properties in the outer heliosphere/LISM. Referring to recent Ulysses measurements, we point out also the need to consider in the modelling the effects of the latitudinal asymmetry of the ionization rate.     

Solar flares and particle acceleration

Energy release in solar flares occurs during the impulsive phase, which is a period of a few to about ten minutes, during which energy is injected into the flare region in bursts with durations of various time scales, from a few tens of seconds down to 0.1 s or even shorter. Non-thermal heating is observed during a short period, not longer than a few minutes, in the very first part of the impulsive phase; in average flares, with ambient particle densities not larger than a few times 10¹⁰ cm^–3 it is due to thick-target electron beam injection, causing chromospheric ablation followed by convection. In flares with larger densities the heating is due to thermal fronts (Section 1). The average energy released in chromospheric regions is a few times 10³⁰ erg, and an average number of 10³⁸ electrons with E 15 keV is accelerated. In subsecond pulses these values are about 10³⁵ electrons and about 10²⁷ erg per subsecond pulse. The total energy released in flares is larger than these values (Section 2). Energization occurs gradually, in a series of fast non-explosive flux-thread interactions, on the average at levels about 10⁴ km above the solar photosphere, a region permeated by a large number ( 10) of fluxthreads, each carrying electric currents of 10¹⁰–10¹¹ A. The energy is fed into the flare by differential motions of magnetic fields driven by photospheric-chromospheric movements (Section 3). In contrast to these are the high-energy flares, characterized by the emission of gamma-radiation and/or very high-frequency (millimeter) radiobursts. Observations of such flares, of the flare neutron emission, as well as the observation of ³He-rich interplanetary plasma clouds from flares all point to a common source, identified with shortlived ( 0.1 s) superhot ( 10⁸ K) flare knots, situated in chromospheric levels (Section 4). Pre-flare phenomena and the existence of homologous flares prove that flare energization can occur repeatedly in the same part of an active region: the consequent conclusions are that only seldom the full energy of an active region is exhausted in one flare, or that the flare energy is generated anew between homologous flares; this latter case looks more probable (Section 5). Flare energization requires the formation of direct electric fields, in value comparable with, or somewhat smaller than the Dreicer field (Section 6). Such fields originate by current-thread reconnection in a regime in which the current sheet is thin enough to let resistive instability originate (Section 7). Particle acceleration occurs by fast reconnection in magnetic fields 100 G and electric fields exceeding about 0.3 times the Dreicer field at fairly low particle densities ( 10¹⁰ cm^–3); for larger densities plasma heating is expected to occur (Section 8). Transport of accelerated particles towards interplanetary space demands a field-line configuration open to space. Such a configuration originates mainly after the gradual gamma-ray/proton flares, and particularly after two-ribbon flares; these flares belong to the dynamic flares in Sturrock and vestka's flare classification. Acceleration to GeV energies occurs subsequently in shock waves, probably by first-order Fermi acceleration (Section 9).     

Probing the solar wind acceleration region using spectroscopic techniques

Measurements of the intensities and profiles of UV and EUV spectral lines can provide a powerful tool for probing the physical conditions in the solar corona out to 8 R and beyond. We discuss here how measurements of spectral line radiation in conjunction with measurements of the white light K-corona can provide information on electron, proton and ion temperatures and velocity distribution functions; densities; chemical abundances and mass flow velocities. Because of the fundamental importance of such information, we provide a comprehensive review of the formation of coronal resonance line radiation, with particular emphasis on the H i L line, and discuss observational considerations such as requirements for rejection of stray light and effects of emission from the geocorona and interplanetary dust. Finally, we summarize some results of coronal H i L and white light observations acquired on sounding rocket flights.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind.     

Characteristics of nearby interstellar matter

There is a warm tenuous partially ionized cloud (T10⁴ K,n(HI)0.1 cm^–3,n(Hii 0.22–0.44 cm^–3) surrounding the solar system which regulates the environment of the solar system, determines the structure of the heliopause region, and feeds neutral interstellar gas into the inner solar system. The velocity (V–20 km s^–1 froml335°,b0° in the local standard of rest) and enhanced Caii and Feii abundances of this cloud suggest an origin as evaporated gas from cloud surfaces in the Scorpius-Centaurus Association. Although the soft X-ray emission attributed to the Local Bubble is enigmatic, optical and ultraviolet data are consistent with bubble formation caused by star formation epochs in the Scorpius-Centaurus Association as regulated by the nearby spiral arm configuration. The cloud surrounding the solar system (the local fluff) appears to be the leading region of an expanding interstellar structure (the squall line) which contains a magnetic field causing polarization of the light of nearby stars, and also absorption features in nearby upwind stars. The velocity vectors of the solar system and local fluff are perpendicular in the local standard of rest. Combining this information with the low column densities seen towards Sirius in the anti-apex direction, and the assumption that the cloud velocity vector is parallel to the surface normal, suggests that the Sun entered the local fluff within the historical past (less than 10 000 years ago) and is skimming the surface of the cloud. Comparison of magnesium absorption lines towards Sirius and anomalous cosmic-ray data suggest the local fluff is in ionization equilibrium.Reason has moons, but moons not hers, Lie mirror'd on her sea, Confounding her astronomers, But, O! delighting me.Ralph Hodgson     

Solar modulation of galactic cosmic radiation

In this review an attempt is made to present an integrated view of the solar modulation process that cause time variation of cosmic ray particles. After briefly surveying the relevant large and small scale properties of the interplanetary magnetic fields and plasma, the motion of cosmic ray particles in the disordered interplanetary magnetic fields is discussed. The experimentally observed long term variations of different species of cosmic ray particles are summarised and compared with the theoretical predictions from the diffusion-convection model. The effect of the energy losses due to decelaration in the expanding solar wind are clearly brought out. The radial density gradient, the modulation parameter and their long term variation are discussed to understand the dynamics of the modulating region. The cosmic ray anisotropy measurements at different energies are summarised. At high energies (E 1 GeV), the average diurnal anisotropy is shown to be energy independent and along the 18.00 h direction consistent with their undergoing partial corotation with the sun. The average semi-diurnal anisotropy seems to vary with energy as E ⁺¹ and incident from a direction perpendicular to the interplanetary field line, consistent with the semi-diurnal component being produced by latitudinal gradients. Both the diurnal and semi-diurnal components are shown to be practically time invariant. On a day to day basis, however, the anisotropy characteristics such as the exponent of variation, the amplitude and the phase show very high variability which are interpreted in terms of convection and variable field aligned diffusion due to the redistribution of the galactic cosmic ray density following transient changes in the interplanetary medium. The anisotropy observation at low energies (E 100 MeV) are, however, not explained by the theory.The rigidity dependence and the anisotropies during short term variations such as Forbush decreases are discussed in terms of the proposed field models for the interplanetary field structure and are compared with the observed rigidity dependence of long term variations. The data pertaining to the 27 day corotating Forbush decreases and their association with enhanced diurnal variation are also presented. The relationship between the energetic storm particle events which are caused by the acceleration of particles in the shock fronts and the Forbush decreases which are caused by the exclusion of galactic particles by the enhanced field structure in the same fronts are clearly brought out. Thus the recurrent increases at low energies and recurrent decreases at high energies may both be caused by the field structure in the shock front. In conclusion, the properties of the very short period fluctuations (18–25 cph) are summarised.     

Tearing instability of reconnecting current sheets in space plasmas

Magnetic reconnection provides an efficient conversion of the so-called free magnetic energy to kinetic and thermal energies of cosmic plasmas, hard electromagnetic radiation, and accelerated particles. This phenomenon was found in laboratory and space, but it is especially well studied in the solar atmosphere where it manifests itself as flares and flare-like events. We review the works devoted to the tearing instability — the inalienable part of the reconnection process — in current sheets which have, inside of them, a transverse (perpendicular to the sheet plain) component of the magnetic field and a longitudinal (parallel to the electric current) component of the field. Such non-neutral current sheets are well known as the energy sources for flare-like processes in the solar corona. In particular, quasi-steady high-temperature turbulent current sheets are the energy sources during the main or hot phase of solar flares. These sheets are stabilized with respect to the collisionless tearing instability by a small transverse component of magnetic fiel, normally existing in the reconnecting and reconnected magnetic fluxes. The collision tearing mode plays, however, an important and perhaps dominant role for non-neutral current sheets in solar flares. In the MHD approximation, the theory shows that the tearing instability can be completely stabilized by the transverse fieldB _n if its value satisfies the conditionB _n /BS ^–3/4 B is the reconnecting component of the magnetic field just near the current sheet,S is the magnetic Reynolds number for the sheet. In this case, stable current sheets become sources of temporal spatial oscillations and usual MHD waves. The application of the theory to the solar atmosphere shows that the effect of the transverse field explains high stability of high-temperature turbulent current sheets in the solar corona. The stable current sheets can be sources of radiation in the radio band. If the sheet is destabilized (atB _n /BS ^–3/4) the compressibility of plasma leads to the arizing of the tearing instability in a long wave region, in which for an incompressible plasma the instability is absent. When a longitudinal magnetic field exists in the current sheet, the compressibility-induces instability can be dumped by the longitudinal field. These effects are significant in destabilization of reconnecting current sheets in solar flares: in particular, the instability with respect to disturbances comparable with the width of the sheet is determined by the effect of compressibility.     

Magnetic field experiment for Voyagers 1 and 2

The magnetic field experiment to be carried on the Voyager 1 and 2 missions consists of dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM's, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronics redundancy. The wide dynamic ranges of ± 0.5 G for the LFM's and ± 20 G for the HFM's, low quantization uncertainty of ± 0.002 ( = 10^–5 G) in the most sensitive (± 8 ) LFM range, low sensor RMS noise level of 0.006 , and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Objectives include the study of planetary fields at Jupiter, Saturn, and possibly Uranus; satellites of these planets; solar wind and satellite interactions with the planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic, field. The interstellar field may also be measured.     

Pulsars as gamma ray sources: Nebular shocks and magnetospheric gaps

I summarize the results of recent research on the structure and particle acceleration properties of relativistic shock waves in which the magnetic field is transverse to the flow direction in the upstream medium, and whose composition is primarily electrons and positrons with an admixture of heavy ions. Shocks which contain heavy ions that are a minority constituent by number but which carry most of the energy density in the upstream medium put 20% of the flow energy into a nonthermal population of pairs downstream, whose distribution in energy space is N(E) E ^-2, where N(E)dE is the number of particles with energy between E and E+dE. Synchrotron maser activity in the shock front, stimulated by the quasi-coherent gyration of the whole particle population as the plasma flowing into the shock reflects from the magnetic field in the shock front, provides the mechanism of thermalization and non-thermal particle acceleration. The maximum energy achievable by the pairs is _± m _± c ² = m _i c ² ₁/Z _i, where ₁ is the Lorentz factor of the upstream flow and Z _i is the atomic number of the ions. The shock's spatial structure contains a series of overshoots in the magnetic field, regions where the gyrating heavy ions compress the magnetic field to levels in excess of the eventual downstream value. These overshoots provide a new interpretation of the structure of the inner regions of the Crab Nebula, in particular of the wisps, surface brightness enhancements near the pulsar. The wisps appear brighter because the small Larmor radius pairs are compressed and radiate more efficiently in the regions of more intense magnetic field. This interpretation suggests that the structure of the shock terminating the pulsar's wind in the Crab Nebula is spatially resolved, and allows one to measure ₁ 4 × 10⁶, the upstream magnetic field B ₁ to be 3 × 10^-5 Gauss, as well as to show that the total ion flow is 3 × 10³⁴ elementary charges/sec, in good agreement with the total current flow predicted by the early Goldreich and Julian (1969) model. The total pair outflow is shown to be about 5 × 10³⁷ pairs per second, in good agreement with the particle flux required to explain the nebular X—ray source.The energetics of particle acceleration within the magnetospheres of rotation powered pulsars and the consequences for pulsed gamma ray emission are also briefly discussed. The gamma ray luminosity above 100 MeV is shown to scale in proportion to _R ^1/2 , as is in accord with some of the simplest ideas about polar cap models. Models based on acceleration in the outer magnetosphere are also briefly discussed.     

Spectral computation of Tandem mirror equilibria with Finite Larmor Radius effects

A direct iterative method of solving for Tandem equilibria by moving magnetic field lines in a manner to satisfy the linearized equilibrium equations converges much more rapidly than standard relaxation techniques, typically in under a fifty iterations. At the highest 's the number of iterations increase, but is still far less than other methods. In quadrupole tandem mirror equilibrium, octupole and higher distortions of the flux surfaces are important which forces us to abandon finite differences in the angle-like flux variable and resort to a spectral decomposition to solve the equilibrium equations. We display equilibria at the high expected for MFTF-B and show how Finite Larmor Radius (FLR) effects strongly suppress these azimuthal distortions.     

Latitude and solar-cycle dependence of radial IMF intensity

I describe a simple procedure for extrapolating the observed solar magnetic field into the heliosphere, which averages the asymptotic fields computed using the standard source surface and current sheet models. The resultant field is characterized by strong latitudinal gradients (maintained by volume currents outside the source surface) and by abrupt reversals in direction at the current sheets. The model yields good agreement with the observed long-term variation of the radial IMF component in the ecliptic, and is used to predict the variation of |B _r | along the latitudinal trajectory of Ulysses during 1990–1994. As found in earlier studies, the magnitude ofB _r at any latitude is determined largely by the strength and relative orientation of the Sun's dipole moment.     

Study of magnetospheric dynamics using energetic solar particles

Information can be obtained from energetic particle measurements through the chemical composition, energy spectrum, directional anisotropy, temporal and spatial intensity variations. This is equivalent to saying that there is a distribution functionf _k(p,r,t) wherek corresponds to thekth particle species of momentump at positionr and timet.Particle transport is described by the Boltzmann equation, and because the densities are generally low in the case of cosmic rays or energetic solar flare particles, collective transport effects can be neglected. In the absence of magnetospheric motion it is relatively easy to treat the problems of particle transport as simple propagation of charged particles in a stationary magnetic field configuration using, for instance, trajectory calculations in model fields. The method here is to use correlated measurements of the particle distribution at two points along a dynamic trajectory, and in this way to learn something about the geomagnetic field. This approach provides a good basis from which to study magnetospheric dynamics. If the magnetosphere moves, large scale electric fields, turbulent electromagnetic fields and sources and sinks affect the propagation of energetic particles considerably. These effects change the distribution functionf _k(p,r,t) and can thus be detected.In this paper, we shall show the importance of the single particle approximation (trajectories in a reference field) in forming the basis of our understanding of the quiet-time penetration of cosmic rays into the magnetosphere, we shall consider the steady dynamics such as wave-particle inter-action and field line reconnection, which is believed to exist nearly all the time, and finally we shall review the work which has been done in the much more complex and less well-understood field of impulsive dynamics such as geomagnetic storms and substorms. This last topic is only just beginning to be investigated in detail, and it is hoped that the study of impulsive dynamics, using energetic particles, may be as successful as the study of the quiet magnetosphere and the steady dynamics.     

The new radiation belt of the earth from trapped anomalous cosmic rays

In this review we briefly present the observational results on the new radiation belt of the Earth originating from the anomalous cosmic rays (ACR) and their implications. Firstly, a brief historical account of the development of our knowledge and ideas on the trapped particles in the geomagnetic field is presented. We then discuss briefly the first observations of the anomalous cosmic rays inside the magnetosphere in theSkylab experiment in 1973–1974 (Biswaset al., 1975). This showed that the measured ACR oxygen flux was at least 25 times higher than the calculated flux from the interplanetary value, indicating the presence of trapped ACR component originating from the Blake-Freisen mechanism (Biswas and Durgaprasad, 1980). In the Cosmos experiment of the USSR, the presence of trapped ACR oxygen was indicated from the observations of double peaked angular distributution (Grigorovet al., 1990). In the recent satellite experiment, MAST-SAMPEX the new results were obtained which confirmed the earlier indications and established the presence of the trapped ACR component in the geomagnetic field from the spatially separated components of the ACR (Cummingset al., 1993). The properties of the trapped ACR ions as measured in the SAMPEX are briefly discussed. The theoretical model of trapped ACR oxygen by Blake and Preisen are briefly summarised. The implications of the new observations are noted.     

Initial ISEE magnetometer results: Shock observation

ISEE-1 and -2 magnetic field profiles across 6 terrestrial bow shock and one interplanetary shock are examined. The interplanetary shock illustrates the behavior of a low Mach number shock. It had an upstream whistler wave precursor with an apparent wavelength of 180 km. The shock thickness was about 90 km for the thickness of the final field jump or 270 km for the exponential growth of the precursor wave packet. The ion inertial length was 50 km, upstream of the shock.Three examples of low or moderate , high Mach number, quasiperpendicular shocks are examined. These did not have upstream waves, but rather had waves growing in the field gradient. The growth length for these waves and the shock profile was of the order of the ion inertial length.Two examples of high shocks showed little coherence in field variation even though the two vehicles were only a few hundred kilometers apart. Thus, we cannot gauge their velocity and turn the time profiles into distances. The final crossing examined shows clearly the effect of changing the orientation of the interplanetary magnetic field. Initially the upstream magnetic field made an angle of about 80° to the shock normal and the shock position remained fairly steady. Then the field rotated to 45° to the normal and the field profiles became very irregular and the shock position very unstable. Discrete wave packets appeared.Finally, we present the joint behavior of wave, particle and field data across some of these shocks to show some of the myriad of shock features whose behavior we are now beginning to investigate.     

The magnetogram inversion technique: Applications to the problem of magnetospheric substorms

The magnetogram inversion technique (MIT) is based upon recordings of geomagnetic variations at the worldwide network of ground-based magnetometers. MIT ensures a calculation of a global spatial distribution of the electric field, currents and Joule heating in the ionosphere. Variant MIT-2 provides, additionally, continuous monitoring of the following parameters: Poynting vector flux from the solar wind into the magnetosphere (); power, both dissipated and accumulated in the magnetosphere; magnetic flux in the open tail; and the magnetotail length (l _T) (distance between the dayside and nightside neutral points in the Dungey model). Using MIT-2 and data of direct measurements in the solar wind, an analysis is made of a number of substorms, and a new scenario of substorms is suggested. The scenario includes the convection model, the model with a neutral line and the model of magnetosphere-ionosphere coupling (outside the current sheet), i.e., the three known models. A brief review is given of these and some other substorms models. A new element in the scenario is the strong positive feedback in the primary generator circuit, which ensures growth of the ratio = / _Aby an order of magnitude or more during the substorms. Here _Ais the Pointing vector flux in the Akasofu-Perrault approximation, i.e., without the feedback taken into account. The growth of during the substorm is caused only by the feedback effect. It is assumed that the feedback arises due to an elongation of the magnetotail, i.e., a growth of l _Tby a factor of (23) during the substorm.In the active phase of substorm, a part (the first active phase) has been identified, where the principal role in the energetics is played by the feedback mechanism and the external energy source (although the internal source plus reconnection inside the plasma sheet make a marked contribution). In the second active phase (expansion) the external generator (solar wind) is switched off, and the main role is now played by the internal energy source (the tail magnetic field and ionospheric wind energy).Models of DP-2 DP-1 transitions are also considered, as well as the magnetospheric substorm-solar flare analogy.