The Magnetic Field of the Earth’s Lithosphere

The lithospheric contribution to the Earth’s magnetic field is concealed in magnetic field data that have now been measured over several decades from ground to satellite altitudes. The lithospheric field results from the superposition of induced and remanent magnetisations. It therefore brings an essential constraint on the magnetic properties of rocks of the Earth’s sub-surface that would otherwise be difficult to characterize. Measuring, extracting, interpreting and even defining the magnetic field of the Earth’s lithosphere is however challenging. In this paper, we review the difficulties encountered. We briefly summarize the various contributions to the Earth’s magnetic field that hamper the correct identification of the lithospheric component. Such difficulties could be partially alleviated with the joint analysis of multi-level magnetic field observations, even though one cannot avoid making compromises in building models and maps of the magnetic field of the Earth’s lithosphere at various altitudes. Keeping in mind these compromises is crucial when lithospheric field models are interpreted and correlated with other geophysical information. We illustrate this discussion with recent advances and results that were exploited to infer statistical properties of the Earth’s lithosphere. The lessons learned in measuring and processing Earth’s magnetic field data may prove fruitful in planetary exploration, where magnetism is one of the few remotely accessible internal properties.     

Unusual visual stimulation in dynamic balance conditions: proposal for a space motion sickness test.

We previously demonstrated the efficiency of normal vision/unusual vestibular cues conflict to induce motion sickness. In the present study, we investigate whether, inversely, unusual visual information/normal vestibular function conflict also elicited motion sickness. The experiments were again carried out in dynamic balance conditions to increase proprioceptive input. Circular translation of the visual field with diplopia were produced by rotating Fresnel prismatic glasses. The stimulation triggered SMS-like symptoms and dynamic balance disturbance. A positive relationship was found between discomfort and balance disturbance. Unusual visual information should therefore be included in Space Motion Sickness susceptibility testing.     

Two-dimensional analyzer with dE-dE silicon detectors for cosmic ray experiments in space

A charged particle semiconductor-telescope is under construction in the CRIP, Budapest, to measure fluxes of 4–30 MeV/AMU protons, alphas, and M nuclei in interplanetary space. Identification and counting of particles are made on-board using microprocessor techniques. Details including some new ideas on economical coding of information and design of electronics are given.     

Balloon-borne beacons for stellar triangulation

The principle of stellar triangulation was suggested by Y. Väisälä, a Finnish astronomer and geometer. The method is based on photographing light signals against a stellar background from at least two stations. The exact time determination of the flashes makes it possible to express these directions in an Earth-fixed frame.The light signals can be produced using various methods. Targets such as balloon-borne beacons, rockets or satellites are possible. The first possibility will be investigated here.     

Hydromagnetics of the magnetosphere

Different models of the magnetosphere are discussed critically. It is pointed out that there is a principal difference between the case when the impinging interplanetary plasma has no initial magnetization, B ₀ = 0, (as in the Chapman-Ferraro theory), and the case when the plasma is initially magnetized, B ₀ 0, even if B ₀ is very small.In the former case the plasma remains unmagnetized (like a superconductor) and cannot penetrate into the magnetosphere. Therefore the plasma is separated by a sharp boundary from the magnetosphere, (closed magnetosphere model).In the latter case when the plasma is magnetized (which is more realistic) there is a possibility that field lines run from the earth to infinity (open magnetosphere model). Particles from the interplanetary space may penetrate into the magnetosphere. At the same time there may be a number of discontinuity surfaces of different character, such as the Cahill discontinuity.It is important to make terrella experiments in order to study the complicated phenomena occurring when a magnetized plasma penetrates into a dipole field.     

Plasma transport during substorm growth phase and relation to breakup

For <_bi,_be, the electron and ion bounce frequencies, the response of a plasma to an externally applied electromagnetic perturbation is nonlocal. This implies, via the quasi-neutrality equation, the development of an electrostatic potential which is constant for a given magnetic field line. In the near equatorial region the corresponding potential electric field is shown to oppose the effect of the induced electric field associated with the externally applied perturbation. Thus the effect of the induced electric field is partially shielded; the total azimuthal electric field (i.e. induced plus potential) tends to be small, which explains why the radial flow velocity is slow during quasi-steady conditions prevailing during the growth phase and after the active phase. The nonlocal response of the plasma also leads to the development of a parallel current that may generate current driven Alfvén (CDA) waves, which mode convert into shear Alfvén (SA) waves. CDA/SA waves are systematically observed at early breakup; they grow very fast and produce a parallel diffusion of electrons. As soon as the diffusion time is shorter than the bounce time (_d<_b), the nonlocal response vanishes. Thus the shielding disappears, and an enhanced transport is restored at the rate fixed by the induced electric field alone. We show that fast flows effectively occur when CDA waves have enough power to diffuse electrons (over _d<_b). Electron parallel diffusion also leads to an interruption of the parallel current and therefore to a disruption of the perpendicular current.     

Survey of MeV proton anisotropies measured by Ulysses

The Anisotropy Telescopes (ATs) instrument, part of the COSPIN experiment on board Ulysses, measures fluxes and anisotropies of protons in the MeV range. We survey data from this instrument throughout the Ulysses mission, with particular emphasis on solar maximum, when large particle intensities were measured. The only significant fluxes detected by the ATs during solar minimum are those associated with corotating interaction regions. We focus on events characterised by very large first-order anisotropies, indicating beam-like streaming along the magnetic field lines, and also on times of unusually low and constant anisotropies. We describe the parameters associated with these events and put forward possible physical explanations of the extreme anisotropies observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plasma effects in the formation,evolution and present configuration of the Saturnian ring system

The Voyager 1 and 2 observations of the fine structure of the Saturnian ring system demonstrate the importance of electric forces in controlling the dynamics of fine (charged) dust in the rings. A new theory (“gravito-electrodynamics”) which combines the electric and the gravitational forces on these grains leads to natural explanations of a number of observed ring phenomena. If plasma processes play a significant role in the dynamics of the ring system at the present time, it is difficult to avoid the conclusion that they also played an important and perhaps crucial role at cosmogonic times during the emplacement and subsequent condensation of the initial dusty plasma. We believe that the Saturnian ring system represents a “time-capsule” containing vital clues about the physical processes operating during the early stages of its formation. We will show that both its overall structure as well as its fine structure, as determined by Voyagers 1 and 2, indicate the crucial importance of plasma processes in its formation and subsequent evolution.     

Study of energy release in flares

Recent advances in the study of energy release in Flares are reviewed. Progress has been made in modelling coronal X-ray emission and the chromospheric response to energy imput. These advances are based on theoretical studies and on the comparison of complementary data obtained from spacecraft and ground-based observatories. We first review the modelling of the coronal flare derived from radio, X-ray and XUV observations. Then we summarize results on the chromospheric response to various energy imput. Observations of X-ray continuum intensity and polarization, transition zone lines and chromospheric lines do not show evidence of particle trapping by a turbulent front. Although they might be in agreement with trapping and partial precipitation. White light flares appear to result from energy deposited above the photosphere. They are probably due to electron bombardment. The implication of these results on the primary energy release process are discussed and prospects for new research are presented.