ALBERT

Notes: Conclusions The study of ways of the solar wind energy penetration into the magnetosphere is one of the most important problems of the magnetosphere physics. The solution of such problems as the radiation belts origin, the determination of the magnetic storms and auroral nature is connected with this problem. The magnetic measurements on the satellite OGO-A [157] probably indicate the possibility of the magnetosheath particles penetration into the tail through its side surface. The laboratory simulation of the solar wind flow around the magnetosphere [44–46] also indicate the comparatively rapid penetration of the incident plasma flow particles into the tail. On the other side the aurorae oval location [139–141] and the similarity of electrons spectrum in the aurorae and in the magnetic tail (according to the data of [138]) suggest that the aurorae on the earth nightside are caused by the penetration of particles from the tail plasmasheet. The dayside aurorae can probably appear as a result of the direct penetration of the solar wind particles (thermalized in the magnetosheath) in the vicinity of neutral points, as the geomagnetic field lines passing in this region intersect the earth's surface in the auroral Zone. It is reasonable to carry out the complex investigations of these regions by means of the special system of satellites. Possible experiments on the satellite passing in the region of the neutral point and requirement to the equipment onboard the satellite have been discussed in detail in [152]. In Figure 8 the sampling satellite orbits are shown passing through the regions of dayside neutral point and of neutral plane of the tail. The orbits with an apogee of about 30 R E allow us to compare the different characteristics of the geomagnetic field, trapped and auroral radiation inside the magnetosphere with the solar wind parameters (such as a direction of frozen-in magnetic field, temperature and particles concentration, etc.) and with the magnetosheath parameters. However it is difficult technically to launch a satellite into the region of the south neutral point. Besides, with the prolonged satellite existence outside the magnetosphere boundary we lose the part of the measurements inside the magnetosphere. That is why it is reasonable instead of the orbit SII in Figure 8 to launch a satellite into the north neutral point region but with a less apogee, of about 15 R E (orbit SII in Figure 9). A system of three satellites shown in Figure 9 (it is more profitable technically than the one shown in Figure 8) allows us to perform different measurements simultaneously in the solar wind, in the magnetosheath, in the vicinity of the neutral points, in the tail plasma sheet (including a neutral plane) and in the zone of auroral and trapped radiation. By means of such a system of satellites it is possible, for example, to make a comparison of particles composition simultaneously in the denoted regions of the earth environment. This is necessary for solving many magnetosphere physics problems, for example, the mystery of aurorae. There are indications [144] that in the aurora the ratio of alpha-particles flux to proton flux (I α/Ip) is approximately the same as in the solar wind. However it is unknown in which way these particles penetrate into the aurora region; no simultaneous measurements of the ratio I α/Ip in the tail were made. The measurements of the particles composition are also of interest in studies of different mechanisms of the particles transfer inside the magnetosphere. For example, the experiments [153–154] indicate that the ratio I α/Ip in the inner magnetosphere is approximately by two orders of magnitude less than in the solar wind, and by one order less than predicted by the theory of particles diffusion under the influence of sudden pulses. The other experimental problems connected with the questions discussed are listed below: 1. The determination of the magnetopause shape above the poles and the magnetic tail shape at large distances from the earth. 2. The investigation of the magnetosphere asymmetry in the north-south direction, as indicated by Explorer 12 experiments [155] (such type of asymmetry is not explained by the existing theories). 3. The continuous magnetic measurements on the synchronous satellite (L ∼ 6.6) allow us to restore the significant parameters of the magnetosphere, if a satisfactory quantitative model is available (see for more details [51]). 4. A detailed study of the magnetic field distribution on the magnetosphere boundary and in its vicinity. In the Hones-Taylor model the lines of force located nearly to the magnetosphere forward end, according to [55], have highlatitude minima of intensity B, topologically connected with the equatorial minima B on the nightside. As a result the particles which were equatorial on the nightside, drifting to the dayside, can be put into the higher latitudes. In the Mead-Williams model drift orbit branchings do not occur [51] due to the lack of a similar topological connection. Thus, these magnetic field measurements allow us to choose between different theoretical models and along with the direct particles measurements give a possibility to determine the boundaries of regions of trapped and quasi-trapped radiation. Besides, a detailed study of magnetopause location can answer the question if the magnetosphere boundary is the surface enveloping a family of the magnetic field lines (i.e. if the magnetic field normal component vanishes on the surface of discontinuity) that is of interest for the problem of the solar wind flow around the magnetosphere. 5. Detailed measurements of the magnetic field intensity vector in different regions of the magnetosphere are significant for an estimation of the quantitative models suitability and provide a distribution of the current density j = c/4π rot B; in particular, an experimental test of the idea about two ring currents [92] is of interest. 6. A construction of the model of the electric field in the magnetosphere is significant for the study of behaviour of particles with the energy of several tens keV and below. For this purpose in addition to the direct measurements of the electric field the Brice method [66] can be evidently used which permits one to restore the pattern of a large-scaled electric field from the position and shape of the plasmapause. Plasma ‘running away’ along the open lines of force (a polar wind [78]) must lead to plasmapause shape distortion on these field lines. An experimental test of this effect is necessary, i.e. the measurements of the plasmasphere boundary at different latitudes. 7. Some convection models [65] suggest that in the vicinity of the magnetopause the directions of plasma movement inside the magnetosphere and in the magneto-sheath can be opposite. This conclusion is not in contradiction with the conditions at the tangential discontinuity: V n1 = V n2, V t1 ≠ V n1. It is interesting to determine if such plasma flows really occur, that is necessary for the construction of an adequate picture of the electric field. In conclusion let us enumerate the outstanding significant problems of the physics of the magnetosphere: 1. In which way is the magnetosphere boundary (including the polar regions and magnetic tail) formed as a result of an interaction between solar wind and geomagnetic field? To what extent is magnetohydrodynamics applicable to a description of these phenomena? 2. How does the energy (and/or particles) of the solar wind penetrate into the magnetosphere? In which way is the momentum transferred to the convective motions of plasma in the magnetosphere? Do the solar wind particles penetrate directly into some regions of the magnetosphere? Are the energy and momentum transferred into the magnetosphere with a constant speed or periodically? 3. Does the energy accumulation in a magnetic tail exist and in what way does it occur? What is the nature of a ‘trigger mechanism’ which releases su

Notes: Abstract Parameters of the plasma in the inner coma of comet Halley are derived from the magnetic field measurements by using single particle approximation. Both the plasma velocity and the temperature obtained by using this approach are self-consistent and happen to be in good agreement within situ measurements whereas the neutral gas production rate happens to be 2–3 times higher than the conventionally cited value 6.9 × 1029 s−1.

Notes: Abstract In this study we test a stream function method suggested by Israelevich and Ershkovich for instantaneous reconstruction of global, high-latitude ionospheric convection patterns from a limited set of experimental observations, namely, from the electric field or ion drift velocity vector measurements taken along two polar satellite orbits only. These two satellite passes subdivide the polar cap into several adjacent areas. Measured electric fields or ion drifts can be considered as boundary conditions (together with the zero electric potential condition at the low-latitude boundary) for those areas, and the entire ionospheric convection pattern can be reconstructed as a solution of the boundary value problem for the stream function without any preliminary information on ionospheric conductivities. In order to validate the stream function method, we utilized the IZMIRAN electrodynamic model (IZMEM) recently calibrated by the DMSP ionospheric electrostatic potential observations. For the sake of simplicity, we took the modeled electric fields along the noon-midnight and dawn-dusk meridians as the boundary conditions. Then, the solution(s) of the boundary value problem (i.e., a reconstructed potential distribution over the entire polar region) is compared with the original IZMEM/DMSP electric potential distribution(s), as well as with the various cross cuts of the polar cap. It is found that reconstructed convection patterns are in good agreement with the original modeled patterns in both the northern and southern polar caps. The analysis is carried out for the winter and summer conditions, as well as for a number of configurations of the interplanetary magnetic field.

Notes: Abstract A new method to reconstruct the instantaneous convection pattern in the Earth’s polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes). The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma veloCity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity.

Notes: Abstract The effect of pressure anisotropy on geomagnetic tail oscillations is studied using the Chew-Goldberger-Low equations. It is shown that anisotropy of the solar wind plasma pressure may result in generation of waves, assuming no waves in the case of isotropy. Anisotropy of the plasma pressure in the magnetospheric tail may also cause a basic distortion of the oscillation spectra.

Notes: Abstract The stability of both the main cometary plasma tail and the tail rays is considered, taking into account the coupling between the plasma and the neutrals that flow out radially from the nucleus. It is shown that this coupling has a negligible effect on wave damping. Rather, we found that the neutral wind tends to destabilize the flanks of the main tail. On the other hand, the cometary rays are subject to both stabilizing and destabilizing effects because of the ion-neutrals drag. As a result, helical perturbations should become azimuthally asymmetric. Our study predicts that the folding rays may become wavy while approaching the tail axis, whereas they should remain straight far away from the tail axis.

Notes: Abstract The model problem simulating a vortex development is solved numerically. Breakdown of the velocity sheared layer due to the nonlinear evolution of the Kelvin-Helmholtz instability is shown to lead to the wave crest overturning and, eventually, to formation of a large-scale vortex. The magnetic field strength in the vortex core turns out to be lower than that in the ambient plasma, so that vortex core may be called “the magnetic channel”. The mechanism of the magnetic field generation by a single vortex is studied analytically within the framework of magnetokinematics. It appeared that there is no magnetic field generation in the vortex core where rotation of the plasma is rigid. Therefore, the magnetic field here is reduced, and hence the plasma density is enhanced. These results seem to support the hypothesis of the comet ray origin as magnetically channeled outflow: the magnetic channel might become visible as a comet ray against adjacent plasma of lesser density outside the magnetic channel.

Notes: Abstract The point source of neutral gas undergoing ionization and expanding into an uniform magnetic field is considered. Friction between the neutral and ionized particles results in the formation of the magnetic field barrier and diamagnetic cavity surrounding the source. At least one neutral point inevitably arises at the boundary of the cavity. When the neutral gas production rate grows, two neutral points may arise at this boundary. In the vicinity of these points magnetic field lines converge, along with the plasma flow which is magnetic field aligned in the steady state. As a result, two plasma jets originate from the neutral points. Possible relation of these jets to cometary rays is discussed.