Yu. I. Galperin’s research while affiliated with Space Research Institute, Russian Academy of Sciences and other places

A unified electrostatic MHD theory is developed to describe small-scale plasma structures with arbitrary amplitude moving in auroral ionosphere, or magnetosphere, with a constant velocity V in respect to ambient plasma, which is drifting under the action of large-scale electric field E. The theoretical model includes additional dissipative terms in comparison with that described in accompanying paper by the same authors. It accounts for ion and electron inertia, dynamic ion viscosity, deviation from quasi-neutrality. The equations are derived in respect to the variable S=x−Vt for one-dimensional models, and S=x+αz−Vt for a two-dimensional model. In the two-dimensional form of the theory for the strongly collisional case, the vector nonlinearity (or, Poisson brackets) gives the main stabilizing effect to the two-stream instability leading to a stationary turbulence level with density fluctuations of order 10% or more. Damped large-amplitude oscillations superimposed on an electrostatic shock are excited which can be VHF radar aurora scatterers for the non-zero aspect angles. Qualitative agreement with the results of radar aurora studies and in situ rocket measurements is found.

Some results of the Soviet–French ARCAD-3 project (AUREOL-3 satellite) are reviewed and discussed. The system of magnetohydrodynamic equations (up to the second moments, neglecting the others), with a rigorous account of all drifts and currents or trapping, in a curved and convergent field tube is derived for a particle population with a bi-Maxwellian particle distribution and with . Its first four integrals are derived for a particular case, when spatial variations of the electric field are much more rapid than those of any other macroscopic parameters or their products. This is a realistic condition for an extended stable double layer in an inverted V structure. A specific feature of these integrals is that the polarization-drift effects inherently affect the field-aligned current (FAC) density carried by a particular population if both field-aligned and perpendicular gradients of the electric field are sufficiently high. This is important for double layers extended along the magnetic field in narrow, oblique inverted V's. A three-dimensional geometry of the plasma-sheet pressure gradients , the FAC's, and the polarization and ionospheric closure currents , and is suggested, which is supposed to lead to the formation of a narrow arc at a side of an inverted-V event. Sample calculation results for a two-dimensional geometry in limited areas of the meridional plane with simplest boundary conditions are shown for illustration.

Long-lasting ground based measurements of a polarization jet (PJ) by the latitudinal chain of ionospheric stations in Yakutia (3 < L < 5; MLT = UT + 9 h) and by 5 subauroral Russian stations were analyzed. A number of cases were found when PJ was recorded simultaneously with energetic ion observations by AMPTE/CCE and INTERBALL 2. The data comparison shows that at least in the considered cases of strong magnetic substorms, PJ was accompanied by strong injection of ions with the energy of ∼ 20 – 50 keV and intensity of ∼ 106 cm −2 c−1 ster−1 keV−1. Close to the injection region in the near midnight sector no ion dispersion was observed, but in the evening sector nose events were detected. In accordance with a mechanism suggested by Southwood and Wolf (1978) PJ was observed near the equatorial boundary of energetic ion penetration into the magnetosphere. Measurements by ionosondes at different longitudes show that the westward velocity of the front of PJ development is close to the gradient drift velocity of 20 keV ions (forming nose events). Thus, the physical mechanism of PJ formation due to energetic ion injection during a strong substorm burst is experimentally confirmed. Satellite measurements show that in the near midnight sector energetic ions reach the shell L = 3.0 in 20 – 30 minutes after a substorm commencement with AE > 500 nT.

A 3D fully nonlinear theory of ion acoustic solitary structures is constructed in three-component plasma consisting of non-thermal electrons, a hot ion background and a cold ion beam. The theory is based on the derivation of a modified Korteweg-de Vries-Zakharov-Kuznetzov (KdV-ZK) equation. The ion motion is treated in the MHD approximation with self-consistent distributions and dynamics of all plasma components. Some numerical examples are presented for plasma conditions pertinent to the subauroral magnetosphere and outer plasmasphere in the stage of refilling after a magnetic storm.

The theoretical models of the formation of the three-dimensional quasi-stationary structures of variations of density and electrostatic potential in a multicomponent magnetosphere plasma are considered. On the basis of the perturbation method, we have studied the domains of the parametric space, where the occurrence of nonlinear quasi-stationary ion-acoustic and electron-acoustic structures are possible. For these structures, the velocities of motion along the direction of the magnetic field are estimated, together with the longitudinal and transverse scales with respect to the direction of the Earth's magnetic field. The calculated dependences of the scales l and l || of the structures on the plasma parameters in the three-component plasma allow one to compare the results of the considered theoretical models with new experimental data of measuring the form of soliton structures onboard the FAST, POLAR, and GEOTAIL satellites.

The results of measuring the fluxes of ionospheric ions in the nightside polar cap at an altitude of about 20 000 km are presented. The data are obtained with the HYPERBOLOID instrument onboard the INTERBALL-2 satellite. The passages without intense precipitation of magnetospheric ions and electrons have been selected using the ION instrument data, so that the observation of ionospheric ion fluxes caused by heating in the auroral regions can be excluded. In addition, an attempt has been made to exclude observations of the cleft ion fountain from the analysis. The measurements in the summer and winter seasons (when the ionosphere was totally sunlit and completely shadowed, respectively) are considered separately. By analyzing the distribution functions of the fluxes measured, we have isolated six different types of ionospheric plasma flows in the polar cap. A strong distinction has been revealed between summer and winter flows. In winter, only weak flows of H+ ions were detected. In the summer period, we detected both H+ and O+ ions. The flux values of the ionosphere ions are found to be strongly dependent on the intensity of the polar rain. The measurements are compared to the existing models of the polar wind. The best models (for the description of our measurements) are indicated. After the choice of measurement periods, the resulting region coincides with the ion depletion zone (IDZ). Based on the earlier measurements by the AKEBONO satellite, nothing could be said about the fluxes of thermal ions in this zone, because of the insufficient sensitivity of the instrument aboard this satellite.

Polarization Jet (PJ), also known as Sub-Auroral Ion Drift (SAID), events are supersonic westward plasma drifts on the equatorward edge of the diffuse aurora in the evening and nighttime sector. Their optical F-region signatures are weak 630.0 nm red arcs colocated with regions of fast convection. These weak arcs resemble Stable Auroral Red (SAR) arcs observed during the recovery phase of magnetic storms, but have lower intensities, shorter lifetimes, and occur without a significant heat flux from the magnetosphere. Previous model studies underestimated the brightness of weak SAR arcs. We present calculations showing that ion-neutral collisional heating and ion composition changes during PJ events may be an additional source of 630.0 nm emission, and propose experimental tests that could verify our modeling results.

The Interball-2 spacecraft travels at altitudes extending up to 20 000 km, and becomes positively charged due to the low-plasma densities encountered and the photoemission on its sunlit surface. Therefore, a knowledge of the spacecraft potential Fs is required for correcting accurately thermal ion measurements on Interball-2. The determination of Fs is based on the balance of currents between escaping photoelectrons and incoming plasma electrons. A three-dimensional model of the potential structure surrounding Interball-2, including a realistic geometry and neglecting the space-charge densities, is used to find, through particle simulations, current-voltage relations of impacting plasma electrons Ie (Fs ) and escaping photoelectrons Iph (Fs ). The inferred relations are compared to analytic relationships in order to quantify the effects of the spacecraft geometry, the ambient magnetic field B0 and the electron temperature Te . We found that the complex geometry has a weak effect on the inferred currents, while the presence of B0 tends to decrease their values. Providing that the photoemission saturation current density Jph0 is known, a relation between Fs and the plasma density Ne can be derived by using the current balance. Since Jph0 is critical to this process, simultaneous measurements of Ne from Z-mode observations in the plasmapause, and data on the potential difference Fs - Fp between the spacecraft and an electric probe (p) are used in order to reverse the process. A value Jph0 ~ = 32 µAm-2 is estimated, close to laboratory tests, but less than typical measurements in space. Using this value, Ne and Fs can be derived systematically from electric field measurements without any additional calculation. These values are needed for correcting the distributions of low-energy ions measured by the Hyperboloid experiment on Interball-2. The effects of the potential structure on ion trajectories reaching Hyperboloid are discussed quantitatively in a companion paper.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)

A review of the observed space scales of the auroral features ranging from the whole auroral oval of bright discrete forms down to the nonlinear moving solitary structures with the scales of the order of Debye length is given. The characteristic physical scale which determines the generation process is indicated whenever possible. Some problems of the auroral theory and modeling are briefly discussed, and a cross-scale coupling between the auroral and magnetospheric altitudes is stressed. It becomes apparent that the first in situ studied real astrophysical plasma object—the Earth's magnetosphere/ionosphere/aurora—is a unified multi-scale system which seems to be ordered at large scales, but sometimes looks as nearly nondeterministic, or chaotic, at small scales. The most powerful processes in this system operate in a very wide range of scales, with multifarious cross-scale couplings. The statistical behavior of magnetospheric/auroral plasmas in the regions of active auroras often can be reasonably described as the near-critical state.

Closely -space multi-spacecraft group of high-altitude satellites allow investigation of magnetosphere plasma physics with the help of satellite radiotomography method for electron density distributions. The original idea of the ROY project is to use a constellation of spacecrafts (one main and several subsatellites) in order to carry out closely-spaced multipoint measurements and 2D tomographic reconstruction of electron density in the space between the main satellite and the subsatellites. The distances between the satellites were chosen to vary from dozens to few hundreds of kilometers. The simplest data interpretation is achieved when the subsatellites are placed along the virtual axis parallel to plasma streamline. Then, whenever a plasma density irregularity moves between the main satellite and the subsatellites it will be scanned in different directions and we can get 2D distribution of plasma using these projections. However in general the plasma streamline is not exactly parallel to subsatellites axis and not necessarily is within the multi-spacecraft plane. The method of plasma velocity determination relative to multi-spacecraft systems is considered. The technique was tested for various modeled structures and random electron density distributions. The results show the reliable tomographic reconstruction of electron density distributions for the plasma velocity deviation from the system axis on the angles of the order of ten degrees. Possibilities of 3D tomographic imaging using multi-spacecraft systems are analyzed. The modeling has shown that efficient scheme for 3D tomographic imaging would be to place ad ditional spacecrafts in different planes so that the angle between the planes would make not more then obtained critical value of ten degrees. Work is supported by grant INTAS 2000-465.