S. Savin

First measurements of plasma waves near Mars

HERE we report preliminary results from electic field measurements in the environment of Mars using the plasma-wave system on board the Soviet spacecraft Phobos 2. It also includes a Lang-muir probe which measured plasma densities. Electron-plasma oscillations observed upstream of the bow shock correspond to a solar-wind density of 2 cm-3. The shock-foot boundary was crossed up to three times on each orbit. The shock ramp was detected at altitudes between 0.45 and 0.75 Mars radii (RM) above the planetary surface. The density increased by about a factor of two at the ramp. The shock position, although variable, seemed to be consistent with previous measurements. The downstream mag-netosheath contained broadband electric-field noise below the plasma frequency. The boundary of the obstacle, or planetopause, was crossed at altitudes of the order of 0.28 RM; the cold plasma density was highly variable within the planetopause and reached the unexpected value of 700 cm-3 on the third orbit, at 0.25 Rm altitude. Bursts of waves with frequencies below the electron cyclotron frequency, possibly in the whistler mode, occur within the planetopause.

The interplanetary shock of September 24, 1998: Arrival at Earth

At close to 2345 UT on September 24, 1998, the magnetosphere was suddenly compressed by the passage of an interplanetary shock. In order to properly interpret the magnetospheric events triggered by the arrival of this shock, we calculate the orientation of the shock, its velocity, and its estimated time of arrival at the nose of the magnetosphere. Our best fit shock normal has an orientation of (−0.981 −0.157 −0.112) in solar ecliptic coordinates, a speed of 769 km/s, and an arrival time of 2344:19 at the magnetopause at 10 RE. Since measurements of the solar wind and interplanetary magnetic field are available from multiple spacecraft, we can compare several different techniques of shock-normal determination. Of the single spacecraft techniques the magnetic coplanarity solution is most accurate and the mixed mode solution is of lesser accuracy. Uncertainty in the timing and location of the IMP 8 spacecraft limits the accuracy of solutions using the time of arrival at the position of IMP 8.

High energy jets in the Earth’s magnetosheath: Implications for plasma dynamics and anomalous transport

High energy density jets in the magnetosheath near the Earth magnetopause were observed by Interball-1 [1]. In this paper, we continue the investigation of this important physical phenomenon. New data provided by Cluster show that the magnetosheath kinetic energy density during more than one hour exhibits an average level and a series of peaks far exceeding the kinetic energy density in the undisturbed solar wind. This is a surprising finding because the kinetic energy of the upstream solar wind in equilibrium should be significantly diminished downstream in the magnetosheath due to plasma braking and thermalization at the bow shock. We suggest resolving the energy conservation problem by the fact that the nonequilibrium jets appear to be locally superimposed on the background equilibrium magnetosheath, and, thus, the energy balance should be settled globally on the spatial scales of the entire dayside magnetosheath. We show that both the Cluster and Interball jets are accompanied by plasma superdiffusion and suggest that they are important for the energy dissipation and plasma transport. The character of the jet-related turbulence strongly differs from that of known standard cascade models. We infer that these jets may represent the phenomenon of the general physical occurrence observed in other natural systems, such as heliosphere, astrophysical, and fusion plasmas [2–10].

Plasma and waves around Mars

Abstract The Plasma Wave System (PWS) on board the Soviet Spacecraft Phobos 2 has performed electron density and, for the first time, electric field measurements in the environment of the planet Mars. Electron plasma oscillations are observed upstream of the bow shock and yield a solar wind density of the order of 2 cm−3; the shock foot and/or ion foreshock are detected on each orbit. The altitude of the bow shock in the noon sector fluctuates between 0.45 and 0.75 Mars radii (Rms) above the planetary surface. The downstream solar wind, in the planetosheath, is characterized by increased plasma density and broadband electrostatic noise. The planetopause is crossed at altitudes of the order of 0.28 Rms. Electromagnetic waves with frequencies below the local gyrofrequency, propagating in the whistler mode, are recorded within the planetosphere, where the electron plasma density reaches unexpectedly large values, of up to 700 cm−3 at an altitude of 0.25 Rms. Intense electrostatic emissions generated by heavy planetary ions are observed upstream of the shock ; these waves are linked with the erosion process of the Martian atmosphere by the solar wind.

The cusp/magnetosheath interface on May 29, 1996: Interball‐1 and Polar observations

On May 29, 1996, under steady strong northward IMF and high solar wind dynamic pressure conditions both Polar and Interball cross field lines that pass through the northern cusp and apparently close to the post-cusp reconnection site. The magnetopause current observed by Interball consists of two quite distinct layers, an inner broad current that is quite turbulent and another current that is quite abrupt and quiet. Polar also crosses current layers, similar to the Interball inner one. These observations support a model in which cusp field lines experience essentially stochastic behavior but on average provide topological connection between the cusp and magnetosheath.

Turbulent Boundary Layer at the Border of Geomagnetic Trap

A new phenomenon was discovered on the basis of analysis of the Interball project data. A hot plasma flow is thermalized through the formation of “long-operating” vortex streets and local discontinuities and solitons in a distributed region over polar cusps. Plasma percolation through the structured boundary and secondary reconnection of fluctuating magnetic fields in a high-latitude turbulent boundary layer account for the main part of solar wind plasma inflow into the magnetospheric trap. Unlike local shocks, the ion thermalization is accompanied by the generation of coherent Alfvén waves on the scales ranging from ion gyroradius to the radius of curvature of the averaged magnetic field, as well as by the generation of diamagnetic bubbles with a demagnetized heated plasma inside. This “boiling” plasma has a frequency region where the spectrum is different from the Kolmogorov law (with slopes 1.2 and 2.4 instead of 5/3 or 3/2). The fluctuation self-organization in the boundary layer (synchronization of three-wave decays) was observed on certain frequency scales.

Observation of the magnetospheric "sash" and its implications relative to solar-wind/magnetospheric coupling: A multisatellite event analysis

Using a unique data set from the Wind, Polar, Interball 1, Magion 4, and Defense Meteorological Satellite Program (DMSP) F11 satellites, comparisons with the Integrated Space Weather Model (ISM) have provided validation of the global structure predicted by the ISM model, which in turn has allowed us to use the model to interpret the data to further understand boundary layers and magnetospheric processes. The comparisons have shown that the magnetospheric “sash” [White et al., 1998], a region of low magnetic field discovered by the MHD modeling which extends along the high-latitude flank of the magnetopause, is related to the turbulent boundary layer on the high-latitude magnetopause, recently mapped by Interball 1. The sash in the data and in the model has rotational discontinuity properties, expected for a reconnection site. At some point near or behind the terminator, the sash becomes a site for reconnection of open field lines, which were previously opened by merging on the dayside. This indicates that significant reconnection in the magnetotail occurs on the flanks. Polar mapped to the high-density extension of the sash into the tilted plasma sheet. The source of the magnetosheath plasma observed by Polar on closed field lines behind the terminator was plasma entry through the low field connection of the sash to the central plasma sheet. The Polar magnetic field line footprints in each hemisphere are moving in different directions. Above and below the tilted plasma sheet the flows in the model are consistent with the corresponding flows in the ionosphere. The turbulence in the plasma sheet allows the convection patterns from each hemisphere to adjust. The boundary layer in the equatorial plane on the flank for this interplanetary magnetic field BY condition, which is below the tilted central plasma sheet, is several RE thick and is on tailward flowing open field lines. This thick boundary layer shields the magnetopause from viscous forces and must be driven by magnetic tension. Above the plasma sheet the boundary layer is dominated by the sash, and the model indicates that the open region inside the sash is considerably thinner.

High-altitude cusp: INTERBALL observation

Abstract The cusp is a funnel-shaped part of the Earths magnetosphere where the magnetospheric magnetic field lines are directly interconnected with the magnetosheath ones. The magnetic field configuration allows the magnetosheath plasma to precipitate toward the ionosphere. This feature is used for the determination of the cusp position in low altitudes. However, it is often difficult to distinguish different plasma populations in high altitudes. The cusp region is bounded with the low-latitude boundary layer (LLBL), entry layer or cleft on the equatorward side, and by the plasma mantle on the poleward side, but the plasma and magnetic field parameters are similar in all these regions. We have used the INTERBALL-1 and MAGION-4 satellites to study the topology and dynamics of high-altitude cusp regions under quiet solar wind conditions but different directions of the interplanetary magnetic field (IMF). Two-point event studies have shown that (1) the topology of the magnetic field in the high-altitude cusp is controlled by the IMF direction, (2) the cusp plasma source is located near the tailward boundary of the cusp during northward IMF, and (3) magnetosheath fluctuations are correlated with the fluctuations of the cusp precipitation.

Intermittency and extended self-similarity in space and fusion plasma: boundary effects

A comparative study of fluctuation features in the edge plasma of fusion devices and in turbulent boundary layers (TBLs) of the Earths magnetosphere has demonstrated similar statistical characteristics including scalings of structure functions and multifractal spectra. The detected intermittency and anomalous transport of mass and momentum is carried by sporadic plasma flux bursts with nonGaussian probability of flux magnitude. The turbulence exhibits a generalized (extended) self-similarity in an extended scale range. The experimental scalings of the structure functions are rather well fitted by the log-Poisson model considering quasi-1D singular dissipative structures. It appears that the turbulence in the edge plasma of fusion devices and in the TBL of the Earths magnetosphere is governed by cross-field motions similar to hydrodynamic turbulence. Here the experimental scalings from the plasma are available for a comparison with experimental results from neutral fluids. The plasma scalings display universal properties of intermittent turbulence. A statistical approach permits us to evaluate turbulent transport scalings. The time dependence of an average squared particle displacements δx2 ∝ τα infers superdiffusion with α ≈ 1.4–1.87 > 1.

Relaxation of plasma at the shock front

Abstract Brief overview of previous studies of ion thermalization at the shock transition is given. One non-quite typical Prognoz-8 quasi-perpendicular bow shock crossing on 11 February 1981 is considered for which high-time resolution data on plasma and ELF electric field fluctuations are available. Strong turbulence in LH-range that is associated with two-stream ion motion upstream of shock transition is characterized by an exponential growth and saturation of these fluctuations at a level of ∼100 mV/m. The heating of ions at the main shock transition is associated with pulse-like increase of these waves amplitude. Relaxation of gyrating beams downstream of the main shock transition appears to be associated with ion-cyclotron waves and additional heating of ions and passes through two phases: hydrodynamic and kinetic ones. Linear and time scales of the events are estimated.