A. Skalsky

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.

Position and shape of the Martian bow shock: the Phobos 2 plasma wave system observations

Abstract We have derived a Martian bow shock model using all the data that are available from the plasma wave system on the Phobos 2 spacecraft. In contrast with a previous study, performed with a limited data set of 26 shock encounters, we have considered about 120 shock crossings, including four new distant downstream shocks. Thus, the shock position is determined accurately at the nose (four inbound shocks with the elliptical orbits), at the terminator (more than 110 inbound and outbound shocks in the circular orbits), and far downstream (four outbound shocks with the elliptical orbits). Emphasis is placed upon comparisons with the results of earlier studies derived from smaller data sets, data sets that come from other experiments and/or other missions. The location of the bow shock of Mars seems to respond to variations in solar activity, as is the case for Venus. On the other hand, the subsolar stand-off distance appears to vary slightly with the solar wind dynamic pressure: the greater the subsolar shock distance is from the planet, the lower the solar wind dynamic pressure. Assuming a sixth-root dependence. an upper limit of a possible Martian magnetic moment of 2.2 × 1012Tm3 has been obtained. Finally, the shock is closer to Mars on the dawn side than on the dusk side at the terminator: the angle between the local bow shock normal and the upstream magnetic field controls this asymmetry.

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.

Anomalous interaction of a plasma flow with the boundary layers of a geomagnetic trap

Using the data from the Interball-1, GEOTAIL, THEMIS and CLUSTER satellites, we propose a mechanism of anomalous magnetosheath dynamics. This mechanism yields that plasma boundaries can be locally deformed over distances comparable to its thickness. In particular, the magnetospheric boundary, the magnetopause, is deformed over distances up to a few Earth radii (RE) under the pressure of supermagnetosonic plasma streams (SPSs), instead of reacting to plasma pressure decreases, as it was previously thought. Supermagnetosonic plasma streams having a kinetic pressure a few times larger than the solar wind pressure and the magnetic pressure behind the magnetopause, can crush the magnetopause and even push it outside the mean bow shock position, as determined through the average pressures balance. Anomalous magnetosheath dynamics is initiated by plasma flow anomalies (FAs), triggered by rotational discontinuities, by jumps in the solar wind pressure and by interplanetary shocks, which all interact with the bow shock. We show that the generation mechanism for SPSs, adjacent to the FA, is connected with the compensation of the FA flow reduction by the SPS enhanced flow, which is produced by polarization electric fields at the FA edges. Statistically, SPSs are extreme events, relayed with intermittency and multifractality inside the boundary layers of the geomagnetic trap. In this way, SPSs provide “long-range” interactions between global and microscales. A similar role may be played by fast concentrated flows in the geomagnetic tail, in fusion devices, in astrophysical plasmas and in hydrodynamics.

Simultaneous plasma wave and electron flux observations upstream of the Martian bow shock

Abstract Flux enhancements of electrons with energies between 100 and 530 eV are observed simultaneously with electron plasma waves in the upstream region of the Martian bow shock. The electron flux appears to reach its maximum when the pitch angle is close to 0°, which corresponds to particles reflected from the shock region and backstreaming in the solar wind along the magnetic field. The correlation between high-frequency waves and enhanced electron fluxes is reminiscent of several studies on the electron foreshock of the Earth. Such a similarity indicates that, in spite of major differences between the global shock structures, the microscopic processes operating in the foreshocks of Earth and Mars are probably identical.

Dynamic Interaction of Plasma Flow with the Hot Boundary Layer of a Geomagnetic Trap

The study of the interaction between collisionless plasma flow and stagnant plasma revealed the presence of an outer boundary layer at the border of a geomagnetic trap, where the super-Alfvén subsonic laminar flow changes over to the dynamic regime characterized by the formation of accelerated magnetosonic jets and decelerated Alfvén flows with characteristic relaxation times of 10–20 min. The nonlinear interaction of fluctuations in the initial flow with the waves reflected from an obstacle explains the observed flow chaotization. The Cherenkov resonance of the magnetosonic jet with the fluctuation beats between the boundary layer and the incoming flow is the possible mechanism of its formation. In the flow reference system, the incoming particles are accelerated by the electric fields at the border of boundary layer that arise self-consistently as a result of the preceding wave-particle interactions; the inertial drift of the incoming ions in a transverse electric field increasing toward the border explains quantitatively the observed ion acceleration. The magnetosonic jets may carry away downstream up to a half of the unperturbed flow momentum, and their dynamic pressure is an order of magnitude higher than the magnetic pressure at the obstacle border. The appearance of nonequilibrium jets and the boundary-layer fluctuations are synchronized by the magnetosonic oscillations of the incoming flow at frequencies of 1–2 mHz.

A comparison between the Earth's and Mars' bow shocks detected by the Phobos plasma-wave system

Abstract Among the scientific instruments on the Phobos spacecraft, one was expected to study the plasma and wave phenomena in the Martian environment: the Plasma-Wave System, PWS. Here we report on the PWS plasma and electric-field spectrum measurements during two Martian bow shock crossings by Phobos 2: one is located near the subsolar point and the other near the dusk terminator. A comparison is also made with the Earths shock crossed by Phobos 1. As at Earth, three main regions were identified: the upstream region, the shock transition region and the downstream region. A shock foot boundary is often observed in front of the bow shock. This foot is known to be associated with gyrating ions reflected from the shock. Electric-field spectra are presented and tentatively interpreted. The dynamic spectrograms shown in this report differ from the ones published previously, for the fact that the filter channels are not sampled at the same time has been taken into account.

On nonlinear cascades and resonances in the outer magnetosphere

The paper addresses nonlinear phenomena that control the interaction between plasma flow (solar wind) and magnetic barrier (magnetosphere). For the first time we demonstrate that the dominant solar wind kinetic energy: (i) excites boundary resonances and their harmonics which modulate plasma jets under the bow shock; (ii) produces discrete three-wave cascades, which could merge into a turbulent-like one; (iii) jet produced cascades provide the effective anomalous plasma transport inside and out of the magnetosphere; (iv) intermittency and multifractality characteristics for the statistic properties of jets result in a super-ballistic turbulent transport regime. Our results could be considered as suggestive for the space weather predictions, for turbulent cascades in different media and for the laboratory plasma confinement (e.g., for fusion devices).

Deceleration of the solar wind upstream of the martian bow shock. Mass-loading or foreshock features?

Abstract The role of different processes which could be responsible for deceleration of the solar wind upstream of the martian bow shock is discussed. It is shown that the geometry of the foreshock strongly controls variations of the solar wind velocity. Deceleration of the solar wind was observed on three elliptical orbits when the spacecraft approached the planet inside the foreshock. Variations of the solar wind speed are not consistent with the ones expected for ring-like distribution of pickup protons. Effects related with deceleration in the foreshock and transient phenomena (Alfven waves) dominate and mask mass-loading effects if they do exist.