Zdenek Nemecek

Comprehensive study of the magnetospheric response to a hot flow anomaly

We present a comprehensive observational study of the magnetospheric response to an interplanetary magnetic field (IMF) tangential discontinuity, which first struck the postnoon bow shock and magnetopause and then swept past the prenoon bow shock and magnetopause on July 24, 1996. Although unaccompanied by any significant plasma variation, the discontinuity interacted with the bow shock to form a hot flow anomaly (HFA), which was observed by Interball-1 just upstream from the prenoon bow shock. Pressures within and Earthward of the HFA were depressed by an order of magnitude, which allowed the magnetopause to briefly (∼7 min) move outward some 5 RE beyond its nominal position and engulf Interball-1. A timing study employing nearby Interball-1 and Magion-4 observations demonstrates that this motion corresponded to an antisunward and northward moving wave on the magnetopause. The same wave then engulfed Geotail, which was nominally located downstream in the outer dawn magnetosheath. Despite its large amplitude, the wave produced only minor effects in GOES-8 geosynchronous observations near local dawn. Polar Ultraviolet Imager (UVI) observed a sudden brightening of the afternoon aurora, followed by an even more intense transient brightening of the morning aurora. Consistent with this asymmetry, the discontinuity produced only weak near-simultaneous perturbations in high-latitude postnoon ground magnetometers but a transient convection vortex in the prenoon Greenland ground magnetograms. The results of this study indicate that the solar wind interaction with the bow shock is far more dynamic than previously imagined and far more significant to the solar wind-magnetosphere interaction.

Magnetopause motion driven by interplanetary magnetic field variations

We use previously reported observations of hot flow anomalies (HFAs) and foreshock cavities to predict the characteristics of corresponding features in the dayside magnetosheath, at the magnetopause, and in the outer dayside magnetosphere. We compare these predictions with Interball 1, Magion 4, and GOES 8/GOES 9 observations of magneto-pause motion on the dusk flank of the magnetosphere from 1800 UT on January 17 to 0200 UT on January 18, 1996. As the model predicts, strong (factor of 2 or more) density enhancements bound regions of depressed magnetosheath densities and/or outward magnetopause displacements. During the most prominent event, the geosynchronous spacecraft observe an interval of depressed magnetospheric magnetic field strength bounded by two enhancements. Simultaneous Wind observations indicate that the intervals of depressed magnetosheath densities and outward magnetopause displacements correspond to periods in which the east/west (By) component of the interplanetary magnetic field (IMF) decreases to values near zero rather than to variations in the solar wind dynamic pressure, the north/south component of the IMF, or the IMF cone angle.

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].

Analysis of the 3-D shape of the terrestrial bow shock by interball/magion 4 observations

Abstract Location and shape of the terrestrial bow shock are analyzed using MAGION 4 (sub satellite of INTERBALL 1) crossings of this boundary and upstream solar wind parameters measured by the WIND spacecraft. Different crossing points were mapped to the Sun — Earth line and to the terminator plane using an analytical model of the planetary bow shock previously developed for the Martian bow shock investigation. Analysis of the subsolar bow shock position as a function of Alfvenic Mach number ( M a ) revealed fine effect that this boundary tends to approach the Earth when M a is decreasing for field-aligned flow of the solar wind, while for non field-aligned flow the bow shock moves away from the planet. Asymmetry of the terrestrial bow shock in the terminator plane is found for non field-aligned flow with anisotropic Friedrichs diagrams.

Mass-loss rate for MF resin microspheres

This paper deals with the influence of experimental conditions on properties of melamine formaldehyde resin particles. Motivation for this study was the fact that many laboratories and experimenters use these particles as samples for dust plasma investigations. We have found that the mass of these grains decreases during long-time exposure in vacuum. This decrease proceeds much faster if the temperature of grains is increased.

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.

Fast measurements of parameters of the Solar Wind using the BMSW instrument

Design of the plasma spectrometer BMSW (Fast Monitor of the Solar Wind, possessing high temporal resolution) is described in the paper, as well as its characteristics and modes of operation. Some examples of measurements of various properties of the solar wind, made with this instrument installed onboard the high-apogee satellite Spektr-R, are presented.

Two‐point measurements of the magnetopause: Interball observations

The impulsive penetration model predicts that blobs of solar wind plasma penetrate the magnetosphere by becoming detached from the magnetopause. If so, negative radial density gradients should be common near the magnetopause. We present the results of case and statistical studies of simultaneous Interball 1 and Magion 4 omnidirectional plasma sensors (VDP) plasma observations during magnetopause passes. The spacecraft observe very similar features when their interspacing is small. By contrast, the spacecraft located farther radially outward invariably observes densities greater than or equal to those seen at the spacecraft nearer Earth when the interspacing increases. The observations are consistent with the standard interpretation in which a boundary layer of plasma with intermediate densities often lies sandwiched between the magnetosheath and the magnetosphere proper. Blobs of magnetosheath or boundary layer plasma rarely, if ever, become detached from the magnetopause.

Cusp and boundary layer observations by INTERBALL

Abstract Interball Tail Probe was launched on August 2, 1995 together with its subsatellite MAGION-4 into a highly elliptical orbit with apogee at 31 RE and inclination 63 degrees. During the course of one year all local times are visited. In this paper we will present initial results obtained from measurements in the cusp, mantle and eveningside plasma sheet in January, 1996. It is found that the cusp was well defined and persistent at altitudes of 4–10 RE. In one case both the main satellite and the subsatellite were in the cusp proper for two uninterrupted hours. We believe this to be the first ever multi-point satellite observation of the high-altitude cusp. The data indicate that the cusp was very stable with a wide entry area and that plasma entry took place at high latitudes rather than at the subsolar point. Pressure pulses, possibly due to Alfven waves were found. Sunward and antisunward moving plasma was measured simultaneously during a case of northward IMF but no convection was discovered. Plenty of plasma of cusp/magnetosheath type was also found mixed with plasma sheet plasma both equatorward of the cusp and in the eveningside plasma sheet.

Dynamic properties of small scale solar wind plasma fluctuations

The paper presents the latest results of the studies of small-scale fluctuations in a turbulent flow of solar wind (SW) using measurements with extremely high temporal resolution (up to 0.03 s) of the bright monitor of SW (BMSW) plasma spectrometer operating on astrophysical SPECTR-R spacecraft at distances up to 350 000 km from the Earth. The spectra of SW ion flux fluctuations in the range of scales between 0.03 and 100 s are systematically analysed. The difference of slopes in low- and high-frequency parts of spectra and the frequency of the break point between these two characteristic slopes was analysed for different conditions in the SW. The statistical properties of the SW ion flux fluctuations were thoroughly analysed on scales less than 10 s. A high level of intermittency is demonstrated. The extended self-similarity of SW ion flux turbulent flow is constantly observed. The approximation of non-Gaussian probability distribution function of ion flux fluctuations by the Tsallis statistics shows the non-extensive character of SW fluctuations. Statistical characteristics of ion flux fluctuations are compared with the predictions of a log-Poisson model. The log-Poisson parametrization of the structure function scaling has shown that well-defined filament-like plasma structures are, as a rule, observed in the turbulent SW flows.