M. Tátrallyay

Planetary bow shocks: Gasdynamic analytic approach

[1]xa0A new analytical model of the bow shock surface is suggested for reasonably accurate and fast prediction of this boundarys position near obstacles of different shape. For axially symmetric obstacles the model was verified by comparison with experiments and results of gasdynamic code application for a wide range of upstream polytropic indexes, 1.15 < γ < 2, and Mach numbers, 1 < Ms < ∞. The model can also be used for prediction of the bow shock position around nonaxially symmetric obstacles.

Magnetic field overshoots in the Martian bow shock

In 1989 the Phobos 2 spacecraft provided sufficient plasma and magnetic field data for statistical investigations of the Martian bow shock structure. Significant magnetic field overshoots were observed in more than 70% of the bow shock crossings detected in the terminator region. According to our studies based on the available low-resolution data set, the features of the Martian overshoots are very similar to those observed in the terrestrial and Venusian bow shock: the magnitude increases with increasing Mach number and the thickness scales as the proton gyroradius computed from the upstream solar wind speed and magnetic field strength. Our investigations seem to support the idea of Mellott and Livesey [1987] suggesting that overshoots may develop not only in supercritical shocks but also when the Mach number is below or around the critical value.

Submicron-sized dust grains in the Martian environment

Abstract The dynamics of small-sized dust grains was studied in the Martian environment in connection with the possible detection of dust particles by the Phobos 2 spacecraft. The motion of submicron-sized particles is influenced not only by gravity but also by solar radiation pressure and electromagnetic forces. Depending on the size and on the actual varying interplanetary parameters, some of these small-sized grains ejected from Phobos at speeds on the order of a few tens m / s , can stay in orbit around Mars for several months forming a non-uniform and time-dependent dust halo.

Analysis of the electron measurements from the Plasmag-1 experiment on board Vega 2 in the vicinity of comet P/Halley

Measurements of electron spectra, as obtained by the Plasmag-1 experiment on board Vega 2 in the vicinity of comet Halley, are presented. It is shown that the temperature for thermal electrons gradually decreases when the comet is approached from about 4 105 K behind the cometary bow shock to about 2 105 K at the cometopause. In the region inside the cometopause a fast increase in the flux of energetic electrons of about 1 keV energy is observed. Various possibilities are discussed regarding the differences in the electron spectra measured by Vega 2 and Giotto, respectively.

Quasi-periodic features and the radial distribution of cometary ions in the cometary plasma region of comet P/Halley

Based on the measurements of the ion electrostatic analyzer CRA of the Plasmag-1 instrument on board Vega-2, which was oriented along the spacecraft-comet relative velocity direction, we present observations (1) of quasi-periodic features in the intensity of cometry ions occurring inside the cometopause, (2) of the mass composition of the cometary ions in the mass range of 1 to 100 atomic mass units (amu), and (3) of the radial dependence of the density of certain, well-defined groups of cometary ions.

On the Growth of Mirror Mode Waves in the Magnetosheath Based on Cluster Observations

The evolution of mirror mode waves was investigated in the magnetosheath based on Cluster magnetic field and plasma measurements during four inbound passes in January–February 2006 when the separation between the spacecraft was about 10,000 km. The growth rates estimated from the amplitudes of the field fluctuations (mainly quasi-sinusoidal oscillations and peaks) observed simultaneously at distant locations were usually smaller than the maximum growth rates calculated from the plasma parameters measured in the magnetosheath suggesting that mirror mode waves do not grow beyond a certain degree, they seem to get saturated. Sudden changes in interplanetary conditions influenced the evolution of mirror mode waves, which were observed when solar wind dynamic pressure and the IMF were relatively quiet and the bow shock region connected to the observation point was quasi-perpendicular, while temperature anisotropy was moderate and ion β was high (left (1.2 1right )) in the local plasma.

Magnetic field overshoots in the Venus bow shock

Abstract An examination of Pioneer Venus Orbiter fluxgate magnetometer data has shown that magnetic field overshoots occur not only behind quasi-perpendicular bow shocks but also behind quasi-parallel shocks. Oveshoots are associated only with supercritical shocks. Their amplitudes increase with increasing fast Mach number. Solar wind β has a lesser effect. The thickness of the overshoot increases with decreasing ΘBN. The thickness of apparent “overshoots” detected behind 4 strong fast interplanetary shocks (M>Mcrit) is about 3 orders of magnitude larger. Multiple crossings of the Venus bow shock were observed mainly at turbulent shocks. Their occurance is not influenced by ΘBN.