scholarly journals ANALYTICAL MODEL OF THE PLANETARY BOW SHOCK FOR VARIOUS MAGNETIC FIELD DIRECTIONS BASED ON MHD CALCULATIONS

2020 ◽  
Vol 6 (4) ◽  
pp. 51-58
Author(s):  
Galina Kotova ◽  
Mikhail Verigin ◽  
Tamash Gomboshi ◽  
Konstantin Kabin
Keyword(s):  
Magnetic Field ◽  
Computer Time ◽  
Bow Shock ◽  
Radius Of Curvature ◽  
Dynamic Flow ◽  
Physical Processes ◽  
Downstream Slope ◽  
Mach Numbers ◽  
Semi Empirical ◽  
The Magnetic Field

Study of physical processes in plasma near planets often requires knowledge of the position and shape of the planetary bow shock. Empirical models are usually used since theoretical MHD and kinetic models consume too much computer time and cannot be used to track fast processes. M.I. Verigin proposed a semi-empirical approach based on the use of exact theoretical expressions with a small number of parameters, which have a clear physical meaning. These parameters are estimated by fitting experimental data or detailed MHD calculations. A model of the bow shock near an arbitrary-shaped obstacle has previously been developed for a gas-dynamic flow. This model can be applied to any sonic Mach numbers and large values of the Alfven Mach number. In addition, the asymptotic Mach cone — the angle of inclination of the shock wave at an infinite distance from the planet — has been calculated analytically in the MHD approximation. In this paper, we propose a model of the bow shock for any direction of the magnetic field with respect to the upcoming flow and for any Mach numbers. Parameters of the model are the distance of the nose point from the obstacle, radius of curvature and bluntness of the bow shock at the nose point, a parameter related to the transition to the asymptotic downstream slope of the shock, and a skewing angle appearing when the interplanetary magnetic field is directed at an angle to the solar wind velocity.

ANALYTICAL MODEL OF THE PLANETARY BOW SHOCK FOR VARIOUS MAGNETIC FIELD DIRECTIONS BASED ON MHD CALCULATIONS

2020 ◽  
Vol 6 (4) ◽  
pp. 44-49
Author(s):  
Galina Kotova ◽  
Mikhail Verigin ◽  
Tamash Gomboshi ◽  
Konstantin Kabin
Keyword(s):  
Magnetic Field ◽  
Computer Time ◽  
Bow Shock ◽  
Radius Of Curvature ◽  
Dynamic Flow ◽  
Physical Processes ◽  
Downstream Slope ◽  
Mach Numbers ◽  
Semi Empirical ◽  
The Magnetic Field

Study of physical processes in plasma near planets often requires knowledge of the position and shape of the planetary bow shock. Empirical models are usually used since theoretical MHD and kinetic models consume too much computer time and cannot be used to track fast processes. M.I. Verigin proposed a semi-empirical approach based on the use of exact theoretical expressions with a small number of parameters, which have a clear physical meaning. These parameters are estimated by fitting experimental data or detailed MHD calculations. A model of the bow shock near an arbitrary-shaped obstacle has previously been developed for a gas-dynamic flow. This model can be applied to any sonic Mach numbers and large values of the Alfven Mach number. In addition, the asymptotic Mach cone — the angle of inclination of the shock wave at an infinite distance from the planet — has been calculated analytically in the MHD approximation. In this paper, we propose a model of the bow shock for any direction of the magnetic field with respect to the upcoming flow and for any Mach numbers. Parameters of the model are the distance of the nose point from the obstacle, radius of curvature and bluntness of the bow shock at the nose point, a parameter related to the transition to the asymptotic downstream slope of the shock, and a skewing angle appearing when the interplanetary magnetic field is directed at an angle to the solar wind velocity.

scholarly journals Experimental and numerical investigation of plasma parameters in the magnetosheath

2018 ◽  
Vol 145 ◽  
pp. 03003
Author(s):  
Polya Dobreva ◽  
Monio Kartalev ◽  
Olga Nitcheva ◽  
Natalia Borodkova ◽  
Georgy Zastenker
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Numerical Investigation ◽  
Euler Equations ◽  
Ideal Gas ◽  
Bow Shock ◽  
Plasma Parameters ◽  
Wind Spacecraft ◽  
The Magnetic Field ◽  
Good Agreement

We investigate the behaviour of the plasma parameters in the magnetosheath in a case when Interball-1 satellite stayed in the magnetosheath, crossing the tail magnetopause. In our analysis we apply the numerical magnetosheath-magnetosphere model as a theoretical tool. The bow shock and the magnetopause are self-consistently determined in the process of the solution. The flow in the magnetosheath is governed by the Euler equations of compressible ideal gas. The magnetic field in the magnetosphere is calculated by a variant of the Tsyganenko model, modified to account for an asymmetric magnetopause. Also, the magnetopause currents in Tsyganenko model are replaced by numericaly calulated ones. Measurements from WIND spacecraft are used as a solar wind monitor. The results demonstrate a good agreement between the model-calculated and measured values of the parameters under investigation.

scholarly journals Scattering of field-aligned beam ions upstream of Earth's bow shock

2007 ◽  
Vol 25 (3) ◽  
pp. 785-799 ◽  
Author(s):  
A. Kis ◽  
M. Scholer ◽  
B. Klecker ◽  
H. Kucharek ◽  
E. A. Lucek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Measurements ◽  
Bow Shock ◽  
Ion Distribution ◽  
Parallel Side ◽  
Earth’S Bow Shock ◽  
High Mach ◽  
The Magnetic Field

Abstract. Field-aligned beams are known to originate from the quasi-perpendicular side of the Earth's bow shock, while the diffuse ion population consists of accelerated ions at the quasi-parallel side of the bow shock. The two distinct ion populations show typical characteristics in their velocity space distributions. By using particle and magnetic field measurements from one Cluster spacecraft we present a case study when the two ion populations are observed simultaneously in the foreshock region during a high Mach number, high solar wind velocity event. We present the spatial-temporal evolution of the field-aligned beam ion distribution in front of the Earth's bow shock, focusing on the processes in the deep foreshock region, i.e. on the quasi-parallel side. Our analysis demonstrates that the scattering of field-aligned beam (FAB) ions combined with convection by the solar wind results in the presence of lower-energy, toroidal gyrating ions at positions deeper in the foreshock region which are magnetically connected to the quasi-parallel bow shock. The gyrating ions are superposed onto a higher energy diffuse ion population. It is suggested that the toroidal gyrating ion population observed deep in the foreshock region has its origins in the FAB and that its characteristics are correlated with its distance from the FAB, but is independent on distance to the bow shock along the magnetic field.

Influence of the magnetic field of stellar wind on hot jupiter’s envelopes

2019 ◽  
Vol 15 (S354) ◽  
pp. 268-279
Author(s):  
Dmitry V. Bisikalo ◽  
Andrey G. Zhilkin
Keyword(s):  
Magnetic Field ◽  
Plasma Flow ◽  
Coronal Mass Ejections ◽  
Stellar Wind ◽  
Roche Lobe ◽  
Bow Shock ◽  
Hot Jupiters ◽  
The Magnetic Field ◽  
Alfven Velocity ◽  
Hot Jupiter

AbstractHot Jupiters have extended gaseous (ionospheric) envelopes, which extend far beyond the Roche lobe. The envelopes are loosely bound to the planet and, therefore, are strongly influenced by fluctuations of the stellar wind. We show that, since hot Jupiters are close to the parent stars, magnetic field of the stellar wind is an important factor defining the structure of their magnetospheres. For a typical hot Jupiter, velocity of the stellar wind plasma flow around the atmosphere is close to the Alfvén velocity. As a result stellar wind fluctuations, such as coronal mass ejections, can affect the conditions for the formation of a bow shock around a hot Jupiter. This effect can affect observational manifestations of hot Jupiters.

scholarly journals Solitary potential structures observed in the magnetosheath by the Cluster spacecraft

2003 ◽  
Vol 10 (1/2) ◽  
pp. 3-11 ◽  
Author(s):  
J. S. Pickett ◽  
J. D. Menietti ◽  
D. A. Gurnett ◽  
B. Tsurutani ◽  
P. M. Kintner ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time Series Data ◽  
Broad Band ◽  
Low Frequency ◽  
Bow Shock ◽  
Local Magnetic Field ◽  
Series Data ◽  
The Individual ◽  
Almost All ◽  
The Magnetic Field

Abstract. Bipolar pulses of ~ 25-100 µs in duration have been observed in the wave electric field data obtained by the Wideband plasma wave instrument on the Cluster spacecraft in the dayside magnetosheath. These pulses are similar in almost all respects to those observed on several spacecraft over the last few years. They represent solitary potential structures, and in this case, electron phase space holes. When the time series data containing the bipolar pulses on Cluster are transformed to the frequency domain by a windowed FFT, the pulses appear as typical broad-band features, extending from the low-frequency cutoff of the bandpass filter, ~ 1 kHz, up to as great as 20-40 kHz in some cases, with decreasing intensity as the frequency increases. The upper frequency cutoff of the broad band is an indication of the individual pulse durations (1/f). The solitary potential structures are detected when the local magnetic field is contained primarily in the spin plane, indicating that they propagate along the magnetic field. Their frequency extent and intensity seem to increase as the angle between the directions of the magnetic field and the plasma flow decreases from 90°. Of major significance is the finding that the overall profile of the broad-band features observed simultaneously by two Cluster spacecraft, separated by a distance of over 750 km, are strikingly similar in terms of onset times, frequency extent, intensity, and termination. This implies that the generation region of the solitary potential structures observed in the magnetosheath near the bow shock is very large and may be located at or near the bow shock, or be connected with the bow shock in some way.

scholarly journals Filaments and striations: anisotropies in observed, supersonic, highly magnetized turbulent clouds

2019 ◽  
Vol 492 (1) ◽  
pp. 668-685 ◽  
Author(s):  
James R Beattie ◽  
Christoph Federrath
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Three Dimensional ◽  
High Density ◽  
Systematic Analysis ◽  
Guide Field ◽  
Degree Of Anisotropy ◽  
Mach Numbers ◽  
Magnetohydrodynamic Simulations ◽  
The Magnetic Field

ABSTRACT Stars form in highly magnetized, supersonic turbulent molecular clouds. Many of the tools and models that we use to carry out star formation studies rely upon the assumption of cloud isotropy. However, structures like high-density filaments in the presence of magnetic fields and magnetosonic striations introduce anisotropies into the cloud. In this study, we use the two-dimensional power spectrum to perform a systematic analysis of the anisotropies in the column density for a range of Alfvén Mach numbers ($\operatorname{\mathcal {M}_{\text{A}}}=0.1{\!-\!10}$) and turbulent Mach numbers ($\operatorname{\mathcal {M}}=2{\!-\!20}$), with 20 high-resolution, three-dimensional turbulent magnetohydrodynamic simulations. We find that for cases with a strong magnetic guide field, corresponding to $\operatorname{\mathcal {M}_{\text{A}}}\lt 1$, and $\operatorname{\mathcal {M}}\lesssim 4$, the anisotropy in the column density is dominated by thin striations aligned with the magnetic field, while for $\operatorname{\mathcal {M}}\gtrsim 4$ the anisotropy is significantly changed by high-density filaments that form perpendicular to the magnetic guide field. Indeed, the strength of the magnetic field controls the degree of anisotropy and whether or not any anisotropy is present, but it is the turbulent motions controlled by $\operatorname{\mathcal {M}}$ that determine which kind of anisotropy dominates the morphology of a cloud.

scholarly journals Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

2014 ◽  
Vol 32 (10) ◽  
pp. 1247-1261 ◽  
Author(s):  
L. Turc ◽  
D. Fontaine ◽  
P. Savoini ◽  
E. K. J. Kilpua
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Bow Shock ◽  
Field Direction ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
The Impact ◽  
The Magnetic Field

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

scholarly journals Jump conditions for pressure anisotropy and comparison with the Earth's bow shock

2001 ◽  
Vol 8 (3) ◽  
pp. 167-174 ◽  
Author(s):  
D. F. Vogl ◽  
H. K. Biernat ◽  
N. V. Erkaev ◽  
C. J. Farrugia ◽  
S. Mühlbachler
Keyword(s):  
Magnetic Field ◽  
Tangential Component ◽  
Bow Shock ◽  
Jump Conditions ◽  
Plasma Parameters ◽  
Pressure Anisotropy ◽  
Threshold Conditions ◽  
Wind Spacecraft ◽  
Earth’S Bow Shock ◽  
The Magnetic Field

Abstract. Taking into account the pressure anisotropy in the solar wind, we study the magnetic field and plasma parameters downstream of a fast shock, as functions of upstream parameters and downstream pressure anisotropy. In our theoretical approach, we model two cases: a) the perpendicular shock and b) the oblique shock. We use two threshold conditions of plasma instabilities as additional equations to bound the range of pressure anisotropy. The criterion of the mirror instability is used for pressure anisotropy p \\perp /p\\parrallel > 1. Analogously, the criterion of the fire-hose instability is taken into account for pressure anisotropy p \\perp /p\\parrallel < 1. We found that the variations of the parallel pressure, the parallel temperature, and the tangential component of the velocity are most sensitive to the pressure anisotropy downstream of the shock. Finally, we compare our theory with plasma and magnetic field parameters measured by the WIND spacecraft.

scholarly journals 29. The internal constitution of sunspots

1958 ◽  
Vol 6 ◽  
pp. 263-274 ◽  
Author(s):  
A. Schlüter ◽  
S. Temesváry
Keyword(s):  
Magnetic Field ◽  
Physical Properties ◽  
Flux Tube ◽  
Energy Transport ◽  
Convection Zone ◽  
Vertical Component ◽  
Relative Distribution ◽  
Physical Processes ◽  
Internal Constitution ◽  
The Magnetic Field

The constitution of stationary single sunspots of circular shape is considered. Account is taken of the mechanical effects of the magnetic field, including those which arise from the curvature of the lines of force. To make the system of magneto-hydrostatic equations manageable, it is assumed that the relative distribution of the vertical component of the magnetic field is the same across the flux-tube of the spot in all depths. Preliminary results indicate that suppression of convective energy transport by the magnetic field in those depths in which ionization of hydrogen takes place, will give the essential observable properties of sunspots, relatively independent on the asumptions about the physical processes in greater depths. There the physical properties of matter can deviate but very little from those of the indisturbed hydrogen convection zone.

scholarly journals Non-stationarity of the quasi-perpendicular bow shock: comparison between Cluster observations and simulations

2011 ◽  
Vol 29 (2) ◽  
pp. 263-274 ◽  
Author(s):  
H. Comişel ◽  
M. Scholer ◽  
J. Soucek ◽  
S. Matsukiyo
Keyword(s):  
Magnetic Field ◽  
Bow Shock ◽  
Field Profile ◽  
Mass Ratio ◽  
Poynting Flux ◽  
Magnetic Field Profile ◽  
Low Mass ◽  
Low Mass Ratio ◽  
The Waves ◽  
The Magnetic Field

Abstract. We have performed full particle electromagnetic simulations of a quasi-perpendicular shock. The shock parameters have been chosen to be appropriate for the quasi-perpendicular Earth's bow shock observed by Cluster on 24 January 2001 (Lobzin et al., 2007). We have performed two simulations with different ion to electron mass ratio: run 1 with mi/me=1840 and run 2 with mi/me=100. In run 1 the growth rate of the modified two-stream instability (MTSI) is large enough to get excited during the reflection and upstream gyration of part of the incident solar wind ions. The waves due to the MTSI are on the whistler mode branch and have downstream directed phase velocities in the shock frame. The Poynting flux (and wave group velocity) far upstream in the foot is also directed in the downstream direction. However, in the density and magnetic field compression region of the overshoot the waves are refracted and the Poynting flux in the shock frame is directed upstream. The MTSI is suppressed in the low mass ratio run 2. The low mass ratio run shows more clearly the non-stationarity of the shock with a larger time scale of the order of an inverse ion gyrofrequency (Ωci): the magnetic field profile flattens and steepens with a period of ~1.5Ωci−1. This non-stationarity is different from reformation seen in previous simulations of perpendicular or quasi-perpendicular shocks. Beginning with a sharp shock ramp the large electric field in the normal direction leads to high reflection rate of solar wind protons. As they propagate upstream, the ion bulk velocity decreases and the magnetic field increases in the foot, which results in a flattening of the magnetic field profile and in a decrease of the normal electric field. Subsequently the reflection rate decreases and the whole shock profile steepens again. Superimposed on this 'breathing' behavior are in the realistic mass ratio case the waves due to the MTSI. The simulations lead us to a re-interpretation of the 24 January 2001 bow shock observations reported by Lobzin et al. (2007). It is suggested that the high frequency waves observed in the magnetic field data are due to the MTSI and are not related to a nonlinear phase standing whistler. Different profiles at the different spacecraft are due to the non-stationary behavior on the larger time scale.

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