Physics of the Ion Composition Boundary: a comparative 3-D hybrid simulation study of Mars and Titan

Abstract. The plasma environments of Mars and Titan have been studied by means of a 3-D hybrid simulation code, treating the electrons as a massless, charge-neutralizing fluid, whereas ion dynamics are covered by a kinetic approach. As neither Mars nor Titan possesses a significant intrinsic magnetic field, the upstream plasma flow interacts directly with the planetary ionosphere. The characteristic features of the interaction region are determined as a function of the alfvénic, sonic and magnetosonic Mach number of the impinging plasma. For the Martian interaction with the solar wind as well as for the case of Titan being located outside Saturn's magnetosphere in times of high solar wind dynamic pressure, all three Mach numbers are larger than 1. In such a scenario, the interaction gives rise to a so-called Ion Composition Boundary, separating the ionospheric plasma from the ambient flow and being highly asymmetric with respect to the direction of the convective electric field. The formation of these features is explained by analyzing the Lorentz forces acting on ionospheric and ambient plasma particles. Titan's plasma environment is highly variable and allows various different combinations of the three Mach numbers. Therefore, the Ion Composition Boundary may vanish under certain circumstances. The relevant physical mechanism is illustrated as a function of the Mach numbers in the upstream plasma flow.

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Three-dimensional multispecies hybrid simulation of Titan's highly variable plasma environment

Annales Geophysicae ◽

10.5194/angeo-25-117-2007 ◽

2007 ◽

Vol 25 (1) ◽

pp. 117-144 ◽

Cited By ~ 35

Author(s):

S. Simon ◽

A. Boesswetter ◽

T. Bagdonat ◽

U. Motschmann ◽

J. Schuele

Keyword(s):

Plasma Flow ◽

Flow Direction ◽

Three Dimensional ◽

Hybrid Simulation ◽

Slight Modification ◽

Magnetospheric Plasma ◽

Particle Model ◽

Tail Region ◽

Simulation Code ◽

Ion Species

Abstract. The interaction between Titan's ionosphere and the Saturnian magnetospheric plasma flow has been studied by means of a three-dimensional (3-D) hybrid simulation code. In the hybrid model, the electrons form a mass-less, charge-neutralizing fluid, whereas a completely kinetic approach is retained to describe ion dynamics. The model includes up to three ionospheric and two magnetospheric ion species. The interaction gives rise to a pronounced magnetic draping pattern and an ionospheric tail that is highly asymmetric with respect to the direction of the convective electric field. Due to the dependence of the ion gyroradii on the ion mass, ions of different masses become spatially dispersed in the tail region. Therefore, Titan's ionospheric tail may be considered a mass-spectrometer, allowing to distinguish between ion species of different masses. The kinetic nature of this effect is emphasized by comparing the simulation with the results obtained from a simple analytical test-particle model of the pick-up process. Besides, the results clearly illustrate the necessity of taking into account the multi-species nature of the magnetospheric plasma flow in the vicinity of Titan. On the one hand, heavy magnetospheric particles, such as atomic Nitrogen or Oxygen, experience only a slight modification of their flow pattern. On the other hand, light ionospheric ions, e.g. atomic Hydrogen, are clearly deflected around the obstacle, yielding a widening of the magnetic draping pattern perpendicular to the flow direction. The simulation results clearly indicate that the nature of this interaction process, especially the formation of sharply pronounced plasma boundaries in the vicinity of Titan, is extremely sensitive to both the temperature of the magnetospheric ions and the orientation of Titan's dayside ionosphere with respect to the corotating magnetospheric plasma flow.

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Plasma environment of magnetized asteroids: a 3-D hybrid simulation study

Annales Geophysicae ◽

10.5194/angeo-24-407-2006 ◽

2006 ◽

Vol 24 (1) ◽

pp. 407-414 ◽

Cited By ~ 24

Author(s):

S. Simon ◽

T. Bagdonat ◽

U. Motschmann ◽

K.-H. Glassmeier

Keyword(s):

Solar Wind ◽

Three Dimensional ◽

Hybrid Simulation ◽

Interaction Region ◽

Bow Shock ◽

The Other ◽

Simulation Code ◽

Kinetic Effects ◽

Intrinsic Magnetic Moment ◽

The One

Abstract. The interaction of a magnetized asteroid with the solar wind is studied by using a three-dimensional hybrid simulation code (fluid electrons, kinetic ions). When the obstacle's intrinsic magnetic moment is sufficiently strong, the interaction region develops signs of magnetospheric structures. On the one hand, an area from which the solar wind is excluded forms downstream of the obstacle. On the other hand, the interaction region is surrounded by a boundary layer which indicates the presence of a bow shock. By analyzing the trajectories of individual ions, it is demonstrated that kinetic effects have global consequences for the structure of the interaction region.

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Plasma environment of Titan: a 3-D hybrid simulation study

Annales Geophysicae ◽

10.5194/angeo-24-1113-2006 ◽

2006 ◽

Vol 24 (3) ◽

pp. 1113-1135 ◽

Cited By ~ 48

Author(s):

S. Simon ◽

A. Bößwetter ◽

T. Bagdonat ◽

U. Motschmann ◽

K.-H. Glassmeier

Keyword(s):

Plasma Flow ◽

Molecular Nitrogen ◽

Hybrid Simulation ◽

Spherical Geometry ◽

Magnetospheric Plasma ◽

Simulation Code ◽

Plasma Environment ◽

Ion Production ◽

Solar Uv ◽

Magnetohydrodynamic Models

Abstract. Titan possesses a dense atmosphere, consisting mainly of molecular nitrogen. Titan's orbit is located within the Saturnian magnetosphere most of the time, where the corotating plasma flow is super-Alfvénic, yet subsonic and submagnetosonic. Since Titan does not possess a significant intrinsic magnetic field, the incident plasma interacts directly with the atmosphere and ionosphere. Due to the characteristic length scales of the interaction region being comparable to the ion gyroradii in the vicinity of Titan, magnetohydrodynamic models can only offer a rough description of Titan's interaction with the corotating magnetospheric plasma flow. For this reason, Titan's plasma environment has been studied by using a 3-D hybrid simulation code, treating the electrons as a massless, charge-neutralizing fluid, whereas a completely kinetic approach is used to cover ion dynamics. The calculations are performed on a curvilinear simulation grid which is adapted to the spherical geometry of the obstacle. In the model, Titan's dayside ionosphere is mainly generated by solar UV radiation; hence, the local ion production rate depends on the solar zenith angle. Because the Titan interaction features the possibility of having the densest ionosphere located on a face not aligned with the ram flow of the magnetospheric plasma, a variety of different scenarios can be studied. The simulations show the formation of a strong magnetic draping pattern and an extended pick-up region, being highly asymmetric with respect to the direction of the convective electric field. In general, the mechanism giving rise to these structures exhibits similarities to the interaction of the ionospheres of Mars and Venus with the supersonic solar wind. The simulation results are in agreement with data from recent Cassini flybys.

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Real-time 3-D hybrid simulation of Titan's plasma interaction during a solar wind excursion

Annales Geophysicae ◽

10.5194/angeo-27-3349-2009 ◽

2009 ◽

Vol 27 (9) ◽

pp. 3349-3365 ◽

Cited By ~ 4

Author(s):

S. Simon

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Real Time ◽

Plasma Flow ◽

Time Scale ◽

Hybrid Simulation ◽

The Moon ◽

Plasma Interaction ◽

Plasma Environment ◽

The Magnetic Field

Abstract. The plasma environment of Saturn's largest satellite Titan is known to be highly variable. Since Titan's orbit is located within the outer magnetosphere of Saturn, the moon can leave the region dominated by the magnetic field of its parent body in times of high solar wind dynamic pressure and interact with the thermalized magnetosheath plasma or even with the unshocked solar wind. By applying a three-dimensional hybrid simulation code (kinetic description of ions, fluid electrons), we study in real-time the transition that Titan's plasma environment undergoes when the moon leaves Saturn's magnetosphere and enters the supermagnetosonic solar wind. In the simulation, the transition between both plasma regimes is mimicked by a reversal of the magnetic field direction as well as a change in the composition and temperature of the impinging plasma flow. When the satellite enters the solar wind, the magnetic draping pattern in its vicinity is reconfigured due to reconnection, with the characteristic time scale of this process being determined by the convection of the field lines in the undisturbed plasma flow at the flanks of the interaction region. The build-up of a bow shock ahead of Titan takes place on a typical time scale of a few minutes as well. We also analyze the erosion of the newly formed shock front upstream of Titan that commences when the moon re-enters the submagnetosonic plasma regime of Saturn's magnetosphere. Although the model presented here is far from governing the full complexity of Titan's plasma interaction during a solar wind excursion, the simulation provides important insights into general plasma-physical processes associated with such a disruptive change of the upstream flow conditions.

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Comparison of plasma data from ASPERA-3/Mars-Express with a 3-D hybrid simulation

Annales Geophysicae ◽

10.5194/angeo-25-1851-2007 ◽

2007 ◽

Vol 25 (8) ◽

pp. 1851-1864 ◽

Cited By ~ 23

Author(s):

A. Bößwetter ◽

S. Simon ◽

T. Bagdonat ◽

U. Motschmann ◽

M. Fränz ◽

...

Keyword(s):

Solar Wind ◽

Hybrid Simulation ◽

Bow Shock ◽

Proton Density ◽

Model Calculations ◽

Mars Express ◽

Characteristic Features ◽

Hybrid Approximation ◽

Individual Particles ◽

Characteristic Scales

Abstract. The ELS and IMA sensors of the ASPERA-3 experiment onboard of Mars-Express (MEX) can measure electron as well as ion moments. We compare these measurements for a specific orbit with the simulation results from a 3-D hybrid model. In the hybrid approximation the electrons are modeled as a massless charge-neutralizing fluid, whereas the ions are treated as individual particles. This approach allows gyroradius effects to be included in our model calculations of the Martian plasma environment because the gyroradii of the solar wind protons are in the range of several hundred kilometers and therefore comparable with the characteristic scales of the subsolar ionospheric interaction region. The position of both the bow shock and the Ion Composition Boundary (ICB) manifest in the MEX data as well as in the results from the hybrid simulation nearly at the same location. The characteristic features of these boundaries, i.e. an increase of proton density and temperature at the Bow Shock and a transition from solar wind to ionospheric particles at the ICB, are clearly identifiable in the data.

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Modulation of Jupiter's plasma flow, polar currents, and auroral precipitation by solar wind-induced compressions and expansions of the magnetosphere: a simple theoretical model

Annales Geophysicae ◽

10.5194/angeo-25-1433-2007 ◽

2007 ◽

Vol 25 (6) ◽

pp. 1433-1463 ◽

Cited By ~ 46

Author(s):

S. W. H. Cowley ◽

J. D. Nichols ◽

D. J. Andrews

Keyword(s):

Solar Wind ◽

Steady State ◽

Plasma Flow ◽

Current System ◽

Dynamic Pressure ◽

Transient State ◽

Electron Precipitation ◽

Closed Field ◽

Compression Region ◽

Field Lines

Abstract. We construct a simple model of the plasma flow, magnetosphere-ionosphere coupling currents, and auroral precipitation in Jupiter's magnetosphere, and examine how they respond to compressions and expansions of the system induced by changes in solar wind dynamic pressure. The main simplifying assumption is axi-symmetry, the system being modelled principally to reflect dayside conditions. The model thus describes three magnetospheric regions, namely the middle and outer magnetosphere on closed magnetic field lines bounded by the magnetopause, together with a region of open field lines mapping to the tail. The calculations assume that the system is initially in a state of steady diffusive outflow of iogenic plasma with a particular equatorial magnetopause radius, and that the magnetopause then moves rapidly in or out due to a change in the solar wind dynamic pressure. If the change is sufficiently rapid (~2–3 h or less) the plasma angular momentum is conserved during the excursion, allowing the modified plasma angular velocity to be calculated from the radial displacement of the field lines, together with the modified magnetosphere-ionosphere coupling currents and auroral precipitation. The properties of these transient states are compared with those of the steady states to which they revert over intervals of ~1–2 days. Results are shown for rapid compressions of the system from an initially expanded state typical of a solar wind rarefaction region, illustrating the reduction in total precipitating electron power that occurs for modest compressions, followed by partial recovery in the emergent steady state. For major compressions, however, typical of the onset of a solar wind compression region, a brightened transient state occurs in which super-rotation is induced on closed field lines, resulting in a reversal in sense of the usual magnetosphere-ionosphere coupling current system. Current system reversal results in accelerated auroral electron precipitation occurring in the outer magnetosphere region rather than in the middle magnetosphere as is usual, with peak energy fluxes occurring just poleward of the boundary between the outer and middle magnetosphere. Plasma sub-corotation is then re-established as steady-state conditions re-emerge, together with the usual sense of flow of the closed field current system and renewed but weakened accelerated electron precipitation in the middle magnetosphere. Results for rapid expansions of the system from an initially compressed state typical of a solar wind compression region are also shown, illustrating the enhancement in precipitating electron power that occurs in the transient state, followed by partial reduction as steady conditions re-emerge.

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Oxygen ion escape from Venus in a global hybrid simulation: role of the ionospheric O<sup>+</sup> ions

Annales Geophysicae ◽

10.5194/angeo-27-4333-2009 ◽

2009 ◽

Vol 27 (11) ◽

pp. 4333-4348 ◽

Cited By ~ 26

Author(s):

R. Jarvinen ◽

E. Kallio ◽

P. Janhunen ◽

S. Barabash ◽

T. L. Zhang ◽

...

Keyword(s):

Solar Wind ◽

Hybrid Simulation ◽

Solar Wind Interaction ◽

Simulation Code ◽

Oxygen Ion ◽

Ion Escape ◽

Global Configuration ◽

Best Fit ◽

The Magnetic Field

Abstract. We study the solar wind induced oxygen ion escape from Venus' upper atmosphere and the Venus Express observations of the Venus-solar wind interaction by the HYB-Venus hybrid simulation code. We compare the simulation to the magnetic field and ion observations during an orbit of nominal upstream conditions. Further, we study the response of the induced magnetosphere to the emission of planetary ions. The hybrid simulation is found to be able to reproduce the main observed regions of the Venusian plasma environment: the bow shock (both perpendicular and parallel regions), the magnetic barrier, the central tail current sheet, the magnetic tail lobes, the magnetosheath and the planetary wake. The simulation is found to best fit the observations when the planetary \\oxy~escape rate is in the range from 3×1024 s−1 to 1.5×1025 s−1. This range was also found to be a limit for a test particle-like behaviour of the planetary ions: the higher escape rates manifest themselves in a different global configuration of the Venusian induced magnetosphere.

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Titan's plasma environment during a magnetosheath excursion: Real-time scenarios for Cassini's T32 flyby from a hybrid simulation

Annales Geophysicae ◽

10.5194/angeo-27-669-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 669-685 ◽

Cited By ~ 15

Author(s):

S. Simon ◽

U. Motschmann ◽

G. Kleindienst ◽

J. Saur ◽

C. L. Bertucci ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Real Time ◽

Dynamic Pressure ◽

Sudden Change ◽

Hybrid Simulation ◽

Solar Wind Plasma ◽

Field Vector ◽

Characteristic Time Scale ◽

Plasma Composition

Abstract. With a Saturnian magnetopause average stand-off distance of about 21 planetary radii, Titan spends most of its time inside the rotating magnetosphere of its parent planet. However, when Saturn's magnetosphere is compressed due to high solar wind dynamic pressure, Titan can cross Saturn's magnetopause in the subsolar region of its orbit and therefore to interact with the shocked solar wind plasma in Saturn's magnetosheath. This situation has been observed during the T32 flyby of the Cassini spacecraft on 13 June 2007. Until a few minutes before closest approach, Titan had been located inside the Saturnian magnetosphere. During the flyby, Titan encountered a sudden change in the direction and magnitude of the ambient magnetic field. The density of the ambient plasma also increased dramatically during the pass. Thus, the moon's exosphere and ionosphere were exposed to a sudden change in the upstream plasma conditions. The resulting reconfiguration of Titan's plasma tail has been studied in real-time by using a three-dimensional, multi-species hybrid simulation model. The hybrid approximation treats the electrons of the plasma as a massless, charge-neutralizing fluid, while ion dynamics are described by a kinetic approach. In the simulations, the magnetopause crossing is modeled by a sudden change of the upstream magnetic field vector as well as a modification of the upstream plasma composition. We present real-time simulation results, illustrating how Titan's induced magnetotail is reconfigured due to magnetic reconnection. The simulations allow to determine a characteristic time scale for the erosion of the original magnetic draping pattern that commences after Titan has crossed Saturn's magnetopause. Besides, the influence of the plasma composition in the magnetosheath on the reconfiguration process is discussed in detail. The question of whether the magnetopause crossing is likely to yield a detachment of Titan's exospheric tail from the satellite is investigated as well.

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