Abstract
Solar windinteraction with a kinetic scale magnetosphere and the resulting momentum transfer process are investigated by 2.5dimensional full kinetic particleincell simulations. The spatial scale of the considered magnetosphere is less than or comparable to the ion inertial length and is relevant for magnetized asteroids or spacecraft with minimagnetosphere plasma propulsion. Momentum transfer is evaluated by studying the Lorentz force between solar windplasma and a hypothetical coil current density that creates the magnetosphere. In the zero interplanetary magnetic field(IMF) limit, solar windinteraction goes into a steady state with constant Lorentz force. The dominant Lorentz force acting on the coil current density is applied by the thin electron current layer at the windfilled front of the magnetosphere. Dynamic pressure of the solar wind balances the magnetic pressure in this region via electrostatic deceleration of ions. The resulting Lorentz force is characterized as a function of the scale of magnetosphere normalized by the electron gyration radius, which determines the local structure of the current layer. For the finite northward IMF case, solar wind electrons flow into the magnetosphere through the reconnecting region. The inner electrons enhance the ion deceleration, and this results in temporal increment of the Lorentz force. It is concluded that the momentum transfer of solar windplasma could take place actively with variety of kinetic plasma phenomena, even in a magnetosphere with a small scale of less than the ion inertial length.
This study was supported by CREST (JST). Computations were performed with the Plasma Simulator at National Institute for Fusion Science and the JAXA Supercomputer System at the Japan Aerospace Exploration Agency. One of the authors (T.M.) acknowledges Professor R. Horiuchi (National Institute for Fusion Science) for useful comments.
I. INTRODUCTION
II. SIMULATION MODEL
A. Simulation parameters
B. Validation of simulation model
III. RESULTS UNDER ZERO INTERPLANETARY MAGNETIC FIELD LIMIT
A. General solar windinteraction
B. Dependence on spatial scale of magnetosphere
C. Force balance at magnetospheric boundary
D. Role of electron and ion dynamics
E. Scale dependency of drag coefficient
IV. RESULTS UNDER FINITE INTERPLANETARY MAGNETIC FIELD
V. SUMMARY AND DISCUSSION
Key Topics
 Solar windmagnetosphere interactions
 88.0
 Current density
 71.0
 Solar wind
 62.0
 Stellar magnetospheres
 49.0
 Magnetic fields
 45.0
B64D
Figures
Schematic diagram of simulation domain. Antiparallel current density is supplied at the center of the domain. Solar wind is assumed to be a uniform plasma flow in the direction.
Schematic diagram of simulation domain. Antiparallel current density is supplied at the center of the domain. Solar wind is assumed to be a uniform plasma flow in the direction.
Time evolutions of Lorentz force acting on coil current density. (a) Dependence on domain size, standoff time, and solar wind flow velocity. Domain size for case B (dashed line) is enlarged compared with that in case A (solid line). The standoff time for case C (dotted line) is twice that for case A. Solar wind flow velocity is set equal to zero for the “stationary” case (dasheddotted line). (b) Relationship between Lorentz force (solid line) and the momentum loss rate of the solar wind plasma (dashed line).
Time evolutions of Lorentz force acting on coil current density. (a) Dependence on domain size, standoff time, and solar wind flow velocity. Domain size for case B (dashed line) is enlarged compared with that in case A (solid line). The standoff time for case C (dotted line) is twice that for case A. Solar wind flow velocity is set equal to zero for the “stationary” case (dasheddotted line). (b) Relationship between Lorentz force (solid line) and the momentum loss rate of the solar wind plasma (dashed line).
(Color) Colorcoded contour plots of (a) mass density Ro, (b) outofplane current density and (c) outofplane magnetic field in a quasisteady state. Green lines represent magnetic field lines. Note: the displayed region is larger in (c) than in (a) and (b).
(Color) Colorcoded contour plots of (a) mass density Ro, (b) outofplane current density and (c) outofplane magnetic field in a quasisteady state. Green lines represent magnetic field lines. Note: the displayed region is larger in (c) than in (a) and (b).
Time evolution of drag coefficient. Interval marked by “()” is used for time averaging the results shown in Fig. 5.
Time evolution of drag coefficient. Interval marked by “()” is used for time averaging the results shown in Fig. 5.
(a) Profiles of magnetic field, , at steady state (dashed line) and for original magnetosphere, , (dotted line) along the equatorial line (). Profile of induced current density, , is also shown as the solid line. (b) Relationship between the induced current, , (solid line) and variations of the magnetic field gradient terms, and (dotted and dashed lines, respectively).
(a) Profiles of magnetic field, , at steady state (dashed line) and for original magnetosphere, , (dotted line) along the equatorial line (). Profile of induced current density, , is also shown as the solid line. (b) Relationship between the induced current, , (solid line) and variations of the magnetic field gradient terms, and (dotted and dashed lines, respectively).
(a) Profiles of magnetic field gradient, , at steady state for runs A1–A7. For comparison, the magnetic field gradient corresponding to the gradient scale is represented by the dashed line. (b) Profiles of induced current density at steady state for runs A1–A7. The current density values corresponding to the gradient scale and are also shown.
(a) Profiles of magnetic field gradient, , at steady state for runs A1–A7. For comparison, the magnetic field gradient corresponding to the gradient scale is represented by the dashed line. (b) Profiles of induced current density at steady state for runs A1–A7. The current density values corresponding to the gradient scale and are also shown.
Dependence of halfwidth of current layer on the scale of original magnetosphere. Halfwidths normalized by the local electron gyration radius and by the scale of magnetosphere are denoted by and , respectively.
Dependence of halfwidth of current layer on the scale of original magnetosphere. Halfwidths normalized by the local electron gyration radius and by the scale of magnetosphere are denoted by and , respectively.
(Color) Profiles of force terms in the twofluid equation. Electron force terms in (a) xdirection and (b) zdirection. (c) Ion force terms in the xdirection. Cyan, green, and red lines stand for inertia, electric, and magnetic force terms along equatorial line, respectively. The pressure term is separated into scalar (blue lines) and offdiagonal (purple lines) components for panels (a) and (c).
(Color) Profiles of force terms in the twofluid equation. Electron force terms in (a) xdirection and (b) zdirection. (c) Ion force terms in the xdirection. Cyan, green, and red lines stand for inertia, electric, and magnetic force terms along equatorial line, respectively. The pressure term is separated into scalar (blue lines) and offdiagonal (purple lines) components for panels (a) and (c).
(a) Profiles of electron force terms from Eq. (5) at steady state for runs A3–A7. Solid and dashed lines denote electric force term and kinetic term including inertia and pressure terms, respectively. (b) Electron number density profiles along equatorial line for runs A3–A7.
(a) Profiles of electron force terms from Eq. (5) at steady state for runs A3–A7. Solid and dashed lines denote electric force term and kinetic term including inertia and pressure terms, respectively. (b) Electron number density profiles along equatorial line for runs A3–A7.
Profiles of induced current density resulting from series B and C. (a) Solid, dashed, and dotted lines represent profiles for runs B1, B2, and B3, respectively. (b) Solid, dashed, and dotted lines represent profiles for runs C1, C2, and C3, respectively. Profiles of original magnetic field, , are given as solid lines marked “original field.”
Profiles of induced current density resulting from series B and C. (a) Solid, dashed, and dotted lines represent profiles for runs B1, B2, and B3, respectively. (b) Solid, dashed, and dotted lines represent profiles for runs C1, C2, and C3, respectively. Profiles of original magnetic field, , are given as solid lines marked “original field.”
Scale dependence of drag coefficients. (a) Solid line marked with represents drag coefficient obtained from series B. Dotted () and dashed () lines represent electron and ion drag coefficients, respectively. (b) Dotted lines marked with and represent estimated electron and ion drag coefficients obtained from series A, respectively. Electron and ion drag coefficients obtained from series C are denoted by large dots and squares, respectively.
Scale dependence of drag coefficients. (a) Solid line marked with represents drag coefficient obtained from series B. Dotted () and dashed () lines represent electron and ion drag coefficients, respectively. (b) Dotted lines marked with and represent estimated electron and ion drag coefficients obtained from series A, respectively. Electron and ion drag coefficients obtained from series C are denoted by large dots and squares, respectively.
(a) Schematic diagram for the evaluation of drag coefficient. (b) Drag coefficient as a function of magnetosphere scale obtained from simulation runs A1A6 (asterisk). Solid line stands for the theoretical relationship (Eq. (15)). Upper and lower horizontal lines represent the limit value of drag coefficient (Eq. (17)) and the typical value in the small magnetosphere regime (Eq. (16)), respectively.
(a) Schematic diagram for the evaluation of drag coefficient. (b) Drag coefficient as a function of magnetosphere scale obtained from simulation runs A1A6 (asterisk). Solid line stands for the theoretical relationship (Eq. (15)). Upper and lower horizontal lines represent the limit value of drag coefficient (Eq. (17)) and the typical value in the small magnetosphere regime (Eq. (16)), respectively.
(Color) (a) Color contours of mass density and (b) outofplane magnetic field resulting from finite IMF. Green lines represent magnetic field lines.
(Color) (a) Color contours of mass density and (b) outofplane magnetic field resulting from finite IMF. Green lines represent magnetic field lines.
(a) Time evolution of drag coefficient. Solid and dashed lines denote the drag coefficient resulting from finite and zero IMF cases, respectively. The interval marked by “()” is used for time averaging the data in panel (b). (b) Spatial profiles for induced current density resulting from finite (solid line) and zero (dashed line) IMF cases.
(a) Time evolution of drag coefficient. Solid and dashed lines denote the drag coefficient resulting from finite and zero IMF cases, respectively. The interval marked by “()” is used for time averaging the data in panel (b). (b) Spatial profiles for induced current density resulting from finite (solid line) and zero (dashed line) IMF cases.
(Color online) Colorcoded contour plots of number density for electrons with (a) A flag of “1,” which have not passed through and (b) A flag of “0,” which have passed through . Curved lines in both panels represent magnetic field lines.
(Color online) Colorcoded contour plots of number density for electrons with (a) A flag of “1,” which have not passed through and (b) A flag of “0,” which have passed through . Curved lines in both panels represent magnetic field lines.
(Color online) Velocity distribution of electrons and ions with flag “1” along the equatorial line. Vertical and horizontal axes are velocity in the xdirection and distance from coil center, respectively. (a) and (b) Electron velocity distributions obtained under finite and zero IMF, respectively. (c) and (d) Ion distributions obtained under finite and zero IMF, respectively.
(Color online) Velocity distribution of electrons and ions with flag “1” along the equatorial line. Vertical and horizontal axes are velocity in the xdirection and distance from coil center, respectively. (a) and (b) Electron velocity distributions obtained under finite and zero IMF, respectively. (c) and (d) Ion distributions obtained under finite and zero IMF, respectively.
Tables
Dimensionless parameters for simulation series A (A1–A7) and the additional example A0.
Dimensionless parameters for simulation series A (A1–A7) and the additional example A0.
Typical dimensionless parameters for simulation series B and C.
Typical dimensionless parameters for simulation series B and C.
Article metrics loading...
Full text loading...
Most read this month
Most cited this month










Electron, photon, and ion beams from the relativistic interaction of Petawatt laser pulses with solid targets
Stephen P. Hatchett, Curtis G. Brown, Thomas E. Cowan, Eugene A. Henry, Joy S. Johnson, Michael H. Key, Jeffrey A. Koch, A. Bruce Langdon, Barbara F. Lasinski, Richard W. Lee, Andrew J. Mackinnon, Deanna M. Pennington, Michael D. Perry, Thomas W. Phillips, Markus Roth, T. Craig Sangster, Mike S. Singh, Richard A. Snavely, Mark A. Stoyer, Scott C. Wilks and Kazuhito Yasuike

Commenting has been disabled for this content