Global numerical simulations of the interaction between Ganymede and Jovian plasma: hybrid simulation status

Transcription

1 Global numerical simulations of the interaction between and Jovian plasma: hybrid simulation status Pavel M. Trávníček 1,2, Petr Hellinger 2, Štěpán Štverák 2, David Herčík 2, and Ondřej Šebek 2 1 Space Sciences Laboratory, University California Berkeley; 2 Astronomical Institute, Academy of Sciences of the Czech Republic, Czech Republic; RPWI meeting, Warsaw, Poland,

2 Introduction, spatio-temporal scaling in plasmas Size of objects in space plasmas is determined by parameters of media (plasma): radius of is 8 d i0, d i0 is an ion inertial length in the Jovian Plasma It is likely, that gyro-motion effects will be important in s magnetospheric system Ion gyro-motion/kinetic effects can be modeled by hybrid code (treats ions as set of so called macro-particles). Hybrid code has a self-consistent closure for temperature anisotropy. Moreover: we can calculate 3-D VDFs! Low plasma flow velocity long simulation times (model reaches t = 300ωi0 1 in 3 weeks on 256 CPU super-computer)

3 Parameters of Jovian plasma at background (Jovian magnetosphere) magnetic field B nt s surface magnetic field 1500 nt plasma density (ambient magnetospheric flow) 1-10 cm 3 average ion charge <Z> 1.3 average ion mass <A> 14 AMU average ion temperature T i0 60 ev average electron temperature T e 300 ev average thermal ion pressure 0.04 npa average energetic ion pressure 3.6 npa average electron pressure (cold and hot) 0.2 npa average magnetic pressure 1.6 npa typical relative plasma flow velocity 140 km/s typical sound speed 280 km/s typical Alfvén speed 290 km/s From (Kivelson et al.)

4 Simulation setup Run Spatial resolution x [in d i0 ] Spatial resolution y = z [in d i0 ] Spatial size of the system L x = N x x [in d i0 ] Spatial size of the system L y = N y y [in d i0 ] Spatial size of the system L z = N z z [in d i0 ] s radius R G 8.3d i0 Temporal resolution (simulation time step) t ωgi0 1 Time sub-stepping for electromagnetic fields t B t/10 = ωgi0 1 Simulation box transition time [in ωgi0 1 ] Duration of each simulation ωgi0 1 β i0 2.0 β e Number of macro-particles per cell (specie AMU = 14) Total number of macro-particles [ 10 9 ] Background plasma velocity v psw 0.5 v A0 s magnetic moment M 1500 nt R 3 M 4π/µ 0 n i0, B 0, v A0, d i0, ω gi0 = 1 (in simulation units)

5 Simulated charge density ni /ni0 Pavel M. Tra vnı c ek et al.

6 Simulated plasma velocity vi /via0 Pavel M. Tra vnı c ek et al.

7 Simulated plasma velocity vi /via0 Pavel M. Tra vnı c ek et al.

8 Simulated magnetic field B/B 0

9 Simulated magnetic field B/B0 Pavel M. Tra vnı c ek et al.

10 Simulated temperature anisotropy Ti /Tik Pavel M. Tra vnı c ek et al.

11 Galileo flyby 01: Trajectory Galileo flyby trajectory around, June 27, 1996.

12 Galileo flyby 01: Magnetic field

13 Galileo flyby 01: VDF VDF along the flyby 01 trajectory: plasma build up due to compression close to outbound magnetopause, plasma belt caused by E B drift.

14 Virtual flyby: VDF VDF across the wing: plasma build up due to compression close to magnetopause, density gradient across the wing.

15 Conclusions The plasma flow is sub-alfvénic. Assumed v i0 = 0.5v A0 Kinetic (gyro-motion) effects might be important. They cause north/south and dawn/dusk asymetries in the interaction between Jovian plasma and s magnetosphere. Plasma is accelerated by the s magnetospheric system. Ionospheric / Exospheric interface is important for the circulation of plasma near (shown also by (Jia et al, 2009) in a MHD model) Higher ion plasma β i supports development temperature anisotropy driven instabilities. However, so far we have not observed electromagnetic waves. T i /T i has low values. Possibly small amplitude waves hiden yet in numerical noise. Drift acceleration looks more important than wave-particle heating (however, no pick-up ions considered so far).