global mhd simulation with batsrus from...

Global MHD Simulation with BATSRUS from CCMC

ESS 265UCLA1

(Yasong Ge, Megan Cartwright, Jared Leisner, and Xianzhe Jia)

Outline

• Description of Model• Global Magnetophere• Dayside Magnetopause and Solar Wind• Cusp Region Investigation • Magnetotail Investigation

BATS-R-US Model• BATS-R-US, the Block-Adaptive-Tree-

Solarwind-Roe-Upwind-Scheme, was developed by the Computational Magnetohydrodynamics (MHD) Group at the University of Michigan, now Center for Space Environment Modeling (CSEM). It was designed using the Message Passing Interface (MPI) and the Fortran90 standard and executes on a massively parallel computer system.

• The BATS-R-US code solves 3D MHD equations in finite volume form using numerical methods related to Roe's Approximate Riemann Solver. BATSRUS uses an adaptive grid composed of rectangular blocks arranged in varying degrees of spatial refinement levels. The magnetosphericMHD part is attached to an ionosphericpotential solver that provides electric potentials and conductances in the ionosphere from magnetospheric field-aligned currents.

Input parameters and boundary conditions

• Fixed Solar Wind velocity of 400km/s, solar wind density of 5X106 protons/m3 and temperature of 1X105.

• Two hours initialization with steady southward IMF.

• Turning IMF northward for the last two hours.

• Default ionosphere without corotation.

Magnetic field lines t=00:00

Pressure + Velocity vectors t= 00:00

Noon-Midnight meridian view

Equatorial view



Equatorial view

Plasma temperature t= 00:00

Jy t= 00:00

Jy t= 01:00

Jy t= 01:58

Jy t= 02:00

Jy t= 02:16

Jy t= 02:30

Jy t= 02:46

Jy t= 03:00

Jy t= 03:16

Jy t= 03:20

Jy t= 03:30

Jy t= 03:46

Jy t= 04:00

Ionospheric potential + velocity vectors

Summary for Global View • 3D B field lines show tail flaring on southward IMF and flux return

(tail field relaxation) on northward IMF. NENL retreats a while after IMF turning.

• Plasma pressure in magnetosheath increases temporarily just after northward IMF hits magnetophere.

• Magnetosheath flows rotate to field-aligned.• Two convection cells in tail shows the ground state of

magnetophere. • Thin plasma sheet is present on southward IMF and has a large y

range. Plasma sheet density and size in y direction decrease, but plasma expansion in z direction follows the NENL retreating.

• Thin current sheet also is shown at Jy plot. • Southward IMF gives strong magnetopause current, and the current

fades off after IMF turning.• DP-2 current system is shown when IMF is southward and dies off

when IMF is turned northward.

Pressure(color) and velocity(vector) and B field lines at t=0:00

Left is noon-midnight meridian Right is equatorial plane

Summary for Magnetopause• At the dayside magnetosheath, the plasma

pressure increases due to the turning of IMF from southward to northward and the turning off of dayside reconnection.

• Plasma pressure in dayside magnetosheathfinally falls off.

• Pressure stabilizes at subsolar point between t = 2:46 and 3:00

• Magnetic field flux piles up at dayside magnetopause due to the turning of IMF.

LogT(color) and JXB(vector) and B field lines at t=0:00

Summary for Cusp Region• In the cusp, the pressure decreases significantly as the IMF turns

northward. • At cusp region, flow is parallel the magnetopause when IMF is

southward, then rotates counter-clockwise until it points perpendicular to the magnetopause. This is the inflow of solar wind particles due to reconnection.

• The cusp region immigrates northward in northward IMF.• Magnetopause moves out, polar cap shrinks (green lines). • Hot particle concentration moves up from the ram side to the upper

flank, settling in the region of reconnection. Polar cap disappears? • JxB force goes from about equal between polar and closed field lines

to much larger on northern side of reconnection region (not exactly sure what to make of this...current in reconnection region is predominantly field-aligned?).

B field lines in tail at t=0:00

Number Density and Velocity in tail at t=0:00

Summary from Tail View• Dayside reconnection in southward IMF

transports magnetic flux into tail. Tail is flaring due to flux pile-up.

• Near-Earth reconnection sustains when IMF is southward.

• Northward IMF decreases dayside reconnection rate and tail reconnection return flux back to dayside. NENL retreats from ~20 RE to distant tail after 3:16.

• Plasma sheet tenuates and extends tailwardwith the retreating of neutral line.

Summary

• Dayside reconnection due to southward IMF erodes dayside magnetosphere and magnetic flux piles up at tail.

• Northward IMF ceases (almost) dayside reconnection and erosion of dayside magnetosphere.

• Tail reconnection returns flux back to dayside, and magnetosphere relaxes to the ground state.

global mhd simulation with batsrus from...

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