3D MHD Modeling of Mercury’s
Magnetosphere During ICMEs
A. Glocer, M. Sarantos, J. Slavin
Outline
Model description.
Validation
Three boundary choices are considered:
1. Floating
2. Float ! and p and v|| pointing inward, reflect v!
and v|| pointing outward
3. Float !, p, v", v#, and vr<0, reflect vr>0
Use M1 and M2 as validation cases
Mercury During ICMEs
Simulation of low MA case
Simulation of Mercury interacting with an ICME
BATS-R-US
BLOCK ADAPTIVE TREE SOLAR-WIND ROE UPWIND
SCHEME
Conservative finite-volume discretization
Shock-capturing TVD schemes
Rusanov, HLL/AW, Roe, HLLD
Parallel block-adaptive grid
Cartesian and generalized coordinates
Explicit and implicit time stepping
Classical, semi-relativistic and Hall MHD
Multi-species and multi-fluid MHD
Splitting the magnetic field into B0 + B1
Various methods to control divergence B
Nearly perfect scaling to more than 1000
processors
MAGNETOSPHERE DOMAIN:
INNER BOUNDARY LOCATION: 1.0 RM
OUTER BOUNDARY: 32 RM UPSTREAM
AND 224 RM DOWNSTREAM
Boundary
The inner boundary condition has a huge effect on the solution.
It is not immediately clear what the proper choice is.
Several possibilities include:
Fixed BCs
Floating BCs
Float, B1 ! and p and v|| pointing inward, reflect v! and v||
pointing outward
Float, B1 !, p, v", v#, and vr<0, reflect vr>0
Other questions: Conductance, FACs
Boundary Testing Strategy
To test the effect of the inner boundary we simulate the M1 and
M2 flybys
The solution is extracted along the MESSENGER trajectory and
directly compared to MAG data
These runs are also used to test dipole strength and
displacement (final choice ~200 nT, displaced .18 northward)
Compare the effect of boundary on closed field line region,
precipitating flux
BC1
BC1
BC2
BC2
BC3
BC3
Boundary Comparison
M1 Flyby
BC-1
BC-2
BC-3
Boundary Comparison
M2 Flyby
BC-1
BC-2
BC-3
Boundary Comparison
Closed B-Field During M2
BC-1
BC-2
BC-3
Boundary Comparison
Precipitating Flux During M2
BC-1
BC-2
BC-3
Boundary Comparison
Precipitating Flux Comparison
BC2
M2
M1
BC3
100
Bx (nT)
Disturbed Solar
Wind At Mercury
50
0
-50
-100
-150
150
To the right, an ICME from Helios 1
measurements.
These data were taken at 0.34AU.
0
-50
50
0
-50
-100
-150
500
400
300
200
100
0
-400
-500
Vx (km/s)
During ICMEs we can see extremely
low Mach numbers
BZ<0
100
Bz GSM (nT)
Low Alfvénic Mach numbers are seen
particularly during ICMEs where |B| !
100nT
50
-100
-150
150
Density (/cc)
MESSENGER enters orbit during
solar max
By GSM (nT)
100
IP
SHOCK
-600
-700
-800
00
03
06
09
Jun 20, 1981 UT Hours
12
15
Solar Wind Ram Pressure, MA, and $A
500
Ram Pressure [nPa]
400
300
200
100
0
-100
15
Mms
10
5
Alfven Conductance
0
6
5
4
3
2
1
0
03
06
Simulation Time [Hr]
09
12
Low MA Case
Velocity
Total Velocity:
Velocity:
MA 1.75Total Velocity:
MA 0.85
MA=3.0MA 3.0TotalTotal
MA=1.75
MA=0.85
500
20
20
400
20
20 400
Predicted Slopes for
10
10
0
00
10
300
Z
10
ZZ
Z
400
-10
-10
-20
-20
300
300
300
200
200
200
100
100
100
-10
100
-20
Alfvén Wings
0
200
-10
400
-20
15 10 5 0 -5 -10 -15 -20
15 10 5 0 -5 -10 -15 -20
15
10 5 0 -5 -10 -15 -20
15 10 5 0 -5 -10 -15 -20
X
X
X
x= 25048,
1, it= 140000, time= X0.0000
1, it= 135000,
time=
x= 25048,
0.0000
1, it=decrease
120000, time=
x=
0.0000
1,Mach
it= 60000,
time= (MA0.0000
We systematically
the25048,
Alfvén
number
) by dropping
the solar wind Bz while holding other quantities constant.
As the MA is reduced, the lobes begin to separate and the shock front
weakens.
Idealized High Ram Pressure
FIG. 5. Logarithm of the magnetic field intensity in a cross-tail section 3RM behind Mercury. The black line is the bow shock position in this plane. The black
arrow shows the direction of the current.
FIG. 7.
Same as Fig. 1 for the Parker spiral with high speed and pressure of the solar wind, allowing it to penetrate to the surface.
Actual ICME Simulation
Total Velocity and B-Field
During IP Shock
4
600
10
400
0
-2
5
600
0
400
-5
200
200
Z
Z
2
Total Velocity and B-Field
-4
0
2
1
0 -1 -2 -3 -4 -5
X
1, it= 70925, time= 2h30m00s
-10
0
0
-5
-10
X
x= 30208, 1, it= 70925, time= 2h30m00s
-15
-20
During Minimum MA
Total
Velocity
BC2
6
1000 6
4
800
2
BC1
Total
Velocity
1000
4
800
2
0
Z
600
500
-2
600
0
400
400
400
-2
Ram Pressure [nPa]
Z
Actual ICME Simulation
-4
-6
0
-2
200
200
100
200
-4
-6
-4
-6
-8
X
-100
5048, 1, it= 207395, time=
4h10m00s
15
0
-10
-12
2
0
-2
-4
-6
-8
X
x= 25048, 1, it= 228928, time= 4h10m00s
10
Mms
2
300
5
0
03
06
Simulation Time [Hr]
09
12
-10
-12
Solution at Minimum MA: The Correct Plane
ORIGINAL CASE: MA=1.78
ENHANCED CASE: MA=1.14
A significant By component can twist the lobes such that the y=0 plane is not
meaningful.
We show the solution in plane cutting through the lobes, and find an angle of 39˚
between the lobes. The angle between Alfvén characteristics is 33˚.
We also show the solution of a case with “enhanced” IMF conditions (right). The
angle between lobes is 77˚, and the angle between characteristics is 72˚.
Conclusions
Boundary conditions can really control the solution
BC1: gives larger dayside magnetosphere, and short tail
BC2: gives long tail and small dayside magnetosphere.
BC3: gives an intermediate result and stronger flux at 0LT
Through an iterative process we found a dipole of 200nT
and an offset of .18RM northward
ICMEs
During the orbital phase we expect to observe several
ICME encounters with Mercury
These times include large ram pressure that can completely
compress the magnetopause.
They also have strong magnetic fields that can bring the
cusps together, and they can lead to very low MA
Thank You