Anti-Parallel Merging and Component Reconnection: Role in Magnetospheric Dynamics

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Anti-Parallel Merging and Component
Reconnection Role in Magnetospheric Dynamics
M.M Kuznetsova, M. Hesse, L. Rastaetter
NASA/GSFC
T. I. Gombosi
University of Michigan
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I. How to reproduce fast reconnection rate of
kinetic/two-fluid models in MHD simulations?
Small- meso-scale simulations with nongyrotropic
corrections Numerical viscosity vs. uniform
resistivity.
II. How global MHD models describe dayside
magnetic reconnection?
What is the impact of the IMF clock angle ?
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Possible Reconnection Sites.
Sub-Solar Flow Stagnation Point V 0 Component
Reconnection for By ? 0 ?
Magnetically Neutral Points (cusp region,
flanks) B 0 What is the Role of High Speed
Flows at Flanks?
Reconnection Line Extended Over the Entire
Dayside Magnetopause
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How global MHD models describe dayside magnetic
reconnection?
Steady-state or impulsive reconnection (FTEs,
flux ropes ?) Role of velocity sheer at neutral
points (K-H instability ?)
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Model
Global MHD simulation model BATSRUS,
University of Michigan
BATSRUS uses an adaptive grid composed of
rectangular blocks arranged in varying degrees of
spatial refinement levels.
Grid
Simulation Box -255 Re lt X lt 33 Re Y, Z lt 96
Re
Medium Resolution Runs 1/4 Re Dayside
Magnetosphere Central Plasma Sheet
High Resolution Runs 1/16 Re Dayside
Magnetopause Including Flanks
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Solar Wind Parameters
N 2 cm 3 , T 20,000 Ko , Vx 300 km/s, B
5 nT
Simulation Startup
000 200 - Startup Bz - 5nT 200 400
Northward IMF Bz 5 nT
IMF Turning From Northward Orientation (? 0)
to IMF Clock angles 105 lt ? lt 180
400 405
Run 1 ? 180 Run 2 ? 135
Run 3 ? 120 Run 4 ? 105
Fixed IMF
405 700
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Time Interval of Interest 400 600 (0 120
min)
After IMF Turning
0400
Prior to Night-Side Reconnection Onset
Rate of dayside reconnection can be estimated as
the rate of the polar cap growth
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Component Reconnection at Sub-Solar Stagnation
Point for Large By (? 105)
X 13.7 Re Y 0 Z 0
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What is going on at magnetically neutral points
at the flanks? What is the role of high speed
flows?
? 135
X 1.5 Re Y 15 Re Z 6 Re
10
? 135
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Open Magnetic Flux Increase Total Reconnected
Flux Growth
? 180
? 135
Wb
? 120
? 105
10 9
Flux
time (min )

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?
? local
L ? total / ? local
Emax
dt 2 Re
L - Effective Length of Reconnection Line
? 180
? 135
? 120
? 105
L Re
L 2 R R 13.7 Re
R - distance to the sub-solar point
time ( min )
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Is the extended reconnection line stable?
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? 180
Z 0
Y 0
15
Y 0
Z 0
? 180
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Flux Rope Formation at Sub-Solar Stagnation
Region for 120 lt ? lt 135?
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Flux Rope Formation
? 120
Pressure
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Flux Rope Formation
? 120
Magnetic Field By
Density
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? 120
Flux Rope Formation
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t 80 min
Flux Rope Evolution
? 120
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• High resolution global MHD simulations
  demonstrated flux ropes (FTEs) generation by
  intermittent component reconnection.
• We show that FTEs are flux ropes of approximate
  size 1-2 Re with strong core magnetic field
  imbedded in the magnetopause.
• FTE bulge is larger on the magnetosheath side
  than on the magnetosphere side. The flow around
  the flux rope is largest at the magnetosphere
  side.
• The plasma pressure pattern within the flux rope
  exhibit a ring-shaped structure surrounding a
  central depression.
• Traveling density depletion.

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Anatomy of flux transfer event seen by Cluster
Sonnerup, Hasegawa, and Paschmann, Geophys. Res.
Letters, L11803, 2004
Pressure
Magnetic Field
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Summary
High resolution global MHD simulations
demonstrated sub-solar component reconnection
for IMF clock angles 105 lt ? lt 180. The rate of
reconnection flux loading vary no more than 5-10
for different IMF orientations in range of IMF
Clock angles 105 lt ? lt 180. Flux budget
analysis indicate that magnetic field is
reconnection along extended region comparable
with magnetopause scale. High resolution
simulation demonstrated instability of extended
reconnection region and formation of plasmoids
and flux ropes. K-H instability is developing
close to neutral points in region of fast flows
at magnetopause flanks.
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Supplemental Slides
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Reconnected Flux at Sub-Solar Region Y lt 1 Re
E0
E1
E2

?
?
E0
dt 2 Re
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Open Magnetic Flux Increase (Resolution 1/16 Re)
Theta 180
Wb
Theta 135
10 9
Theta 120
Flux
Theta 105
time (min )

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Reconnected Flux ? at Subsolar Region Y lt 1 Re
Total Reconnected Flux
med resolution (1/4 Re)
high resolution (1/16 Re)
(1/4 Re)
(1/16 Re)
0.6 0.5 0.4 0.3 0.2 0.1 0.0
0.6 0.5 0.4 0.3 0.2 0.1 0.0
? 180
? 135
Wb
Wb
10 9
10 9
Flux
Flux
0 20 40 60 80
100 120
0 20 40 60 80
100 120
time (min)
time (min)
0.6 0.5 0.4 0.3 0.2 0.1 0.0
0.6 0.5 0.4 0.3 0.2 0.1 0.0
? 120
? 105
Wb
Wb
10 9
10 9
Flux
Flux
0 20 40 60 80
100 120
0 20 40 60 80
100 120
time (min)
time (min)
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? 180
? 135
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t 84 min
Flux Rope Evolution
? 120
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