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

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 ?

Sub-Solar Flow Stagnation Point: V = 0Component Reconnection for By 0 ?

Magnetically Neutral Points (cusp region, flanks): B = 0What is the Role of High Speed Flows at Flanks?

Reconnection Line Extended Over the Entire Dayside Magnetopause

Possible Reconnection Sites.

Steady-state or impulsive reconnection (FTEs, flux ropes ?)

Role of velocity sheer at neutral points (K-H instability ?)

How global MHD models describe dayside magnetic reconnection?

BATSRUS uses an adaptive grid composed of rectangular blocks arranged in varying degrees of spatial refinement levels.

Medium Resolution Runs1/4 Re: Dayside Magnetosphere + Central Plasma Sheet

High Resolution Runs1/16 Re: Dayside Magnetopause Including Flanks

Model

Global MHD simulation model: BATSRUS, University of Michigan

Grid

Simulation Box-255 Re < X < 33 Re|Y|, |Z| < 96 Re

N = 2 cm –3 , T = 20,000 Ko , Vx = 300 km/s, |B| = 5 nT

0:00 – 2:00 - Startup Bz = - 5nT2:00 – 4:00 – Northward IMF Bz = 5 nT

Simulation Startup:

Solar Wind Parameters:

Fixed IMF

Run 1: θ = 180

Run 2: θ = 135

4:00 – 4:05

IMF Turning From Northward Orientation (θ = 0)

to IMF Clock angles 105 < θ < 180:

4:05 – 7:00

Run 3: θ = 120

Run 4: θ = 105

After IMF Turning

Prior to Night-Side Reconnection Onset

04:00

Time Interval of Interest 4:00 – 6:00 (0 – 120 min)

Rate of dayside reconnection can be estimated as the rate of the polar cap growth

Component Reconnection at Sub-Solar Stagnation Point for Large By (θ = 105)

X = 13.7 ReY = 0Z = 0

What is going on at magnetically neutral points at the flanks? What is the role of high speed flows?

θ = 135

X = 1.5 ReY = 15 ReZ = 6 Re

θ = 135

Open Magnetic Flux Increase = Total Reconnected Flux Growth [1

0 9

Wb

]F

lux

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120

time (min )

θ = 180

θ = 135

θ = 105

θ = 120

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

20 40 60 80 100 120

θ = 180

θ = 135

θ = 105

θ = 120

L [Re]

time ( min )

L ~ 2 * RR = 13.7 Re

R - distance to the sub-solar point

Ψ local = Emaxdt * 2 ReL = Ψ total / Ψ local

L - Effective Length of Reconnection Line

Is the extended reconnection line stable?

Z = 0 Y = 0θ = 180

Y = 0 Z = 0 θ = 180

Flux Rope Formation at Sub-Solar Stagnation Region for 120 < < 135?

Flux Rope Formation θ = 120

Pressure

Flux Rope Formation θ = 120

Density Magnetic Field By

Flux Rope Formation θ = 120

Flux Rope Evolution = 120 t = 80 min

• 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.

Anatomy of flux transfer event seen by ClusterSonnerup, Hasegawa, and Paschmann, Geophys. Res. Letters, L11803, 2004

Pressure Magnetic Field

High resolution global MHD simulations demonstrated sub-solar component reconnection for IMF clock angles

105 < θ < 180.

The rate of reconnection flux loading vary no more than 5-10 % for different IMF orientations in range of IMF Clock angles

105 < θ < 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.

Summary

Supplemental Slides

Reconnected Flux at Sub-Solar Region |Y| < 1 Re

E1

E2

E0

Ψ = E0 dt * 2 Re

Open Magnetic Flux Increase (Resolution 1/16 Re)[1

0 9

Wb

]F

lux

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120 140

Theta = 180

Theta = 135

Theta = 105

Theta = 120

time (min )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 1200.0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120

[10

9W

b ]

Flu

x

[10

9W

b ]

Flu

x

[10

9W

b ]

Flu

x

[10

9W

b ]

Flu

x

time (min) time (min)

time (min) time (min)

θ = 180

θ = 120

θ = 135

θ = 105

Total Reconnected Flux Reconnected Flux Ψ at Subsolar Region |Y| < 1 Re

med resolution (1/4 Re)

(1/4 Re)high resolution (1/16 Re) (1/16 Re)

0 20 40 60 80 100 120

0 20 40 60 80 100 120

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

0.6

0.5

0.4

0.3

0.2

0.1

0.00 20 40 60 80 100 120

0 20 40 60 80 100 120

0.6

0.5

0.4

0.3

0.2

0.1

0.0

θ = 180

θ = 135

Flux Rope Evolution = 120 t = 84 min