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 = 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 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 Runs 1/4 Re: Dayside Magnetosphere + Central Plasma Sheet High Resolution Runs 1/16 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 K o, Vx = 300 km/s, |B| = 5 nT 0:00 – 2:00 - Startup Bz = - 5nT 2:00 – 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 Re Y = 0 Z = 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 Re Y = 15 Re Z = 6 Re

θ = 135

Open Magnetic Flux Increase = Total Reconnected Flux Growth [10 9 Wb ] Flux time (min ) θ = 180 θ = 135 θ = 105 θ = 120

θ = 180 θ = 135 θ = 105 θ = 120 L [Re] time ( min ) L ~ 2 * R R = 13.7 Re R - distance to the sub-solar point  Ψ local = E max dt * 2 Re L = Ψ total / Ψ local L - Effective Length of Reconnection Line

Is the extended reconnection line stable?

Z = 0Y = 0 θ = 180

Y = 0Z = 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 Cluster Sonnerup, Hasegawa, and Paschmann, Geophys. Res. Letters, L11803, 2004 PressureMagnetic 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 E1E1 E2E2  E0E0 Ψ = E0E0 dt * 2 Re

Open Magnetic Flux Increase (Resolution 1/16 Re) [10 9 Wb ] Flux Theta = 180 Theta = 135 Theta = 105 Theta = 120 time (min )

[10 9 Wb ] Flux [10 9 Wb ] Flux [10 9 Wb ] Flux [10 9 Wb ] Flux 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)

θ = 180 θ = 135

Flux Rope Evolution  = 120 t = 84 min