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Three Species Collisionless Reconnection: Effect of O + on Magnetotail Reconnection Michael Shay – Univ. of Maryland Preprints at:

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Presentation on theme: "Three Species Collisionless Reconnection: Effect of O + on Magnetotail Reconnection Michael Shay – Univ. of Maryland Preprints at:"— Presentation transcript:

1 Three Species Collisionless Reconnection: Effect of O + on Magnetotail Reconnection Michael Shay – Univ. of Maryland Preprints at:

2 Overview 3-species reconnection –What length scales? –Signatures? –Reconnection rate? Examples and background Linear theory of 3-species waves 3-Fluid simulations

3 Magnetospheric O + Earth’s magnetosphere –ionospheric outflows can lead to significant O + population. –Active Times Oct. 1, 2001: Geomagnetic storm –CLUSTER, spacecraft 4 –CIS/CODIF data –More O + than protons. –Chicken or Egg? March 18, 2002

4 Astrophysical Plasmas Star and planet forming regions –Molecular clouds and protoplanetary disks. –Lots of dust. –Wide range of conditions. Dust –negatively charged –mass >> proton mass. Collisions with neutrals important also. Hubble Orion Nebula Panorama

5 Previous Computational Work Birn et al. (2001, 2004) –Global MHD magnetotail simulations. –Test particle O + to examine acceleration and beam generation. Winglee et al. (2002, 2004) –Global MHD 2-fluid magnetospheric simulations. –Reduction of cross polar cap potential. –Did not resolve inner reconnection scales. Hesse et al., 2004 –3-species full particle simulations. –O + had no effect on reconnection, although an increase in proton density did. –Simulation size not large enough to fully couple O +.

6 Three-Fluid Equations Three species: {e,i,h} = {electrons, protons, heavy species} m h* = m h /m i Normalize: t 0 = 1/  i and L 0 = d i  c/  pi E =  V e  B   P e /n e

7 1D Linear waves Examine linear waves –Assume k || B o –Compressional modes decouple. -Z Y X V in V out 

8 Dispersion Relation Slow Alfven  h 2nd and 4th terms Fast Waves  h,  i >>  h

9 3-Species Waves: Magnetotail Lengths Previous Astrophysical Work. Heavy dust whistler (n h > m i n i ) has been examined but not in the context of reconnection. Shukla et al, Rudakov et al., Ganguli et al., SmallerLarger n i = 0.05 cm -3 n o+ /n i = 0.64 d   = c/  p 

10 Heavy Whistler Assume: –V h << V i,V e –Ignore ion inertia => V i  V e 1dhdh

11 The Nature of Heavy Whistlers 1.Heavy species is unmagnetized and almost unmoving. 2.Primary current consists of frozen-in ions and electrons E  B drifting. Ions+Electron fluid has a small net charge: charge density = e z h n h. 3.This frozen-in current drags the magnetic field along with it. Z Y -X Frozen-in Ion/Electron current Z Y -X 

12 Effect on Reconnection? Dissipation region –3-4 scale structure. Reconnection rate –V in ~  /D V out –V out ~ C At C At = [ B 2 /4  (n i m i + n h m h ) ] 1/2 –n h m h << n i m i Slower outflow, slower reconnection. Signatures of reconnection –Quadrupolar B z out to much larger scales. –Parallel Hall Ion currents Analogue of Hall electron currents. V in V out y x z

13 Simulations: Heavy Ions Initial conditions: –No Guide Field. –Reconnection plane: (x,y) => Different from GSM – 2048 x 1024 grid points x c/  pi.  x =  y = 0.1 Run on 64 processors of IBM SP. m e = 0.0,  4  4 B term breaks frozen-in,  4 = Time normalized to  i -1, Length to d i  c/  pi. Isothermal approximation,  = 1 V in CACA z x y

14 Reconnection Simulations Double current sheet –Reconnects robustly Initial x-line perturbation X X X X Y Y Current along Z Density t = 0 t = 1200

15 Equilibrium Double current sheet –Double tearing mode. Harris equilibrium –T e = T i –Ions and electrons carry current. Background heavy ion species. –n h = –T h = 0.5 –m h = {1,16,10 4 } –d h = {1,5,125} Seed system with x-lines. Note that all differences in c At is due to mass difference. Z Z Z JzJz BxBx density Electrons Ions Heavy Ions nV z

16 2-Fluid case m h* = 1 Quadrupolar B y –about d i scale size. V ix = V hx B y with proton flow vectors V ix with B-field lines. V hx X Z X Z X Z

17 Quadrupolar B y –Both light and heavy whistler. V i participates in Hall currents. V hx acts like V ix in two-fluid case. X Z Z Light Whistler Heavy Whistler B y with proton flow vectors V ix with B-field lines. V hx O + Case: m h* = 16

18 Quadrupolar B y –System size heavy whistler. V ix –Global proton hall currents. V hx basically immovable. B y with proton flow vectors V ix with B-field lines. V hx Whistler dominated m h* = 10 4

19 Reconnection Rate Reconnection rate is significantly slower for larger heavy ion mass. –n h same for all 3 runs. This effect is purely due to m h.. Slowdown in m h* = 10 4 ? System size scales: –Alfven wave: V  c Ah –Whistler: V  k d h c Ah V  d h c Ah /L => As island width increases, global speed decreases. m h* = 1 m h* = 16 m h* = 10 4 Reconnection Rate Island Width Time

20 Key Signatures O + Case Heavy Whistler –Large scale quadrupolar B y –Ion flows Ion flows slower. Parallel ion streams near separatrix. Maximum outflow not at center of current sheet. –Electric field? ByBy Cut through x=55 Velocity m h* = 1 m h* = 16 proton V x O + V x m h* = 16 Z Z symmetry axis X Z Light Whistler Heavy Whistler

21 Physical Regions Cuts through x-line along outflow direction. –Inner regions substantially compressed for m h* = –V ix minimum. light whistler light Alfven heavy whistler heavy Alfven V ex V ix V hx X X Z Z Z X V ex V ix light whistler light Alfven heavy whistler m h* = 1 m h* = 16 m h* = 10 4

22 Scaling of Outflow speed Maximum outflow speed –m h* = 1: V out1  1.0 –m h* = 16: V out16  0.35 Expected scaling: –V out  c At C At = [ B 2 /4  (n i m i + n h m h ) ] 1/2 V out1 /V out16  2.9 c At1 /c At16  2.6

23 Consequences for magnetotail reconnection When n o+ m o+ > n i m i –Slowdown of outflow normalized to upstream c Ai –Slowdown of reconnection rate normalized to upstream c Ai. However: –Strongly dependent on lobe B x. –Strongly active times: c Ai may change dramatically.

24 Specific Signatures: O + Modified Reconnection O + outflow at same speed as proton outflow. –Reduction of proton flow. Larger scale quadrupolar B y (GSM). Parallel ion currents near the separatrices. –Upstream ions flow towards x-line. The CIS/CODIF CLUSTER instrument has the potential to examine these signatures.

25 Questions for the Future How is O + spatially distributed in the lobes? –Not uniform like in the simulations. How does O + affect the scaling of reconnection? –Will angle of separatrices (tan  D) change? Effect on onset of reconnection? Effect on instabilities associated with substorms? –Lower-hybrid, ballooning,kinking, …

26 Conclusion 3-Species reconnection: New hierarchy of scales. –3-4 scale structure dissipation region. –Heavy whistler Reconnection rate –V in ~  /D V out –V out ~ C At C At = [ B 2 /4  (n i m i + n h m h ) ] 1/2 –n h m h << n i m i Slower outflow, slower reconnection. Signatures of reconnection –Quadrupolar B z out to much larger scales. –Parallel Hall Ion currents Analogue of Hall electron currents.


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