The Case for Component Reconnection

1
The Case for Component Reconnection

• Indicators
• Reconnection in subsolar region for most Bz.
• Reconnection poleward of the cusp near NBz.
• Ionospheric leakage suggests subsolar even for
  NBz.
• Extent of the X-line is inferred to be 4-5 Re.
• An anti-parallel X-line has little extent.
• X-line integrates to an S or Z shape, looping
  cusps.
• Sunward sub-solar plasma flows inside
  magnetopause.
• Objections
• Non-reconnecting field magnetizes electrons,
  inhibits rate.
• Counterpoint guide field does not obstruct
  current flow.
• Counterpoint 3D PIC simulations support this
  assertion.

2
Component vs Antiparallel Reconnexion
Crooker, 1979 Luhmann, 1984
Cowley 1976 Moore, 2000 AGU SM
3
Component Reconnection

• Observations
• Gosling et al., 1990 JGR.
• Chandler et al. 1999 JGR (sub-cusp even for NBz)
• Scudder et al. 2002 JGR in press (large, stable
  region)
• Mozer et al., 2002 PRL (near antiparallel, near
  equator)
• Khan et al. 2002 GRL
• Chandler and Avanov, 2002 (in review)
• Theory
• Gonzalez and Mozer, 1974 JGR.
• Cowley and Owen, 1989 PSS.
• Shay et al., 2001 JGR Pritchett, 2001 JGR.
• also Drake, Rogers, Shay AGU presentations)
• Moore et al., 2002 JGR in press
• DOI 10.1029/2002JA009381

4
X-line Integrates to S or Z Loop
Antiparallel Sites
Component X-Line
5
Open Flux Tube Motion at Mpause

• Cowley and Owen PSS 1989
• Assume SH and BL fields are equal in magnitude
• (MP as rotational discontinuity)
• Plasma flows across boundary freely
• pressure balance established inward of BL, where
  SH plasma drops in pressure and MS field
  increases.
• Assume HT frame where
• Vplasma // BSH, in SH
• Vplasma VHT, at MP
• Vplasma // BBL, in BL
• Geometric Construction
• Flux tube motion at MP (HT)
• Plasma motion in SH, BL
• Results along straight X-line

Velocity Space Diagram
VBL
BBL
VBLVAbBL
VSHVAbSH
HT
VSH
VHT
BSH
Earth
6
Subsolar Sunward Plasma Flows
03/20/01
Vz
GSE
Vx
04/02/02
Vy
Sun
Vx
7
Conclusion

• Component reconnection certainly exists.
• Along an integrable X-line, rate will vary with
  local conditions.
• Rate may vanish only for exactly parallel fields.
• Subsolar limiting rate high latitude rate
  except exact NBz
• Carried to the low shear extreme
• Do slightly sheared auroral flux tubes reconnect?
• Produce spiral flux tubes wrapped around
  currents?
• Diffusion of auroral shear significant as
  viscosity?
• Smooth transition to high shear case.
• Anti-parallel sites tend to have largest rates,
  potential energy
• Hypothesis begins at or near anti-parallel sites
  and spreads
• Actions
• Cluster investigations map X-line orientation
• Global simulations map X-lines