Solar Wind-Magnetosphere Interaction for Northward Interplanetary Magnetic Field

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Solar Wind-Magnetosphere Interaction for
Northward Interplanetary Magnetic Field

• Paul Song
• Center for Atmospheric Research
• University of Massachusetts Lowell

• LLBL formation
• Global model
• Summary

Acknowledgments C. T. Russell, T.I. Gombosi,
D.L. DeZeeuw
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Structure of the Magnetopause
Northward IMF
Southward IMF
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Distribution Functions Across the Magnetopause
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Summary of LLBL Observationsfor Northward IMF

• Density and temperature change in steps against
  diffusion to be important
• Indication of mixtures of plasmas of
  magnetosphere and magnetosheath origins at
  different ratios
• Thicker and faster on the nightside
• Smaller density gradient and velocity shear on
  the nightside

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Northward IMFDungey, 1963
Southward IMFDungey, 1961
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Song and Russell Model 1992
Reconnection takes place on the stagnant field
line at regions of high field shear
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After Cusp Reconnection

• As Alfvenic kink propagates to lower latitudes,
  the newly reconnected field line sinks into the
  magnetosphere
• Note the foot of the field moves sunward

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NBZ Model

• Entry Mechanism
• Through reconnection at two hemispheres the
  magnetosphere captures a segment of a solar wind
  flux tube
• The newly captured flux tube sinks into the
  magnetosphere via propagating Alfven waves.

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Formation of the LLBL

• After the captured flux tube becomes a
  magnetospheric flux tube
• The original flux tube is compressed and
  shortened (magnetic volume
  decreases gtB and ? increases)
• Total pressure of the flux tube increases.
• The flux tube expands (increase in length or
  volume) along the magnetopause to the flank via
  interchange instability
• Ionospheric dissipation drags the motion
• Successive reconnection events form multiple
  layers of LLBL
• Interpenetration and mixing of plasmas of two
  origins result in decreased ratio of
  magnetosheath-to-magnetosphere population an
  aging process

How can the flux tube flow back?
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Global Modeling the Solar Wing-Magnetosphere-Ionos
phere System
Challenges

• The topological status of the magnetosphere open
  or closed?
• Driver(s) of ionospheric sunward flow
• Source(s) of NBZ currents
• Key problem are viscous cells driven by
  viscosity?

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Ionospheric Observations for NBZ

• Field-aligned current
  Precipitation particles
• Ijima and Potemra, 1978 Newell and
  Meng, 1994

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Ionospheric Convection and Field Perturbations
for NBZ Potemra et al., 1984
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Oginos code, NBZ, Ogino and Walker, 1984

• Cusp reconnection
• Closed magnetosphere

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Rice Model, NBZ Usadi et al., 1993

• Cusp merging
• Closed magnetosphere
• Shorter tail for large IMF magnitude

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Fedder and Lyon (1995), NBZ MHD Simulation
Noon-midnight meridian
Equatorial Plane

• Cusp merging
• Closed magnetosphere
• 4-cell ionosphere convection
• NBZ currents
• Flow diversion at 95 Re

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Raeders Model, NBZ Raeder et al., 1995

• Cusp reconnection
• Tail reconnection
• Open tail
• No ionospheric convection is shown

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Oginos code, NBZ, Bargatze et al., 1999

• Cusp reconnection
• Closed magnetosphere

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Global MHD Simulation For Northward IMF

• Reconnection Tail Tail-length Ionosphere
• Ogino-Walker cusp closed 1/B
• Wu cusp closed 1/B
• Usadi et al. cusp closed 1/B
• Fedder-Lyon cusp closed 1/B 4-cell/NBZ
• Raeder cusptail open
• Michigan cusp closed 1/B 4-cell/NBZ
• Bargatze cusp closed 1/B 4-cell/NBZ
• ISM cusp closed 4-cell/NBZ

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Raeders Model, NBZ Raeder et al., 1995

• Cusp reconnection
• Tail reconnection
• Open tail
• No ionospheric convection is shown

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Global Picture

• Solar wind and magnetosphere are coupled through
  high latitude reconnection.
• For due NBZ, the magnetosphere is closed except
  the cusps
• Three topological boundaries and regions.
• Outer magnetosphere two convection channels and
  two cells.
• LLBL is driven by pressure gradients.
• Viscous cells are driven at ionosphere by
  Pedersen currents.
• A region of stagnant flow near midnight in the
  tail between 20-50 Re depending on the IMF
  strength cold-density plasma sheet.
• Ionosphere
• 4-cell convection.
• NBZ, Region I, and (Region II currents, not
  modeled).
• Polar caps, although closed, see solar wind
  particles

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NBZ MHD Simulation (Michigan Code)
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Summary

• Chris and I first proposed a model of formation
  of LLBL for northward IMF
• We then collaborated with Michigan group and
  developed a self-consistent global model for
  northward IMF
• Solar wind entry reconnection.
• LLBL flow driven by pressure force.
• Magnetotail length increases with 1/BIMF, NSW,
  MSW.
• Reverse cells driven by reconnection and LLBL.
• Viscous cells driven at ionosphere by Pedersen
  currents.
• Magnetopause definition the magnetopause
  currents may differ from the topological
  boundary.
• Stagnation line/point dilemma No stagnation
  region in the magnetosheath. A stagnation line
  occurs in the magnetospheric field.
• Ionosphere Precipitation within (outside) the
  polar cap is of solar wind (magnetospheric)
  origin (mistaken by some people as evidence of an
  open region).
• The most important things I learned from Chris
• A positive view toward referees and referees
  reports
• There are only 3 ways to prove truth!
  (simulation is NOT among them!)
• Can you summarize your thesis in one sentence, or
  two sentences, or (an anti- correlation between
  the number of sentences with the significance of
  work)