UNH MURI Workshop: Planned Numerical Experiments

1
UNH MURI Workshop Planned Numerical Experiments

• 3-d Emerged Bipole Form flux-rope in simulated
  corona by converging footpoints of coronal
  fields.
• computational domain is 3-d non-periodic box with
  high b 10?) on bottom boundary,
  w/stratification such that b ltlt 1 within lower
  part of simulation volume.
• intial condition (IC) has volume-filling dipole
  field.
• impose incompressible converging flows on bottom
  boundary .

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3d emeged bipole (contd)

• initial magnetic field ought to be sheared, such
  that some component of the magnetic field is
  parallel to the magnetic neutral line at the
  bottom boundary or
• if initial magnetic field is unsheared
  (potential?), imposed flow should have non-zero
  vorticity, to ensure some component of magnetic
  field is tangential to the magnetic neutral line
  on the bottom boundary
• primary goal is to form flux rope subsequent
  efforts to erupt flux rope envisioned upon
  attainment of flux rope in corona
• this experiment involves some modification of
  existing codes.
• Critical issue 3-d necessary (no 2.5-d, or
  periodicity)

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3-d Emerging Bipole

• Flux rope in coronal volume via emergence of a
  pre-existing twisted flux tube from a region of
  high b to low b
• IC buoyantly unstable horizontal twisted flux
  tube immersed in high-b plasma at base of
  gravitationally stratified 3-d box.
• Follow rise of twisted flux tube from deep in
  convection zone through photosphere into corona.
  Critical issue initial position of tube cannot
  be too near surface, as flux tube curvature
  matters.
• Unspecified parameter degree of twist in
  emerging tube. Twist too high perhaps prevents
  mass drainage, hampering emergence twist too low
  does not give true flux rope in corona.

4
3d emerging bipole (contd)

• Unspecified parameter Magnetic field
  configuration in corona prior to flux rope
  emergence. Intial runs w/field-free corona
  envisioned.
• As above, primary goal is to get flux rope in
  corona subsequent efforts to attain eruption
  envisioned after attainment of primary.
• As above, some modification of existing codes
  necessary.

5
Bipole emergence in 3d multi-polar field

• Emerge one flux tube into into background
  magnetic field sheared arcade/flux rope
  formation by reconnection between emerging flux
  and pre-existing flux.

6
Bipole emergence in multi-polar field (contd)

• IC buoyantly unstable flux tube immersed in
  high-b plasma at base of gravitationally
  stratified 3-d box with background magnetic field
  configuration composed of a pre-emerged flux tube
  and large scale "restraining field," and form
  sheared arcade/flux rope by reconnection between
  the two flux tubes.
• Critical issue without restraining field,
  reconnected flux expected to rise to top of
  computational volume in non-explosive manner.

7
Bipole emergence in multi-polar field (contd)

• Primary goal is attainment of sheared arcade/flux
  rope in corona subsequent effort to attain
  eruption envisioned.
• In one effort to attain eruption, additional
  polarity will be added to restraining field to
  make it quadrupolar.
• Unspecified parameter twist in either
  pre-emerged or newly-emerging flux ropes.
  Presence of twist might either enhance or
  diminish storage of energy in the field, and
  hence likelihood of eruption.