Ward Manchester University of Michigan
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Transcript of Ward Manchester University of Michigan
Ward Manchester Ward Manchester
University of MichiganUniversity of Michigan
Coupling of the Coupling of the Coronal and Coronal and
Subphotospheric Subphotospheric Magnetic Field in Magnetic Field in Active Regions by Active Regions by
Shear Flows Driven by Shear Flows Driven by The Lorentz ForceThe Lorentz Force
OutlineOutline Universal feature of active regions Universal feature of active regions
that produce CMEs: magnetic shearthat produce CMEs: magnetic shear Source of magnetic shear: a subtle Source of magnetic shear: a subtle
combination of the Lorentz force and combination of the Lorentz force and gravitational pressure stratification gravitational pressure stratification of the solar atmosphereof the solar atmosphere
Examples of shearing motions in flux Examples of shearing motions in flux ropes, and magnetic layersropes, and magnetic layers
Picture of magnetic activity that Picture of magnetic activity that couples the subphotospheric couples the subphotospheric magnetic field to the coronamagnetic field to the corona
Velocity and Magnetic Velocity and Magnetic Shear in AR 10486 Shear in AR 10486
Source of the Halloween Source of the Halloween EventsEvents Velocity Shear Yang et al. 2004, ApJ 617 L151, Velocity Shear Yang et al. 2004, ApJ 617 L151,
Magnetic Shear Liu et al. 2005, ApJ 622, 722 Magnetic Shear Liu et al. 2005, ApJ 622, 722
Recent CME Models That Impose Recent CME Models That Impose Shear Shear
Magnetic Arcade ModelsMagnetic Arcade Models Imposed Imposed shearing of foot points with magnetic shearing of foot points with magnetic
reconnect at the base of the arcade (Amari et al. 2003 reconnect at the base of the arcade (Amari et al. 2003 ApJ 595, 1231 )ApJ 595, 1231 )
Break-out model: Break-out model: Imposed Imposed shearing motions and shearing motions and reconnection above the arcade in a quadruple system reconnection above the arcade in a quadruple system (Antiochos 1999 ApJ 510, 485)(Antiochos 1999 ApJ 510, 485)
Emergence of a 3D flux ropeEmergence of a 3D flux rope
Manchester, Manchester, Gombosi, De Zeeuw Gombosi, De Zeeuw and Fan. 2004, ApJ and Fan. 2004, ApJ 610, 588610, 588
Flux Rope Emerging From the Flux Rope Emerging From the Convection Zone into the CoronaConvection Zone into the Corona
Buoyant Buoyant section of section of the flux the flux rope rope reduced by reduced by a factor of a factor of twotwo
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Spontaneous Shearing MotionsSpontaneous Shearing Motions
Opposite sides Opposite sides of the flux rope of the flux rope move in move in opposite opposite directions as directions as the flux rope the flux rope expands. expands.
Motions are Motions are driven by the driven by the Lorentz force!Lorentz force!
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Development and Development and Eruption of Magnetic Eruption of Magnetic
Shear CoreShear Core
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The Lorentz Force Drives The Lorentz Force Drives the Shearing!!the Shearing!!
Shearing motions transport Bx flux into the expanding portion of Shearing motions transport Bx flux into the expanding portion of the flux rope and tends to return Bx to constant values along field the flux rope and tends to return Bx to constant values along field lines to restore force balance lines to restore force balance
Dynamic Coupling By Dynamic Coupling By Shear FlowsShear Flows
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Shearing During Flux Emergence Shearing During Flux Emergence From a Magnetic LayerFrom a Magnetic Layer
Comparison of Shear VelocityComparison of Shear Velocity
The image on the left, the shear velocity at the mid-plane of the The image on the left, the shear velocity at the mid-plane of the simulation is shown.simulation is shown.
On the right, Doppler velocity maps of active regions at the limb made On the right, Doppler velocity maps of active regions at the limb made with SUMER with SUMER
Chae et al. 2000, ApJ 533, 535, Chae et al. 2000, ApJ 533, 535,
Conclusions Conclusions Shearing motions are a consequence of the Lorentz Shearing motions are a consequence of the Lorentz
force that arises as the magnetic field expands in a force that arises as the magnetic field expands in a highly stratified atmosphere which naturally explains:highly stratified atmosphere which naturally explains:
Magnitude of the shear velocity in the photosphere, Magnitude of the shear velocity in the photosphere, chromosphere and corona that occur at a chromosphere and corona that occur at a characteristic fraction of the local Alfven speed. characteristic fraction of the local Alfven speed.
Shearing motions transport axial flux into Shearing motions transport axial flux into expanding portion of flux rope or arcade and acts expanding portion of flux rope or arcade and acts to return the axial component to constant values to return the axial component to constant values along field linesalong field lines
These shear flows strongly couple the low These shear flows strongly couple the low corona to the high corona to the high photosphere and photosphere and convection zoneconvection zone
Fundamental AssumptionsFundamental Assumptions
The Sun possesses a gravitational field that results The Sun possesses a gravitational field that results in large pressure stratification of the atmospherein large pressure stratification of the atmosphere
Non-force-free magnetic structures pass that Non-force-free magnetic structures pass that through the photosphere into the corona to form through the photosphere into the corona to form active regions are MUCH larger than pressure active regions are MUCH larger than pressure scale height at the photosphere (140 km)scale height at the photosphere (140 km)
Magnetic fields possess a horizontal axial Magnetic fields possess a horizontal axial component in addition to an azimuthal componentcomponent in addition to an azimuthal component
The Lorentz force represented as (curl B) X B The Lorentz force represented as (curl B) X B reverses direction across the expanding structurereverses direction across the expanding structure
Very general as it applies to flux ropes, arcades Very general as it applies to flux ropes, arcades and magnetic layersand magnetic layers
Thank YouThank You