Modeling Magnetoconvection in Active Regions

Neal Hurlburt, David Alexander, Marc DeRosa

Lockheed Martin Solar & Astrophysics Laboratory

Alastair RucklidgeUniversity of Leeds

(Or what Solar B can do for me)

Questions

• How does turbulent convection disperse magnetic field?

• How does large-scale field influence convection?

• How does convection structure & heat corona?

• What do coronal structures tell us about solar magnetoconvection?

• How can Solar B help answer these questions?

Approach

• Explicit model of compressible magnetoconvection

• Potential extrapolation• Hydrostatic loop models heated by

fraction of local Poynting flux • Simulated observations

Large Scale Axisymmetric Model:

Q=100 Q=1000

Q=100 1000300

r

Heating

Energy Inputs

• Peaks near penumbra/umbra boundary

• Weak heating by “grains”

• Time dependent

Pointing Flux at surface for various field strengths

Coronal Heating: Q=100171• Moss

– footpoints are bright in TRACE, dark in SXT

– tops are bright in SXT, dark in TRACE

• Repeated brightenings in all wavelength bands– MMFs– Collar flow

• Apparent motion due to change in foot point sources

• Solar-B can directly test these links

Hurlburt, Alexander & Rucklidge, ApJ 2002

Coronal Heating: Q=100SXT• Moss

– footpoints are bright in TRACE, dark in SXT

– tops are bright in SXT, dark in TRACE

• Repeated brightenings in all wavelength bands– MMFs– Collar flow

• Apparent motion due to change in foot point sources

• Solar-B can directly test these links

Hurlburt, Alexander & Rucklidge, ApJ 2002

3D Model Penumbra• 3D Cylindrical Segment

(CCS code)– 10Mm x 40Mm

• As aspect ratio of layer depth to radius increases, convection cells form at outer edge and migrate inwards

• Flow is outwards along bright, narrow filaments

• Solar-B will observe flows & field structure

Low

Entropy

Hurlburt & Rucklidge 2002 Adv Space Res.

3D Cylindrial Potential Extrapolation• Unipolar model

embedded in larger domain with uniform flux

• Fieldlines foot points chosen by Poynting flux distribution

Hurlburt & Rucklidge 2002 Adv Space Res.

Uniform Heating Model

• High loops from penumbra/umbra boundary

• Bright low-lying loops from edges of penumbral filaments

Hurlburt & Rucklidge 2002 Adv Space Res.

3D Compressible Spherical Segment Code (CSS)• Fully-compressible

magnetoconvection• Initial radial field

with no net flux• Parameters

– Ray=1e5– Pr=1, Pm=.2– 5 Hp

DeRosa & Hurlburt, 2002

+15-30 +30

-15

Br

Ur

Moderate field Q=100

• Dots form in strong field regions

• Cells move • Pattern not random

• Evolves from previous state

• Dynamo action • Solar B/FPP clarify

dynamics of SG magnetoconvection

DeRosa & Hurlburt, 2002

Into the Corona: Structure

• Potential field extrapolation – source surface at r=2.5Rs

• Most lines closed (black)• Which lines are heated?

Simulated AR Observation (Alexander et.al.)• Loops

– Potential Extrapolation

– MDI Magnetogram

• Emission– Hydrostatic model

(Aschwanden & Schrijver 2002)

– TRACE 284 Response

• Uniform Heating On Disk

On Limb

Conclusions• Solar B can

– Seek signs of dynamo action– Observe weak, horizontal fields in SG and

granules– Investigate supergranule evolution– Observe detailed coupling between

photospheric flows and coronal heating

• Complete models of Sunspots & active regions will be available to compare directly with Solar B observations