MRT workshop, August 10, 2004

Active-region magnetic structures and their

perturbations by flares

H.S. Hudson

SSL/UCB

MRT workshop, August 10, 2004

Outline

• Description of a solar active region

• Magnetic structure

• Waves, oscillations, and restructuring

• RHESSI observations of eruptive flares

MRT workshop, August 10, 2004

TRACE 171A view of an active region,courtesy LMSAL “cool stars” Web material

MRT workshop, August 10, 2004

Mechanical properties of an active region in the corona

• Flares and CMEs are magnetically driven, according to consensus, from energy stored in the corona

• In such conditions, (low plasma ), the mechanical stresses can be represented as a pressure and a tension

• Dissipation is normally slow• The volume is electrically equipotential except for

the Rosseland-Pannekoek potential

MRT workshop, August 10, 2004

G. A. Gary, Solar Phys. 203, 71 (2001)

CH

MRT workshop, August 10, 2004

What are the loops?

• The loops show the direction of the magnetic field• The X-ray visibility of the corona is a monotonic

increasing function of the gas pressure• In an active region, the loop dimensions are

typically smaller than the scale height• The footpoints of a loop lie in a transition layer at

the appropriate pressure• The magnetic field must be slightly depressed in

the visible loops

MRT workshop, August 10, 2004

Lundquist et al., SPD 2004

MRT workshop, August 10, 2004

NOAA 10486, Haleakala IVM data, cube

Roumeliotis-Wheatland-McTiernan methodpixel size ~3000 km

Scaled Not scaled

MRT workshop, August 10, 2004

AR8210 courtesy J. McTiernan

MRT workshop, August 10, 2004

Conjecture: Most of the free energy in an active region is concentrated very near its base

MRT workshop, August 10, 2004

The normal state of the active-region corona is an equilibrium

• An equilibrium system will oscillate around its rest configuration if perturbed slightly

• We observe coronal oscillations via spectroscopy, photometry, and in movies

• The oscillations have small amplitudes and can be studied via MHD theory

MRT workshop, August 10, 2004

Kink-mode oscillations

• Flare waves associated with metric type II bursts often (12/30 cases) appear with TRACE loop oscillations

• These oscillations allow us to study the equilibrium state of the non-erupting part of the corona

MRT workshop, August 10, 2004Aschwanden et al., Solar Phys. 206, 99 (2002)

MRT workshop, August 10, 2004

Narukage et al., PASJ 56, L5 (2004)

MRT workshop, August 10, 2004

SUMER’s oscillations

Wang, T. J. et al., ApJ 574, L101 (2003)

MRT workshop, August 10, 2004

Yohkoh’s oscillations (BCS)

Mariska, J. et al., SPD poster (2004)

MRT workshop, August 10, 2004

QuickTime™ and aPhoto decompressor

are needed to see this picture.

Schrijver et al., Solar Phys. 206, 69, 2002

MRT workshop, August 10, 2004

Three things the movie showed

• Early inward motions, prior to the eruption

• Dimming - the CME starting off

• Excitation of coupled normal modes in the arcade

• (arcade blowout)

MRT workshop, August 10, 2004

SXT observations of the blow-out of anX-ray “loop prominence system”

MRT workshop, August 10, 2004

Studying coronal equilibria

• On large scales the corona tends be stable

• We can study the equilibrium states via the oscillations; there are several modalities

• Propose to use “instrumented hammer” approach to characterize eigenstates

• Propose to study before/after equilibrium states using FASR and Solar-B

MRT workshop, August 10, 2004

H. Wang et al., ApJ 576, 497 (2002)

MRT workshop, August 10, 2004

Magnetic challenge: Can any existingmodel of a flare or CME properly describethe change in the coronal magnetic field?

MRT workshop, August 10, 2004

Cartoon showing magnetic implosion

Post-event fieldPre-event field

Isomagnetobars

Limb

Hudson & Cliver, JGR 106, 25,199 (2001)

MRT workshop, August 10, 2004

Conclusions

• Unlike the cosmologists, we don’t have a standard model for a flare/CME - we do have cartoons, though: http://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/

MRT workshop, August 10, 2004

Serious conclusions

• Extrapolation techniques to learn about the coronal magnetic field are inherently flawed• It will be better in the future to assimilate more precise methods, such as - TRACE coronal imagery (direction of B) - FASR gyroresonance surfaces (magnitude of B) - Mechanical models (matching eigenfrequencies)

MRT workshop, August 10, 2004

From the Flare/CME Cartoon Archivehttp://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/

MRT workshop, August 10, 2004

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Null?

Separatrices?

Anzer-Pneuman, 1982

MRT workshop, August 10, 2004

Forbes, T., JGR 105, 23,153, 2000Gallagher, P. personal communication 2004

MRT workshop, August 10, 2004

QuickTime™ and aPhoto decompressor

are needed to see this picture.

MRT workshop, August 10, 2004

RHESSI observations of early inward motions

MRT workshop, August 10, 2004Sui et al., 2004

MRT workshop, August 10, 2004

Sui et al., 2004