what can hmi teach us about flares & cmes?
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What can HMI teach us about flares & CMEs?. Some Discussion-Starting Ideas by Brian Welsch, SSL UC-Berkeley. WARNING : My ideas tend to be half-baked, hand-wavy, and embarrassingly speculative. Please consume with 6.02 x 10 23 grains of salt. - PowerPoint PPT PresentationTRANSCRIPT
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What can HMI teach us about flares & CMEs?
Some Discussion-Starting Ideasby Brian Welsch, SSL UC-Berkeley
WARNING: My ideas tend to be half-baked, hand-wavy, and embarrassingly speculative. Please consume with 6.02 x 1023 grains of salt.
(You can lend more credence to others’ ideas that I present.)
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Outline
1. Pre-flare/CME, “ultimate causes:” Study AR flows. – Delta-spot formation– Filament / sigmoid formation processes:
flux emergence vs. converging vs. shearing
2. Pre-flare/CME, “proximate causes:” – Compare helioseismic & tracking flows, to
estimate fluxes of magnetic energy & helicity – Current injection– Acoustic signatures of subsurface flow evolution
3. Post-flare/CME: flare-induced quakes
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SDO documents list ‘official’ helioseismology
science objectives related to flares & CMEs.
• See: http://hmi.stanford.edu/Requirements/HMI_Objectives.html
• One, in particular, seems relevant here:“Origin and dynamics of magnetic sheared structures and d-type sunspots.” “It is important to determine what processes beneath the surface lead to development of these spots and allow them to become flare and CME productive.”
• Helicial kink instability studies by Linton et al. (1999, 2001) are relevant here.
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Filaments & sigmoids are prone to flare and
erupt, but how do they form?
• Hindman, Haber, & Toomre (2006) found shear flow underneath a filament in MDI data.– HMI “will permit direct sampling of flows with a spatial scale
comparable to supergranulation. More importantly, we should be able to resolve the region lying directly underneath the filament channel.”
– Supergranulation probably plays a key role in flux cancellation --- a “necessary condition” (Martin 1998) for filament formation.
• Filaments are ~ubiquitous, but sigmoids are not.
Are there helioseismic signatures of sigmoids? SDO’s HMI + AIA should make such studies straightforward (relatively!)
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With vector B, estimating flows permits estimating the fluxes of magnetic energy & helicity.
• Both helioseismic and tracking techniques could work for this.
• Both must be validated with synthetic data, and compared to each other with real data.
Hagenaar & Shine 2005Gizon et al. 2000
f-modeTracking (LCT)
Als
o,
DeR
osa
et
al.
1999
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Photospheric magnetic torque and measured angular
acceleration constrain the subphotospheric B field.
• Pressure gradients cannot sustain torques (McClymont et al. 1997)
• Differences in magnetic twist lead to net torques (Longcope & Klapper 1997):
• Net torques/ twist inhomogeneity will lead to angular acceleration (Longcope & Welsch 2000).
• Lack of angular acceleration implies lack of torque, or twist uniformity with depth.
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Are there helioseismic signatures of coronal current loading & saturation?
Solar interior acts as “reservoir of twist,” i.e., a current driver.
• twisting motions tranport twist into corona until… • coronal current saturates, then…• flares/CMEs dissipate current, after which…• goto 1…
Prediction: Twisting motions should decrease before flares. The following slides were shamelessly lifted from Alex
Pevtsov’s talk at SHINE 2007.
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Kinetic Helicity and flares
See poster by F. Hill et al From old poster by F. Hill et al.
From A. Pevtsov’s SHINE 2007 talk.
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Courtesy R. Nightingale
From A. Pevtsov’s SHINE 2007 talk.
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From A. Pevtsov’s SHINE 2007 talk.
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How These All Might Fit Together?
• Helicity is created in upper CZN (-effect explains large scatter and helicity amplitude; solar cycle variations???).
• Helicity is removed from AR as a result of eruption.
• Subphotospheric portion of flux tube may serve as “reservoir” of helicity, supplying helicity between flares/CMEs.
• Sunspot rotation and subphotospheric pattern of kinetic helicity may be indications of helicity transport via torsional waves.
From A. Pevtsov’s SHINE 2007 talk.
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Acoustic waves above the photosphere can vary on timescales relevant to flare/CME initiation.
“Seismology of the solar atmosphere,”
Finsterle et al., 2004: “upward- and downward-propagating waves are detected in areas of strong magnetic field such as sunspots and plage: even at frequencies below the acoustic cut-off frequency…
… the wave behavior in regions of strong magnetic field can change over
periods of a few hours from propagating to evanescent.”
Is there correspondence between waves above, at, & below the photosphere?
Do changes in wave character correspond with flares/CMEs?
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Several observations of flare-induced changes
to the photospheric B have been reported.
• Here’s a cartoon of one model for the process, from Fletcher & Hudson 2008:
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Are flare-induced changes in photo-spheric B related to “sunquakes”?
• Pre- & post-flare vector magnetograms can tell us!
• Hudson, Fisher, & Welsch 2008:
• Will measurements of fz be consistent with observed properties of sunquakes?
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Outline, Repeated.
1. Pre-flare/CME, “ultimate causes:” Study AR flows. – Delta-spot formation– Filament / sigmoid formation processes:
flux emergence vs. converging vs. shearing
2. Pre-flare/CME, “proximate causes:” – Compare helioseismic & tracking flows, to
estimate fluxes of magnetic energy & helicity – Current injection– Acoustic signatures of subsurface flow evolution
3. Post-flare/CME: flare-induced quakes