What can HMI teach us about flares & CMEs?

1. 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 1023 grains of salt. (You can lend more credence to others’ ideas that I present.)

2. Outline • Pre-flare/CME, “ultimate causes:” Study AR flows. • Delta-spot formation • Filament / sigmoid formation processes: flux emergence vs. converging vs. shearing • Pre-flare/CME, “proximate causes:” • Compare helioseismic & tracking flows, to estimate fluxes of magnetic energy & helicity • Current injection • Acoustic signatures of subsurface flow evolution • Post-flare/CME: flare-induced quakes

3. 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.

4. 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!)

5. 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. Tracking (LCT) f-mode Also, DeRosa et al. 1999 Gizon et al. 2000 Hagenaar & Shine 2005

6. 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.

7. 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.

8. Kinetic Helicity and flares From old poster by F. Hill et al. From A. Pevtsov’s SHINE 2007 talk. See poster by F. Hill et al

9. Courtesy R. Nightingale From A. Pevtsov’s SHINE 2007 talk.

10. From A. Pevtsov’s SHINE 2007 talk.

11. How These All Might Fit Together? • Helicity is created in upper CZN (S-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.

12. 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?

13. 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:

14. 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?

15. Outline, Repeated. • Pre-flare/CME, “ultimate causes:” Study AR flows. • Delta-spot formation • Filament / sigmoid formation processes: flux emergence vs. converging vs. shearing • Pre-flare/CME, “proximate causes:” • Compare helioseismic & tracking flows, to estimate fluxes of magnetic energy & helicity • Current injection • Acoustic signatures of subsurface flow evolution • Post-flare/CME: flare-induced quakes