1. Momentum Conservation in Flares H. S. Hudson Space Sciences Laboratory, University of California, Berkeley, USA Canfield 08/09/10

2. Momentum Conservation in Flares H. S. Hudson Space Sciences Laboratory, University of California, Berkeley, USA Canfield 08/09/10 Or, have all of us (except for Dick) missed a trick here?

3. History of flare momentum studies “The importance of particle beam momentum in beam-heated models of solar flares,” Brown & Craig 1984 (14 citations) “The unimportance of beam momentum in electron- heated models of solar flares,” McClymont & Canfield, 1984 (12 citations) “Momentum balance in four solar flares,” Canfield et al., 1990 (49 citations) Canfield 08/09/10

4. Impulses in a flare Chromospheric heating leads to balanced up and down momenta The upward flow is arrested in closed loops Momentum is also associated with the energy flow, transported either by the beam or by S = (E x B)/v A Canfield 08/09/10

5. What imparts the thick-target momentum in the first place? Canfield 08/09/10 Energy source Evaporative recoil Impulse on Photosphere Low-  loop

6. Nature of Impulses Evaporation into a closed magnetic loop would result in a bipolar pulse, with time separation L/c s of order 10-300 s The second pulse (an upward tug on the photosphere) will be transmitted by waves The initial impulse is mediated by beams or waves (most likely waves) and does not contribute to the seismic wave excitation The area over which the impulse is exerted is important for the seismic signatures Canfield 08/09/10

7. Momentum Conservation Flare CME P1P1 - P 1 P1P1

8. Canfield 08/09/10 Energies of global waves IP shock: ~ 0.1(Mewaldt et al. 2008) Moreton wave: >10 -6 (Gilbert) Seismic wave: ~10 -4 (Lindsey) CME~1 a (Emslie et al. 2005) a (if present)

9. Canfield 08/09/10 Energetic inferences Flare energy scales are consistent with wave energies, except possibly that of the IP wave Flare energy sources are compact and brief, and can excite coronal waves via the Lorentz force Seismic wave excitation may require an intermediary atmospheric shock wave, or radiative coupling, or Alfvénic coupling

10. Canfield 08/09/10 Seismic wave morphology Seismic wave: example of 28-Oct-03 multiple radiant points HXR association now many examples (Kosovichev 2007) Acoustic source: holographic imaging WLF (left) matches source “egression power” (right) easier to see in umbra (Source Lindsey & Donea 2008)

11. Canfield 08/09/10 Significance of low β In the active-region corona, except possibly for small inclusions, β is low. Thus gas pressure is explicitly unimportant. At low β all visible structures are mere tracers and can’t be dynamically important. This also applies to the sunspot regions where seismic waves are launched.

12. Canfield 08/09/10 Momentum estimates 1 1 Scaled to X1

13. Canfield 08/09/10 Momentum inferences There is sufficient momentum in the coronal energy flux to explain the seismic wave CME excitation predicts one pulse, evaporative excitation two of opposite sign These considerations suggest that flares without CMEs will have weaker seismic signatures The area over which the CME impulse is exerted probably excludes it as the driver of the seismic wave

14. Canfield 08/09/10

15. Conclusions There is not much literature on momentum conservation in flare/CME physics, but we have to pay attention to it The back-reaction of evaporative flow will tend to cancel flare impulses at low frequencies (< few mHz) Detailed understanding requires knowledge of the full geometrical development of the flare instability Canfield 08/09/10

16. Flare energy Woods et al 2004 Hudson et al 2006 Short-lived Small-scale 1 1 TRACE 0.5” pixels

17. Canfield 08/09/10 The Lorentz force in context “…an enormous amount of magnetic energy…seems to be annihilated during the flare. This should cause a subsequent relaxation of the entire field structure…moving large masses…” - Wolff 1972 “The magnetic force applied to the photosphere…1.2 x 10 22 dyne…” - Anwar et al. 1993 (McClymont) “Magnetic forces should be of particular significance… where the magnetic field is significantly inclined from vertical.” - Donea & Lindsey 2005 “Our estimates suggest that the work done by Lorentz forces in this back reaction could supply enough energy to explain observations of flare-driven seismic waves.” - Hudson et al. 2008 (“Jerk”)

18. Canfield 08/09/10 Magnetic changes during flares “Confusogram” legend: 10x10 2.5” pixels 240 minutes time base 500 G magnetic range (Sudol & Harvey 2005)