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Q: How is flux removed from the photosphere?

Q: How is flux removed from the photosphere?. Each 11-year cycle, c . 3000 active regions, each with c . 10 22 Mx , emerge. What processes remove all this flux?

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Q: How is flux removed from the photosphere?

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  1. Q: How is flux removed from the photosphere? • Each 11-year cycle, c. 3000 active regions, each with c. 1022Mx, emerge. • What processes remove all this flux? • The short answer is CANCELLATION --- the “mutual apparent loss of flux in closely spaced magnetogram features of opposite polarity” (Livi et al. 1985)

  2. Changes in LOS flux are quantitatively related to PIL Doppler shifts multiplied by transverse field strengths. From LOS m’gram: (Eqn. 1) From Faraday’s law, Since flux can only emerge or submerge at a PIL, (Eqn. 2) Summed Dopplergram and transverse field along PIL pixels. • Inthe absence of errors, ΔΦLOS/Δt =ΔΦPIL/Δt.

  3. Let’s test the method with HMI data! An automated method (Welsch & Li 2008) identified PILs in a subregion of AR 11117. Note predominance of redshifts.

  4. Problem: We must remove the convective blueshift! HMI’s Doppler shifts are not absolutely calibrated! (Helioseismology uses time differences in Doppler shifts.) There’s a well-known intensity-blueshift correlation, because rising plasma (which is hotter) is brighter (see, e.g., Gray 2009; Hamilton and Lester 1999; or talk to P. Scherrer). Because magnetic fields suppress convection, lines are redshifted in magnetized regions. From Gray (2009): Bisectors for 5 spectral lines on the Sun are shown on an absolute velocity scale. The dots indicate the lowest point on the bisectors. (The dashed bisector is for λ6256.) Lines formed deeper in the atmosphere, where convective upflows are present, are blue-shifted.

  5. So we must calibrate the bias in the zero-velocity v0 in estimated Doppler shifts before we can study cancellation. From Eqn. 2, a bias velocity v0 implies := “magnetic length” of PIL • ButΔΦLOSshould match ΔΦPIL, so we can solve for v0: (Eqn. 3) NB: v0 should be the SAME for ALLPILs==> solve statistically!

  6. The inferred offset velocity v0 can be used to correct Doppler shifts along PILs.

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