Solar magnetic fields 3

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Solar magnetic fields 3. Philip Judge, High Altitude Observatory, NCAR. What is it we really want to know? [Different from stellar case] How do we measure what we want to know? …solar spectropolarimetry. Examples of what we really need/want to know?. Which processes control: - PowerPoint PPT Presentation

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Solar magnetic fields 3

1Philip Judge, High Altitude Observatory, NCAR

What is it we really want to know? [Different from stellar case]

How do we measure what we want to know? solar spectropolarimetry

IAC Winter School 2013Solar magnetic fields 2Philip Judge12Examples of what we really need/want to know?Which processes control:surface field evolution and the magnetic solar cycleB at the surface, constraints on magnetic flux and helicity A.BdV over a solar cycle

requires measurements of B(r,t) on longer length and time scalesIAC Winter School 2013Solar magnetic fields 2Philip Judge3Examples of what we really need/want to know?what processes controlsurface field evolution andchromospheric/coronal heating dynamicsflaring

We should attempt to measure surface B, magnetic free energy (total - potential)Lorentz force jB, including current sheets

requires measurements of B(r,t) on small length and time scales (flares) up to and including the base of the coronaIAC Winter School 2013Solar magnetic fields 2Philip Judge

coronal magnetic free energy can be derived from measurements of magnetic fields at the base in force-free plasmaIAC Winter School 2013Solar magnetic fields 2Philip JudgeConclusion: We must measure vector BMagnetograph measurements give BLOS onlyyield potential fields (no free energy) in overlying coronano curl (currents) or uncurl (vector potential) or helicity

5IAC Winter School 2013Solar magnetic fields 2Philip JudgeAn example: Flare physics (Shibata et al 2007)

Its time to try tomeasure the evolving magnetic fieldWe can measureplasma nowNotice- reconnectionsiteIAC Winter School 2013Solar magnetic fields 2Philip Judge7

For vector B we must use spectropolarimetry(most lines are not fully split, field is intermittent)IAC Winter School 2013Solar magnetic fields 2Philip Judge

Polarization modulation in timeThis is consequential. unlike in stars, because of

solar evolution (t ~ v / l), l ~ 100 km, v ~ 0.3 cs atmospheric seeing

lets look at a rotating waveplate 15

16

Spatial as well as temporal modulationremoval of I-> QUV crosstalk with 2 beamsIn absence of seeing/jitter, a single beam suffices (Solar B SP)17

D(t) = M3 M2(t) (MC) XT S

= M S

S = M-1 D ideal solution for Stokes vectorDiagonality mattersIn reality we have noise and crosstalk S = (M+)-1 (D+), only statistical properties of , are knowable Non-Mueller 4xn matrices, n4beam splitterSPINOR spectropolarimeter18

19

SOLIS VSMEffects of seeing-

good seeing, destretchedgood seeingbad seeing

bad seeing good good+destretched20precise spectropolarimetry is starved of photons!21

08/12/122108/12/122121Landi Degl'Innocenti (2012 EWASS meeting):Nphot = 1.2 x 109 D2 x2 t T Critically sampling R = 1.22 /D gives for any aperture D: Nphot = 5 x 106 t T photons/ px

Realistically, t 1 kHz to remove seeing

e.g. ZIMPOL instrument (charge-caching detector 100 kHz)

otherwise limited to sensitivity P/I > 0.01 %

1st2nd order in dw/w0=wB/w0Zeeman line splitting26

Lites 2000IAC Winter School 2013Solar magnetic fields 1Philip JudgeZeeman-induced polarization 27Zeeman parameter :

= L / D,

L = B, D= line V/c.

If