Solar Magnetism

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Solar Magnetism. Differential Rotation, Sunspots, Solar Cycle Guest lecture: Dr. Jeffrey Morgenthaler Jan 30, 2006. Neutrino Summary. Principle of CONSERVATION OF ENERGY led to proposal of neutrino by Wolfgang Pauli - PowerPoint PPT Presentation

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  • Solar MagnetismDifferential Rotation, Sunspots, Solar Cycle

    Guest lecture: Dr. Jeffrey MorgenthalerJan 30, 2006

  • Neutrino SummaryPrinciple of CONSERVATION OF ENERGY led to proposal of neutrino by Wolfgang PauliNeutrino flux from sun measured by several experiments (in units of SNU) fell short from solar model expectations (solar neutrino problem)Solar model proves reliable for many thingLed to proposal of MSW (neutrino oscillations)

    Solar astronomy helped particle physics

  • Review HelioseismologyReview effect of sound speed on wavesVacuum cleaner analogyCar hitting puddle on freeway analogyWaves propagate faster towards center of SunRefraction (bending) depends on wavelengthBigger wheels on vacuum cleanerBetter treads on tiresParticular wavelengths reinforce constructivelyhttp://gong.nso.edu/gallery/images/harmonics/pmode.mpg

  • Solar Oscillations

  • Global Oscillations Network Group (GONG)Allows continuous viewing of Sun

  • Helioseismology probes solar interior

  • GONG resultsBlow-up of GONG results (axes reversed) shows fantastic detailGives accurate depth of convective zone0.713 of solar radiusMeasures differential rotationRotation speed as a function of depth

  • Differential rotationpre GONG

  • Differential rotation seen by GONGGONG has been operating for more than 10 yearsPattern of rotation vs. depth in 1995 was almost the same now as it was in 2005What is going on?

  • Solar and Heliospheric ObservatoryOrbits Sun every 365 daysPulled equally by Suns and Earths gravityLagrange point L1Has 12 scientific instruments, including 3 for Helioseismology

  • SOHO Michelson Doppler Imager (MDI)Measures rotation speeds (red faster, blue slower than average)Shows plasma flow under equatorHint of flow towards poles

  • SOHO GOLF (Global Oscillations at Low Frequencies)Measured sound speed compared to theorySomething funny going on at base of convection zone

  • Brief Review

  • SunspotsFirst recorded observations by Chinese astronomers around 28 BCFirst detailed study by Galileo and other astronomers around 1610Profound implications for Aristotelian cosmology

  • Sunspot structureRecall granulesRecall black body radiationSunspot darker because it is coolerUmbra darkest partSize of 1-10 earthsPenumbra is transition zoneFibrils are penumbral intrusions into umbraPlages (beaches) light regions beyond penumbra

    Photo Credit (T.Rimmele (NSO), M.Hanna (NOAO)/AURA/NSF)

  • Sunspot behaviorTend to come in pairsCome and go in a few days to a monthWere first evidence of differential rotationBut move around themselves (mostly north/south)

    Movie from SOHO SOI instrument

  • Sunspot number variationSunspot number varies with an 11-year periodSOLAR CYCLEPeriod discovered by amateur astronomerHeinrich Schwabe of Dessau, Germany, ~184017 years of observationsAlmost certainly related to period observed helioseimologicallySunspots start each solar cycle appearing 30 deg above and below equatorAs cycle progresses, spots appear more toward equator

  • Sunspots are related to magnetic fieldFirst proposed by George Ellery Hale around 1900Looked at sun a different way (narrow-band filter)Discovered chromosphere, above photosphereSaw light only emitted by Hydrogen atomsSunspots looked like cyclonic whirlsHypothesized electrons in whirls would generate a magnetic fieldDevised an experiment to measure magnetic field using the Zeeman effectFound magnetic fieldDoes that mean electrons generated magnetic field?Magnetic field is buried in Sun and bubbles up

  • Big Bear Solar Observatory H-alpha imageshttp://www.bbso.njit.edu/images.html

  • Zeeman EffectQuantum mechanical effectAllows measurement of magnetic fieldStrength is distance between spectral linesPolarization is direction of magnetic fieldSun spot field is 1000-4000 gaussEarth at surface is 0.3 gausshttp://csep10.phys.utk.edu/astr162/lect/light/zeeman-split.html

  • Babcock Model for Sunspot formationSee fig 5-13 in textDifferential rotation distorts N/S field so it starts to run E/WExplains why sunspots come in pairsMagnetic field pokes out of sun and back inLike a thread stitching through fabricExplains generally why sunspots start at 30 degrees N and S latitudeExplains why sunspots get squeezed into lower latitudesGenerally explains why sunspot activity dies down after spots reach equatorMagnetic field cancels itself outExplains why sunspots show up with reverse polarity the next time aroundDetails of where magnetic field is formed might be wrong in Babcock model field seems to be deeper than he thought

  • Arch ProminencesH-alpha emission traces out magnetic field linesOut one sunspot, in anotherNSO/Sac Peak/NOAO

  • Sunspot, Differential Rotation, Magnetic field SummarySunspots observed on an 11-year cycleSOLAR CYCLESunspots linked to magnetic fieldObserved using Zeeman effectDifferential rotation winds up magnetic fieldDifferential rotation best observed with helioseismology25 days at equator, 35 days at poleSunspots also show differential rotationDifferential rotations effect on magnetic field most likely reason for sunspot activity