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Helioseismology of the Tachocline

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Helioseismology of the Tachocline HISTORY OF SOLAR ACTIVITY RECORDED IN POLAR ICE Helioseismology of the Tachocline arkus Roth $iepenheuer-Institut für Sonnen%hysi" History of Solar Acti(ity Reco!)e) in Polar Ice Düben)orf, ,-.,,./0,1 HISTORY OF Theoretical Kno2ledge abo#t SOLAR ACTIVITY RECORDED IN the Solar Interio! POLAR ICE What is the structure of the Sun? Theo!y of the inte!nal st!#ct#!e of the sta!s is *ase) on the f#n)amental %!inci%les of %hysics: Energy conservation, Mass conservation, Momentum conservation P!essu!e an) gra(ity a!e in *alance4 hy)!ostatic e5#ili*!i#m 6 the Sun is stable A theo!etical mo)el of the S#n can *e *#ilt on these %hysical la2s. Is there a possibility to „look inside“ the Sun? HISTORY OF SOLAR ACTIVITY RECORDED IN Oscillations in the Sun and the Sta!s POLAR ICE The Sun and the stars exhibit resonance oscillations! Excitation Mechanism: Small perturbations of the equilibrium lead to oscillations Origin: Granulation (turbulences) that generate sound waves, i.e. pressure perturbations (430.5 nm; courtesy to KIS -) 5 Mm HISTORY OF SOLAR ACTIVITY RECORDED IN Oscillations in the Sun and the Sta!s POLAR ICE The Sun and the stars exhibit resonance oscillations! Excitation Mechanism: Small perturbations of the equilibrium lead to oscillations Origin: Granulation (turbulences) that generate sound waves, i.e. pressure perturbations The superposition of sound waves lead to interferences: amplifications or annihilations. Sun and stars act as resonators ? Fundamental mode and higher harmonics are possible Roth, 2004, SuW 8, 24 10 million10 oscillations, simultaneouslyexcited o)ern Era of Helioseismology in andtime space Fourier transform Frequency [7Hz] Spectral Energy Density Solar p modes Harmonic degree l degree Harmonic SOLAR ACTIVITY SOLAR RECORDED IN RECORDED HISTORY OF OF HISTORY POLAR ICE POLAR HISTORY OF SOLAR ACTIVITY First Successes of Helioseismology3 RECORDED IN Internal Struct#!e of the Sun POLAR ICE Sound Speed Density ] 3 m ] 2 c s / / 2 Base of convection zone: g [ m [ 0.713 8 0.001 R 2 ρ c Difference between theoretical model on the Sun`s internal structure and helioseismology: approximately 3% Transition between radiative interior and convection zone shows most significant differences (Christensen-Dalsgaard et al., 1985, Nature 315, 378) (Kosovichev et al., 1997, Solar Phys.170, 43) Antia & Chitre, 1995, Astrophys. J. 442, 434 ) HISTORY OF SOLAR ACTIVITY RECORDED IN Tachocline Studies with Local Helioseismology POLAR ICE So#nd s%ee) %ert#rbation at the base of the convection >one is not #niform Clear )i% around the eq#ato! Stronger so#nd s%ee) %ertu!*ation at higher latitudes North-So#th asymmetry 9:hao et al. /00; A%<= HISTORY OF Large&scale Flows: SOLAR ACTIVITY RECORDED IN Diffe!ential Rotation @ eri)ional Flow POLAR ICE The Sun rotates differentially: The Sun has a meridional flow: Equator rotates faster than the On the surface the flow is poleward polar regions v ? 15 m/s Surface flow must sink inward at poles and return to the equator at some depth HISTORY OF SOLAR ACTIVITY RECORDED IN The Solar Dynamo POLAR ICE lo!s inside the Sun are important for solar dynamo action" A %ossi*le sola!Astella! )ynamo · #t cycle minimum" a )i%ola! Bel) th!eads th!o#gh a shallo2 laye! belo2 the s#!face. · Di?e!ential !otation shea!s o#t this )i%ola! Bel) to %!o)#ce a strong to!oi)al Bel) 9B!st at the mi)&latitu)es then %!og!essi(ely lo2e! latitu)es=. · #round solar ma$imum" C#oyant Bel)s e!#%t th!o#gh the %hotos%he!e fo!ming+ e.g. s#ns%ots an) acti(e !egions · The me!i)ional Do2 a2ay f!om the mi)&latit#)es gi(es !econnection at the %oles an) e5#ato!. %he Sun’s internal rotation and meridional 'o! need to be measured (Babcock, 1961; and later developments) HISTORY OF SOLAR ACTIVITY RECORDED IN Pe!t#!*ation of Wa(es *y Flo2s POLAR ICE Equation of motion for sound waves: Flow induces advection of the sound wave: Surface B Distance Δ A Surface B Distance Δ A Flow u Advection E Perturbation of wave eigenfunction and eigenfrequency HISTORY OF SOLAR ACTIVITY Global Diagnostics for Different RECORDED IN Flow Geometries POLAR ICE (Figure: R. Arlt) · (lassical helioseismic approach" To!oi)al aHissymmet!ic flo2s 9)i?e!ential !otation= meas#!e) from f!e5#ency splittings HISTORY OF Analysis of SOLAR ACTIVITY RECORDED IN Eigenfunction Perturbations POLAR ICE . ξk ~ spherical harmonic Ylm Y . Wave ¹shapeª deformation l m wi th (l= 18,m =10) Ylm with (l=20,m=10) ) =10 2,m (l=2 with Y lm . k k` SHT + Spectralanalysis n n+1 Cross-talk between SH time series of adjacent (l,m) Cross-spectral analysis of Dopplergrams ωk ωk' New: Toroidal & Poloidal flows to be measured by measuring eigenfunction perturbations HISTORY OF SOLAR ACTIVITY RECORDED IN What Theo!y %re)icte) POLAR ICE Bottom of convection >one HISTORY OF SOLAR ACTIVITY RECORDED IN Rotation in the Solar Inte!io! POLAR ICE Long-term North-South average derived from 12 years of SoHO/MDI observations of ªfrequency splittingsº (Howe 2009): Below the surface: Extended area of fast rotation Depth: ca. 200.000 km Width: ca. 500.000 km Red areas move faster than the blue areas by approximately 2000 km/h Tachocline: Shear layer at the bottom of the convection zone is important for generation of toroidal magnetic field Higher latitudes & deep interior? HISTORY OF SOLAR ACTIVITY RECORDED IN Rotational Resi)uals POLAR ICE Here 2e )ifference rotation inversions !elati(e to sola! minim#m at s#ccessi(e ,-year epochs. The e(ol#tion of the rotation rate in the 2hole convection >one can be seen. HISTORY OF Solar Rotation & Zonal Flows – SOLAR ACTIVITY RECORDED IN Temporal E(olution POLAR ICE Torsional oscillations Flow residuals + unsigned magnetic field (Howe et al. 2013) · Temporal variations around mean rotation - equator/poleward propagating branches · 1% of mean rotation · Extends to the bottom of the convection zone (e.g. Vorontsov et al. 2002) Precursor for upcoming surface activity? (Howe et al. 2011, 2013, Komm et al. 2014) Connection to merdional flow? Solar minimum ªOnsetª of activity (surface) HISTORY OF SOLAR ACTIVITY ean Position of the Tachocline ean Fi)th of the tachocline RECORDED IN POLAR ICE Re): DI Blac"3 GONG Prolate st!#cure of tachocline? Difference bet2een 0K and 10K: 0.0,/L0.00/ Rsun 9GONG=; 0.0-0L0.00M Rsun9 DI= 9Antia @ Bas#+ A%JL, /0,,= in(e!sion of s%litting coe?. fo! 2M&2; · · Interesting for differential rotation studiesin depth rotation differential for Interesting toSensitive MDI 2004-2010 MDI antisymmetric rotation rate component rate rotation antisymmetric Eigenfunction Perturbations DifferentialRotation from in(e!sion of a/&a; fo! 2M&2; MDI 2004-2010 MDI (ªfrequency splittingsª are not!) splittingsª are (ªfrequency HMI 2010-2014 HMI (Schad & Roth., prep.)in SOLAR ACTIVITY SOLAR RECORDED IN RECORDED HISTORY OF OF HISTORY POLAR ICE POLAR HISTORY OF SOLAR ACTIVITY Rotatonal Resi)ues at the RECORDED IN Case of the Con(ection Zone POLAR ICE At mean latit#)es, there might be a 5uasi&%erio)ic oscillation near the bottom of the convection >one. To%: 0.N/R Bottom: 0.1MR 9See Ho2e, R., et al., Science, /000= HISTORY OF SOLAR ACTIVITY The Solar e!i)ional Flo2 RECORDED IN POLAR ICE Magnetic butterfly diagram return flow N surface flow e d u t i t a l S (Figure: Hathaway, NASA) · Essential element of flux transport dynamo models (Wang & Sheeley 1991, Choudhuri et al. 1995, Dikpati & Schüssler 1999,... ) · Location & amplitude of return flow determines timing and strength of solar activity cycle (Hathaway et al. 2003, Dikpati et al. 2004,...) · Where is the return flow? Measurement of the flow profile in depth helps to constrain models/simulations of dynamo & convection zone (Dikpati et al. 2006, Miesch et al. 2012,...) POLAR ICE POLAR HISTORY OF OF HISTORY RECORDED IN RECORDED SOLAR ACTIVITY SOLAR H I /0,0& /0,- /0,0 DI /00-& (Schad et al. /0,M4 Scha) @ Roth /0,1 in /0,1 Roth @ Scha) /0,M4 al. et (Schad %!e%.= H I /0,0& /0,/ H I /0,0& /0,/ et(Zhao al. 2013) (Schad et al. 2013); Comparison of eri)ionalFlow easurements GONG /00-&/0,/ (Jackiewicz et al 2015., Rajaguru et al. 2015), 9<ac"ie2ic> et al. /0,O4 :hao et al. /0,M4 Rajag#!# @ Antia Antia @ Rajag#!# /0,M4 al. et :hao /0,O4 al. et 9<ac"ie2ic> /0,O= Flow reversalFlow at 0.93 byR Time-Distance not present in Eigenfunction perturbation analysis result (only weakening) Single cell Double-cell flow Multiple ªcellsº incorporating mass conservation to (Rajaguru TDA et al. 2015) - no clear double cell structure · · Various Various Results: HISTORY OF Conse5#ences of Helioseismic SOLAR ACTIVITY RECORDED IN Results on Dynamo o)els POLAR ICE (Nandy, 2004) · Helioseismic results with multiple cells (depth, latitude) have inspired new dynamo simulations (e.g. Hazra et al. 2014, Belucz et al., 2015) · Multiple cells produce solar-like dynamos given there is an equatorward flow near BCZ (Jouve et al. 2007, Hazra et al. 2014, Choudhuri 2015, Passos et al. 2016) · HD convection simulations ± Sun at transition from single to multiple meridional flow cells with anti-solar (poles faster) to solar rotation (poles slower) profile (e.g., Featherstone et al., 2015) (Featherstone et al. 2015) (Belucz et al., 2015) (Hazra et al. 2014) /M HISTORY OF SOLAR ACTIVITY RECORDED IN Summary POLAR ICE Helioseismology %ro(i)es insight on tachocline !egion · Always an average o(er time & longitude · Classical helioseismology in a))ition a(erages o(er No!th @ South · New metho)s are #n)er )e(elopment to %!obe for the tachocline region In Fut#!e3 Hope on Solar Orbiter to %ro(i)e possiblities for stereoscopic seismology (Roth, 2007).
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