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Lecture 13: Sunspots Outline 1 Terminology and History 2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 1

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Page 1: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Lecture 13: Sunspots

Outline

1 Terminology and History2 Sunspot Structure3 Sunspot Evolution

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 1

Page 2: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Overview

Sunspot Terminology

DOT Blue Continuum Movie of AR10425

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 2

Page 3: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Basic Appearance

sunspots often appear in sunspot groupssunspots consist of umbra and penumbrapores are sunspots without penumbraeumbral structures: umbral dots and light bridgespenumbral filamentsumbra and penumbra have well-defined, structured boundariessunspot is much more stable than granulationbright penumbral grains move inward

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 3

Page 4: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Active Region Numbers

www.solarmonitor.org

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 4

Page 5: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

History before Telescopes

www.hao.ucar.edu/Public/images/worcester.jpg

Theophrastus of Athens reports sunspots around 330 BC112 descriptions of sunspots in official historical records fromChina between 28 BC and 1638 AD8 December 1128, John of Worcester makes the first diagram ofthe Sun containing two large spotsKepler misinterpreted sunspot as Mercury transit in 1607

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 5

Page 6: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

web.hao.ucar.edu/

public/education/sp/images/fabricius.html

Johann Goldsmid (Fabricius)... Having adjusted the telescope, we allowedthe sun’s rays to enter it, at first from the edgeonly, gradually approaching the center, until oureyes were accustomed to the force of the raysand we could observe the whole body of thesun. We then saw more distinctly and surely thethings I have described [sunspots]. Meanwhileclouds interfered, and also the sun hastening tothe meridian destroyed our hopes of longerobservations; for indeed it was to be feared thatan indiscreet examination of a lower sun wouldcause great injury to the eyes, for even theweaker rays of the setting or rising sun ofteninflame the eye with a strange redness, whichmay last for two days, not without affecting theappearance of objects.

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 6

Page 7: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

galileo.rice.edu/sci/observations/sunspot_drawings.html

History after TelescopesOther contemporary observations by Galileo Galilei (Italy), ChristophScheiner (Germany), and Thomas Harriott (England)

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 7

Page 8: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Drawings by Christoph Scheiner

galileo.rice.edu/sci/observations/sunspots.html

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 8

Page 9: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Drawings by Samuel Langley (1834–1906)

www.ociw.edu/ociw/babcock/howardtalk.pdf

Why are these drawings comparable in quality to some of the bestpictures from modern telesopes?

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 9

Page 10: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspots in Numbersdiameter: 10’000 – 100’000 kmintensity of umbra: 5% of quiet photosphere at 500 nmintensity of penumbra: 80% of quiet photosphere at 500 nmtemperature of umbra: 3500 K

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 10

Page 11: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspot Field Strengths: 2000-4000 Gauss

www.noao.edu/image_gallery/html/im0972.html

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 11

Page 12: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Empirical Temperature - Field Strength Relation

Kopp & Rabin 1992

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 12

Page 13: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Theoretical Temperature – Field Strength Relation

magnetohydrostatic force balance

∇(

p +B2

2µ0

)− 1µ0

(~B · ∇

)~B = ~Fgravity

radial component in cylindrical coordinate system

∂r

(p +

B2

2µ0

)− 1µ0

(Br∂Br

∂r+

r∂Br

∂φ+ Bz

∂Br

∂z−

B2φ

r

)= 0

for untwisted field (Bφ = 0)

∂p∂r

=Bz

µ0

(∂Br

∂z− ∂Bz

∂r

)integrate from radius r to field-free region outside of spot

pe (z)− p (r , z) =B2

z (r , z)

2µ0+

1µ0

∫ ∞r

Bz∂Br

∂zdr ′

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 13

Page 14: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

continuing ...

from previous slide

pe (z)− p (r , z) =B2

z (r , z)

2µ0+

1µ0

∫ ∞r

Bz∂Br

∂zdr ′

for simple magnetic field configurations can rewrite this as

pe (z)− p (r , z) =B2 (r , z)

2µ0(1 + f (r , z))

and using perfect gas law, write this as

T (r , z)

Te (z)=µ (r , z)

µe (z)

ρe (z)

ρ (r , z)

(1− 1 + f (r , z)

2µ0pe (z)B2 (r , z)

)

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 14

Page 15: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Empirical Temperature - Field Strength Relation

Kopp & Rabin 1992

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 15

Page 16: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Azimuthally Averaged Sunspot Quantities

Keppens & Martinez Pillet 1996

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 16

Page 17: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Wilson Depression

sunspot umbrae are lower than quiet photosphere (Wilson 1769)

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 17

Page 18: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Umbral Dots

Tritschler & Schmidt 2002

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 18

Page 19: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Umbral Dots Simulations

Schüssler & Vögler 2006

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 19

Page 20: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Evershed Effect: Radial Outflow

Penn et al. 2003

spectral lines show outflow of up to 10 km/s−1

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 20

Page 21: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Penumbral Filament Simulations (R.Schlichenmaier)

www.kis.uni-freiburg.de/ schliche/index-Dateien/video.html

thin magnetic flux tube in magnetohydrostatic sunspot modelsurrounding field-free area heats tube, it becomes buoyantcools off when reaching photospheresince field in tube decreases faster than background field, gaspressure builds up leading to outward flow

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 21

Page 22: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspot Oscillations

DOT 2005-07-13 AR10789

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 22

Page 23: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Large Sunspot Region from early 2001

Best of SOHO Movies

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 23

Page 24: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspot Region Evolution

www.noao.edu/image_gallery/html/im0605.html

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 24

Page 25: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspot Evolution

Zhang & Tian 2005

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 25

Page 26: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Active Region Development

science.nasa.gov/ssl/pad/solar/dynamo.htm

sunspots occur in two belts, symmetric around and parallel to theequator at ± (5◦– 35◦) lattitudesunspots are areas of strong magnetic fieldssunspots often appear in pairs with opposite magnetic polarity(bipolar groups)polarity changes with hemisphere and solar cycle (Hale’s Law)sunspot groups are inclined with respect to the equator

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 26

Page 27: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspot Groups

science.nasa.gov/ssl/pad/solar/dynamo.htm www.ociw.edu/ociw/babcock/howardtalk.pdf

sunspot groups are tilted with respect to equatortilt angle depends on lattitude (Joy’s Law)

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 27

Page 28: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Sunspot Lifecycleappearance and disppearance of sunspot groups is alwaysrelated to the same phenomena⇒ everything together makes upan active regionappearance of magnetic field within a few days, strong increase infaculae, magnetic field becomes bipolar, small pores and spotsappear, corona becomes bright above active regionmaximum activity takes 2 to 3 weeks, large bipolar groups form,active region expands to 200’000 km, flares occurdisappearance takes 6 to 9 months, active region expands to500’000 km, spots disappear, faculae of opposite polaritiesappear that are separated by a quiet prominence, slowdisappearance of these phenomenasunspot lifetime: days to months, most less than 11 days

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 28

Page 29: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Zürich Sunspot Classification: Evolutionary Sequence

Waldmeier (1955)

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 29

Page 30: Terminology and History Sunspot Structure Sunspot Evolutionhome.strw.leidenuniv.nl/.../SolPhys_2010_L13_Sunspots.pdf2 Sunspot Structure 3 Sunspot Evolution Christoph U. Keller, Utrecht

Rudolf Wolf

web.hao.ucar.edu/public/education/sp/images/wolf.html

Sunspot Numbersdiscovery of sunspot cycle byHeinrich Schwabe in 1843Rudolf Wolf at ETH Zurichcompares sunspot observationsfrom different observersinvents Sonnenflecken Relativzahlin 1847number of sunspot groups g,number of sunspots f

R = k(10g + f )

k ≈ 1: observer-dependentcalibration factorSunspot Number is a goodmeasure of fractional area of Suncovered by spots

Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 30