terminology and history sunspot structure sunspot...
TRANSCRIPT
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
Overview
Sunspot Terminology
DOT Blue Continuum Movie of AR10425
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 2
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
Active Region Numbers
www.solarmonitor.org
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 4
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
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
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
Drawings by Christoph Scheiner
galileo.rice.edu/sci/observations/sunspots.html
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 8
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
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
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
Empirical Temperature - Field Strength Relation
Kopp & Rabin 1992
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 12
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+
Bφ
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
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
Empirical Temperature - Field Strength Relation
Kopp & Rabin 1992
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 15
Azimuthally Averaged Sunspot Quantities
Keppens & Martinez Pillet 1996
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 16
Wilson Depression
sunspot umbrae are lower than quiet photosphere (Wilson 1769)
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 17
Umbral Dots
Tritschler & Schmidt 2002
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 18
Umbral Dots Simulations
Schüssler & Vögler 2006
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 19
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
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
Sunspot Oscillations
DOT 2005-07-13 AR10789
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 22
Large Sunspot Region from early 2001
Best of SOHO Movies
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 23
Sunspot Region Evolution
www.noao.edu/image_gallery/html/im0605.html
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 24
Sunspot Evolution
Zhang & Tian 2005
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 25
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
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
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
Zürich Sunspot Classification: Evolutionary Sequence
Waldmeier (1955)
Christoph U. Keller, Utrecht University, [email protected] Solar Physics, Lecture 13: Sunspots 29
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