Sunspots

•Measuring the Period of Solar Rotation •Solar Activity and Terrestrial Climate

NOAA #0759 Gary Palmer, May 18, ’05 Los Angeles, CA fig 1

What Is a Sunspot?

• Sunspots are dark regions on the solar surface. – They appear dark because they are generally between 1,500 and 2,000 K cooler than their surroundings.

1 » It is generally accepted that sunspots manifest as a result of interactions between the Sun’s magnetic field and convection currents.

Caprino Bergamasco of Italy penciled this Image of sunspot group 0756 in May.

Courtesy of spaceweather.com

fig 2

Why do they form?

• Modern theory suggests that twisted, convoluted magnetic field lines disrupt normal convection flows, which prevents cooler regions from sinking.

– Sunspots can last anywhere from a period of a few hours to a few months and groups can be as large as the planet Jupiter.

2 fig 3 This close-up digital photo image of 0756, taken using a coolpix camera and 8” reflector telescope, compares with Bergamasco’s masterpiece.

Observation

• We made our first observation on April 26 th 2005.

8” Orion Dobsonian mounted Newtonian reflector telesope, and the sunspotter projection device.

Observation Summary

• The first 10 days of observing met with cooperative skies.

• Observing conditions worsened thereafter.

May 3 rd 2005 image captured With Nikon coolpix and 8” Orion Reflector.

NOAA 0756 3

Complications with Observation

• Weather was a complicating factor.

• Determining the latitude of the sunspots.

• Although there were complications, having any sunspots at all was fortunate, due to the proximity to solar minimum.

– This illustrates the Sun’s unpredictable behavior!

• If we were aiming for extremely accurate data, we would have to account for torsional oscillations and meridional flows.

4

Sunspotter Images

0756 near the Eastern Limb, April 26th

Image captured April 26th at 2:20 PM at TESC

Image was captured Tuesday, May 1st, at 11 AM with digital camera.

Image from May 6th, about 24 hours before NOAA sunspot group 0756 traveled beyond the Sun’s Western limb. It was cloudy on the 7th.

Following in the footsteps of great astronomers, May 16th, at Noon

Calculations

• The period of rotation is roughly 25 days at the equator and 35 near the poles, thus the rotation is dependent on heliographic latitude.

• W=14.37 -3.1sin

degrees per day.

2 5 x , where x is the latitude in degrees, gives the daily progress of a sunspot at a certain latitude in • So, 360°/W= the number of days for sidereal rotation.

• Synodic rotation period: 360º+x(1°/day)= wx, where x=days and w=sunspot angular velocity.

6 • 360/(w-1)=x gives the synodic rotation period.

The Sun’s Magnetism

• Magnetism is caused by the interaction of highly ionized particles.

7 • The Sun has a strong magnetic field.

– The magnetic field around sunspots is roughly 2,500 times as powerful as Earth’s.

8 • Distortion of the magnetic field is caused by the peculiar phenomenon of solar differential rotation.

Differential Rotation

• The convective envelope does not rotate according to the laws of a fixed body.

9 • Equatorial regions travel much faster than the polar regions.

– They actually complete full rotation in less time even though they have much further to travel.

– The difference is as much as ten days!

Differential Rotation and Magnetism

Solar activity and magnetism are directly related.

Fig. 4

Why does the Sun exhibit differential rotation?

• The jury is still out on differential rotation.

• Solar differential rotation defies Kepler’s third law.

• Rob’s Theory: Since there is so much more mass rotating around the equatorial region, it has to spin faster to keep from collapsing! (Are there some problems with Rob’s theory?) DOH!

Sunspots, Magnetism and Differential Rotation

• Differential rotation distorts the magnetic field.

– The distorted magnetic field lines interfere with convection.

• Sunspots result from disrupted convection currents.

10 • Distortion of the magnetic field causes the 11 and 22 year solar cycle. – This culminates in magnetic pole reversal.

11

Sunspot Evolution

• Generally, sunspots appear at mid all upper right solar images courtesy of sohowww.nascom.nasa.gov

latitudes at times of low solar activity.

• Sunspots progressively develop (generally) nearer the equator toward solar maximum.

Sunspots travel in groups which have opposing polarities, with the preceding member having the same polarity as that hemisphere’s pole.

12 fig 5

Helioseismology

• The magnetic opposition of polarity should cause sunspots to dissipate rapidly, but in many cases it does not.

– SOHO enabled helioseismology is helping scientists to discover why.

13 • A vortex, or whirlpool, beneath sunspots maintains them and continuously pulls in magnetic field lines and plasma.

14 • This explains the Wilson depression, why sunspots don’t dissipate, and possibly the increase in solar luminosity.

15

Sunspots in History

• Historians have evidence that Theophrastus of Athens observed sunspots in 350 B.C.E.

16 • Records indicate Chinese astronomers have observed sunspots since 28 B.C.E.

17 • The first telescopic observations of record were made by Fabricus of Germany and Galileo of Italy in 1611.

18

Modern History

• • In 1858 the use of helio-photography greatly enhanced the study of sunspots.

– This enabled a much higher degree of accuracy in measuring rotation.

19 Doppler imaging of the red and blue shifts at the limbs of the solar disk is used to measure rotation (including differential) to a higher degree of accuracy.

20

Cosmology

• Sunspots have been interpreted with a wide array of ideas as to their origin.

• There is little mention of sunspots in mythology due to the difficulty in observation, because the sun is very bright.

• Pictures of Egyptian Sun-God’s solar disk with spots.

21 • Aztec creation myths have a Sun-God with a pockmarked face.

22

How do sunspots affect climate on Earth?

• Sunspots are indicative of solar activity. • There is a wide array of opinion and study on how solar activity affects climate on Earth.

– Some say there is little to no affect on Earth’s climate from variance in solar activity – Some say there is overwhelmingly dominant influence on Earth climate from solar activity.

– Reality is somewhere in between these extremes.

fig 6

Arguments for great influence:

• The Maunder minimum occurred between about 1645 and 1715. This was a period of virtually no sunspot (hence low solar) activity. It was also associated with a “little ice age” during which the river Thames in London froze.

23 • Javaraiah, “On long time scales from decades to millenia, the solar luminosity variations associated with solar activity are known to cause significant variations in terrestrial climate on global scales.” 24 • There are also certain industries which favor a solar influence view of climate change.

Arguments Against

• The lack of high quality observational data fig 8 makes the correlation of solar activity and Earth climate change tenuous at best.

• Solar radiation levels vary on the order of +/ 0.1% between solar minima and maxima.

25 • Earth’s climate doesn’t always respond to solar activity in predicted ways. Sometimes the predicted result is magnified beyond what would be expected. It may even be the reverse of what would be expected.

26

Conclusion

• Earth’s climate is a complex system of interactions and feed-back mechanisms which humanity does not fully understand. This makes an evaluation of the Sun’s impact quite difficult.

• Accurate measurement the period of solar rotation is possible using sunspots.

• • • • • • • • • • • • • • • • • • • • • • • • • • Endnotes 18.

19.

20.

21.

22.

23.

24.

25.

26.

5.

6.

7.

8.

1.

2.

3.

4.

http://brahms.phy.vanderbilt.edu/a102/web_sunspots.shtml

http://www.meadows3.demon.co.uk/html/glossary.html

http://www.ngdc.noaa.gov/stp/SOLAR/SSN/ssn.html

Javaraiah J, Gokhale M.H. (2002), The Sun’s Rotation, New York: Nova Science Publications pp 53-61 Javaraiah, p. 3 ibid.

Equation developed by Bryan http://www.es.ucl.ac.uk/research/planetaryweb/undergraduate/dom/magrev/sunmag.htm

http://www.crh.noaa.gov/fsd/astro/sunspots.htm

9.

10.

15.

16.

17.

http://solarphysics.livingreviews.org/Articles/lrsp-2005-1/index.html

http://en.wikipedia.org/wiki/Sunspot 11.

12.

Freeman, (2005) Universe Freeman, ibid.

13.

Britt, R. R. (2001, Nov. 6). Inside sunspots: New view solves old puzzle.

Space.com

. Retrieved May 1, 2005, from http://www.space.com/news/sunspot_inside_011106.html

14.

http://www.space.com/news/sunspot_inside_011106.html

ibid http://www.space.com/news/sunspot_inside_011106.html

ibid Benestad (2002), Solar Activity and Earth’s Climate, Chichester, UK: Praxis Publishing page 12.

Benestad, ibid. pg 12 Benestad, ibid pg 13 Benestad, ibid pg 15 http://cat.middlebury.edu/~PHManual/doppler.html

http://www.eclipse-chasers.com/egypt1.htm

http://www.exploratorium.edu/sunspots/history.html

Hoyt and Schatten, (1997), The Role of the Sun in Climate Change, Oxford: Oxford University Press pg. 197 Javaraiah J. and Gokhale M.H. pg 21 Hoyt and Schatten, pg. 223.

Hoyt and Schatten, pg. 223.

Image and figures reference: 1.

2.

3.

4.

5.

6.

7.

8.

www.spaceweather.com

www.spaceweather.com

Rob Whitlock, digital camera Freedman, Universe, pg 398 Science.nasa.gov/ssl/pad/solar/sunspots.htm

Images.google.com search for solar wind http://web.dmi.dk/fsweb/solarterrestrial/sunclimate/welcome.shtml

http://www.exploratorium.edu/sunspots/research5.html