SUNSPOT SSU - SOHO reveals how sunspots keep their stranglehold on the Sun
The puzzle: Why do sunspots last for weeks instead of flying apart? Like huge magnets, strong magnetic fields in sunspots naturally repel each other. What holds them together?
A theory: Astrophysicists trying to understand sunspots have developed theories that require inward flows of material to stabilize the structure, in spite of the fact that at the surface material clearly flows out of the spots.
New observations: Scientists using SOHO/MDI data have looked just below the Sun's surface and clearly observed inward flowing material for the first time.
The explanation: The strong magnetic fields in the sunspots promote cooling. Cool material contracts and sinks at speeds of up to 3000 miles per hour. This drives an inward flow, like a planet-sized whirlpool, that holds the sunspot together as long as the field is strong enough.
The method: They discovered this using a technique called acoustic tomography - a novel method similar to ultrasound diagnostics in medicine that uses sound waves to image structures inside the human body.
Another surprise: Sunspots are surprisingly shallow. Conditions in sunspots change from cooler than the surrounding plasma to hotter than the surrounding plasma just 3000 miles below the surface. The cool part of a sunspot has the shape of a stack of two or three nickels.
Deeper explanation: Sunspot magnetic fields block the flows that carry heat energy up from the hot solar interior. That results in higher temperatures below the blockage and cooler temperatures above. The downward flows mentioned above dissipate at the same depth. With these data one cannot get a sharp enough picture to really explain the details.
An analogy. Until now we've looked down at the top of sunspots like we might look down at the leaves in the treetops. For the first time we're able to observe the branches and trunk of the tree that give it structure. The roots of the tree are still a mystery.
Why do we care? Understanding sunspots is essential for understanding the 11-year solar cycle, solar flare explosions, and huge coronal mass ejections that affect life and society on Earth.
Published paper (J. Zhao, A.G. Kosovichev, T.L. Duvall, Jr.
2001, Investigation of Mass Flows beneath a Sunspot by Time-Distance
Helioseismology , Ap. J., 557, 384-388):
The NASA Press Release Site
The ESA Press Release
|Topic||Sample Image||Image or Video links||Notes|
|Below the Sunspot||BelowSunspot_rendering.mp3 (3 Meg)||Tom Bridgman|
|Sunspots Observed in 2001||
(6 Meg) 512x512 version
Sunspots2001.mpg (6 Meg) rectangular
|MDI via Tom Bridgman|
|Slices Through the Solar Interior||
UnderSunspot_combined.mpg (12.6 Meg)
SolarOscillations.mpg part 1 (3.3 Meg)
UnderSunspot_slices.mpg part 2 (3.7 Meg)
UnderSunspot_flows.mpg part 3 (5.7 Meg)
|Wave Propagation||Solarwaves_raypath.mpg (1 Meg)||Sasha Kosovichev|
|Rising Magnetic Flux||RisingFlux.mov (10.6 Meg) RisingFlux.mpg (5.1 Meg)||Neal Hurlburt|
|Topic||Sample Image||Image or Video links||Source Notes|
Rice Galileo Web Site
Rice General Sunspot Web Site
|Rice Galileo Project|
|Big Bear Spot||Big Bear sunspot Image .gif|
|Comparison of model and observation||theory_obs.jpg||Neal Hurlburt|
|Irradiance variations||jpeg image prepared by Steele Hill at GSFC||SOHO/VIRGO|
|MDI HR Spot frame 185 of movie||mdi0185.tif||SOHO/MDI|
|MDI Sound Speed frame 327 of movie||mdi0327.tif||SOHO/MDI|
|MDI Sound Speed frame 510 of movie||mdi0510.tif||SOHO/MDI|
|MDI 1998 Continuum frame 12 of movie||
Observed 1998.05.03_17:36:00_TAI, shown distorted.
|MDI 2001 Continuum frame 393 of movie||
Observed 2001.03.28_19:12:00_TAI, shown distorted.
|TRACE Spot 19June01||TRACE/sunspot_june2001_w1600.mov||Neal Hurlburt|
dot.mov (52meg QT)
|Tom Berger, data from Dutch Open Telescope|
|Connect CZ flux||TRACE/Rising.mpg||Neal Hurlburt|
|4/15/01 Flare (red, yellow)||TRACE/T1600_X14_010415.mov||Neal Hurlburt|
|4/15/01 Flare (red, yellow)||TRACE/T171_010415_22.mov||Neal Hurlburt|
|4/15/01 Flare (red, yellow)||TRACE/T171_X14_010415.mov||Neal Hurlburt|
|Active Region||TRACE/sunspot2_w171.mov||Neal Hurlburt|
|TRACE Sunspot||TRACE/sunspot2_w1600.mov||Neal Hurlburt|
|1998 MDI Continuum||
MPG/Ic.1998.mpg 512x512 1 meg
MDI raw images page
|MDI via Tom Bridgman|
|Global Flows||combined.ps||MDI Rivers release|
|Orange EIT Image||NASA/eitplumeg.gif||EIT via NASA|
|Big Bear pores||BIGBEAR/speckle_pores.gif|
|SOHO Spacecraft||GIFS/artist-FM.gif||SOHO drawing, MDI on left facing side|
|MDI||MDI Images||MDI - LMSAL|
|TRACE spot||TRACE/sunspot_17-18june1998.mov||Neal Hurlburt|
|TRACE June 98||tri980616.tif||Neal Hurlburt|
|TRACE WL rotation||TRACE/TWL_010727at00_30to010806at15_20.mov||Neal Hurlburt|
Meyer et al (1974) M.N.R.A.S. 169, 35-57.
Parker, E.N. (1979) Ap. J., 232, 291-296.
Schatten, K.H., Mayr, H.G. (1985) Ap. J., 299, 1051-1062.
Permission to use: These images are available for educational, news, and informational purposes, as long as the proper attribution is given:
For SOHO images: