SOHO's MDI shows view beneath sunspots


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):

See also:

The NASA Press Release Site

The ESA Press Release

Video and Image Resources

Videos from Space Science Update

TopicSample ImageImage or Video links Notes
Below the Sunspot Sunspot Surface BelowSunspot_rendering.mp3 (3 Meg) Tom Bridgman
Sunspots Observed in 2001 Continuum Image Sunspots2001.mpg (6 Meg) 512x512 version
Sunspots2001.mpg (6 Meg) rectangular
MDI via Tom Bridgman
Slices Through the Solar Interior Under Sunspot 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)
Sasha Kosovichev
Wave Propagation Solarwaves_raypath.mpg (1 Meg) Sasha Kosovichev
Rising Magnetic Flux (10.6 Meg)
RisingFlux.mpg (5.1 Meg)
Neal Hurlburt

Still Images from Space Science Update

TopicSample ImageImage or Video linksSource Notes
Galileo Sunspots 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 Image showing internal structure of sunspot, model on left and
   observation on right, model structure is deeper than observation theory_obs.jpg Neal Hurlburt
Irradiance variations jpeg image prepared by Steele Hill at GSFC SOHO/VIRGO

High Resolution Stills

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 FD1998.0012.gif
Observed 1998.05.03_17:36:00_TAI, shown distorted.
see also
MDI 2001 Continuum frame 393 of movie FD2001.0393.gif Observed 2001.03.28_19:12:00_TAI, shown distorted.
see also

Other Images and Videos - random order

TRACE Spot 19June01 TRACE/ Neal Hurlburt
Spot closeup dot_ar8704_20sep99_sunspot.mpeg (2-meg) (52meg QT)
Tom Berger, data from Dutch Open Telescope
Connect CZ flux TRACE/Rising.mpg Neal Hurlburt
4/15/01 Flare (red, yellow) TRACE/ Neal Hurlburt
4/15/01 Flare (red, yellow) TRACE/ Neal Hurlburt
4/15/01 Flare (red, yellow) TRACE/ Neal Hurlburt
Active Region TRACE/ Neal Hurlburt
TRACE Sunspot TRACE/ Neal Hurlburt
1998 MDI Continuum NASA/FullDisk1998.mpg
MPG/Ic.1998.mpg 512x512 1 meg
MDI raw images page
MDI via Tom Bridgman
Global Flows MDI Rivers release
Orange EIT Image NASA/eitplumeg.gif EIT via NASA
Solar Sounds NASA/3tones_21sec.mpg MDI
Big Bear pores BIGBEAR/speckle_pores.gif
SOHO Spacecraft GIFS/artist-FM.gif SOHO drawing, MDI on left facing side
TRACE spot TRACE/ Neal Hurlburt
TRACE June 98 tri980616.tif Neal Hurlburt
TRACE WL rotation TRACE/ Neal Hurlburt
Irradiance variations SOHO/VIRGO
Irradiance variations SOHO/VIRGO

Coverage in the Media

References in Scientific Journals

N.E. Hurlburt, A.M. Rucklidge (2000) M.N.R.A.S. 314, 793-806:

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: