Illustrations of Solar Physics Terminology

• barb: features extending off from the axis of a filament; the direction in which barbs extend from the axis depends upon the chirality, or handedness, of the filament.
  1. High-resolution H-alpha image of chromospheric filaments and barbs, observed 2002 October 30, 14:46 UT (USAF, ISOON image courtesy D. Neidig; from work of A.A. Pevtsov). Barbs are the "spurs" that stick out from the filaments' axes. Upper left corner corresponds to N34E22, lower right corner to N06W02.

• cavity: a region of hot coronal plasma, associated with a filament or filament channel; magnetic field of cavity is thought to be topologically isolated from surrouding corona; cavity plasma is thought to be much hotter but less dense than filament it contains
  1. A 752 kB mpeg movie of a cavity w/filament, associated with the CME below (swiped from the Hot Shots from SOHO page on the 4 Jan. 2002 event)

• chirality: also known as handedness, used to distinguish between the two ways in which filaments break symmetry. As illustrated below, their barbs point in different directions.
  1. High-resolution H-alpha image of filaments of differing chirality, observed 2002 October 30, 14:46 UT (USAF, ISOON image courtesy D. Neidig; from work of A.A. Pevtsov). Upper right and lower left corners: Dextral and sinistral patterns. Small filament in lower right corner exhibits both sinistral and dextral barbs. (Upper left corner corresponds to N34E22, lower right corner to N06W02.)
  2. See also my notes on the hemispheric patterns of chirality.
  3. See also Alex Pevtsov's handedness diagram, from Multi-Wavelength Observations of Coronal Structure and Dynamics (Yohkoh 10th Anniv. Mtg.), P.C.H. Martens and D. Cauffman, eds., Elsevier/COSPAR, COSPAR Colloq. Series (2002), p.125

• coronal mass ejection (CME): magnetized plasma ejected from Sun, usu. taken to have been a prominence/filament before ejection; typical params: speed = ~700 km/s; mass = 10¹⁵ g; size = ~R_Sun = ~7 x 10⁵ km
  1. An APOD image of a CME from taken with SoHO LASCO
  2. A 245 kB mpeg movie of a CME, associated with the filment eruption of below (swiped from the Hot Shots from SOHO page on the 4 Jan. 2002 event)

• emerging flux:
  1. movie from SXT Nuggets, Dec. 22, 2000 -- and the full Nugget

• Evershed effect: Doppler shift in weak lines of sunspot penumbre, consistent with ~ 2 km/s radial outflows in dark penumbral filaments, but interpretation is not unambiguous. Effect is reversed in stronger H-alpha, Na I D, and Mg I b lines, perhaps sign of infalling coronal/chromospheric material above photosphere. Inflow of umbral grains is also seen in penumbrae at photospher.

• filament: a long, thin, cool collection of magnetized plasma above the photospheric surface, when seen on the Sun's disk (a "filament" differs from a "prominence" only in viewing angle -- latter viewed over limb); ejected filaments are called coronal mass ejections
  1. TRACE image of an erupting filament, from APOD
  2. A 752 kB mpeg movie of a filament eruption (w/nice cavity!), associated with the CME of 04 Jan. '02 above (swiped from the Hot Shots from SOHO page on the 4 Jan. 2002 event)

• Hale's Law: tendency of leading (in sense of Sun's rotation) polarity in active region fields to differ in N & S hemispheres; named after George Ellory Hale, who first showed (using spectroscopic techniques -- Zeeman splitting, I believe) that sunspots were magnetic phenomena.
  1. A SoHO MDI full-disk image of longitudinal magnetic fields, 7 July 2000

• Joy's Law: tendency of the tilt of axis of bipolar active region sunpots to increase with increasing latitude; coined by H. Zirin, named after a grad student of Hale's.
  1. GIF of fig. 5 (p.168) from Hale, Ellerman, Nicholson, & Joy, in ApJ,v.49, p.153 (1919)
  2. GIF of fig. 6 (p.89) from Wang & Sheeley, in Sol. Phys.,v.124, p.81 (1989)

• Kolmogorov spectrum: -5/3 power law dependence on turbulent velocity field's energy spectrum E(k) on wave number k; energy is input at scale k₀ and dissipated at scale k_nu (this is also a good definition of the spectral index: the value of the exponent in a power-law relation, equal to 5/3 in this case)
  1. sketch of a Kolmogorov-like energy spectrum

• linking number: net number of times loops of two "directed lines" link each other, with sign determined by ``right hand rule'' sense of linkage: if the thumb of one's right hand points in the direction of line 2 where line 2 intersects the surface interior to line 1, the linkage will be positive if the fingers of the right hand point in the direction of line 1, and negative if they point in the direction opposite line 1. (This sketch provided courtesy of Mitch Berger.)
  1. sketch of a flux tubes w/linking number of -3
  2. black & white (bitmap) postscript version of same

• -Effect/Babcock Mechanism: shear from differential rotation turns initially poloidal field lines into toroidal field lines. (Sketches taken from TRACE's page, "the Sun's Magnetic Personality.")
  1. initial, poloidal field
  2. midpoint of field evolution
  3. final, toroidal field

• Pevtsov's Law: The power-law scaling of X-ray luminosity with magnetic flux over fifteen (!) decades, with approximate power law spectral index of one. A.A. Pevtsov, G.H. Fisher, L.W. Acton, D.W. Longcope, C.M. Johns-Krull, C.C. Kankelborg, and T.R. Metcalf, showed, in Figure 1. (and caption) of their ApJ paper (v. 598 p. 1397), that X-ray spectral radiance is strongly correlated to magnetic flux for the Sun and other magnetically active stars.

• prominence: a filament (see above) viewed above the limb

• supergranule: convective cells tens of Mm (or tens of arc sec) in diameter
  1. A SoHO MDI high res. image of supergranular disruption of active region magnetic fields, 7 July 2000

• turbulent diffusion: dispersion of magnetic flux in turbulent velocity fields, as in the solar convection zone
  1. A SoHO MDI high res. image of supergranular disruption of active region magnetic fields, 7 July 2000

• sigmoid: An "S"-shaped or "backwards-S"-shaped collection of coronal loops, often seen in SXT.
  1. Two beautiful SXT sigmoids. The first was seen on 1998 June 7; observers predicted an eruption, which then occurred on June 8 and produced a halo CME. The same region subsequently formed another sigmoid, and another eruption occurred on June 19. (Image swiped from Dr. Charles Kankelborg.)

Links to Other Solar Physics Imagery, Glossaries, and Info

• Lockheed-Martin's Space/Aerospace Lab (LMSAL) has compiled a nice page, "Images of Our Magnetic Star," which has images suitable for conveying complex ideas, including the Sun's cyclic activity, and imaging in different wavelengths. Very many good images here.

• The Sun Acts Up is collection of images and sketches maintained by the good people at NASA's Goddard Space Flight Center, including images of dramatic events such as CME's & flares. Very many good images here.

• The Sun: A Pictorial Introduction: A Slide Set by P. Charbonneau and O.R. White has slides and detailed explanations covering many basic ideas in the field. It's an excellent introduction to the "zoology" of solar phyics.

• Hugh Hudson has compiled sketches from the solar physics literature into a Grand Archive of Flare and CME Cartoons.

• Our star, the Sun is a collection of facts, images, and sketches from the SoHO E.P.O. program. (See also their FAQ page and Not-so FAQ page.)

• This GLOSSARY OF SOLAR-TERRESTRIAL TERMS, maintained by NOAA, is primitive but very comprehensive: it's got a lot that no other glossary does.

• This ON-LINE GLOSSARY OF SOLAR-TERRESTRIAL TERMS, also maintained by NOAA, is fairly comprehensive.

• There is yet another Solar Physics Glossary, this one maintained by NASA employees.

• David Knisely has compiled a Glossary of H-Alpha terms, as part of his "Complete H-Alpha Handbook."

• Bill Arnett has compiled a nifty page entitled simply, "The Sun."

• I have compiled approximate solar parameters ("bag numbers") from the literature in a web-viewable look-up table, or postscript format for printing.