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Solar Dermatology A brief tour through the esoteric terminology
Basic principle of medical dermatology: “If it’s dry, wet it. If it’s wet, dry it.”
Anemone
Arcade
Bright Point
Coronal Hole
Coronal Mass Ejection
Coronal Rain
Cusp
Disparation Brusque
Erupting Filament
Eruptive Prominence
Evershed Flow
Faculae
Filamant
Filigree
Moreton Wave
Nanoflare
Network
Neutral Line
Plage
Polar Plume
Pore
Postflare Loops
Prominence
Streamer Belt
Spicule
Sunspot Penumbra
Sunspot Umbra
Supergranulation
Two-Ribbon Flare
Tadpole
The blemished sun!
Ourselves,
the dermatologists.
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In 1611, Galileo wrote: "Spots are on the surface of the solar body where they are produced
and also dissolved, some in shorter and others in longer periods. They are carried around the
Sun; an important occurrence in itself." Galileo's drawings from 2 June 8 July 1613 are
shown as a movie above. Galileo’s ideas got him into trouble with church leaders, because
all heavenly bodies were supposed to be perfect, that is “without blemish”.
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Coronal Hole: A region of the Sun’s
corona that appears dark in pictures taken
with a coronagraph, and that shows up as
a void in X-ray and extreme ultraviolet
images. Coronal holes are of very low
density (typically 100 times lower than
the rest of the corona) and have an open
magnetic field structure. This open
structure allows charged particles to
escape from the Sun and results in
coronal holes being the primary source of
the solar wind.
Anemone (Windflower): An active region that, when
viewed in the corona, does not have connections to any
other magnetic concentrations. This often happens
when an active region emerges in a coronal hole.
Arcade: A system of loops observed in the
solar atmosphere, thought to be structured by
magnetic fields and brightened after a flare.
Trace 171 Angstrom image,~1 x 106 K
8 Nov 2000. (Loops are on the order of 100
Mm above the loop footpoints.)
Coronal Rain: Material that condenses in the Sun’s
corona and falls along curved paths onto the
chromosphere. Observed in H-alpha light at the solar
limb above strong sunspots, coronal rain consists of gas
ejected by a loop prominence that returns, several hours
later, along the outline of the now invisible loop.
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Coronal Mass Ejection: A huge eruption of
material from the Sun’s corona into
interplanetary space. CMEs are the most
energetic of solar explosions and eject up to100
billion kilograms of multi-million-degree
plasma at speeds ranging from 10 to 2,000
km/s. They often look like bubbles. CMEs
originate in regions where the magnetic field is
closed. These storms can disrupt power grids,
damage satellite systems, and threaten the
safety of astronauts. (X17 and X10 flares and
the two associated CME’s, LASCO C2)
Filament: A strand of
relatively cool gas
suspended by
magnetic fields over
the solar photosphere
so that it appears as a
dark line over the
Sun’s disk. A filament
on the limb of the Sun
seen in emission
against the dark sky is
called a prominence.
Filaments often mark
areas of magnetic
shearing and can be
seen only in the
centers of strong
spectral line, such as
H-alpha or the H and
K lines of calcium.
Filament: This brief movie
shows 3 frames. The first
shows the Sun in white light
taken by the MDI instrument.
This instrument observes the
Sun's surface and does not
"see" the filaments at all.
However, this image is then
replaced by an EIT 195
instrument image in which the
subtly darker filaments can be
discerned. Finally, an EIT 304
image is revealed underneath
in which the filaments are even
easier to see.
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Erupting Filament: The disappearance of a filament,
often associated with a flare. The filament erupts into
the corona. There is an activation phase with increased
mass motions, expansion, etc. When these eruptions
are observed on the limb - they are known as erupting
prominences.
Disparation Brusque: The sudden disappearance of
a filament.
A filament in Jan 2007 shown in O V line
and a day later caught as it is erupting.
Sunspot Umbra: the dark
core of a sunspot, cooler
than the surrounding
photosphere because is
suppresses convection.
Average size is ~10000
km, but can be as large as
60000 km.
Sunspot Penumbra: the
lighter areas, marked by a
radial filamentary
structure. Typical size is
~5000 km. Waves are
observed to move across
the penumbral structures.
Structure is thought to be
‘uncombed’.
Image credit: Friedrich
Woeger, KIS, and Chris
Berst and Mark Komsa taken here at the Dunn
Tower.
Evershed Flow: The horizontal flow of gas in the penumbrae of a sunspots; the effect is named after
its discoverer, the English astronomer John Evershed (1864-1956). The maximum outflow velocity is
about 2 km/s. Image from Tom Berger, Dutch Open Telescope.
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Granulation: caused by convection, the grainy appearance of the solar photosphere is produced by the tops
of these convective cells.The rising part of the granules is located in the center where the plasma is hotter.
The outer edge of the granules is darker due to the cooler descending plasma. The diameter of a typical
granule is on the order of 1000km and lasts 8 to 20 minutes before dissipating. The vertical flow is ~ 1
km/s. Hinode movie in G-band (430 nm) and Ca II H (397 nm) showing granules and flux.
Bright Point: bright regions observed in intergranular lanes. They are thought to be magnetic flux
tubes and are bright due to hot-wall radiation. Often observed in ‘G-band’ - 430.5 nm.
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Filigree: A string of bright points on the Sun's photosphere that are sometimes visible in
intergranular lanes in continuum images; the smallest points are only about 150 km and last for
hours. Filigrees are thought to be places where flux tubes penetrate the photosphere. Filigree
were originally observed in H-alpha, but are also seen in G-band.
Plage: observed as bright features in
chromospheric emission and are found
surrounding sunspots (active regions).
Plage are linked to the increased
irradiance during solar maximum.
Faculae: A bright area observed near
the limb, commonly seen near an active
region, such as a sunspot, or where
such a region is about to form. Faculae,
which last on average about 15 days.
Faculae are the chromospheric
signature of filigree. In high-res, the
facular grains appear as brightenings
projected on the limbward neighboring
granule - the ‘hot wall’ effect.
www.uni-sw.gwdg.de/.../
solphys/egranulen.html
Moreton Wave: A shock wave in the Sun’s
chromosphere that is produced by a large solar flare and
expands outward at about 1,000 km/s. It usually appears
as a slowly moving diffuse arc of brightening in Halpha or coronal line, and may travel for several
hundred thousand km. Moreton waves are always
accompanied by meter-wave radio bursts; they are
named after the American solar astronomer Gail
Moreton.
Nanoflare: A proposed coronal heating
mechanism in which small-scale currents are
dissipated through impulsive magnetic
reconnection (Parker, 1988). Each event
releases ~ 1024 ergs and has an associated
plasma flow that broadens coronal lines.
Supergranulation: interpreted as the largest scale of
convection, roughly 30,000 km cell size. It is a
predominantly horizontal flow with velocities of 300500 m/s observed in the photosphere. In comparison,
the vertical upflow at the cell center is on the order of
50 m/s and downflow at the cell boundaries is 100 m/s.
“Orange peel” image: doppler velocity with rotation
subtracted and p-modes removed. (Hathaway, MDI)
Network: Chromospheric emission spatially
correlated with the supergranulation cell
boundaries. It is believed that the horizontal
flow of supergranulation sweeps magnetic
fields into the cell boundaries. Lifetime of the
network is ~ 1 day. Best seen in Ca II H & K.
Polar Plumes: Polar plumes appear
prominently in white light coronagraph
observations of coronal holes as distinct,
strongly collimated flow tubes. They
might carry the bulk of the mass and
energy of the solar wind emanating
from polar regions. Electron density is
greater in plumes (8x). Temperature is
lower (20%). Density contrast between
plume and inter-plume area disappears
by 7 Rsun.
The image (Dec 23 1996) shows the
Streamer Belt along the Sun's
equator, where the low latitude solar
wind originates. Over the polar
regions, one sees the polar plumes all
the way out to the edge of the field of
view. The frame was selected to show
Comet SOHO-6, one of seven
sungrazers discovered by LASCO,
before it plunged into the Sun.
Pore: the smallest magnetic phenomena on the Sun which can be distinguished in white light. They
have no penumbra and are much smaller than sunspots - the size of one or a few granules. Lifetimes
are on the order of a day. Magnetic field is ~ 1500 Gauss.
Two ribbon flare: Two ribbons lie at the feet of the flare loops, often occurs in a decaying active region.
Neutral line runs parallel to and in between the ribbons - 195 Angstroms Trace. The backbone is the
Cusp , it would be the apex of the loops if viewed edge-on.
NEXT MOVIE: Post-flare loops: Transverse structures located between the two ribbons after a flare,
seen in H-alpha, transition zone and coronal lines. Arcade & Tadpoles also seen in the next movie.
Trace 171 Angstroms.
Prominence: an elongated structure full of material 100x cooler and denser than the corona (like
cool clouds). Held up by magnetic structures, they can live for weeks/months, and are seen as
bright against the black background of space. They can reach heights of several 100,000 km
above the limb. They eventually become unstable and erupt. A prominence would be a filament
if observed on the disk.
Hedgerow: A series of filament/prominence loops that appear like croquet loops and have
adjacent ‘legs’.
Prominence,
spicule forest,
Hinode SOT
wing of Halpha
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Spicules: jets of hot material seen in the
chromosphere, flowing 20 km/sec from the
photosphere, lasting about 5 minutes,
structured by the magnetic field. Thought
to be caused by acoustic waves leaking
through the atmosphere. Swedish Solar
Telescope. Spicules are also referred to as
fibrils and mottles.