Halpha_%2B700_limb_spicules_08Aug2007_SST

In solar physics, a spicule, also known as a fibril or mottle, is a dynamic jet of plasma in the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

chromosphere A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively. In the ...

about 300 km in diameter.Quantifying Spicules, Tiago M. D. Pereira, Bart De Pontieu, and Mats Carlsson, ''The Astrophysical Journal'' 759, #1 (October 2012), pp. 18-34, , . They move upwards with speeds between 15 and 110 km/s from the

photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

and last a few minutes each. They were discovered in 1877 by

Angelo Secchi Angelo Secchi (; 28 June 1818 – 26 February 1878) was an Italian Catholic priest, astronomer from the Italian region of Emilia. He was director of the observatory at the Pontifical Gregorian University (then called the Roman College) for ...

, but the physical mechanism that generates them is still hotly debated.

Description

Spicules last for about 15 minutes; at the

solar limb Limb darkening is an optical effect seen in stars (including the Sun), where the central part of the disk appears brighter than the edge, or ''limb''. Its understanding offered early solar astronomers an opportunity to construct models with such ...

they appear elongated (if seen on the disk, they are known as "mottles" or "fibrils"). They are usually associated with regions of high

magnetic flux In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ...

; their mass flux is about 100 times that of the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

. They rise at a rate of 20 km/s (or 72,000 km/h) and can reach several thousand kilometers in height before collapsing and fading away.

Prevalence

There are about 3,000,000 active spicules at any one time on the

. An individual spicule typically reaches 3,000–10,000 km altitude above the photosphere.§1, Two Dynamical Models for Solar Spicules, Paul Lorrain and Serge Koutchmy, ''Solar Physics'' 165, #1 (April 1996), pp. 115–137, , .

Causes

Bart De Pontieu Bart is a masculine given name, usually a diminutive of Bartholomew, sometimes of Barton, Bartolomeo, etc. Bart is a Dutch and Ashkenazi Jewish surname, and derives from the name ''Bartholomäus'', a German form of the biblical name ''Bartholo ...

( Lockheed Martin Solar and Astrophysics Laboratory,

Palo Alto, California Palo Alto (; Spanish for "tall stick") is a charter city in the northwestern corner of Santa Clara County, California, United States, in the San Francisco Bay Area, named after a coastal redwood tree known as El Palo Alto. The city was es ...

, United States), Robert Erdélyi and Stewart James (both from the

University of Sheffield , mottoeng = To discover the causes of things , established = – University of SheffieldPredecessor institutions: – Sheffield Medical School – Firth College – Sheffield Technical School – University College of Sheffield , type = Pu ...

, United Kingdom) hypothesised in 2004 that spicules formed as a result of P-mode oscillations in the Sun's surface, sound waves with a period of about five minutes that causes the Sun's surface to rise and fall at several hundred meters per second (see helioseismology). Magnetic flux tubes that tilted away from the vertical can focus and guide the rising material up into the solar atmosphere to form a spicule. There is still however some controversy about the issue in the solar physics community.

Notes

References

Literature

* De Pontieu, B., Erdélyi, R. and James, S: ''Solar chromospheric spicules from the leakage of photospheric oscillations and flows'' In: ''Nature.'' 430/2004, p. 536–539,

External links

* {{DEFAULTSORT:Spicule (Solar Physics) Solar phenomena