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's

chromosphere A chromosphere ("sphere of color", from the Ancient Greek words χρῶμα (''khrôma'') 'color' and σφαῖρα (''sphaîra'') 'sphere') is the second layer of a Stellar atmosphere, star's atmosphere, located above the photosphere and below t ...

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. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

and last a few minutes each before falling back to the solar atmosphere. They were discovered in 1877 by Angelo Secchi, but the physical mechanism that generates them is still hotly debated.

Description

Spicules last for about 15 minutes; at the solar limb 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; their mass flux is about 100 times that of the

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

. 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 Sun's

. An individual spicule typically reaches 3,000–10,000 km altitude above the photosphere.

Causes

Bart De Pontieu ( Lockheed Martin Solar and Astrophysics Laboratory,

Palo Alto, California Palo Alto ( ; Spanish language, Spanish for ) is a charter city in northwestern Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree known as El Palo Alto. Th ...

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

University of Sheffield The University of Sheffield (informally Sheffield University or TUOS) is a public university, public research university in Sheffield, South Yorkshire, England. Its history traces back to the foundation of Sheffield Medical School in 1828, Fir ...

, United Kingdom) hypothesised in 2004 that spicules form 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 are tilted away from the vertical can focus and guide the rising material up into the solar atmosphere to form a spicule. However, there is still some controversy about the issue in the solar physics community.

Notes

References

External links

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