Spicule is an elongated projection of solar atomosphere of which sticks out
from the chromosphere to the corona. It is well found at the edge of super
granules. Its diameter is about 1000km and its hight is 5000-10000 km.
Mostly observed in Hydrogen alpha line. Each spicule is moving continuously,
some moves upward (up rising speed is about 20 km/s) from upper chromosphere
and then changes to desent, and the others are fade away after acension.
Anyhow its time span is about 5 minutes.
The reason why the spicule is formed is not well known.
One of well accepted models is that it is formed by the transmission of sound
or magneto hydrodynamic (MHD) wave along with the strong magnetic tube swept
toward the edge of granule. When the wave transmits from the photosphere to
the upper chromosphere, the density decreases rapidly. Therefore the velosity
disturbance in the sound and/ or MHD wave becomes larger (sometimes the shock
is formed), it becomes possible to lift the upper chromosphere up to the
corona.
Here we will simulate a magnetic tube with fixed foot points with perturbation
on the foot points and follow its evolution as the perturbation grows and
lifts the upper chromosphere to the corona.
To show initial state, please place the mouse on figures.
Initially there are two layers; high density chromosphere and high temperature
corona. By the Alfven wave originated in the chromosphere, the surface of the
chromosphere will be lifted.
Spherically symmetric Magneto Hydrodynamic equations
Please refer THIS document (PDF file in Japanese)
for detailed explanation.