The Solar Wind
The sun is surrounded by the corona which has a
temperature of one to two
million degrees. The corona is so hot that it boils over and
emits a continuous stream of protons and electrons which expands
into interplanetary space. This so called solar wind
needs about four days to travel from the Sun to the Earth.
It has a strong influence on the Earth's magnetic field.
The atoms and molecules sublimating
from the surface of a cometary nucleus are picked up by
the solar wind as soon as they become ionized.
They are shaped to the long straight plasma tail.
The Sun, its magnetic field, and the Solar Wind
The large scale magnetic field of the sun is the field
of a dipole which is inclined to the rotation axis.
Along the magnetic equator the fieldlines are carried into
the interplanetary space. This results in an open field structure
as shown in the
Figure.
A certain surface separates field of opposite
polarity. Since such a field topology can only be maintained by
an electric current, this surface is called the heliospheric
current sheet. In the vicinity of this sheet the solar wind has a
velocity of about 400 km/s. Farther out the wind has
a velocity of about 750 km/s. This fast wind,
also called high speed stream, originates
from the polar coronal holes. It is
less dense than the slow wind.
These simple
topological conditions prevail only during periods of
quiet sun.
Last modified: Fri Oct 1 15:12:02 MDT 1999
by Rudolf Wegmann
Comments to:
ruw@mpa-garching.mpg.de