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: