Solar wind definition
The solar wind is a plasma, a stream of charged particles (ions and electrons) which are continuously escaping from the Sun into the interplanetary medium.
The particles can escape from the hold of the Sun because the solar corona consists of a very hot plasma of which the temperature exceeds millions of degrees. As a consequence, the plasma particles acquire a significant thermal agitation speed, just like the molecules in boiling liquid acquiring high speeds on microscopic scale.
At a certain altitude above the Sun’s surface, the thermal agitation speed of the electrons gets so high (several thousands of km/s) that they can escape the gravitational attraction of the Sun carrying with them positively charged ions. In this way the solar wind is dispersed into the interplanetary medium.
What particles does the solar wind consist of?
The composition of the solar wind is similar to that of the corona: mainly protons (hydrogen nuclei), with about ten percent of alpha particles (helium nuclei) and traces of heavy ions (carbon, nitrogen, oxygen , silicon, iron, magnesium, ...).
The high temperature in the corona is responsible for the complete ionization of hydrogen and helium, and the elevated ionization rate of heavier atoms like oxygen and iron. The presence of electrons ensures the maintenance of an electrically quasi-neutral space.
The solar wind is a very sparse plasma: in the vicinity of Earth, it contains on average barely 10 protons per cubic centimeter. Particles of the solar wind rarely collide: electrons and ions cannot bond to form neutral atoms. The solar wind varies continuously, with time scales ranging from a few seconds to a few years.
Earth is protected against the Solar wind particles
The magnetic field of our planet protects us almost completely against the incoming solar wind particles by deflecting them. But there are weak zones in this natural shield. Near the poles of Earth, the funnel-like openings in the magnetic shield (the polar cusps) allow these particles to enter. This results in a visible phenomenon called Aurora.
The solar wind collides head-on with the magnetosphere. The collision zone constitutes the outermost boundary of the magnetosphere. To understand the perturbations of the magnetosphere by the solar wind, we need to know the properties of the solar wind itself.
The solar wind is
- the outermost part of the solar atmosphere
- fast (up to 800 km/s and more) (Solar wind speeds, fast and slow)
It is indeed important to know how much matter and energy can penetrate from the solar wind through that boundary into the magnetosphere.
At times of strong perturbations of the solar wind (during periods of strong solar activity) such transfers of mass and energy can cause magnetic storms, dramatic temporary changes in the structure of the magnetosphere.
The solar wind also affects the other bodies in our Solar System