 Photo credit: moondaily.com
What is solar wind?
The Sun is Earth's nearest star and it is made up of mostly of hydrogen gas. The sun boils off protons, electrons, and lesser amounts of positively charged nuclei of elements heavier than hydrogen and turns these charged particles into the fourth state of matter known as plasma. The Sun's plasma is so hot that the most energeticly charged particles escape from the Sun's gravity and fly out into space. This plasma makes up what is known as the solar wind.
The solar wind is an outward flow that travels from the sun, towards the Earth at speeds of 200 to 1000 kilometers per second, bringing the particles to Earth several days after they are ejected from the sun. The solar wind also carries along an irregular but somewhat extension of the Sun’s magnetic field. The charged particles in the solar wind act as an adhesive attaching the weak solar magnetic field to the wind which carries it along. All planet's are surrounded by the magnetized, hot, supersonic collisionless solar wind plasma capable of conducting electrical current and carrying large amounts of electrical and kinetic energy.
How does the solar wind affect the Earth's magnetosphere?
As the solar wind approaches the earth, at a distance of approximately 10 RE (earth radii) the charged particles in the wind begin to interact with the Earth’s magnetosphere. On the sun-earth line, the geomagnetic field lines are approximately perpendicular to the flow of the solar wind, allowing the geomagnetic field lines to impede the wind. As the oncoming particles try to penetrate the geomagnetic field they are turned aside, the negatively charged particles to the west, and the positively charged particles to the east. This induced west-east motion creates an electrical current in a direction that causes the solar magnetic field to add to the geomagnetic field. As the pressure of the solar wind compresses the geomagnetic field it gets stronger resulting in a sharp demarcation called the magnetosphere boundary. Within the boundary lies the magnetosphere, a region where the geomagnetic field pertains and the solar wind does not. Outside the boundary the diverted solar wind continues to flow around the sides of the magnetosphere.
The solar wind flow along the magnetosphere boundary thereby drags the geomagnetic field lines back towards the night side direction of the earth, referred to as the anti-solar side. The geomagnetic field acts as a stretchy rubber band, thick near the earth, but thinning outward until near the magnetosphere boundary where the magnetic field lines lose their strength and become so weak that they stretch easily. These stretched out magnetic field lines are a result of the continual supersonic outflow of the solar wind that confines and distorts the Earth's magnetic field into a cavity, with a long tail extending hundreds of earth radii in the anti-solar direction. This long tail is called the magnetotail.
 Photo credit: NASA.gov |