Interplanetary Magnetic Field

ECE120 Space Physics.

The sun is the origin of most of the plasma and interplanetary magnetic effects felt within the solar system. A wide spectrum of electromagnetic radiation is produced by the sun and a solar wind of hot plasma radiates at supersonic speeds from its surface.

Plasma is often refered to as "the fourth state of matter", it is a gas in which the atoms are free floating charged ions. The sun's corona is so hot that all of its atoms are ionized and have many of the electrons stripped off. The extreme temperature of the sun allows the solar plasma to escape the sun's gravity and flow out into space. Through heating, compression, and expansion the solar wind becomes supersonic a few solar radii from the sun. The solar wind flows out in all directions reaching far beyond all the planets of the solar system. The expanding solar plasma drags along the solar magnetic field forming what is called "the interplanetary magnetic field" (IMF). The region of space where the sun's magnetic field is dominant is called the heliosphere.

The solar wind moves out radially from the sun but due to the sun's rotation the magnetic field has a spiral form (garden-hose effect).

Figure 3 Figure 3.

At the orbit of the earth the magnetic field lines from the sun are at an angle of 45 degrees to the radial. The velocity of the solar wind is typically 400 km/s when it reaches the earth. The IMF strength is 5nT and consists mostly of hot electrons and protons with a small fraction of He++ ions (3-5%). This hot magnetized, supersonic plasma is capable of conducting electricity and transporting large amounts of energy. Most of this solar wind passes the earth, but some finds its way into the magnetosphere and ionosphere.

Figure 4
Figure 4.

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