The Earth’s Magnetic Field - Ultra and Extremely Low Frequency Electromagnetic Fields - page 19

1.2 The Earth Magnetosphere

1.2.1 Solar Wind

The Earth magnetic field is immersed in the atmosphere of the Sun. As far as the
temperature of the upper atmosphere/corona of the Sun is as high as 1:5 10 6 K, the
corona consists of a fully ionized plasma. The gravitational pressure of the upper
layers of the corona is unable to equilibrate the gas pressure of the corona material
so that the Sun corona expands into outer space. Because of high temperature of the
corona, the electrons, protons, alpha particles, and other ions can thus escape the
Sun gravitational attraction and form a steadily streaming outflow of solar plasma
called the solar wind. The solar wind expands radially from the Sun at speeds of
about 300-800 km/s and fill the solar system up to the heliocentric distance of
about 100 AU (astronomical units). The solar wind is also pervaded by a large-
scale interplanetary magnetic field. Since the solar wind plasma conductivity is
high enough, the magnetic field is frozen into the plasma. This yields that the solar
magnetic field is transported outward into the solar system by the solar wind plasma.
Owing to the combination of plasma heating, compression, and subsequent
expansion, the solar wind becomes a supersonic flow above a few solar radii (e.g.,
see monograph by Parker ( 1979 ), and references therein). The solar wind speed
relative to the Earth is much greater than the speed of Alfvén, magnetosonic and
other kind of MHD waves providing energy transfer inside the solar wind. The
solar wind energy flux incident upon the cross section of Earth's magnetosphere is
estimated as 2 10 13 W. The solar wind flowing to the Earth brings the aurora, heats
the polar upper atmosphere, and provides the plasma on the Earth's magnetic field
lines thereby energizing a spacious revolving system of magnetospheric plasma.
When the solar flares give rise to significant perturbations of the solar wind
it produces magnetic storms and substorms which result in interferences in the
communication system.

1.2.2 Interaction Between the Solar Wind and Earth's

Magnetic Field

The basic concept of the Earth's magnetosphere was first deduced by Chapman
and Ferraro ( 1931 , 1932 , 1933 , 1940 ) in early 1930s. The magnetosphere is
the near-earth space confined by the solar wind plasma blowing outward from
the Sun. The Earth's magnetosphere is formed due to the interaction between the
Earth's magnetic field and the electrically conducting plasma of the solar wind.
This interaction brings the solar wind deform the Earth's dipolar magnetic field,
compressing the field lines on the day side and stretching them out to form the
elongated magnetotail on the night side.