Electrodynamic Properties of Space - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 25

2

Electrodynamic Properties of Space

2.1 The Solar Wind and the Earth's Magnetosphere

The theoretical studies of Chapman [16], Parker ([27], [28] and later papers),
Gold [21], and Chamberlain [14] predicted that Sun's very high temperature
should generate a permanent plasma flux. Satellite measurements have con-
firmed the existence of a corpuscular flux called 'solar wind' with a charac-
teristic velocity of 300 800 km/s. Proton concentration in a quiet solar wind

is usually between 1 and 10 cm − 3 and grows by approximately an order of
magnitude in disturbed periods. The solar wind drags out a magnetic field
from the Sun whose magnitude is 3

−

7 nT. Under disturbed conditions the
field may noticeably increase. Measurements have also shown that the proton
temperature is anisotropic and maximal along the interplanetary magnetic
field-lines. The temperature anisotropy coecient is 3. The proton tempera-
ture is usually of the order of several eV. Measurements have demonstrated
the presence in the solar wind of a percentage of He ++ ions with the same ve-
locity as protons. The thermal velocity of He ++ is also about the same as the
proton thermal velocity. That means the He ++ temperature is about 4 times
more than the proton temperature. The electron temperature is 10

−

50 eV.
Longitudinal and transversal specific electric conductivities are 10 14 s − 1

−

and

10 5 s − 1 , respectively.
On approaching the Earth, the solar wind interacts with the geomagnetic
field, confining it ([2], [3], [4]). The field is encapsulated on the day side at a
distance of 5 to 10 Earth's radii R e and extends for hundreds of Earth's radii
on the night side. This region is designated as the Earth's magnetosphere.
The shape and size of the magnetosphere depend not only on the velocity
and density of the solar wind, but also on the magnitude and direction of the
interplanetary magnetic field ([16], [20]).
The earliest data on the magnetosphere boundary were obtained in 1961
from measurements of the magnetic field and of low-energy solar plasma