The existence of the hot corona is responsible for the existence of
the solar wind. As the solar wind plasma escapes into interplanetary
space it carries with it the solar magnetic field thus stretching it
away from the Sun. To understand the physical processes that drive the
solar wind and lead to the formation of two distinc states: the fast
wind that can travel at more than 700 km/s, and the slow more variable
wind that can coast at speeds as low as 300 km/s, one needs to
understand the physical characteristics of the corona and the sources
of the solar wind. The
Solar Physics Group use spectroscopic observations of the corona acquired
from the ground during total solar eclipses and from space, primarily
from SOHO, the Solar Heliospheric Observatory, to explore the physical
characteristics of the source regions of the solar wind. Through the
study of the distribution of the plasma density in the corona, the
Group found the surprising result that the solar wind expands from a
much larger fraction of the solar surface than had been commonly
believed for the past 30 years. Their analyis of earlier polarization
measurements of coronal forbidden lines of iron led to the discovery
that a large fraction of the magnetic field extends radially from the
solar surface thus pointing to the possible existence of two sources
of the magnetic field rooted at different depths in the solar
interior. Observations made with the Ultraviolet Coronagraph
Spectrometer (UVCS) on SOHO led to the first results showing that the
slow solar wind in the inner corona originates in streamers, and
that the transition from the fast to the slow wind produces a strong
velocity shear within a few solar radii from the surface. The Group is
currently preparing for total solar eclipse observations to be made
from South Africa on December 4. They continue to pursue their
research in exploring the hidden secrets of the Sun by tapping into
the solar wind.