Abstract:
In the early 1990s, it was found that the strongest disturbances
of the space–weather were associated with huge ejections of plasma from
the solar corona, which took the form of magnetic clouds when moved
from the Sun. It is the collisions of the magnetic clouds with the Earth’s
magnetosphere that lead to strong, sometimes catastrophic changes in
space–weather. The onset of a coronal mass ejection (CME) is sudden
and no reliable forerunners of CMEs have been found till date. The CME
prediction methodologies are less developed compared to the methods
developed for the prediction of solar flares. Themost probable initialmagnetic
configuration of a CME is a flux rope consisting of twisted field lines
which fill the whole volume of a dark coronal cavity. The flux ropes can
be in stable equilibrium in the coronal magnetic field for weeks and even
months, but suddenly they lose their stability and erupt with high speed.
Their transition to the unstable phase depends on the parameters of the
flux rope (i.e., total electric current, twist, mass loading, etc.), as well as
on the properties of the ambient coronal magnetic field. One of the major
governing factors is the vertical gradient of the coronal magnetic field,
which is estimated as decay index (n). Cold dense prominence material
can be collected in the lower parts of the helical flux tubes. Filaments are,
therefore, good tracers of the flux ropes in the corona, which become visible
long before the beginning of the eruption. The perspectives of the
filament eruptions and following CMEs can be estimated by a comparison
of observed filament heights with calculated decay index distributions.
The present paper reviews the formation of magnetic flux ropes, their
stable and unstable phases, eruption conditions, and also discusses their
physical implications in the solar corona.
