The corona -
here an actual view by the
of ESA and NASA - is the outer part of the
solar atmosphere and the source of the solar wind. It
represents an inhomogeneous, hot, dilute, and fully ionized
plasma. Its spatial structures are governed by the magnetic
field. Important effects of stellar activity can be observed
with unprecedended accuracy, such as coronal mass
ejections (CMEs), flares and prominence eruptions, shock
wave formation, and last but not least particle acceleration.
Despite being of general astrophysical relevance these
processes are not yet fully understood until now.
Plasma processes associated with solar activity take place
on small spatial and temporal scales. If these processes are
accompanied by electron acceleration (up to a few MeV) they
can emit radio radiation. Consequently, such "nonthermal"
electrons can be traced by radio methods. Solar radio
observations are in
some respect different from general radio astronomy. Signals
are not extremely weak but highly varying in time and space.
The background (the solar disc and its surroundings) is
spatially extended and varying, too.
Various plasma processes (particle acceleration, storage,
and escape; excitation of various wave modes) manifest
themselves as solar radio burst patterns in dynamic spectral
diagrams. The radio spectra can be used as one starting
point of the theoretical study of basic plasma processes in
the corona. Further, due to good spectral coverage, high
time resolution, and high sensitivity, the
observations yield an excellent guide and time line for
assembling associated data sets from complementary ground-
and space-based instrumentation.