Abstract
The analysis of
the Nobeyama Radio Heliograph (NRH) data at 17 GHz have
revealed a new
remarkable feature: an existence of large-scale (comparable with the
size of the solar disk)
chains shining at microwaves. Such chains can be seen clearly at the NRH
images with a
restricted range of the brightness temperature (for example, for T_{b}
<= 2 times 10^{4} K) when
the most intense sources are suppressed. The blobs consisting the chains
are characterized by the
angular sizes of 30-60 arcseconds and the brightness temperature of
about T_{b} ~(11-15)
times 10^{3} K.
At least two types of the microwave chains should be distinguished.
Firstly, there are so-called
long-living chains which exist and keep their general form during many
days, stretch from one
active region to another remote active region/plage and rotate together
with these formations.
The microwave chains of the second type with a characteristic time scale
of tens of hours appear
to be associated with coronal mass ejections (CMEs) and post-CME energy
release that are
revealed, in particular, by long-duration events (LDEs) in the soft
X-ray and microwave ranges.
In some cases, such events are accompanied by strong changes of the form
and location of the
pre-existing chains, especially near the LDE source. In other cases, new
chains and cells arise
also in an extended region around the LDE source.
The comparison with other solar images and maps shows that the form and
location of the
microwave chains (particularly, of the long-living ones) may coincide
with sharp boundaries of
coronal holes, observed with Yohkoh/SXT. They may outline also footpoint
lines of some large
X-ray arcades and correspond to the general picture of large-scale
magnetic fields and filaments.
In the latter case, the chains repeat the form of the corresponding
filaments but are located at
considerable distance from these filaments.
These features mean that some large-scale structures shine at microwaves
as a result of energy
release associated either with long-term evolution of large-scale
magnetic fields or with
disturbances of extended magnetic fields identified with CMEs. The most
probable mechanism
responsible for the radio emission of the blobs forming the chains is
the thermal free-free
emission.
The more detailed study of this phenomenon and especially detailed
comparisons with other solar
images and magnetograms are in progress.