• - K. Jiricka

• - M. Karlicky
• -A. Tlamicha

• - H. Meszarosova, E-mail: hmeszaro@asu.cas.cz

   The  main goal  of the  group is  the study  of solar radio
 emission  with  emphasis  on  fast  dynamic  flare phenomena,
 especially on  fast solar radio  bursts. For this  purpose we
 have developed two basic instruments:
 a)  a  1.0-4.4  GHz  radio  spectrograph  with  512 frequency
 channels  for  measuring  dynamic  spectra  with  100 ms time
 resolution
 b)  a 3.0  GHz single  frequency radiometer  with 10  ms time
   resolution for monitoring solar radio activity and studying
   short-duration phenomena
     These  observational  data,   together  with  complementary
   observations   from   other    radio   observatories,   X-ray
   observations (GOES, YOHKOH), as  well as optical observations
   we use  for modelling and interpreting  physical processes in
   the solar corona.  In this we exchange data  and cooperate in
   joint  projects  with  several  other observatories (Potsdam,
   Meudon, Bologna, ..).
     The  list  of  observed  events,  as  well  as  pictures of
   observed  radio  bursts  in  GIF  format,  are  available  to
   interested parties via the Ondrejov FTP server as well as via
   our WWW  page. The information about  observed events is also
   regularly sent  to Boulder, where  it appears in  the monthly
   "Solar  Geophysical  Data".

        Recent results:

 By analysing  data from a new  1-4 GHz radiospectrograph, two
 important  results were  obtained: firstly,  the existence of
 fine structures in radio  bursts at high frequencies strongly
 supports the plasma emission mechanism of these bursts, which
 essentially  changes the  common opinion  about their origin.
 Secondly, the  slowly and negatively  drifting high-frequency
 bursts,  indicating the  propagation of  flare shocks  in the
 transition  region layers  during the  flare impulsive phase,
 were observed for the first time. The July 9, 1996 flare with
 the  slowly drifting  type II-like  high-frequency burst  was
 analyzed simultaneously with the  hard X-ray emission. It has
 found a sequence of events corresponding to the chromospheric
 evaporation process.