NRO Heliograph Tohban's Report for Week 21 (18 May 1998 - 24 May 1998)

                                    Tohbans : K. Hori and H. Nakajima 

1. Solar Activity

   Solar activity is low. The GOES X-ray background level keeps low-B.
   We observed one small flare, one plasmoid eruption, and one prominence 
   eruption.
   AR NOAA 8222, which is moving over the north-western limb,  
   shows a bright arcade structure in soft X-ray. 
   There is a large dark filament in the southern hemisphere. 
   At the weekend, a small flare occurred at 22:45UT (May 23).
   Its peak correlation index is only 22.    

2.  Remarkable Events found by NRH

   2.1 Plasmoid eruption on May 19 (00:26 -- 01:46UT)
        
      A plasmoid eruption occurred at the south-eastern limb,
      however, no associated flare was observed.
 
   2.2 Prominence eruption on May 21 (03:30 -- 05:30UT)

      Because this eruption was detected with both 17 and 34 GHz channels,
      it is considered to be an optical thick plasma.
      Its brightness temperature is at most 10^4 K.
      The projected expansion speed is about 10 km/s, which is almost
      same as a sound speed of 10^4 K plasma.