This work was supported by the Major Project 19791090, funded by the National Natural Science Foundation of China (NSFC). The authors are indebted to the Huairou staff for obtaining good observations. We are grateful to all members of YOHKOH team for providing the wonderful Yohkoh data. We also would like to thank the SOHO MDI and EIT teams for observing the data. SOHO is a project of international cooperation between ESA and NASA.
© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001