Some Characteristics of the Slowly Varying Sources Producing Proton Events During Cycle 21

Twelve slowly varying sources producing proton events observed at Yunnan Observatory from 1980 to 1982 are analysed.According to the observations made with three radio telescopes with the working frequencies of 9375 MHz,3653 MHz and 2902 MHz,respectively,some characteristics of the sources are given.The effect of the changes in the solar radiation flux of slowly varying sources on the production of proton events is preliminarily discussed.