Decameter storm radiation,II

The physical properties of six decametric storms, observed at Clark Lake Radio Observatory are studied. The height of the storm continuum sources was determined from the rotation rate. Assuming that the radiation originates at the plasma frequency we computed the gradient of electron density for the regions where the storms originate. The mean angular size of the decametric continuum sources is large; it increases with decreasing frequency. The storm continuum is found to be strongly directive toward the disk center. The east-west asymmetry, well observed at meter wavelengths is also observed at decameter wavelengths. The occurrence of two distinct classes of type III bursts in storms is discussed: ‘off-fringe’ and ‘onfringe’ type Ill's. The ‘off-fringe’ Ill's are found to be displaced in position from the continuum source ; on the other hand, the ‘on-fringe’ ones coincide in position with the continuum. These two kinds of bursts differ in other properties as well. A model of the storm region is proposed. The continuum radiation and the ‘on-fringe’ type III's are believed to originate above closed magnetic loops, in regions of diverging field lines; the ‘offfringe’ type Ill's are thought to be excited by energetic electron streams, having access to open magnetic field lines at the base of the loops.