Some Studies on the Occurrence of Type IV Solar Bursts of Continuum Radiation.

It is shown that type IV emission in the range of frequencies 25-580 Mc/s occurs in two distinct phases: (a) The first phase, usually observed at frequencies higher than about 250 Mc/s, appears to be an extension of the associated centimeter-wave burst which is also a broad-band continuum emission. This emission occurs earlier than the associated type II burst and can even occur independent of any type II burst. The source of this emission is situated low in the chromosphere, has no significant movement, and has a small angular size, usually less than 4'. The observed properties of this phase of continuum emission are consistent with the suggestion that it is caused low in the chromosphere by synchrotron radiation of electrons generated during the flare. (b) The second phase, usually observed at frequencies lower than about 250 Mc/s, is closely associated with a type II burst preceding it. The source of this continuum emission is situated high in the corona and moves with velocities of more than 1000 km/sec. It has a large angular size, usually 10' or larger. This second phase of type IV emission was previously explained as due to synchrotron radiation of electrons higher in the corona, when a cloud of gas with a shock front (which excites the type II burst) moving at high velocities carries a frozen-in magnetic field to the appropriate heights in the corona.