Bipolar magnetic field regions and solar microwave bursts

A solar microwave burst with nonthermal electrons trapped in a mirror region in a bipolar sunspot group is modeled. The electrons are trapped in an arc and oscillate between two mirror points with a period of three to five seconds. This arc resembles the X-ray loop structure connecting the sunspots of an active region. The model was applied to five microwave bursts to determine the energies of the electrons and the value of the mirror point field. The bursts selected for study met these criteria: (1) the burst had to occur within 300 of central meridian; (2) the burst had to have been observed at a number of frequencies; (3) the burst had to be free of other events; and (4) accurate records of the burst had to be available. The standard model had electrons trapped in an arc structure with a mirror point magnetic field of 1200 gauss. This produced the typical inverted U type spectra for mono-energetic electrons in the range of 50 to 1600 KeV. Above 1.6 MeV, the theoretical spectra is a monotonic increasing function of frequency. By varying the parameters of the standard model, changes in the spectra could be made. Most of the emission originates very near the sunspots for frequencies above 2695 Mhz. The apparent size of the emitting volume increases as one goes from higher to lower frequencies. The region of the microwave burst is associated with the x-ray loops linking bipolar regions on the solar surface. When applied to five bursts, it was found that the electron energies ranged from 160 to 500 KeV. The height of formation ranged from 8600 to 36,000 kilometers. The mirror point field strengths ranged from 1200 to 1800 gauss