Solar Microwave Burst from Behind-the-Limb Proton Flare

Abstract

THE solar microwave burst of March 30, 1969, was unusual in two respects. First, the values of the peak flux densities included in Table 1 rank it as the largest ever recorded in the cm range^1,2. Second, the burst can be associated with a behind-the-limb proton flare. A similar proton flare on November 20, 1960, was recorded with a modest cm burst³. At the time of the March 30, 1969, solar radio burst, Manila Observatory recorded an eruptive prominence on the west limb (EPL). The EPL came from McMath region 9994, the location of which was projected to be 18° N and 15° behind the west limb. The tops of postflare loops were visible 45 minutes after the start of the microwave burst (R. A. Miller, private communication). Preliminary data from Pioneer satellites indicated the arrival of solar protons about an hour after the radio event⁴. At 2119 UT or 18.5 h after the radio event, Manila Observatory recorded a sudden commencement (SSC) of 22 gammas. The average delay time for SSC is about 20 h.