Solar burst with millimetre-wave emission at high frequency only

The first high sensitivity and high time-resolution observations of a solar burst taken simultaneously at 90 GHz and at 30 GHz are presented. These identify a unique impulsive burst on May 21, 1984 with fast pulsed emission that was considerably more intense at 90 GHz than at lower frequencies. Hard X-ray time structures at energies above 25 keV were almost identical to the 90 GHz structures to better than 1 s. The structure of the onset of the major 90 GHz burst coincided with the hard X-ray structure to within 128 ms. All 90 GHz major time structures consisted of trains of multiple subsecond pulses with rise times as short as 0.03 s and amplitudes that were large compared with the mean flux. When detectable, the 30 GHz subsecond pulses had smaller relative amplitude and were in phase with the corresponding 90 GHz pulses.