Published online by Cambridge University Press: 25 April 2016
On 1971 January 24 a 3B flare at 18° N., 49° W. was associated with the acceleration of protons to relativistic energies; it was one of the rare events recorded by ground-level neutron monitors. Excellent radio coverage was obtained with single-frequency radiometers in the range 1000-9400 MHz, and at Culgoora with the 8-8000 MHz spectrograph and the 80 MHz radioheliograph. At the Earth relativistic protons and electrons arrived very promptly from the flare, whose site was near the foot of the nominal interplanetary field line which connects to the Earth.