Direct measurement of particles producing visible auroras

The nature of the particles producing two visible auroras at Fort Churchill, Canada, has been determined with the aid of rocket-borne detectors. Magnetic fields were used to separate the proton and electron components of the particle flux. It was found in each case that a major fraction of the auroral light was produced by electrons with energies of less than 10 kev. IGY rocket II6.26F was fired into a quiescent auroral glow of about intensity I. The integral number energy spectrum of protons incident upon the atmosphere during this flight was measured to be approximately 2.5×106 exp (-E/30) protons/sec cm2 ster over the range 80 to 250 kev, where E is the proton energy in kev. The observed altitude dependence of the electron energy flux could have been produced by an integral number energy spectrum equal to 2.5×109 exp (-E/5) electrons/sec cm2 ster over the range 3 to 30 kev. IGY rocket II6.27F was fired into a bright active auroral arc. At least 75 per cent of the light in this aurora was produced by nearly monoenergetic electrons with about 6-kev energy. The electron flux varied rapidly with time; peak values were about 5×1010 electrons/sec cm2 ster. The presence of monoenergetic electrons strongly suggests an electrostatic acceleration mechanism.