Observation of Bremsstrahlung from solar electrons in the Earth's atmosphere

Energetic photons (23–142 keV) were detected by a balloon-borne scintillator at 74.8° invariant latitude during the solar particle event originating in a flare observed at 0507 UT on 14 August 1982. An abrupt onset of excess radiation was recorded at 0511 UT both in the Earth's atmosphere by the balloon instrumentation at 34 km altitude and also by ground-based riometers located in the central polar caps (>75° inv. lat.). Solar protons did not appear in the inner magnetosphere until after 06 UT. Comparison of the balloon measurements with Bremsstrahlung calculations for solar electron impact has confirmed the solitary role of solar electrons during the early part of the event. Later on, when solar protons were also present in the magnetosphere, energetic photons arising from nuclear reactions of protons with atmospheric nuclei also contributed. Although the rapid access of energetic solar electrons to the Earth's magnetosphere has been recognized for some time, this is the first reported observation of the Bremmstrahlung radiation produced by solar electrons striking the terrestrial atmosphere.