X-Rays from Visible Aurorae at Minneapolis

Abstract

During three auroral storms on June 30-July 1, September 12-13, and September 22-23, 1957, we have observed bursts of x-rays during balloon flights at 10 g/${\mathrm{cm}}^2$ depth in the atmosphere over Minneapolis. The x-rays have an energy of from 50 to 100 kev, an integrated intensity from 0.03 to 0.14 mr, and a maximum measured peak intensity of 0.4 mr/hr. One burst was observed at 47 g/${\mathrm{cm}}^2$ atmospheric depth (70 000 ft), and we estimate that above the atmosphere this may have corresponded to 500 mr/hr for at least 10 minutes. The current of high-energy electrons is at least 3×${10}^6$ electrons/${\mathrm{cm}}^2$ sec, and probably an order of magnitude greater, and is therefore approximately equal to auroral proton fluxes, and to the fluxes observed in soft radiation at rocket heights. The x-ray bursts usually appear when a homogeneous auroral arc develops a strong ray structure, or when rays increase in intensity. The inferred energy and high velocity of the primary auroral electrons necessitates an acceleration mechanism near the earth to avoid contradictions with the commonly accepted sun-earth transit times for corpuscular beams.