Observations of x-rays produced by strong electric fields in thunderstorms.

Abstract

A balloon-borne x-ray spectrometer was developed to fly on free balloons into thunderstorms in order to test hypotheses that strong electric-fields could accelerate cosmic-ray secondary electrons and produce bremsstrahlung x-rays. Five flights were made over a period of two years into the stratiform regions of mesoscale convective systems. The x-ray spectrometer flew with an electric-field meter and a meteorological radiosonde. In four instances, increases in x-ray intensity were observed during these flights. All were observed in conjunction with strong electric fields. Both negative and positive polarities (referenced to the vertical field) produced x-rays. These events lasted on the order of 10's of seconds. In three of the cases, the increased x-ray intensity returned to near background levels when lightning flashes reduced the local electric field. These two observations appear to indicate that the increases in x-ray intensity observed are associated with the strong electric field present in thunderstorms. However, the time resolution of these observations does not allow any conclusions to be made about the production of x-rays by lightning.