ATMOSPHERIC X-RAYS IN THE SOUTHERN-HEMISPHERE

Atmospheric X-rays in the energy range from 30 to 150 keV were measure d in the Southern hemisphere extending from 53 to 81 degrees magnetic latitude during two long-duration balloon flights. The measurements we re obtained during the Extended Life Balloon Borne Observatories (ELBB O) experiment. The experiment consisted of five superpressure balloon flights launched from Dunedin, New Zealand, in November and December 1 992. The ELBBO X-ray data can be considered the longest continuous dat a set ever obtained in the Southern hemisphere, and extend over 30 deg rees of magnetic latitude previously unmeasured. The X-ray measurement s are compared to similar data obtained in the past by several groups in the Southern and Northern hemispheres, as well as with available mo del results. Most ELBBO results confirm earlier findings about the flu x and spectra of atmospheric X-rays and are in general agreement with model results for higher energies. However, they indicate that the X-r ay flux in the Southern hemisphere is almost constant from high latitu des up to 30 magnetic degrees, in contrast to the model results that i ndicate a drop off around 50 magnetic degrees. Whether such discrepanc y should be attributed to the different energies involved or to the pr esence of the South Atlantic magnetic anomaly is a point that remains to be investigated. (C) 1997 Elsevier Science Ltd.