Nighttime auroral energy deposition in the middle atmosphere

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Abstract
From 1976 through 1982, eight distinct nighttime auroral events have been probed with rocket payloads in a series of high latitude studies at Poker Flat Research Range, Alaska, and Andøya, Norway. The instrument packages have contained X ray and energetic electron detectors, permitting a measure of these energy forms and their absorption in the middle atmosphere. Although the specifics of each event show a wide range of values for energy flux and spectral hardness, certain general characteristics persist in all cases. The primary energy sources for the middle atmosphere under the active conditions examined here are mainly relativistic electrons and bremsstrahlung X rays. Each of these sources is found to dominate ionization in a separate altitude region, with the electrons usually controlling ionization in the upper heights above 55–60 km and the X rays below to about 40 km, where cosmic rays take over. The relativistic electron ionizing radiation source has not usually been considered in modeling studies for the ion chemistry of the lower mesosphere (55–70 km), yet this radiation is capable of increasing ion concentration and electrical conductivity in excess of a factor of 10. Moreover, the persistence of relativistic electrons as an important source in all events studied here strongly suggests that this deficiency be corrected.

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