STRATOSPHERIC EVIDENCE OF RELATIVISTIC ELECTRON-PRECIPITATION

The hypothesis that relativistic electron precipitation is modifying the high-latitude southern hemisphere ozone distribution is tested by examining simultaneous electron density data as measured with a ground-based partial reflections sounder and ozone mixing ratios data in the 40 to 50 km region obtained from the satellite-borne SBUV instrument. Electrons with energies in the 1 to 3 MeV range are stopped in this altitude region creating ionization, which can be observed as an enhancement in electron density. The resulting nitric oxide should destroy ozone. Ionization enhancement events at 50 km are observed at least 20% of the time by the partial reflections sounder at Scott Base, Antarctica. On January 15, 1984, the electron density at 50 km was 800 cm-3 (von Biel, 1989, 1991). Since the ion-pair production function requited to produce this amount of ionization was 300 cm-3 s-1 and acted over a day, the corresponding reduction in ozone is expected to be more than 40%. Examination of ozone mixing ratio data from the SBUV instrument on Nimbus 7 shows no corresponding ozone decrease in the January 15 to 17, 1984 period. Possible explanations for this failure to observe an ozone decrease include another mechanism for producing the electron density enhancement or relativistic electron precipitation in a very limited area. The relativistic electron fluxes in the 1 to 3 MeV range required to produce the partial reflection electron density profiles are the same as observed by geosynchronously orbiting spacecraft. In addition to finding no ozone decrease there are two difficulties with assuming that the partial reflection electron densities are caused by the electrons observed in orbit. The L value of die field lines containing the electrons are L = 3 to 8, while Scott Base is located at L = 33. The electron density profiles observed at Scott Base are not enhanced above 70 km indicating a lack of precipitating electron with energies less than 1 MeV. It is suggested that a more complete study be undertaken, including many events, corresponding in-orbit electron flux changes and ground-based riometer data in addition to ozone and partial reflection data.