G. Stiller

Abstract During a polarity transition of the Earth magnetic field, the structure and strength of the terrestrial magnetic field change significantly from their present values. This will change the global pattern of charged particle precipitation into the atmosphere. Thus, particle precipitation is possible into regions that are at the moment effectively shielded by the Earth magnetic field. Large increases of extraterrestrial charged particle influxes occur during solar particle events (SPEs) following coronal mass ejections. During those events, proton and electron fluxes into the Earth system increase over several orders of magnitude, ionising the middle atmosphere. Fast ion chemistry reactions form HOx and NOx radicals, which in turn destroy ozone in the stratosphere and mesosphere. We investigate how the ozone loss due to solar energetic particle events changes with a changing magnetic field, using data from different sources, including MHD simulations of the magnetic field, a Monte-Carlo simulation of the atmospheric ionisation, and a 2 dimensional global chemistry, photolysis and transport model of the middle atmosphere. We find that ozone losses resulting from large energetic particle events increase significantly for a decreasing dipole field, with resultant losses similar to those observed in the Antarctic ozone hole of the 1990s. However, both the global distribution and the temporal behavior of ozone losses are determined not only by the structure of the magnetic field, but also by the global circulation of the middle atmosphere. 1