The Impact of Energetic Particle Precipitation on the Earths Atmosphere

Energetic particle precipitation (EPP) represents an important Sun-Earth coupling mechanism with important implications on polar stratospheric ozone chemistry. Solar protons generated during solar storms cause sporadically in situ production of stratospheric NO<SUB> x </SUB> and HO<SUB> x </SUB> radicals involved in catalytic ozone destruction. Further, NO produced continuously in the mesosphere and lower thermosphere by medium energy electron precipitation (EEP) descends to the stratosphere during the polar winter, where it represents an additional, though variable source of NO<SUB> x </SUB>. The capability of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) to measure all important NO<SUB> y </SUB> species, as well as ClO and HOCl with global coverage including the polar night regions make it an ideal instrument for studying EPP effects on stratospheric chemistry. We present a quantitative assessment of EPP-induced composition changes as observed by MIPAS during 2002-2004, including the unusually strong solar proton event in October/November 2003. The impact of EPP on the stratospheric ozone budget has been studied with chemical models. The stratospheric ozone loss in the polar regions reached 18DU and lasted over months to years.