Computed contributions to odd nitrogen concentrations in the Earth's polar middle atmosphere by energetic charged particles

A two-dimensional photochemical transport model which has inputs that characterize the odd nitrogen production associated with galactic cosmic rays, solar particle events (SPEs), and lower thermospheric contributions (auroral electrons and solar EUV and soft X-rays) is used to compute odd nitrogen concentrations in the polar middle atmosphere from 1 January 1970 to 31 December 1994. We are able to separate out of the total odd nitrogen budget the contributions of the energetic charged particles according to type. The SPE contributions to annual average odd nitrogen concentrations in the polar stratosphere (latitudes > 50 degrees) are computed to be significant (>10%) only for the larger events of August 1972 and October 1989. The SPE contributions to odd nitrogen concentrations in the polar middle atmosphere are found to be asymmetric with respect to hemispheres. The computed SPE contributions to odd nitrogen concentrations at 30 km are significant more often over the South Pole than the North Pole. The thermospheric contributions to odd nitrogen concentrations in the polar middle atmosphere are asymmetric with respect to hemispheres. A stronger thermospheric influence in the stratosphere is computed over the South Pole than the North Pole, An attempt has been made to compare the modeled odd nitrogen of the polar middle atmosphere to an ultra-high resolution polar ice cap nitrate sequence to examine the hypothesis that the nitrate sequences exhibit a signal associated with energetic particles. Variations of odd nitrogen production and modeled concentrations associated with energetic particles themselves cannot explain all of the huge variations observed in the fine structure present in nitrate data from the polar ice cap nitrates, but may be able to explain Darts of some of them, (C) 2000 Elsevier Science Ltd. All rights reserved.