Solar disturbances and mesospheric odd nitrogen

The odd nitrogen (NOsub(x)) abundance of the high latitude mesosphere exhibits a large variability in response to energetic particle precipitation. Model calculations for a very large particle event predict increases in the NOsub(x) mixing ratio that can exceed a factor of ten over time periods of the order of one week in the summer hemisphere. A more typical sized event can still lead to an enhancement of a factor of three in summer. Relative changes in the winter hemisphere are less dramatic due to a larger ambient NOsub(x) mixing ratio predicted here. However, a factor of two increase in NOsub(x) is possible during a very large event. Owing to the large variability, it is difficult to define a physically meaningful mean state profile in the high latitude mesosphere. Rather, the NOsub(x) abundance likely displays an erratic behavior which is correlated with the level of solar activity. (author)