35th Scientific Assembly of COSPAR, Paris, France, 18-25 July 2004

Modelling the local effect of energetic auroral electron precipitation on nitric oxide levels in the high-latitude ionosphere

P. T. Verronen1, E. Turunen2, Th. Ulich2, R. J. Steiner3

1Finnish Meteorological Institute, Geophysical Research, Helsinki, Finland
2Sodankylä Geophysical Observatory, Sodankylä, Finland
3International Space University, Illkirch, France


Results from the Sodankylä Ion Chemistry Model are used to show how nitric oxide is produced and sustained in the high-altitude ionosphere in response to energetic auroral electron precipitation. Taking as a starting point altitude profiles of neutral and ionised atmospheric constituents typical for equinox nighttime conditions, and electron spectra with energies and fluxes characteristic of energetic and discrete aurora observed with incoherent scatter radar and ground-based optical imagers, we find order-ofmagnitude local increases in nitric oxide above background levels. The enhancements persist into the dayside, and only decrease significantly once photo-ionisation and dissociation takes over from chemical loss. The persistence of nitric oxide enhanced as the result of auroral activity leads also to elevated electron densities long after the activity has subsided, with implications for radio propagation.