Effects of precipitating auroral particles on the neutral chemistry of the lower thermosphere

Thomas Ulich1, Esa Turunen2, Pekka Verronen3, Tuomo Nygrén1, and Francis Sedgemore-Schulthess4

1Dept. of Physical Sciences, University of Oulu, Oulu, Finland
2Sodankylä Geophysical Observatory, Sodankylä, Finland
3Finnish Meteorological Institute, Geophysical Research, Helsinki, Finland
4Danish Space Research Institute, Copenhagen, Denmark


On 17th December 1990, the UHF radar of the EISCAT Scientific Association in Tromsø, Norway, was running the Finnish PULSE experiment, which has a very temporal and spatial resolution. During the experiment, between 0245 UT and 0330 UT, a series of precipitation bursts of auroral electrons was observed by the radar. A near-by photometer, whose field of view coincided with that of the radar, observed pulsating aurora. In the present paper, we study the event by means of the revised Sodankylä Ion Chemistry (SIC) model. Recently, the model was upgraded in order to to quantify the effects of particle precipitation on neutral mesospheric chemical composition. Ionization caused by precipitating particles leads to enhanced production of some minor neutral constituents (such as NO) through reaction chains in which ionic reactions play an important role. Nitric oxides, in turn, are responsible for the destruction of mesospheric ozone. We model the temporal evolution of selected neutral and ionic species during the event between 90 and 100 km altitude by means of the time-dependent SIC model. Furthermore, we will study the temporal and spatial behaviour of the effective recombination coefficient.