38th Annual Conference of the Finnish Physical Society, Oulu, Finland, 18-20 March 2004

High-altitude transient luminous events (TLEs) as a mechanism for solar-terrestrial coupling

C.-F. Enell1, E. Turunen1, P. T. Verronen2, Th. Ulich1

1University of Oulu, Sodankylä Geophysical Observatory, Sodankylä, Finland
2Geophysical Research Division, Finnish Meteorological Institute, Helsinki


Observations of luminous phenomena above thunderstorms have been reported, e.g. by airline pilots, for a very long time. However, only in the 1990s did these phenomena attract scientific interest, to a large extent due to the fact that video cameras suitable for capturing these rapid light emissions had become available. An entire field of research has emerged since then and made clear that the middle atmosphere is not a passive region. A number of phenomena, named e.g. red sprites, blue jets and elves, appear in relation to thunderstorms. Collectively these are named transient luminous events (TLEs). It is thus natural that the question "Are sprites and blue jets only pretty and beautiful like rainbows, or do they significantly impact the atmosphere?" arises. The European research training network CAL (Coupling of Atmospheric Layers), involving scientists at 11 institutes around Europe, has been founded with this particular question in mind. The aeronomical research group of Sodankylä Geophysical Observatory (SGO) is one of the participants.

The specific task of SGO within CAL is to estimate chemical modifications to the atmosphere due to high-altitude discharges. The basis of this work is the 1–dimensional coupled ion and neutral chemistry model SIC (Sodankylä Ion Chemistry). SIC was developed for interpretation of ionospheric D–region measurements and has recently been extended to allow modelling of energetic particle precipitation events by including negative ion reactions.

SIC will be used as a basis for modelling the possible chemical importance of TLE events. However, the application is not entirely straightforward. Excited states of neutral molecules such as N2 appear and must be treated as separate components. Furthermore, neutral, ion and electron temperatures must be separated. Thus a revision of the code is in progress.

TLE-induced changes in the concentrations of components significantly affecting the chemical or radiative balance of the atmosphere, such as ozone, OH and NO, will be estimated using the modified model. This presentation will discuss preliminary results from this work in the context of the above question, i.e.: Could chemical changes caused by TLEs possibly be a link between the upper and lower parts of the atmosphere and thus a mechanism coupling solar activity to climate-related parameters?