Global Change in the North Seminar, University of Oulu, Oulu, Finland, 16 November 2005

Global Change In The Upper Atmosphere

E. Turunen¹, Th. Ulich¹, C.-F. Enell¹, A. Kero¹, P. T. Verronen², A. Seppälä²

¹Sodankylä Geophysical Observatory, Sodankylä, Finland,
²Finnish Meteorological Institute, Helsinki, Finland.

Abstract

The question of what is the relative importance of the various forcing factors on global climate is an essential problem in understanding the global change. Another important question is how much of the observed global change is natural variability and how much is anthropogenic. According to the IPCC (IPCC 2001) the Sun was probably responsible for a large part of climate change until the early 20th century. However, the IPCC also states that the current level scientific understanding of forcing on climate due to solar and aerosol effects is "very low" and that even stratospheric ozone effects are only understood at a "medium" level. In our project "Long Term Trends and Monitoring the Polar Atmosphere", funded by the Thule Institute at University of Oulu, we are studying important parts of these gaps in our understanding, which are relevant especially in the polar region and affect the Arctic and Antarctic environment. These include the effects of forcing on the middle atmosphere, from both above, e.g. due to extra-terrestrial phenomena like solar and cosmic high-energy particle precipitation and the varying UV and X-ray radiation, as well as from below, in effects due to changes of the chemical composition of the atmosphere.

The well-known phenomenon of global warming due to excess emission of greenhouse gases in troposphere has it's less-known counterpart in the upper atmosphere, the predicted upper atmospheric cooling. We have studied the long-term behaviour of the altitude of the ionospheric F2-layer peak on a global scale. It has been suggested the altitude of this layer will decrease as a consequence of doubled greenhouse gases. Even though clear trends were observed, the results were inconclusive globally and research into the reasons for the changes continues. Recently we began a theoretical study of whether or not lowcost radio receivers monitoring the cosmic background noise reaching the Earth's surface could be used to detect changes in chemical composition of the middle atmosphere. In addition to long-term data sets of atmospheric parameters, and especially those deduced by radio methods, our main research tool is a detailed 1-dimensional computer model of the chemistry of the lower ionosphere, developed by ourselves. In its current version, it is a coupled ion-neutral chemical model containing more than 100 chemical constituents and well over 400 chemical reactions extending from 20 to 150 km altitude. The model is well established, referred to in the scientific literature and used in about 20 peer-reviewed scientific publications. The model has been succesfully used to infer the in-situ production of odd nitrogen in the upper atmopshere due high energy particle precipitation and the subsequent local destruction of ozone in the mesosphere and stratosphere. Comparisons with ENVISAT satellite data and VLF radio wave propagation data show good consistency with our model results.