One Solar Cycle and a Half of EISCAT Observations

Thomas Ulich, Arto Karinen, and Esa Turunen

Geophysical Observatory, FIN-99600 Sodankylä, Finland

In 1989 Roble and Dickinson estimated using their thermosphere-ionosphere general circulation model, that doubling of carbon dioxide and methane concentrations at mesospheric altitudes would result in a cooling of the mesosphere and thermosphere by 10 K and 50 K, respectively. Since then many authors have studied trends in related long-term data sets. Trends hinting on a possible greenhouse cooling have been found in, e.g., temperature data from lidar observations, in records of noctilucent cloud occurences, in the record of F2-layer peak heights measured by ionosondes, and in cosmic radio noise absorption data. Still controversial is the question of what are the causes for the observed trends, whether they are of solar or anthropogenic origin.

In this paper we analyse data of more than 15 years of EISCAT incoherent scatter radar observations above Northern Scandinavia with special emphasis on the regular mesospheric observations. We discuss their behaviour with respect to the trends recently observed in the ionosphere taking into account solar activity variations.