One Solar Cycle and a Half of EISCAT Operations:
Did the Atmosphere Change During This Time?

Thomas Ulich, Arto Karinen, and Esa Turunen

Sodankylä 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 work we show more than 10 years of various data measured by the EISCAT incoherent scatter radars. We emphazise on the trand of the F2-layer peak height deduced from EISCAT data and on the evolution of the ion temperature at various altitudes starting slightly above the mesopause region. Additionally we will give an overview of other measured ionspheric parameter such as electron concentration.