Effects of Solar Cycle Variability seen in long-term
EISCAT Radar Observations of the Lower Ionosphere
Thomas Ulich, Arto Karinen, and Esa Turunen
Geophysical Observatory, FIN-99600 Sodankylä, Finland
Abstract
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 observations around the mesopause. We discuss their behaviour
with respect to the trends recently observed in cosmic radio noise
absorption data of the Finnish Riometer Chain taking into account solar
activity variations.