GEOPHYSICAL RESEARCH LETTERS, VOL. 24, NO. 9, PAGES 1103-1106, MAY 1,
1997
Evidence for long-term cooling of the upper atmosphere in
ionosonde data
Thomas Ulich and Esa Turunen
Geophysical Observatory, FIN-99600 Sodankylä, Finland
Abstract
While several model estimates predict cooling of the upper atmosphere
as a result of increasing concentrations of greenhouse gases, direct
observational evidence of such a trend is scarce and partly
susceptible, because the relevant data series do not cover sufficiently long
time periods. We study the long-term data set from the ionosonde
station at Sodankylä (67.4° N, 26.7° E), which has been
operated during almost 4 solar cycles. We find a close to linear
decrease in the altitude of the F2 layer peak during the last 39
years, when the effect of solar cycle variations is removed from the
data. This local trend is qualitatively consistent with the model
predictions of a cooling of the lower thermosphere.
© 1997 by the American Geophysical Union. Further electronic
publication not allowed.
On-line version (might require subscription):
here.