Cannon, P. S.; Hall, Chris; Brekke, Asgeir (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-11-29)
We have examined the long time series of observations
of E-region virtual height (1948–2006) and critical frequency
(1935-2006) hitherto made by the Tromsø ionosonde
at 70 degrees N, 19 degrees E. Combining a simplistic trend analysis with
a rigorous treatment of errors we identify a negative trend
in critical frequency. While a similar analysis of the virtual
height h'E also suggests a negative ...