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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 25, issue 11
Ann. Geophys., 25, 2351–2357, 2007
https://doi.org/10.5194/angeo-25-2351-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 25, 2351–2357, 2007
https://doi.org/10.5194/angeo-25-2351-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.

  29 Nov 2007

29 Nov 2007

Climatic trends in E-region critical frequency and virtual height above Tromsø (70° N, 10° E)

C. M. Hall1, A. Brekke2, and P. S. Cannon3 C. M. Hall et al.
  • 1Tromsø Geophysical Observatory, University of Tromsø, Norway
  • 2Dept. of Physics and Technology, University of Tromsø, Norway
  • 3Qinetiq, Malvern, UK

Abstract. 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° N, 19° 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 trend, a closer examination reveals a possible weak positive trend prior to ~1975 and a strong negative trend from ~1975 to present. These two metrics of essentially the same feature of the ionosphere do not exhibit the same signature since critical frequency is controlled by photochemistry within the E-layer while height is controlled by pressure level. We further find that the trend in critical frequency is a daylight/summer phenomenon, no significant trend being evident in the winter subset of the data. On the other hand, the trends in virtual height are independent of season/daylight.

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