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

• Main Authors: Cannon, P. S., Hall, Chris, Brekke, Asgeir
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications on behalf of the European Geosciences Union 2007
• Subjects: VDP::Mathematics and natural science: 400::Physics: 430::Space and plasma physics: 437; Ionosphere; Auroral ionosphere; Ionosphereatmosphere interactions; Tromsø
• Online Access: https://hdl.handle.net/10037/2385

This is the publishers version/PDF (published in Annales Geophysicae, an open access journal of the European Geosciences Union) 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 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.