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

• Main Authors: Hall, C. M., Brekke, A., Cannon, P. S.
• Other Authors: Tromsø Geophysical Observatory (TGO), The Arctic University of Norway Tromsø, Norway (UiT), Dept. of Physics and Technology, Qinetiq, QinetiQ
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2007
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Tromsø
• Online Access: https://hal.science/hal-00318408; https://hal.science/hal-00318408/document; https://hal.science/hal-00318408/file/angeo-25-2351-2007.pdf

International audience 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.