Climatic trends in E-region critical frequency and virtual height above Tromsø (70° N, 10° E)
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 fr...
| Published in: | Annales Geophysicae |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Copernicus Publications
2007
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/angeo-25-2351-2007 https://doaj.org/article/ea672498e1d9495591c2164e9f7e1c2a |
| Summary: | 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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