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...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2007-11-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/25/2351/2007/angeo-25-2351-2007.pdf |
| 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 <i>h'E</i> 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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| ISSN: | 0992-7689 1432-0576 |