www.ann-geophys.net/25/2351/2007/ © European Geosciences Union 2007
Abstract. We have examined the long time series of observa-tions of E-region virtual height (1948–2006) and critical fre-quency (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...
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| Other Authors: | |
| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1031.7609 http://munin.uit.no/bitstream/handle/10037/2385/article.pdf%3Bjsessionid%3DB327341F321078AD57227B276E697584?sequence%3D1 |
| Summary: | Abstract. We have examined the long time series of observa-tions of E-region virtual height (1948–2006) and critical fre-quency (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 examina-tion 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 inde-pendent of season/daylight. |
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