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

C. M. Hall, A. Brekke, P. S. Cannon
2007 Annales Geophysicae  
<p><strong>Abstract.</strong> We have examined the long time series of observations of E-region virtual height (1948&amp;ndash;2006) and critical frequency (1935-2006) hitherto made by the Tromsø ionosonde at 70&amp;deg; N, 19&amp;deg; 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
more » ... als 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.</p>
doi:10.5194/angeo-25-2351-2007 fatcat:iwef4mspgjcg3jzhr3eidwqlyi