Residual height variation of F2 Trend in hmF2 from 1950 to 2000 is -4.16 km per decade Practical Implications of Long Term Trends in the Critical Frequency and the Height of the F2 Layer above Tromsø (70°N, 19°E) Many HF propagation tools based on CCIR ionogram characteristics database CCIR database ('Oslo coefficients') measured at ionosondes worldwide in 1954 to 1958 and in 1964 Lesser problem for URSI '88 coefficients (1975-1979) ITU-R propagation tools reliant on old CCIR (Oslo) database will yield ground range errors ~ 100km per hop (c.
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