* This estimate is based on a TEC of 1018 electrons/m2, which is a high value of TEC encountered at low latitudes in daytime with high solar activity
** Ionospheric effects above 10 GHz are negligible.
(1) Values observed near the geomagnetic equator during the early night-time hours (local time) at equinox under conditions of high sunspot number.
Distribution of mid-latitude fade depths due to ionospheric scintillation (dB)
Percentage of time
Each of these contributions has its own characteristics as a function of frequency, geographic location and elevation angle. As a rule, at elevation angles above 10, only gaseous attenuation, rain and cloud attenuation and possibly scintillation will be significant, depending on propagation conditions. For non-GSO systems, the variation in elevation angle should be included in the calculations, as described in § 8.
(In certain climatic zones, snow and ice accumulations on the surfaces of antenna reflectors and feeds can produce prolonged periods with severe attenuation, which might dominate even the annual cumulative distribution of attenuation.)