When discussing propagation, important to appreciate concept of natural variability – behaviour of propagation will not be the same everywhere because of natural variability of propagation medium.
When the propagation medium is the neutral atmosphere, climate is all important
T, P, e govern refractive effects
precipitation and cloud cause attenuation and scattering
Such climatic parameters display
significant temporal variability – one year is unlikely to be like the next
significant regional variability – great differences between temperate and low latitudes.
Such differences are often reflected in statistical representation of propagation data, e.g. annual or worst month values for a particular region.
