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About weather
The troposhpere is the lowest part of our Earth's atmosphere and varies in height between around 7 and 18 kilometers (about 4.3 to 11 miles) above the surface of the Earth. It is at its shortest at the poles and heighest around the Equator and almost all of our weather exists in the troposphere.
Whilst much of the HF radio wave propagation occurs in the ionosphere, weather conditions in the troposhphere can also have an affect on how radio waves are propagated.
It is a given that radio waves travel in straight lines and we know that HF radio waves can be refracted by the E and F layers of the Ionosphere back to earth, increasing the distance that our signal can be received over.
Two of the ways in which the troposphere can effect radio waves are troposcatter and tropospheric ducting.
Troposcatter
Troposcatter can affect VHF signals and above, increasing the range of the signal from around 30 kilometers to 100 - 700 kilometers. It is caused by the radio waves being reflected off small objects in the troposphere - usually droplets of water.
Because the radio waves are being refracted in all directions off these objects, the amount of signal received is very weak.
Tropospheric ducting
Tropospheric ducting can occur at VHF and above when denser cold air gets trapped between two layers of less dense warm air. The radio waves bounce off the layers of warm air and our signal range gets extended until the density difference reduces enough to let our signal bounce back to earth.
Ducting can be predicted by looking at pressure charts - ducting can occur along warm and cold fronts.
