Broadcast range
The local terrain can also play a major role in limiting broadcast range. Mountain ranges block FM broadcasts, AM broadcasts, and TV broadcasts, and other signals in the VHF and especially UHF ranges, respectively. This terrain shielding occurs when the line of sight is blocked by something through which the radio waves cannot pass, particularly stone. At times this may be moot due to weather, such as when the tall cumulonimbus clouds of a squall line of thunderstorms reflect the signal over the top, like an extremely tall radio tower. Conversely, heavy rain may attenuate the range of even local stations. ATSC digital television is affected by wind and trees (even if not surrounding the transmitter or receiver locations), apparently related to its use of 8VSB modulation instead of COFDM.
Coronal cloud
Specific reasons as to why these clouds are dangerous to electronic and communication equipment include the overloading of large power transformers, which can cause lengthy power outages over wide geographical areas. Long, metallic structures like oil and gas pipes, water pipes, and communications antennae can also carry excessive electric current from the air, causing them to corrode faster than normal. This can possibly lead to early, unexpected ruptures. These signals also create anomalies in the ionosphere, disrupting wireless technologies such as GPS, cellular phones, television, and radio.