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.
Actinoform cloud
The effect of actinoform clouds on weather systems and climate patterns is still being analyzed. Meteorology professor Bjorn Stevens of the University of California, Los Angeles theorizes that they, in conjunction with open-cell stratocumulus clouds, are associated with drizzle formation. Observations from field studies in both the Northeast and Southeast Pacific seem to indicate that when marine stratus and stratocumulus clouds exist alone, in the absence of these open cells, the cloud formations are associated with light, or no, drizzle.