Martin Audio W8L Longbow Application Manual page 82

Conversely, a wind gradient associated with wind blowing from behind a loudspeaker
system will "speed up" its vertical wavefront differentially. The vertical wavefront will
be speeded up less near the ground and its sound path will veer downwards.
Local winds
Air absorbs very little heat from the sun's rays. It is indirectly heated by contact with
warm surfaces. It also relies on contact with cooling surfaces to loose heat.
An anabatic wind can be set up by air rising up a slope warmed by the morning sun.
At night, cool air may flow down hill to form a katabatic wind. To maintain coverage,
loudspeaker cluster tilts may need to be readjusted between morning orchestral
rehearsals for a major outdoor event and the actual show.
Gusts and squalls
On a fair day when the ground is warm and clouds are forming and being moved by a
very light breeze, local winds may vary in direction and strength as illustrated below.
All material © 2007. Martin Audio Ltd. Subject to change without notice.