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Sometimes we soar in atmospheric waves upwind of mountains. This is often refered to as 'pressure wave'. I have flown in 'pressure wave' off the southern North Island and upwind of the Southern Alps ahead of the Northwest Arch. I've heard few explanations of what causes this.
I think what we are flying in is an atmospheric undular bore. Here are some academic papers describing undular bores.
The take away information here is that undular bores propagate upstream when conditions for their formation are met. They happen in stable airmasses, similar to lee waves. The bore moves upstream of the trigger and can have a series of standing waves propogate down stream in the same way as a lee wave.
Because the undular bore sets up a standing wave similar to a lee wave we soar it the same way. Fly upwind of the cloud and go fast.
Briefing prepared by Phil Plane.
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