"Chris W" wrote in message
news:gj%ae.640$zv1.481@lakeread07...
Is there an altitude above the ridge line at which the "mountain wave"
effect isn't significant?

Probably would be pretty negligible at 23,000 miles. For example.

Seriously though, yes...you can sometimes fly high enough to avoid the wave.
But that depends on the height of the terrain, the strength of the wind, and
of course the type of aircraft. There is no reliable way to know ahead of
time how high you need to fly to avoid it.

That said, there's being high enough to get all the way out of any
noticeable effects of the wave, and then there's being high enough to avoid
the wave forcing you too close to the terrain. The former may be
impossible, depending on the situation. The latter is usually possible. I
have rarely experienced altitude excursions of greater than 2000-3000 feet
as a result of mountain wave, so that's a pretty reliable margin for
crossing ridges.

Of course, there is the question of whether mountain wave can actually push
you into the ground. I've never actually heard of that happening, and for
it to do so, the part of the air mass you're flying in would have to hit the
ground as well. That happens in microbursts, or under virga, for example,
but you'd have to be pretty darn close to the ground in the first place for
a mountain wave to push you into it.

From a practical perspective, a couple of things to consider: higher up may
provide less turbulence (though, don't try to fly through a rotor cloud).
Also, if you want to most efficiently use the mountain wave to your
advantage, pitch up and slow down while it's making you go up, and pitch
down and speed up while it's making you go down. This will increase the
magnitude of your altitude changes, but you'll be spending less time during
the "bad" down areas and more time during the "good" up areas. Fighting the
mountain wave is just that: fighting. And no one wins a fight with Mother
Nature.

Of course, in practice you may have upper and lower limits to acceptable
altitudes, and those need to be taken into account. But inasmuch as you can
allow your altitude to vary with the wave, let it.

Pete