Severe (or more) turbulence... how common?

"John Harper" wrote in message
news:1075755778.686463@sj-nntpcache-5...
Yes, that's pretty much what my math came up with too. But for sure
I lost 2000' (I couldn't believe it when I looked at the altimeter after
recovering the plane - I'd been pretty focussed on the ASI since I
was close to redline). And I don't think the whole thing lasted more
than 10 seconds, although of course I wasn't timing it. Maybe it
was longer, but usually these things seem to last longer than they
really do, not less.

The terrain there is a bit special - there's a first ridgeline which is
at 6000-7500', then after a couple of miles there's a lower ridge
at around 4000', with a valley in between at about 2000'. I think
the only reason I recovered (much though I'd like to take credit for
my excellent airmanship :-) ) is that we flew through the downdraft.

I don't know whether this was "severe turbulence" according to
the definition. It was actually quite smooth, except that we were
going down at something around -1G. I did keep the plane under
control - my main concern being to avoid hitting Vne. We came out
about 30 degrees off heading. My wife says we did bank quite
steeply - she was looking out of the windshield, I was focussed on
the instruments. Whether it was "severe" or not, it was certainly quite
an experience, one I'm not in a big hurry to repeat.

John


If its smooth, its not turbulence. When you are flying roughly
perpendicular to a ridgeline and encounter a rotor there is a very strong
updraft and then an equally strong downdraft (of course the order is
reversed if you are going the other way). The terrain sounds like a good
setup for a wave if the air is stable and the wind is perpendicular to the
ridges and increases with height.

The numbers don't really match up with the reported conditions. To get
2000' of altitude loss in 10 seconds would require winds of well over 100kts
since the vertical speed is going to average 120kts. If you are interested
in mountain waves you should read the book "Exploring the Monster" which is
about the Sierra Wave Project which studied the very powerful wave systems
on the east side of the Sierra Nevada near Bishop. The Owens Valley is an
ideal wave generator being 10,000' deep, perpendicular to the jetstream and
about one wavelength wide. Gliders regularly reach 40,000' there and in the
Carson Valley farther north.

Mike
MU-2