Hydraulic Jumps?

On Thursday, August 24, 2017 at 11:08:40 PM UTC-4, Tony wrote:
Described very well in the fantastic book "Dancing with the Wind" as well

Yes, excerpts are in Bernard's article.

On Thursday, August 24, 2017 at 9:47:19 PM UTC-4, wrote:
I am sure you are familiar with Bob Whelan's "Exploring the Monster."
about the early wave experiments in the Owens Valley in the 1950's.
The Owens and Sierra Nevada wave is a classic example of what a hydraulic jump
can offer. 49,000 ft. off of a 14,000 foot mountain range is pretty impressive.
(Bob Harris 1986, G-102)

Yes, Bob Seyman's classic photo is well known...

But, to my question: Have you ever flown in a hydraulic jump?
Again, all my wave experiences in the Sierra have been classical wave.

I got to fly in one in New Zealand, with Gavin in the back. The first sign of the jump was all sorts of excited noise coming from the back seat. Then gradually the picture ahead made sense. Fortunately it was perfectly marked by clouds -- a hill, lenticular cap cloud, gap, then sort of a wall of turbulent cloud. We went to the wall and climbed in smooth wave like conditions in front of it. Really cool.
John Cochrane

On Friday, August 25, 2017 at 11:13:23 AM UTC-4, John Cochrane wrote:
I got to fly in one in New Zealand, with Gavin in the back....
-- a hill, lenticular cap cloud, gap, then sort of a wall of turbulent cloud.

Cool! Did the wall look like the picture in Bernard's article?
What was the discontinuity that provoked the jump?

On Saturday, August 26, 2017 at 3:21:05 AM UTC+12, Dave Nadler wrote:
On Friday, August 25, 2017 at 11:13:23 AM UTC-4, John Cochrane wrote:
I got to fly in one in New Zealand, with Gavin in the back....
-- a hill, lenticular cap cloud, gap, then sort of a wall of turbulent cloud.

Cool! Did the wall look like the picture in Bernard's article?
What was the discontinuity that provoked the jump?

The hydraulic jump is more common than most people realise.

Often what is referred to as the 'primary' of the wave is closer to the trigger (back of the hill) than the wavelength of the rest of the wave train. The wave is actually not being triggered by the back of the hill. A hydraulic jump is being triggered on the back of the hill, and the wave train sets up behind the hydraulic jump.

We see this a lot at Omarama because the cool air from the ocean is being pushed onto the Southern Alps by the prevailing westerly. This is much denser than the air east of the divide and this density difference helps make a hydraulic jump.

On weak days we often get just the hydraulic jump, no wave train setting up behind. The jump is often very close to the cap cloud, just a few hundred meters downwind of the trailing edge of the cloud. I think this is because the back edge of the best triggers are very steep.