Hydraulic Jumps?

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.

On Friday, August 25, 2017 at 6:11:29 PM UTC-4, wrote:
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.

Thanks Phillip! I look forward to getting down their one of these days;
hopefully you can show me...
Thanks again, Best Regards, Dave

On Thursday, August 24, 2017 at 7:52:49 PM UTC-4, Sean Franke wrote:
Warner Springs, CA is known for its hydraulic jump.

Flyable - you've flown it?
What discontinuity causes the jump?
How can you recognize it (vs. classc wave)?

Thanks!
See ya, Dave

PS: Good job at Uvalde!

On Friday, August 25, 2017 at 9:18:40 AM UTC-4, Tim Taylor wrote:
We tend to get both traditional wave and hydraulic jumps in northern Utah.. We also get compression wave in areas where two ranges are close enough to cause interference. I would love to see models that predict some of the dynamic flying we see in the fall through spring. I have had 10 knots straight off a ridgeline to 18,000 feet and other unexpected lift areas.

Compression wave? We have had real wave and low lying rotor here in Michigan which is flat as a pancake. Could this be a compression wave phenomenon? Would love to have some literature reference to read about this! Any references?

Thanks!

Compression wave is when wave from one ridge ends up intersecting with a downwind ridge. If the wavelength is correct you end up with the downward flow of a primary or secondary flowing into the face of the second ridge. This causes the wave to deflect upward on the face of the second ridge. We have ridges about 15 miles apart and often get a interference from the secondary wave from the first ridge on the face of the second ridge.

On Sunday, August 27, 2017 at 7:57:40 PM UTC+3, wrote:
On Friday, August 25, 2017 at 9:18:40 AM UTC-4, Tim Taylor wrote:
We tend to get both traditional wave and hydraulic jumps in northern Utah. We also get compression wave in areas where two ranges are close enough to cause interference. I would love to see models that predict some of the dynamic flying we see in the fall through spring. I have had 10 knots straight off a ridgeline to 18,000 feet and other unexpected lift areas.

Compression wave? We have had real wave and low lying rotor here in Michigan which is flat as a pancake. Could this be a compression wave phenomenon? Would love to have some literature reference to read about this! Any references?

I've read somewhere that in the right conditions (profiles of stability and wind speed with altitude) cumulus cloud streets can trigger wave. Or convergences.