Mountain Wave

[vk3auu]

Here is a photo of a Mountain Wave sourced from AVweb photo of the week.

 

http://www.avweb.com/newspics/potw/large/potw03_1329.jpg

 

Something to watch out for when you fly across "Them thar hills"

 

David

 

 

[Ultralights]

having just come back from a lovely snow trip last week, you quite regularly see wave formed lenticular clouds up close! and driving back towards cooma as you pass over the ridge from the valley where Jyndabine is located, you can see the lenticular clouds forming as the wave moves east towards the coast.

 

 

[Guest pelorus32]

Wave is brilliant stuff - gliding in wave is like riding a lift. It's worth remembering that where there's wave there will be lee rotor - not such brilliant stuff.

 

M

 

 

[PaulN]

Having just come back from a lovely snow trip last week and driving back towards cooma ...

And you didn't stop by to say hello???

 

Paul

 

 

[PaulN]

Wave is brilliant stuff - gliding in wave is like riding a lift. It's worth remembering that where there's wave there will be lee rotor - not such brilliant stuff.M

On my last flight, returning from Camden Haven, at 10k ft (to avoid reported mod to severe turb due to westerly, and in the care of CN APP) over top of Michelago (hilly terrain just sth of Canberra and around 5000 AGL) I experienced this rotor effect. Cruising in level flt at 110kt (indicated) the CT began losing alt at about 600 fpm which I countered by trimming up and up and up bringing the nose into an obviously upward pitch and airspeed down to 80kt to regain level flt. This lasted for about 30 secs and then went away as quickly as it came. Makes one glad to have plenty of height over those hills.

 

Like Mike says "worth remembering the rotor effect".

 

Paul

 

 

[Ultralights]

when i drove past Cooma on this last trip it was at 10Pm and still snowing all the way to past cooma!

 

the snow is the best i have ever seen it so early in the season!

 

 

 

[Guest pelorus32]

On my last flight, returning from Camden Haven, at 10k ft (to avoid reported mod to severe turb due to westerly, and in the care of CN APP) over top of Michelago (hilly terrain just sth of Canberra and around 5000 AGL) I experienced this rotor effect. Cruising in level flt at 110kt (indicated) the CT began losing alt at about 600 fpm which I countered by trimming up and up and up bringing the nose into an obviously upward pitch and airspeed down to 80kt to regain level flt. This lasted for about 30 secs and then went away as quickly as it came. Makes one glad to have plenty of height over those hills.Like Mike says "worth remembering the rotor effect".

 

Paul

G'day Paul,

 

I think that what you likely encountered was wave, not rotor.

 

Can't draw pictures here so description. If you imagine the side on view - you are looking along the spine of a mountain chain. The wind is perpendicular to the ridge and it sets up a set of waves - well above the height of the ridge and mainly to leeward of it. These waves are standing waves - the peaks are in one place and the troughs in another and they tend to stay there and generate lenticular clouds on their crests. What you very likely experienced was the downward side of a wave - to leeward of a wave peak. The trick is to be in the upgoing air to windward of a peak and to leeward of the downgoing bit. The giveaway is that wave - up or down - is generally smooth or smoothish.

 

Now go back to our ridgeline. In the lee of the ridge and below the wave the air tumbles and churns. This is caused by the ridge upsetting the airflow. This is the rotor. Rotor is generally extremely turbulent and highly unpredictable.

 

A friend of mine inadvertently flew a fully loaded B747-400 through extreme rotor. His description was that he alternated between full thrust and full airbrakes and still had uncommanded IAS variations of 50 knots and uncontrolled roll of 30 degrees each way. Afterwards they found the cabin covered in vomit and one person had broken a leg. A B767 encountered the same rotor and was grounded after landing having exceeded its g limits.

 

Gliding at Mt Cook it was notorious that you would have to tow up through rotor in order to get the wave. Before my time a glider pilot fractured several vertebrae in the rotor at Mt Cook - being thrown about so much.

 

Regards

 

Mike

 

 

[Ben Longden]

Thats probably the best description of rotors and waves I have read, yet.

 

Ben

 

 

[Guest disperse]

can i get an explenation on these two words please

 

lenticular,leeward

 

 

[Guest Crezzi]

Leeward is downwind of (in this case) the mountains.

 

Lenticular refers to a particular form of cloud often associated with mountain wave. They are stationary and lens shaped (hence the name)

 

pics here http://www.met.rdg.ac.uk/~brugge/cloudwatch/cloudtypes.html#lenticularis

 

 

[Guest pelorus32]

I should also have been more specific in saying that lenticulars form on the crest of the wave. They often do but wave can exist either without cloud associated or with a modified lenticular.

 

Perhaps one of the most famous modified lenticulars is the Norwest Arch in the South Island of New Zealand.

 

http://www.gliding.co.nz/BestPic/Soper/Norwest_Arch.JPG

 

In the photo the wind is blowing towards the camera and the arch forms from one of the waves. It is an amazing sight which I will remember always.

 

In just the same way rotor is sometimes marked by clouds but can equally well exist without cloud markers.

 

Regards

 

Mike

 

 

[PaulN]

When i drove past Cooma on this last trip it was at 10pm and still snowing all the way to past Cooma!

Our lights were still on Rob. Never mind, next trip maybe ;).

 

Paul

 

 

[PaulN]

Right again Mike, mine was most definitely the lee side of a wave ... smooth but no cloud to indicate it.

 

I have experienced light rotor activity on the east side of the snowies. It can be very rough indeed. A good place to avoid when the westerlies get up.

 

Thanks for your informative input on this forum .

 

Paul

 

 

[Guest disperse]

THANKS EVERYONE:big_grin: