I've picked up the book authored by Jean-Marie Clément, Dancing With The Wind. He makes a point regarding valley breezes channeled by mountains becoming either dextrorotatory vs levorotatory. Supposedly, climbs will be better on mountains facing the valley breeze on a levorotatory rotation of the breeze (in the northern hemisphere). Any high time experienced alpine soaring pilots care to venture their opinion on this topic? Any specific examples?

On Monday, February 1, 2016 at 7:14:34 PM UTC-6, wrote:
> I've picked up the book authored by Jean-Marie Clément, Dancing With The Wind. He makes a point regarding valley breezes channeled by mountains becoming either dextrorotatory vs levorotatory. Supposedly, climbs will be better on mountains facing the valley breeze on a levorotatory rotation of the breeze (in the northern hemisphere). Any high time experienced alpine soaring pilots care to venture their opinion on this topic? Any specific examples?

Man, I haven't heard the words, "dextrorotary" and "levorotary," (spelled the way we did) since organic chemistry in college! Brings back fond memor.. oh, wait...

And, sorry, I don't have any experience with this.

Jeff

Hi John. While I am not high-time in the alpine theatre, if he is referring to the Coriolis effect I suspect he is splitting hairs.

On Friday, February 5, 2016 at 6:43:04 AM UTC-7, Brett wrote:
> Hi John. While I am not high-time in the alpine theatre, if he is
> referring to the Coriolis effect I suspect he is splitting hairs.
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> Brett

Those terms are not ones I have ever heard used to describe wind or air rotation in the atmosphere - I wonder if it's a bad translation from the French?

....and yes, if he's referring to Coriolis forces, they are negligible on such a small scale.

Mike

It's much shorter in French: "dextrogyre" and "lévogyre"...

JMC expressly states that he has no idea if Coriolis forces can play a role in this matter, his theory being based purely on experience.

According to him, in the northern hemisphere, when the wind is forced to turn to the left by the configuration of the slope, lift along the exposed slope will be better than if it is forced to turn to the right (the opposite occuring in the southern hemisphere).

He gives some examples in the French Alps (the Prachaval slope versus the slopes coming from the col de Vars, both facing the valley breeze mounting from the Serre-Ponçon lake) and even connects his theory with the accident of Giorgio Galetto some years ago.

Well, you can try it out...

I live in France and have years of experience soaring in the Alps. We've discussed this subject over many beers, and the experienced pilots (including myself) agree that, all other things being equal, lift always seems stronger where the breeze turns left against a slope. Tête de Siguret, Prachaval, and Tête d'Amont are the classic left-turn climbs going northbound through the French Alps, and you can expect to share your slope-side thermal with several other gliders. The effect is weaker the farther up long valleys, such as in the Vallée de la Maurienne.

Chris