Welcome to SP!  -   
 
 MbPost.com -- It's SP for Mountain Biking!
Areas & Ranges·Mountains & Rocks·Routes·Images·Articles·Trip Reports·Gear·Other·People·Plans & Partners·What's New·Forum

 Forums Home > General > Thread

Foehn effect

[ Start New Topic | Reply to This Topic ] All times are GMT  
 Author Topic: Foehn effect
visentin


Joined: 13 Jan 2008
Posts: 322


[ Profile | PM ]
PostPosted: Wed Nov 26, 2008 12:24 pm GMT  Quote
 
http://www.summitpost.org/article/466432/foehn-effect.html
scooter12ga


Joined: 29 Jan 2008
Posts: 127


[ Profile | PM ]
PostPosted: Wed Nov 26, 2008 3:35 pm GMT  Quote
 
Great article! I always wondered what to call that.
cb294


Joined: 12 Jun 2008
Posts: 123


[ Profile | PM ]
PostPosted: Wed Nov 26, 2008 3:46 pm GMT  Quote
 
Good description of the meteorology, just one minor piece of pointless trivia: The word Föhn in German originally referred (and still does) to the warm southerly wind coming over the Alps. AEG used Fön as brand name for their electrical hairdriers. Subsequently that brand name has replaced the generic word and is now used for all electrical hairdriers.

CB
visentin


Joined: 13 Jan 2008
Posts: 322


[ Profile | PM ]
PostPosted: Thu Nov 27, 2008 7:33 am GMT  Quote
 
cb294 wrote:
Good description of the meteorology, just one minor piece of pointless trivia: The word Föhn in German originally referred (and still does) to the warm southerly wind coming over the Alps. AEG used Fön as brand name for their electrical hairdriers. Subsequently that brand name has replaced the generic word and is now used for all electrical hairdriers.

CB


Thanks ! I'll include this correction
MoapaPk


Joined: 13 May 2005
Posts: 4403


[ Profile | PM ]
PostPosted: Thu Nov 27, 2008 9:13 am GMT  Quote
 
"While rising along the mountain slopes, in contact with the ground, it gets colder. "

Actually, it would get colder just from adiabatic expansion. Because of the added latent heat of condensation, the cooling effect (degree per m of elevation change) is less for the rising wet air, than the warming effect for descending dry air.

"spannish" = Spanish?
visentin


Joined: 13 Jan 2008
Posts: 322


[ Profile | PM ]
PostPosted: Fri Nov 28, 2008 12:21 pm GMT  Quote
 
MoapaPk wrote:
"
Actually, it would get colder just from adiabatic expansion. Because of the added latent heat of condensation, the cooling effect (degree per m of elevation change) is less for the rising wet air, than the warming effect for descending dry air.

"spannish" = Spanish?


Thanks for this addition. Included ! And sorry for "spannnnnnish" Wink
den dzjow


Joined: 07 Nov 2004
Posts: 4


[ Profile | PM ]
PostPosted: Sun Nov 30, 2008 9:36 pm GMT  Quote
 
There is no other meteorological phenomenon spreading so much confusion and mistakes than the foehn. It all started in the 19th century when an Austrian meteorologist Julius von Hann came up with the "thermodynamical foehn theory" which is summarised in the figure in the article. Unfortunatly his unrealistic theory has been widely accepted throughout history. The result is that similar figures and explanations are still found in almost any meteorological handbook nowadays (and now also here on summitpost).

Unfortunatly this theory is wrong. Or let say it's role in the whole foehn principle is almost negligible. Foehn in the Alps always starts when there isn't precipitation falling on the loefside at all! The airmass doesn't rise entirely from ground level on the loefside to the mountain summits. In reality most of the airmass in the lowest levels is blocked ahead of the mountains while air with a warmer potential temperature from aloft (from around summit level) sinks dry adiabatically on the leeward side in a supercritical flow in terms of fluid dynamics. That's in breef how foehn works in reality.

People who are further interested in the meteorological background should try to read for example the works of Petra Seibert. http://www.meteohistory.org/2004polling_preprints/docs/abstracts/seibert_abstract.pdf
Here you can read about the confusion resulting from Hann's theory.
Display posts from previous:   
[ Start New Topic | Reply to This Topic ]


 
Jump to:  




© 2006 SummitPost.org. All Rights Reserved.