Fohn Effect
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Joined: Feb 2006
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From: Daventry
Fohn Effect
Struggling a bit with this one.I think I get the principle but whenever I see an example I always seem to get the wrong answer.
Question on Airquiz:
Air at +19C at sea level and dew point of +3C rises 4000ft over a mountain.What is the air temp at 2000ft on the leeward side?
Correct answer is 16C
How so?
Modelman
Question on Airquiz:
Air at +19C at sea level and dew point of +3C rises 4000ft over a mountain.What is the air temp at 2000ft on the leeward side?
Correct answer is 16C
How so?
Modelman
Joined: Oct 2005
Posts: 201
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From: uk
By my reckoning the air temp at the top of the mountain would be 7C (DALR 3C/1000') and the dew point 1C (DPLR 0.5C/1000'). Since no cloud formation and moisture loss takes place there is no fohn effect, and the temp at 2000' on the leeward side will be 13C with a dew point of 2C
Tabs please!
Joined: Jun 2004
Aviation Qualifications: PPL
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From: Biffins Bridge
Dr Eckener is perfectly correct. The air has very low humidity however this is indicated by the huge difference in temperature and dewpoint given in the question.
Had the question started with a dewpoint of +16c, you would need a tephigram (horribly complicated chart) to work out the temperature increase on the leeward side.
Had the question started with a dewpoint of +16c, you would need a tephigram (horribly complicated chart) to work out the temperature increase on the leeward side.
