Is atmospheric pressure higher or lower on the lee side of a mountain ridge?

interesting question.





the air is a bit lighter, because it has less water, which is a bit lighter than air in general.





also, when air goes over a mountain, and the water condenses out. it gives up it's energy to the air, so that on the downwind side the air is warmer. as it is warmer, it expands, and thus is lighter.





but that's not pressure.





there will be an almost unmeasurable increase in pressure on the windward side because the wind must change direction, from level to up, and that will cause a slight compression.





I've never encountered your question, but i think that the pressure will be higher on the windward side, because of the last reason stated above. however, i really don't know.





BTW, the question should have been worded ';... windward side, or lee side, of a mountain';?





David, as far as the Bernoulli principle, that wasn't the question asked.


however, there's a point that i'm not sure of.


specifically, if you were to attach a pressure gage to a balloon, so that it rode along with the wind, it would not see air movement.


in that case, would the pressure reading be lower than, for example, a similar gage, at a similar altitude, not at the peak?Is atmospheric pressure higher or lower on the lee side of a mountain ridge?
The pressure is actually lowest at the peak, or ridge. This is due to Bernoulli's principle, also known as the Venturi principle.





As the air must rise to go over the mountain, one of two things must happen. It must either compress to squeeze between the ridge, and the column of air above, OR the velocity must increase so that an equal volume of air/ unit time also crosses the ridge. What happens is that the air velocity increases.





This is also the principle that procuces lift on an airplane wing. If you look at the cross section you will notice that the upper surface has a thicker curve than the lower surface. This causes the air velocity ofver the top of the wing to be faster than the air velocity going over the bottom, causin a lower pressure on the top, thus keeping the aircraft airbourne.





Bernoulli's principle states that pressure is inversely proportional to velocity.





This produces a condition that is counter-intuitive, but true. The pressure is higher in the foot hills on BOTH sides, than at the peak. This does not take into account the pressure drop from altitude, which also contributes.Is atmospheric pressure higher or lower on the lee side of a mountain ridge?
It depends on your definition of atmospheric pressure.





If your definition is the station pressure, i.e. the actual pressure, then David is correct: the lowest pressure is at the highest elevation. If your definition is the mean-sea-level pressure, which is the station pressure normalized for elevation differences, then Linlyons is correct: the lower pressure is on the lee side.





Engineering problems would use the former definition, because it is the actual physical pressure; meteorology uses the latter definition, because pressure maps are more useful if you first normalize the pressure for elevation.

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