upslope flows. prandtl (1942) one-dimensional theory defant (1949) continued with prandtl’s model...
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Upslope Flows
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Prandtl (1942) one-dimensional theory
Defant (1949) continued with Prandtl’s model
Egger (1981) 2-D model
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“Slope winds are spontaneous and intermittent in space and time. They are not continuous and stationary, but a succession of thermal bubbles from favorable, rocky, dry spots on the slope.”
Slope flows react instantly to insolation.Upslope breezes start a few minutes after sunrise.
(Vergeiner and Dreiseitl 1987)
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(Vergeiner and Dreiseitl 1987)
“Slope wind field experiments, rare anyway, give random inconclusive results from which representative values of mass and heat transport in the slope layer cannot be derived.”
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x
p
1
1T1 2T2
x
z
2
21 )(
T
TTg
T1 > T2
1 < 2
warm
cold
PGF
Buoyancy
Forces in Idealized Upslope Flow
(Adapted from Atkinson 1981)
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Air parcel above slopes surface has a higher potential temperature and therefore lower density than air parcel at same height above sea level over the plain (valley).
Two forces acting on the parcel above the slope:
1. Pressure Gradient Force: pushing air towards the slope.
2. Buoyancy Force: drives air parcel vertically.
Sum of both forces results in upward movement of air over slope, which is replaced by air coming from valley atmosphere.
Forces in Idealized Upslope Flow
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Banta 1984)
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Reuten et al. 2005
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Reuten et al. 2005
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Reuten et al. 2005
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Reuten et al. 2005
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Reuten et al. 2005
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Reuten et al. 2005
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Reuten et al. 2005