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Upslope Flows
Prandtl (1942) one-dimensional theory
Defant (1949) continued with Prandtl’s model
Egger (1981) 2-D model
“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)
“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.”
(Vergeiner and Dreiseitl 1987)
Forces in Idealized Upslope Flow
g (T1  T2 )
T2
z
2T2
1 p

 x
cold
warm
Buoyancy
1T1
PGF
1 < 2
T1 > T2

x
(Adapted from Atkinson 1981)
Forces in Idealized Upslope Flow
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.
Banta 1984)
Reuten et al. 2005
Reuten et al. 2005
Reuten et al. 2005
Reuten et al. 2005
Reuten et al. 2005
Reuten et al. 2005
Reuten et al. 2005