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)

(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.”

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)

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

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