1. Local Wind Systems and Temperature Structure in Mountainous Terrain
Met 130
6 May 2008
Dr. Craig Clements

2. Types of Thermally-Driven Winds found in Mountainous Regions
1. Plain-Mountain Winds
2. Valley Winds
3. Slope Winds
Thermally-driven refers to the forcing
due to temperature differences!

3. Thermally-Driven Winds Found in Mountains
Whiteman(2000)

4. Cross-section of a Mountain Valley
Whiteman(2000)

5. Valley Winds Daytime: Air is warmer in the valley than over the plain
Pressure is lower in the valley and higher over the plain at the same elevation
The pressure gradient force is directed from the plain to the valley
A up-valley wind is produced that blows from the plain into the valley.
Nighttime:
Pressure gradient force reverses direction
A down-valley wind occurs
Up-Valley Winds
Down-Valley Winds
Whiteman(2000)

6. Up-Valley and Down-Valley Surface Winds
(Measured in Yosemite National Park)
Date and Time

7. A SODAR (sound-detection-ranging) is similar to RADAR

8. Vertical Structure of Down-Valley Winds
Yosemite National Park, 12 Aug. 2003
‘Nose’ of
Down-valley
wind
Nose is location of
Wind speed
maximum

9. Conceptual wind models for mountain valleys

10. (Whiteman 1982)

11. The Volume Effect of Valleys
Whiteman(2000)

12. Examples of Valley Shapes
Whiteman(2000)

13. Yosemite Valley, Yosemite National Park

14. Pattern 1 Inversion destruction Models in mountain
Valleys (Whiteman 1982):
Pattern 1

15. Pattern 2 Inversion destruction Models in mountain
Valleys (Whiteman 1982):
Pattern 2

16. Pattern 3 Inversion destruction Model in mountain
Valleys (Whiteman 1982):
Pattern 3

17. Diurnal Temperature Evolution in Mountain Valleys
(from Stull 1988; adapted from Whiteman 1982)

18. A Simplified Heat Budget of the Valley Atmosphere
Term 1: local rate of change of potential temperature
Term 2: convergence of potential temperature flux by mean wind
Term 3: convergence of radiative flux
Term 4: convergence of turbulent sensible heat flux

19. Mass conservation in a valley

20. Topographic Amplification Factor (TAF)

21. The thermodynamic model developed by
Whiteman and McKee (1982):

22. Tethersonde Profiles from Yosemite Valley
Height (m AGL)
100
200
300
400
500
600
700
282
284
286
288
290
292
294
296
298
600 PST
630
725
955
1035 2 3 4 5 6 7 8 -6 -4 -2
Up-valley Wind Component (m s-1)
Mixing Ratio(g kg-1)
Potential Temperature (K)

23. (a) (b) Modeled Inversion destruction
Inversion breakup according to Eq. 2 with Ao = 0.45, (a)  = K m-1 and (b)  = K m-1 TAF () values are indicated in legend.
(b)

25. Slope winds
Whiteman(2000)
Slopes winds are usually in the range of 1-4 m/s (2-8 mph); are weaker and more gentle than valley winds.
Peak wind speed occurs a few meters above the the slope surface.
Daytime upslope winds are typically stronger and deeper than nighttime downslope winds.
A transition period occurs between the upslope and downslope winds in evening and morning. (See Time-Lapse Video)

26. Consequences of downslope flows: movie
Whiteman(2000)
Downslope winds are often called drainage winds
Downslope winds can produce a cold air pool in a valley or basin. Some of these cold air pools can last several days to a week, trapping pollutants in the valley/basin. Cold air pools are often associated with dense fog, which is hazardous to aviation.

27. Glacier Winds
A cold air layer forms over ice surface and flows downhill.
Whiteman(2000)

29. Diurnal Evolution of the Boundary Layer over Mountains
The layer of air influenced by the earth’s surface
is called the planetary boundary layer (PBL).
Whiteman(2000)