1. Mountain Impacts on Climate Local to Planetary Scale
Maura Hahnenberger
Meteo 6030

2. Outline Scales of Impact Planetary Scale Synoptic Scale Mesoscale
Considerations
Summary

3. Scales of Impact Planetary scale wave motion
Modification of Synoptic scale weather systems
Mesoscale wave motion through local gravitional effects
Local thermally and mechanically driven flows
Blocking and channeling of flows

4. Planetary Scale Effects
1000mb Height
850mb Height
Planetary waves
Mountains create semi-permanent stationary waves
Conservation of potential vorticity
Causes ridge over mountain barrier and trough downstream
Observed
M - model
NM -model
(Manabe, 1974)

5. Planetary Scale Effects
Distribution of Arid Climates
Mountains help spread aridity into the midlatitudes (>35º)
Aridity co-located with mountain induced ridging
M - model
NM -model
Observed
(Broccoli, 1992)

6. Planetary Scale Effects
Monsoon circulations
Intensification of
Pacific High
Easterly Trades
Asian Monsoon
Mountains act as elevated heat source to global system
Observed
No Mountains
Current Mountains
(Kitoh, 2004)

7. Planetary Scale Effects
Monsoon circulations
Results in increased moisture flux into Southeast Asia
Similar processes take place in Southwestern U.S.
(Kitoh, 2004)

8. Synoptic Scale Effects
Deformation of fronts
Retardation by mountains
Acceleration in valleys
Sometimes become decoupled and reform in the lee
(Steenburgh, 2001)

9. Synoptic Scale Effects
Lee Cyclogenesis
Also based on conservation of potential vorticity
Aided by less stable environment in lee
Often primary and secondary lows form
(Schultz, 2000)

10. Mesoscale Effects Orographic Precipitation
Also acts as source of elevated latent heating
(Steenburgh, 2003)

11. Mesoscale Effects Thermally Driven Winds
Downslope & downvalley during nighttime
Upslope & upvalley during day
Can help create cold pools leading to vegetation inversions
(Stewart, 2002)

12. Mesoscale Effects Mechanically produced winds Channeled flow
Downslope windstorms
Lee waves
Channeled flow
Barrier jets
Gap winds
Can lead to significant local climate variations
(Beran, 1967)

13. Mesoscale Effects
Foehn & Rotor Clouds
Downsloping

14. Other Considerations Scale of mountains determine scale of impact
Southern Hemisphere exhibits far fewer effects – Much less topography
Impacts vary with time of year
Effects are coupled with other large scale phenomena, e.g. ENSO
Not clear if and how these impact may change in a changing climate (good area for future research!)

15. Summary Mountains impact climate by:
Determining position of troughs & ridges
Acts as an elevated heat source
Produce orographic convective precipitation
Impacts synoptic & mesoscale circulations
Blocks & channels flows

16. Questions?