Mountain Impacts on Climate Local to Planetary Scale

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Mountain Impacts on ClimateLocal to Planetary
Scale

• Maura Hahnenberger
• Meteo 6030

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Outline

• Scales of Impact
• Planetary Scale
• Synoptic Scale
• Mesoscale
• Considerations
• Summary

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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

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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)
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Planetary Scale Effects

• Distribution of Arid Climates
• Mountains help spread aridity into the
  midlatitudes (gt35º)
• Aridity co-located with mountain induced ridging

M - model
NM -model
Observed
(Broccoli, 1992)
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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)
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Planetary Scale Effects

• Monsoon circulations
• Results in increased moisture flux into Southeast
  Asia
• Similar processes take place in Southwestern U.S.

(Kitoh, 2004)
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Synoptic Scale Effects

• Deformation of fronts
• Retardation by mountains
• Acceleration in valleys
• Sometimes become decoupled and reform in the lee

(Steenburgh, 2001)
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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)
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Mesoscale Effects

• Orographic Precipitation
• Also acts as source of elevated latent heating

(Steenburgh, 2003)
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Mesoscale Effects

• Thermally Driven Winds
• Downslope downvalley during nighttime
• Upslope upvalley during day
• Can help create cold pools leading to vegetation
  inversions

(Stewart, 2002)
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Mesoscale Effects

• Mechanically produced winds
• Downslope windstorms
• Lee waves
• Channeled flow
• Barrier jets
• Gap winds
• Can lead to significant local climate variations

(Beran, 1967)
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Mesoscale Effects

• Foehn Rotor Clouds
• Downsloping

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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!)

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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

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Questions?