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

Outline Scales of Impact Planetary Scale Synoptic Scale Mesoscale Considerations Summary

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

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)

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)

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)

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

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

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)

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

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

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)

Mesoscale Effects Foehn & Rotor Clouds Downsloping

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!)

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

Questions?