ABSTRACT
Our knowledge of the climatic characteristics of mountain regions is limited by both paucity of observations—short records that seldom span 100 years and a sparse station network—and insufficient theoretical attention given to the complex interaction of spatial scales in weather and climate phenomena in mountains. Meteorological research has tended to focus on the upstream and downstream influences of barriers to flow and on orographic effects on weather systems (Smith, 1979), rather than on conditions in the mountain environment. Atmospheric phenomena themselves display a hierarchy of spatial and temporal scales as illustrated in Table 1.1. Microscale features of the atmosphere—wind gusts, for example—are superimposed on larger scales of motion and are not fixed in place, whereas small-scale elements of the landscape surface, such as vegetation canopy, large rocks and hollows, can create microclimatic contrasts in surface healing, soil moisture or snow-cover duration that have longer-lasting significance. The role of sunny (adret) and shaded (ubac) slopes in the Alps in influencing land use and settlement location has been long recognized (Garnett, 1935). Local wind systems, generated by radiational and thermal contrasts in complex terrain, are best developed when synoptic-scale pressure gradients are weak and there is little cloud cover; hence, they are intermittent components of the climate. Synoptic-scale systems—midlatitude cyclones, for instance—are extensively modified as they move across a mountain barrier. Modifications occur on a large scale in terms of changes in frontal structure and cloud systems, and on a local scale in terms of wind systems, such as Föhn (Chinook) occurrence, or precipitation intensity. Isolating these processes in order to understand Scales in mountain weather and climate
|
Microscale |
Local scale |
Regional scale |
|
|---|---|---|---|
|
Meteorological phenomena |
Turbulent motion (gusts) |
Slope and valley winds; fall winds |
Thunderstorm cluster; synoptic system |
|
Landscape elements |
Rocks; vegetation clumps |
Terrain elements (slopes; valleys) |
Mountain range; plateau |
|
Climatic features |
Snow patches |
Adret/ubac radiational contrasts; thermal belts |
Plateau; monsoon |
|
Factors |
Primary effects |
Secondary effects |
|---|---|---|
|
Altitude |
Reduced air density, vapour pressure; increased solar radiation receipts; lower temperatures |
Increased wind velocity and precipitation (mid-latitudes); reduced evaporation; physiological stress |
|
Continentality |
Annual/diurnal temperature range increased; cloud and precipitation regimes modified |
Snowline altitude increases |
|
Latitude |
Daylength and solar radiation totals vary seasonally |
Snowfall proportion increases; annual temperatures decrease |
|
Topography |
Spatial contrasts in solar radiation and temperature regimes; precipitation as a result of slope and aspect |
Diurnal wind regimes; snow cover related to topography |
