Mountain environments - Fundamentals of the Physical Environment - page 766

compared with north-facing ( ubac ) slopes at 5°, 25° and 45° latitude. Differences
between east-west facing slopes are more subtle and their impact depends on other
conditions and processes. Thus afternoon direct sunlight may melt more snow than a
similar morning flux because ambient heat during the day has already raised its
temperature. Insolation asymmetry accentuates other differences. Anabatic flow, for
example, may be accompanied and enhanced by progressive morning development of
mountain cumulus on sunlit slopes (Figure 25.11c).
Slope variability also generates random changes in parameters such as shade, wind
exposure, air and water drainage. We move imperceptibly into the microclimate zone,
with its most subtle interactions between atmosphere and surface. Energy and moisture
transfers are influenced at successively smaller scales by the presence or absence of
vegetation, the juxtaposition of snow, soil and vegetation surfaces, the albedo of snow,
and the specific heat capacity and thermal conductivity of soils. An example of the
extremely small spatial and temporal scales of microclimate occurs where the influence
of albedo and diurnal shifts in radiation and air temperature on melt potential at a glacier
surface is evident in the evolution of sun cups of more than 10 cm vertical amplitude
(Plate 25.5).

Plate 25.5 Sun cups formed on the sunlit face of snowpack
micro-relief. Their shape and orientation will change as the
sun moves around during the day.
Photo: Ken Addison.

LIVING AT ALTITUDE
human impact
Atmosphere and climate at high altitude pose a range of problems for human living and
socioeconomic activity, caused by lower atmospheric pressure and extreme cold; the
latter is shared with polar environments. They cause problems for human
biometeorology although the human body also displays short term facilitative