Geoscience Reference
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subtropical highs alternate with winter
cyclones bringing ample rain.
of body heat is lost by radiation and 25 percent by
evaporation from the lungs and skin. Outdoors,
additional heat is lost by convective transfer due
to the wind. Human comfort depends primarily
on air temperature, relative humidity and wind
speed (Buettner, 1962). Comfort indices have
been developed by physiological experiments in
test chambers. They include measures of heat
stress and windchill.
Windchill describes the cooling effect of
low temperature and wind on bare skin. It is
commonly expressed via a windchill equivalent
temperature. For example, a 15 m s -1 wind with
an air temperature of -10°C has a windchill
equivalent of -25
Mid-latitude continental desert and steppe
(35
N and S). Summer cT air alter-
nates with winter cP air. Hot summers and
cold winters give a large annual temperature
range.
°
-50
°
Humid continental climate (35°-60°N).
Central and eastern continental locations.
Frontal cyclones. Cold winters, warm to hot
summers, large annual temperature range.
Well distributed precipitation.
3 High-latitude climates controlled by polar and
Arctic air masses
C denotes
a high risk of frostbite and corresponds to a heat
loss of approximately 1600 W m -2 . Nomograms to
determine windchill have been proposed, as well
as other formulae that include the protective effect
of clothing.
Heat discomfort is assessed from measurements
of air temperature and relative humidity. The U.S.
National Weather Service uses a Heat Index based
on a measure of apparent temperature devel-
oped by R. G. Steadman for normally clothed
individuals. The value of apparent temperature in
the shade (TAPP) is approximately:
TAPP = - 2.7 + 1.04 T A + 2.0e - 0.65 V 10
where T A = midday temperature (°C),
e = vapour pressure (mb), V 10 = 10m wind speed
(m s -1 ). Warnings are issued in the United States
when the apparent temperature reaches 40.5
°
C. A windchill of -30
°
Continental sub-Arctic climates (50
°
-
70
N). Source region for cP air. Very cold
winters, short, cool summers, extreme
annual temperature range. Year-round
cyclonic precipitation.
°
Marine sub-Arctic climate (50°-60°N and
45
S). Dominated by the winter arctic
frontal zone. Cold, moist winters, cool
summers; small annual temperature range.
°
-60
°
Polar tundra climates (north of 55
°
-60
°
N
and south of 60
S). Arctic coastal margins
dominated by cyclonic storms. Humid and
cold, moderated somewhat by maritime
influences in winter.
°
Ice sheet climates (Greenland and Antarc-
tica). Source regions of Arctic and Antarctic
air. Perpetual frost, low snowfall except near
coasts.
C for
more than three hours/day on two consecutive
days.
Another approach measures the thermal
insulation provided by clothing. One 'c lo ' unit
maintains a seated/resting person comfortable in
surroundings of 21°C, relative humidity below 50
percent and air movement of 10 cm s -1 . For
example, the clo values of representative clothing
are: tropical wear <0.25, light summer clothes 0.5,
typical male/female day wear, 1.0, winter wear
with hat and over- coat 2.0-2.5, woollen winter
sportswear 3.0, and polar clothing 3.6-4.5. The clo
°
4 Highland climates - localized and varied in
character.
D CLASSIFICATIONS OF
CLIMATIC COMFORT
The body's thermal equilibrium is determined
by metabolic rate, heat storage in body tissues,
radiative and convective exchanges with the
surroundings, and evaporative heat loss by
sweating. In indoor conditions, about 60 percent
 
 
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