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ENVS450
Environmental Hydrology
Circulation, Temperature, Wind
Lesson 5, Module 1
To discuss circulation in the atmosphere
and wind patterns
ENVS450: Environmental Hydrology
Introduction
•  Moisture laden air masses are
source for precipitation
•  Atmospheric circulation affected
by location on earth, season of
year, location of land and water
•  The result of atmospheric
circulation is the weather we
observe*
*
From Bloomsburg et al. (1989) Hydrology. Unpublished Course Notes.
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ENVS450: Environmental Hydrology
Weather and Climate Defined
•  Weather is the state of the
atmosphere relative to heat or cold,
wetness or dryness, calm or
storms, clearness or cloudiness.
•  Climate represents the historical
record or long-term characteristics
of weather at a particular location
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ENVS450: Environmental Hydrology
Solar and Terrestrial Radiation
•  Solar energy is driving force for
atmospheric circulation
•  Solar radiation is in the short-wave
range (0.4 – 0.8 mm)
•  Terrestrial radiation is in the long-wave
range (10 mm)
•  The solar constant is the rate at which
radiation is received at the upper limits
of the atmosphere (1374 W/m2)
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ENVS450: Environmental Hydrology
Solar Radiation at Earth’s Surface
•  Scattering and absorption by
atmosphere and reflection by
clouds reduces solar radiation
•  Albedo is ratio (%) of reflected
light to total incident light on a
surface
•  An example of high albedo is new
snow, while wet soils have a low
albedo
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ENVS450: Environmental Hydrology
Solar Radiation at Earth’s Surface
•  Temperature variations between
equatorial and polar regions are caused
by variation in radiation and albedo
•  Radiation varies due to the angle of the
sun
•  Albedo varies due to the surface cover
(snow versus sand)
•  The average energy received on the
earth’s surface is ¼ of the solar constant
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ENVS450: Environmental Hydrology
Circulation and Pressure
Northern hemisphere:
•  Circulation in a low pressure
system is counterclockwise
•  Circulation in a high pressure
system is clockwise
Reversed in southern hemisphere
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ENVS450: Environmental Hydrology
Wind
•  Wind is flow of air due to a pressure
gradient, and sometimes due to
temperature differences
•  Coastal areas have on-shore breezes
during the daytime, and off-shore
breezes during the night time
•  In mountainous areas, up-valley
(slope) in daytime, and down-valley
(slope) breezes at night
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ENVS450: Environmental Hydrology
Wind
•  Wind speed is measured with an
anemometer
•  Wind direction is measured with a
vane
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ENVS450: Environmental Hydrology
Terminology in Circulation
•  Stephan-Boltzmann Law
•  Greenhouse effect
•  Westerlies and trade winds
•  Coriolis effect
•  Jet stream
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