Download Chapter 4

The Physical Environment
Climate
Climate vs. Weather
Climate—long-term average pattern of
weather
--local, regional, or global
Weather—the combination of factors
--temperature
--humidity
--precipitation
--wind
--cloudiness
--atmospheric conditions
The greatest constraint
Availability of heat and water
 Influences amount of solar energy that
plants can capture
 Controls distribution and abundance of
plants and animals

I. Solar radiation
A. The earth is covered with solar
radiation as photons.
--51% reaches surface of earth
--most of this % is converted back to
heat warming the atmosphere
--small % used in photosynthesis
--this radiation causes thermal patterns
B. Thermal patterns + earth’s rotation +
movement around sun =
prevailing winds and ocean currents
These winds and ocean currents
influence distribution of rainfall.
II. Greenhouse effect
Intercepted solar radiation varies with
latitude—2 influencing factors
A.
•
•
The radiation hits earth’s surface at a
greater angle, spreading
over a larger area
Also traveling through
more atmosphere,
or a deeper layer of air
B.
Tilt of earth is 23.5o with respect to sun
—results in seasonal variation in
temperature and length of day
1. Spring (vernal) equinox
2. Fall (autumnal) equinox
3. Summer solstice—June 22nd
4. Winter solstice—December 22nd
III. Seasonality of solar
radiation

Temperature variation /day length
increases with latitude

Arctic and Antarctic –day length varies
from 0-24 hours
Variations in
solar radiation




Explain latitudinal changes
Seasonal changes
Daily changes in temperature
BUT, do not explain
why temperature gets
colder with altitude…
BUT, do not explain
why temperature gets
colder with altitude…
As air reaches a higher altitude it
becomes less dense—
Adiabatic cooling—results from the
fewer collisions of the air molecules
--the rate of temperature change with
elevation is called adiabatic lapse rate
IV. Circulation of air masses
Air masses circulate globally
 Warmest air at equator
 Moves north and south toward poles
 Cools, becomes heavier
 Sinks over Arctic/Antarctic
regions
 Then flows toward equator
—replacing warm air

V. Rotation of earth

East-west rotation of earth
– Deflects pattern of air
– Causes Coriolis force/effect
– Causes right deflection
in N. hemisphere
» Including air masses
– Causes left deflection
in S. hemisphere
» Including air masses
Wind flows
Prevailing winds formed by Coriolis force
Series of belts of prevailing winds
Polar regions—Polar easterlies
Equator region—Easterly trade winds
Middle latitudes—Westerlies
Doldrums—
low pressure around
equator
Wind patterns
Initiate surface flow in oceans
 Each ocean dominated by 2 great
circular water motions—gyres

– Northern hemisphere—
clockwise currents
– Southern
hemisphere—
counterclockwise
current
VI. Temperature/moisture
1.
Influences amount of moisture air can hold
»
2.
3.
4.
Warm air holds more moisture than cold air
Amount of water vapor held in a volume
of air = saturation vapor pressure
Amount of water expressed as percentage of
saturation vapor pressure = relative humidity
Temperature which saturation vapor pressure
is dew point temperature
VII. Global patterns
Precipitation exhibits a global pattern
 Temperature, wind and ocean currents
determine global pattern of precipitation
 Westerly winds move across tropical
oceans—gather moisture
 Warm air cools as it rises—dew point
reached
 Clouds form—precipitation falls

Annual world precipitation
VII. Global patterns con’t
Winds move northward and
southward—cooling
 Cool air descends
 2 belts of dry climate encircle the world
 Descending air warms/holds more
moisture
 Draws water from
the surface of earth

VIII. Microclimates
A. Small areas where environmental
conditions are different
– Organisms find their niche in microclimates
– Vegetation can reduce ground temperature
7-12oC
– Heavy grass cover can
reduce wind at ground
level
B.
Common microclimates
North facing slopes
Exhibit one type of microclimate
South facing slopes
Exhibit another microclimate
C. Mountainous topography
1.
Influences local/regional microclimates
»
2.
3.
4.
5.
Changes patterns of precipitation
Intercepts air flow
Air mass reaches mountains-ascendscools-becomes saturated
Releases moisture
on windward side
Cool, dry air descends
other side—picks up
moisture from land
Phenomenon is called rain shadow
 Found at continental divide
 Found on Hawaiian Islands
