Climates
What is Climate
Climate is an average of weather
conditions in a region over a longterm period of time.
Weather is the short-term condition
of the atmosphere over a region.
Global Climate
Global climate is determined by the
interaction of solar energy with the
Earth’s surface and atmosphere:
- by conditions of temperature and humidity.
Climate is important is determining:
habitability
land use
Effect of climate is the availability of water
at the surface and within the ground.
The Water Cycle and Climate
• The water cycle involves the transfer of
moisture between the land and sea, and
between different latitudes.
• Since climate is determined by the amount
of moisture and the potential for
evapotranspiration, climate is tied to the
water cycle.
The Earth’s Water Cycle
Is a Closed System
Latitude Affects Moisture Exchange
• Some latitudes have a surplus of
precipitation over evaporation, other
latitudes have a precipitation deficit.
– 3 main belts of surplus are:
• the equatorial zone 0o to 10o North and South
• mid-latitude zones 40o to 70o in each hemisphere
– 2 main belts of deficit are:
• ~10o to 40o in each hemisphere
Insolation
INcoming SOLar radiATION
Insolation is the term that refers to the
amount of radiation from the Sun that is
received by the Earth.
Intensity of insolation is the rate at which
solar energy is received by a given area of
the Earth’s surface per unit of time.
Intensity and Area
Intensity of insolation is inversely related to
the area of the Earth’s surface receiving
it.
As area gets bigger, intensity gets lower.
Intensity
vs Area
Factors Affecting Insolation
• Some of the many factors that affect
insolation are:
– Angle of insolation
– Type of surface
– Length of time insolation is received
– Atmospheric conditions
Angle of Insolation
The angle which the Sun’s rays strike the
surface is called the angle of insolation.
The angle can be from 0o to 90o.
Rays at a 90o angle are called direct, or
vertical, rays.
Areas receiving more direct rays will have
higher temperatures.
Angle of Insolation
Time and Intensity
• Angle of the Sun varies with time, so time
will affect intensity.
– At sunrise and sunset the angle of the Sun’s
rays is the least and so the intensity is least.
– At noon the Sun’s rays are at their greatest
angle (most direct) and so the intensity of
insolation is also the greatest.
Time and Angle
Earth’s Shape Affects Intensity of
Insolation
• Since the Earth is an oblate sphere,
there is only one location that
receives vertical rays from the sun.
• The more you move away from the
direct rays, the lower the angle of the
rays and the lower the intensity.
Intensity of Insolation Diagram
Vertical Rays at Summer in
Northern Hemisphere
Seasons and Intensity of Insolation
• Intensity of isolation varies with the
seasons of the year.
• Seasons are caused by the tilt of the
Earth’s axis and the revolution around the
Sun.
Seasons of the Earth
Latitude and Intensity of Insolation
• At noon on the date of the equinoxes, the
sun is directly over the equator.
• At this time the angle of the sun is the
same as the observers latitude.
Seasonal Angles of the Sun
Duration of Insolation
• The duration of insolation is the number
of daylight hours at a given location.
• Daylight hours vary with latitude and time
of year.
• There is a direct correlation between angle
and intensity of insolation and duration of
insolation.
– Ex. Jun. 21 in Northern Hemisphere when
angle and intensity are greatest, duration is
longest.
Length of Day / Duration
Radiative Balance
• Radiative balance exists when a substance
gains the same amount of radiation as it
gives off.
• The Earth continuously receives insolation
and radiates infrared energy from its
surface.
Maximum and Minimum
Temperatures
• Maximum radiative energy reaches the
Earth when the angle and intensity of
insolation are the greatest.
– On a daily basis this is at solar noon (when
the Sun’s rays are most direct).
• Highest temperatures are after this time.
– Earth begins to receive more energy than it
gives off (reradiates).
– Highest temperatures occur mid-afternoon.
– Lowest temperatures occur just after sunrise.
Time of Year
• In the Northern Hemisphere the hottest
time of year is after June 21 (greatest
angle and duration of insolation).
• Hottest time of year is in August when the
amounts of incoming and outgoing energy
are in radiative balance.
• Coldest time of year is after Dec 21 (least
angle and duration) occuring in February.
Duration and Temperature
Temperature at the surface is directly related to
duration of insolation.
The longer the duration the higher the temperature
Note: the shortest days also have the lowest angle.