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Heating the Atmosphere
How do heat and temperature differ?
Heat is the ENERGY transferred from one
object to another due to a difference in
their temperatures. Heat flows from
HIGHER to LOWER temperatures.
TEMPERATURE is the average kinetic
energy of the individual atoms or
molecules in a substance.
Energy Transfer
• Conduction
• Convection
(through
movement of a
fluid like water or
air)
• Radiation
Conduction
Conduction is heat flow through matter by
collisions of one molecule with another
(molecular activity). The materials have to be
TOUCHING.
Some materials, like metals, are very good
conductors, while others, like air, are very poor.
In the atmosphere, conduction is only important at
the surface for the air directly in contact with the
surface. LEAST IMPORTANT method of heat
transfer.
Convection
Heat flow through mass movement of a fluid
(like water or air) where the molecules or
atoms are free to move about or circulate
within a substance.
Convection depends on unequal
heating. As heat is absorbed by
some of the fluid, it expands,
becomes less dense, and rises due
to buoyancy. Colder, denser fluid
sinks, flows in (to replace the heated
fluid), and becomes heated in its turn,
continuing the circulation pattern.
Convection (cont.)
In the atmosphere, most of the heat
acquired by the lower atmosphere through
radiation and conduction is transfered by
convection in the air.
Convection is also important in the oceans
and within the Earth, in the mantle.
Radiation
• The Sun is ultimately the
source of the energy that
creates weather.
• Energy gets from the Sun
to Earth via RADIATION
(the electromagnetic
spectrum, from short
wavelengths like x-rays
and gamma rays to long
wavelengths like radio
waves) which travels
through space at 300,000
kps.
Radiation (cont.)
•
Radiation is emitted from a source in all
directions.
• Radiation does NOT need a medium through
which to travel (no matter needed!)
Here are the 4 laws of radiation:
1. All objects, of any temperature, emit radiant
energy.
2. Hotter objects radiate more total energy than do
cold objects.
3. The hotter the radiating body, the shorter the
wavelength of radiation.
4. Objects that are good absorbers of radiation are
good emitters as well.
What happens to solar radiation?
1. Absorption
2. Passes through
(water and air are
transparent to
certain wavelengths)
3. Bounces off without
being absorbed or
transmitted
(reflection)
Reflection and Scattering
• REFLECTION is light bouncing off an object. The
reflected light has the same intensity as the incident
radiation.
• SCATTERING disperses light as weaker rays that
travel in different directions, although most energy is in
the forward direction. Dust and gas molecules scatter
light, giving us our blue sky and light on cloudy days.
About 50% of the solar radiation that is absorbed at
Earth’s surface arrives as scattered light.
Incoming Solar Radiation
• 50% of incoming solar radiation is
absorbed by land and sea
• 5% is reflected from land/sea interface
• 20% is absorbed by atmosphere and
clouds
• 20% is reflected from clouds
• 5% is backscattered to space from the
atmosphere
Absorption
• About 50% of the solar radiation that
reaches the top of the atmosphere
reaches the surface and is absorbed
• The atmosphere also plays a major role in
heating Earth’s surface.
‘Greenhouse Effect’
• The Earth reradiates some of
the absorbed solar energy
skyward, but at lower
temperatures (and longer
wavelengths like infrared).
• The atmosphere (especially
water vapor and carbon
dioxide) absorbs this energy
and in turn radiates it both
earthward and skyward.
• The skyward energy can be
absorbed by other gases or it
may be lost to space
• The earthward energy is again
absorbed by Earth.
Why do temperatures
on Earth vary?
We have already looked at differences in
how much solar radiation is received at a
place due to its latitude. The tropics have
warmer temperatures than the polar
regions due to more direct solar rays and
more daylight.
FACTORS AFFECTING
TEMPERATURE
• A TEMPERATURE CONTROL is any
factor that causes temperatures to vary
from place to place and from time to time.
• Other factors beside LATITUDE are
HEATING of LAND and WATER,
ALTITUDE, GEOGRAPHIC POSITION,
CLOUD COVER, and OCEAN
CURRENTS.
LAND AND WATER
• The heating of Earth’s surface controls the
temperature of the air above it.
• Being near a large body of water affects
temperatures because land heats more rapidly
and to higher temperatures than water does.
Land also cools more rapidly and to lower
temperatures than water does.
• The more constant temperature of the water
causes the air passing over it to have less
temperature change throughout a year than air
over land.
Vancouver, BC is at about the same latitude
as Winnipeg, Manitoba, so they both have
the same solar angle and length of
daylight. Vancouver, however, is on the
windward Pacific coast while Winnipeg is
far inland. The influence of the ocean is
that Vancouver’s year-round temperatures
are more moderate, cooler in summer and
warmer in winter, than Winnipeg’s.
“More moderate” also means fewer
temperature extremes.
Differences in Hemispheres
Another important land and water effect is
due to the different amounts of land and
water in the Northern and Southern
Hemispheres.
The Northern Hemisphere has 61% water
and 39% land.
The Southern Hemisphere has 81% water
and 19% land.
Which hemisphere would you predict has
smaller annual temperature variations (is
more moderate)?
Geographic Position
Coastal locations where the wind blows onto
the land (WINDWARD) or away from the
land (LEEWARD) have very different
weather. A windward coast gets the
moderating influence of the water (cool
summers and mild winters) while the
leeward coast does not.
Mountains can act as barriers, cutting an
area off from a moderating influence.
Altitude
For the same latitude, higher elevations
experience lower overall temperatures
than do lower elevations.
Understanding check:
Denver is far inland but at a high elevation; San
Francisco is on the Pacific Coast. They have similar
latitudes.
What would you expect to be the differences in climate
between them?
Cloud Cover
Many clouds reflect a significant portion of
the sunlight that reaches them back
towards space so they have a high albedo.
ALBEDO is the fraction of total radiation that
is reflected from a surface.
How much cloud cover there is strongly
affects how much sunlight reaches the
Earth’s surface.
A cloudy day is a cooler day.
Nighttime Clouds
But, clouds at night have
the OPPOSITE effect.
They act like a
BLANKET.
Clouds absorb the
outgoing radiation from
the Earth, trapping it
and reradiating some of
it back toward the
surface.
Overall, clouds act to lower daytime
temperatures while raising nighttime temps,
moderating the daily temperature range.
Ocean Currents
The Gulf Stream is a warm current that flows
from Florida across the Atlantic Ocean to
Great Britain and moderates its climate.
Worldwide Temperature Distribution
If you look at world map that show
ISOTHERMS, lines that connect points
with the same temperatures, you see that
temperatures are warmest near the tropics
and coldest near the poles, even though
there are differences due to the other
factors.
This shows that the largest influence on
temperature is a locations’ latitude.