Download Heating the Atmosphere

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 a measure of the
average kinetic energy of the individual
atoms or molecules in a substance.
When air transfers energy to a cooler object,
the air’s particles move slower and its
temperature drops.
Energy Transfer
Three mechanisms of
heat transfer are:
• Conduction
• Convection (through
movement of a fluid
like water or air)
• Radiation
These mechanisms operate to transfer energy
between Earth’s surface (both land and water) and
the atmosphere.
Conduction
Conduction is heat flow through matter by
molecular activity (collisions of one molecule
with another). 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
between Earth’s surface and the air directly in
contact with the surface (touching the ground).
For the atmosphere as a whole, conduction is the
LEAST IMPORTANT method of heat transfer.
Much of the HEAT transfer that occurs in the
atmosphere is carried on by CONVECTION.
Convection
Heat flow through mass movement or
circulation of a fluid (like water or air)
where the molecules or atoms are free to
move about 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 transferred by convective flow in
the air.
Convection is also important in the oceans and
within the Earth’s mantle, which is solid but
behaves like a liquid over long periods of time.
Radiation
• The Sun is ultimately the source of the energy that
creates our weather.
• Light and heat are forms of energy that are only part of a
large array of energy called the electromagnetic
spectrum.
Radiation (cont.)
• All radiation, whether short wavelengths like
x-rays, gamma rays or UV rays or long
wavelengths like radio waves, travels through
the vacuum of space at 300,000 kps.
• Radiation is emitted from a source (it moves
away from it) in all directions and in a mixture
of wavelengths (sizes).
• Unlike conduction and convection, radiant
energy can travel through the vacuum of space
(no matter or stuff needed!). Solar energy
reaches Earth by radiation.
Electromagnetic Spectrum
• Radio waves have the LONGEST wavelengths.
• Gamma waves have the SHORTEST
wavelengths.
• Visible light is the only portion of the spectrum you
can see. Each color corresponds to a specific
RANGE OF WAVELENGTHS.
• RADIATION travels out in all directions from its
source.
• Unlike conduction and convection, which need
material to travel through, radiant energy can
travel through the vacuum of space.
Radiation (cont.)
Here are the 4 laws governing radiation:
1. All objects, of any temperature, emit
radiant energy.
2. Hotter objects radiate more total energy
than do cold objects.
3. The hottest radiating bodies produce the
shortest wavelengths of radiation.
4. Objects that are good absorbers of
radiation are good emitters as well.
Radiation’s Effect on Objects
When radiation strikes an object, there usually
are three different results:
1. Some energy is absorbed by the object.
When radiant energy is absorbed, it is
converted to heat and causes a temperature
increase.
2. Substances such as water and air are
transparent to certain wavelengths of
radiation. Radiation is that is transmitted
does not contribute energy to the object.
What happens to solar radiation?
3. Some radiation may
bounce off without
being absorbed or
transmitted.
Reflection occurs
when radiation
bounces off an
object.
This is the transmitted
radiation—it goes right
through the atmosphere,
being neither absorbed or
reflected.
Reflection and Scattering of Light
• REFLECTION is light bouncing off an
object. The reflected light has the same
intensity as the incident (incoming) radiation.
• SCATTERING produces a larger number of
weaker rays that travel in different
directions, although most energy is in the
forward direction.
Scattering
• Dust and gas
molecules scatter light,
giving us our blue sky
and diffuse light on
cloudy days.
• About 50% of the solar
radiation that is
absorbed at Earth’s
surface arrives as
scattered light.
Earth’s Energy Budget
• 51% of incoming solar
radiation is absorbed by
land and sea
• 4% is reflected from
land/sea interface
• 19% is absorbed by
atmosphere and clouds
• 20% is reflected from
clouds
• 6% is backscattered to
space from the
atmosphere
Earth’s Energy Budget
• The atmosphere also plays a major role in
heating Earth’s surface.
• Remember that all objects radiate heat
according to their temperature. Hot
objects radiate energy at shorter
wavelengths than do cool objects.
• Because Earth has a much lower surface
temperature than the sun, the radiation
that it emits has longer wavelengths than
solar radiation does.
Earth Radiates in the Infrared
Earth’s energy budget is balanced: incoming solar
radiation is balanced by outgoing terrestrial
radiation. This outgoing radiation is longwave
INFRARED radiation.
Greenhouse Effect
1) Solar radiation
(including light)
is absorbed by
and warms
Earth’s surface
(The reflected sunlight
isn’t important here,
because it doesn’t warm
Earth’s surface!)
1
Greenhouse Effect (cont.)
2) Earth’s surface
radiates heat
energy toward
space but at a
cooler
temperature
(as infrared
radiation)
2
Greenhouse Effect (cont.)
3) Certain gases in
the atmosphere
—especially
carbon dioxide
(CO2) and water
vapor—absorb
some of this
escaping heat
energy
3
This has NOTHING to do
with the OZONE LAYER!!
Greenhouse Effect (cont.)
4) These gases, in
turn, radiate
energy both
toward space
and back
towards Earth
5) This ‘extra’ heat
energy keeps
Earth habitable
4
The nitrogen and oxygen gas
molecules in the atmosphere
also play NO role in GE.
3
2
4
1
Remember, the reflected sunlight doesn’t play a role in
the Greenhouse Effect, so ignore it!
Greenhouse Effect
• Without the
Greenhouse
Effect, our oceans
would be frozen
solid!
Is the Greenhouse Effect the
same thing as Global Warming?
• NO! GE is a natural effect caused by
certain gases in our atmosphere—CO2,
water vapor, methane, and some others—
that keeps our planet warm enough to be
habitable (Remember: 59°F instead of 0°F!)
Global warming is the increase of global
temperatures as a result of increases in
carbon dioxide and other greenhouse
gases (such as water vapor and methane) in
the atmosphere.
Global Warming
• During the 20th Century, Earth’s average
surface temperature has increased about
0.6°C, and by 2100 climate scientists predict
temperatures will increase by 1.4°C to 5.8°C
(2.5°F to 10.4 °F)
• What is debated is whether the temperature
increase is due to human activities or not.
We will discuss this topic in more detail later in
the year.
What are the basic elements
of weather?
• When someone asks what it is like
outside, what do we respond?
• When someone from another part of the
US or another country asks you what the
climate is like in Hobbs, what do you
answer?
• TEMPERATURE is one of the basic
elements of weather and climate. We’re
going to focus on this element of weather.
Why do temperatures
on Earth vary?
• When the sun’s rays strike
the Earth’s surface from
directly overhead, they heat
the surface more than
sunlight that strikes at an
angle.
• We have already learned
that the angle of sunlight
depends on the season,
because Earth’s axis is tilted
23.5° from vertical.
• Another
thing that
depends on season is
the how long the
sun is above the
horizon (daylength)
• Because variations
in the angle of the
sun’s rays and
daylength depend
upon WHERE you
are on Earth (along a
circle of LATITUDE),
some latitudes get
more direct
sunlight and
therefore more heat
than others.
• Averaged over a year, the
regions near the equator
(low latitudes) get much
more heat than do polar
regions (high latitudes).
• These variations are
responsible for warmer
temperatures in the
tropics and colder
temperatures at the
poles.
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.
Let’s make a foldable for this:
LATITUDE
Once again,
• Averaged over a year, the
regions near the equator
(low latitudes) get much
more heat than do polar
regions (high latitudes).
• These variations are
responsible for warmer
temperatures in the
tropics and colder
temperatures at the poles.
HEATING OF LAND AND WATER
• The heating of Earth’s surface controls
the temperature of the air above it.
• Land heats FASTER and HOTTER during the
day and cools FASTER and COLDER during
the night than water does so…
Effect of a Large Body of Water
on Temperatures
. . . Being near a large body of water affects
temperatures. The RANGE of yearly
temperatures is NOT as GREAT near a
large body of water. The more constant
temperature of the water causes the air
passing over it to have a smaller
temperature range throughout a year than
air over land does.
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.
ON THE OCEAN = warmer
in winter and cooler in
summer overall than inland
INLAND = more extreme
temps
Mean Monthly Temperatures for
Vancouver and Winnipeg
Another Land-Water Effect
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)?
Altitude
For the same latitude, higher
elevations experience lower overall
temperatures than do lower
elevations.
This means that at HIGHER elevations,
winter temperatures are COLDER
and summer temperatures are
COOLER than at lower elevations.
Mean Monthly Tems for
Quito and Guayaquil
Geographic Position
1. 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 (stuck with hot
summers and cold winters).
2. Mountains can act as barriers, cutting
an area off from a moderating influence
that it would otherwise have.
Mean Monthly Temps for Eureka and NYC
Mean Monthly Temps for
Seattle and Spokane
Understanding Check
We have looked at the effects of LATITUDE,
LAND and WATER, ALTITUDE, and
GEOGRAPHICAL POSITION.
Consider this situation:
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?
Talk with a partner and answer this on your white
board (2 min).
Cloud Cover During the Day
Clouds reflect a significant portion of the
sunlight that reaches them back towards
space because they have a high albedo.
Cloud Cover Effects
ALBEDO is the fraction of total radiation
that is reflected from a surface. Clouds
and snow have a high albedo, asphalt has
a low albedo.
The amount of cloud cover strongly affects
how much sunlight reaches the Earth’s
surface. The more cloudy it is, the less
sunlight reaches the surface.
A cloudy day will be cooler than if it
were a clear 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 keep temperatures
cooler during the day and warmer at night,
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.
Computer Model of the Gulf Stream Surface Temperature, 2005,
http://www.education.noaa.gov/Ocean_and_Coasts/Ocean_Currents.html
Worldwide Temperature Distribution
ISOTHERMS are lines that connect
points with the same temperature.
If you look at world map that shows
isotherms, you’ll notice that isotherms
generally trend east and west and show a
decrease in temperatures from the
tropics toward the poles.
NOTE: Isotherms are NOT the same as
latitude even if they trend east and west.
Global Map Showing Isotherms
Did you see that temperatures are
warmest near the tropics and coldest
near the poles? (We do know that
there are differences due to the other
factors, though.)
This result shows that the largest
influence on temperature is
(drumroll, please)
a locations’ latitude.