Transcript The Earth's Global Energy Balance

Meteorology
Geography Department
East China Normal University
Shu Jiong
The Earth’s Global Energy
Balance
◆ Solar radiation is the driving power source
for wind, waves, weather, rivers, and ocean
currents.
◆ The earth’s energy balance, which includes
land and ocean surfaces and the atmosphere,
controls the seasonal and daily changes in
the earth’s surface temperature.
Electromagnetic Radiation
◆ Wavelength describes the distance
separating one wave crest from the next
crest.
◆ The unit to measure wavelength is the
micrometer.
◆ Radiant energy can exist at any
wavelength.
Radiation and Temperature
◆ There is an inverse relationship between
the radiation that an object emits and the
temperature of the object.
◆ Hot objects radiate more energy, and at
shorter wavelengths, than cooler objects.
Solar radiation
◆ The Sun is a ball of constantly churning
gases that are heated by continuous nuclear
reactions. It has a surface temperature of
about 6000oC. Like all objects, it emits
energy in the form of electromagnetic
radiation.
electromagnetic spectrum
Shortwave radiation
◆ Ultraviolet radiation (0.2 to 0.4 μm)
◆ Visible light radiation(0.4 to 0.7μm)
◆ Shortwave infrared radiation (0.7 to
3μm)
Longwave radiation
◆ Thermal infrared wavelengths (>3μm)
Characteristics of solar
energy
◆ The sun does not emit all wavelengths
of radiation equally
◆ The intensity of solar energy is
strongest in visible wavelengths
Longwave radiation from
the Earth
◆ The earth’s surface and atmosphere
are much colder than the sun’s
surface,so the energy from the Earth
has longer wavelength
The global radiation balance
◆ The earth constantly absorbs solar
shortwave radiation and emits longwave
radiation.
◆ The sun provides a nearly constant flow of
shortwave radiation toward earth.
◆ The atmosphere, land, and ocean also emit
energy in the form of longwave radiation.
Figure 1 Global Energy Balance
Insolation over the Globe
◆
Insolation(incoming solar radiation)
depends on the angle of the sun above
the horizon.
The Path of the Sun in the
Sky
The sun’s path in the sky changes greatly in
position and height above horizon from
summer to winter.
◆ At equinox, the sun rises directly to the east
and sets directly to the west.
◆ The noon sun is positioned at an angle of
50o above the horizon in the southern sky.
The sun is above the horizon for
exactly 12 hours.
◆ At noon it will be 73.5o above the
horizon.
◆ The sun is above the horizon for about
15 hour
◆
Daily Insolation Through the
Year
◆ Daily
insolation depends on two factors:
◆ the angle at which the sun’s rays strike
the earth
◆ the length of time of exposure to the rays
◆ the equator has two periods of maximum
daily insolation, these periods occur near
the equinoxes.
There are also two minimum periods
near the solstices, when the subsolar
point moves farthest north and south
from the equator. All latitudes between
the tropic of cancer 23.5oN and the
tropic of Capricorn 23.5oS have two
maximum and minimum values .
◆ Seasonal pattern of daily insolation is
directly related to latitude.
◆
Annual Insolation by Latitude
◆ Annual insolation varies smoothly from the
equator to the pole
◆ The annual insolation value at the pole is
about 40% of the value at the equator.
◆ The tilting of the earth’s axis redistributes a
significant portion of the earth’s insolation
from the equatorial regions toward the poles.
World Latitude Zones
◆ The equatorial zone encompasses the
equator and covers the latitude belt roughly
10oN to 10oS
◆ Spanning the tropics of cancer and
Capricorn are the tropical zones, ranging
from latitudes 10o to 25o north and south
◆ Moving toward the poles from each of the
tropical zones are transitional regions
called the subtropical zones, ranging
from latitudes 25o to 35o north and south
◆ The midlatitude zones lie between 35o
and 55o latitudes in the northern and
southern hemispheres
◆ Bordering the midlatitude zones on the
poleward side are the subarctic zone and
subantarctic zone, 55o to 60o north and
south latitudes
◆ Astride the arctic and Antarctic circles
from latitudes 60o to 75o N and S lie the
arctic and Antarctic zones
◆ The polar zones, north and south, are
circular areas between about 75o latitude
and the poles
Composition of the
Atmosphere
◆ The earth’s atmosphere consists of air-a
mixture of various gases surrounding the
earth to a height of many kilometers.
◆ Almost all the atmosphere 97% lies within
30km of the earth’s surface.
The upper limit of the atmosphere is at
a height of approximately 10,000km
above the earth’s surface, a distance
approaching the diameter of the earth
itself.
◆ Pure, dry air consists largely of nitrogen,
about 78% by volume, and oxygen, about
21%. Other gases account for the
remaining 1%
◆ Water vapor is an important component of
the atmosphere that varies in concentration
from place to place and time to time
Ozone in the Upper
Atmosphere
Ozone (O3) is found mostly in the
upper part of the atmosphere, in a layer
termed the stratosphere. Ozone in the
stratosphere absorbs ultraviolet
radiation from the sun as this radiation
passes through the atmosphere
◆
At both polar regions, climate and chemistry combine to deplete
ozone during spring months. Dark blue indicates lowest ozone
amounts. Arctic total ozone amounts seen by TOMS in March
2003 (above, left) were among the lowest ever observed in the
northern hemisphere. The Antarctic ozone hole of 2003 (above,
right) was the second largest ever observed.
Sensible Heat and Latent Heat
Transfer
◆ Sensible Heat-the quantity of heat held by
an object that can be sensed by touching or
feeling
◆ When two objects of unlike temperature
contact each other, heat energy moves by
conduction from the warmer to the cooler.
This type of heat flow is referred to as
sensible heat transfer
The Global Energy System
◆ Insolation losses in the Atmosphere
◆ Albedo
◆ Counterradiation and the Greenhouse
Effect
◆ Global Energy Budget of the Atmosphere
and Surface
◆ Net Radiation, Latitude, and the Energy
Balance
Winds and the Pressure
Gradient Force
◆ Wind is air motion with respect to the
earth’s surface, and it is dominantly
horizontal.
◆ Barometric pressure falls with
increasing altitude above the earth’s
surface.
◆ The change in barometric pressure
across the horizontal surface of a map
constitutes a pressure gradient.
The gradient is in the direction from
higher pressure to lower pressure.
◆ Where a pressure gradient exists, air
molecules tend to drift in the same
direction as that gradient.
This tendency for mass movement of
the air is referred to as the pressure
gradient force.
Sea and Land Breezes
◆ During the daytime, more rapid
heating of the lower air layer over the
land than over the ocean causes a
pressure gradient from sea to land. Air
moving landward in response to this
gradient from higher to lower pressure
constitutes the sea breeze.
At higher levels, a reverse flow sets in.
Together with weak rising and sinking
air motions, a complete flow circuit is
formed.
◆ During the night, when radiational
cooling of the land is rapid, the
lower air becomes colder over the
land than over the water. Higher
pressure now develops over land and
the barometric gradient is reversed.
Air now moves from land to sea as
a land breeze.
Figure 2 Sea breeze and land breeze
Cyclones and Anticyclones
◆A center of low pressure is called a
cyclone; a center of high pressure is an
anticyclone.
◆Winds in a cyclone in the northern
hemisphere show an anticlockwise
inspiral. In an anticyclone, there is a
clockwise outspiral.
◆ The surface winds spiral inward on
the center of the cyclone, so the air is
converging on the center and must
also rise to be disposed of at higher
levels.
◆ For the anticyclone, by contrast,
surface winds spiral out from the
center. This motion represents a
diverging of airflow and must be
accompanied by a sinking of air in the
center of the anticyclone to replace
the outmoving air.
Figure 3 Surface winds in cyclones and anticyclones
Global Distribution of Surface
Pressure Systems
◆ Over the equatorial zone is a belt of
somewhat lower than normal pressure,
between 1011 and 1008 mb, which is
known as the equatorial trough.
◆ Lower pressure is conspicuous by
contrast with belts of higher
pressure lying to the north and
south and centered at about
lat.30°N and S. These are the
subtropical belts of high pressure,
in which pressure exceed 1020mb.
◆ In the southern hemisphere, south of
the subtropical high-pressure belt, is a
broad belt of low pressure, extending
from the midlatitude zone to the arctic
zone. The axis of low pressure is
centered at about lat.65S. This pressure
trough is called the subantactic lowpressure belt.
◆ Lying over the continuous expanse of
Southern Ocean, this trough has
average pressure as low as 984mb.
Over the continent of Antarctica is a
permanent center of high pressure
known as the polar high.
The Global Pattern of Surface
Winds
◆ From the two subtropical high-pressure
belts the pressure gradient is
equatorward, leading down to the
equatorial trough of low pressure. Air
moving from high to low pressure is
deflected by the Coriolis effect. As a
result, two belts of trade winds are
produced.
◆ Meeting of the trades takes place
within a narrow zone called the
intertropical convergence zone.
◆ Along parts of the equatorial trough of
low pressure at certain times of year,
the trades do not come together in
convergence. Instead, a belt of calms
and varible winds, called the doldrums,
forms.
◆ Between lat.35 and 60N and S is the
belt of prevailing westerly winds, or
westerlies.
◆ A wind system called the polar
easterlies is characteristic of the
arctic and polar zones.
Figure 4 Surface winds
Monsoon Winds of
Southeast Asia
◆ In summer southern Asia develops a
cyclone into which there is strong flow of
air. From the Indian Ocean and the
southwestern Pacific, warm, humid air
moves northward and northwestward into
Asia. This airflow constitutes the summer
monsoon and is accompanied by heavy
rainfall in southeastern Asia.
◆ In winter, Asia is dominated by a
strong center of high pressure from
which there is an outward flow of air
reversing that of the summer monsoon.
Blowing southward and southeastward
toward the equatorial oceans, this
airflow
constitutes
the
winter
monsoon and brings dry weather for a
period of several months.
Mountain winds and
valley winds
◆ During the daylight hours the air
along the slopes of the mountains is
heated more intensely than the air at
the same elevation over the valley floor.
This warm air glides up along the slope
and generates a valley wind.
◆ After sunset the pattern is reversed.
Rapid radiation heat loss along the
mountain slopes results in cool air
drainage into the valley below and
causes the mountain wind.
Global Circulation
◆ The Hadley Cell Circulation
In the zone between the equator and
roughly 30° latitude, the surface flow
is equatorward while the flow aloft is
poleward. Near the equator the warm
rising air that releases latent heat
during the formation of cumulus
towers is believed to provide the
energy to drive this cell
◆ The circulation between 30 and 60
latitude is just opposite that of the
Hadley cell. The net surface flow is
poleward, and because of the Coriolis
effect, the winds have a strong
westerly component.
◆ About the circulation in the high
latitudes, it is generally believed that
subsidencenear the poles produces a
surface flow that moves equatorward
and is deflected into the polar easterlies
of both hemisphere. The region where
the cold polar winds and the warmer
westerly flow of the midlatitudes clash
has been named the polar front.
The global Circulation and
Man’s Environment
◆ In low latitudes, the Hadley cell
operates like a simple heat engine to
transport heat from the equatorial
zone to the subtropical zone.
◆ Upper-air waves take up the transport
and move warm air poleward in
exchange for cold air.
◆ The global atmospheric circulation
also transports heat in the latent form
held by water vapor.
◆ Winds carry a large amount of water
vapor, which is deposited as
precipitation on the coast.
◆ Winds also transport atmospheric
pollutants, carrying them tens and
hundreds of kilometers from the
sources of pollution.
Air temperature
◆ Temperature is a measure of the
level of sensible heat of matter,
whether it is gaseous, liquid, or solid.
◆ Conduction describes the flow of
heat from a warmer substance to a
colder one when the two are touching.
◆ Evaporation, the process by which
water changes from a liquid to a gas by
absorbing heat, tends to lower the
temperature of a wet surface.
Measurement of air
temperature
Air temperatures are now automatically
recorded by thermometers at a uniform
height above the ground.
The daily cycle of air
temperature
◆ Because the earth rotates on its axis,
incoming solar energy at a location can vary
widely throughout the 24-hour period.
◆ Insolation is greatest in the middle of the
daylight period, when the sun is at its highest
position in the sky, and falls to zero at night.
Daily insolation and net
radiation
The daily cycle of temperature is
controlled by the daily cycle of net
radiation.
◆ At the equinox, insolation begins at
about sunrise (6 a.m.),rises to a peak
value at noon, and declines to zero at
sunset (6 p.m.).
◆
◆ At the June solstice, insolation begins
about two hours earlier (4 a.m.) and
ends about two hours later (8 p.m.).
◆ At the December solstice, insolation
begins about two hours later than the
equinox curve (8 a.m.) and ends about
two hours earlier (4 p.m.).
◆ When net radiation is positive, the
surface gains heat, and when negative, it
loses heat.
◆ Net radiation begins the 24-hour day as
a negative value-a deficit-at midnight.
The deficit continues into the early
morning hours. Net radiation shows a
positive value- a surplus-shortly after
sunrise and rises sharply to a peak at
noon.
Daily temperature
The minimum daily temperature usually
occurs about a half hour after sunrise. Air
temperature rises sharply in the morning
hours and continues to rise long after the
noon peak of net radiation. Air temperature
rises as long as net radiation is positive.
Temperatures are lowest just after sunrise
and highest in midafternoon.
Urban and rural temperature
contrasts
◆ Urban surfaces lack moisture and so
are warmer than rural surfaces during
the day. At night, urban materials
conduct stored heat to the surface, also
keeping temperatures warmer.
The urban heat island
◆ As a result of the above effects, air
temperatures in the central region of a
city are typically several degrees
warmer than those of the surrounding
suburbs and countryside. This is called
a heat island.
◆ The heat island persists through the
night because of the availability of a
heat stored in the ground during the
daytime hours.
◆ Another important factor in warming
the city is fuel consumption. In
summer, city temperatures are raised
through the use of air conditioning.
Temperature structure of the
Atmosphere
Troposphere
◆The
troposphere
is
the
lowest
atmospheric layer, in which temperature
decreases with increasing elevation.
Everyday weather phenomena, such as
clouds or storms, occur mainly in this layer.
◆ The troposphere contains significant
amounts of water vapor and countless
tiny dust particles.
Stratosphere
◆
Above the troposphere lies the
stratosphere in which the air becomes
slightly warmer as altitude increases.
◆ The stratosphere extends to a height
of roughly 50km above the earth’s
surface.
◆ It is the home of strong, persistent
winds that blow from west to east.
◆One
important feature of the
stratosphere is that it contains the
ozone layer.
High-Mountain Environments
◆ At high elevations, air temperatures
are generally cooler and show a greater
day-to-night range.
Temperature Inversion and
Frost
◆
In a temperature inversion, air
temperature increases with altitude.
◆
Low-level temperature inversions
often occur over snow-covered
surfaces in winter.
◆ Inversions can also result when a
warm air layer overlies a colder one.
This type of inversion is often found
along the west coasts of major
continents.
Frost
◆ If the temperature of the lowermost
air falls below the freezing point, for
sensitive plants during the growing
season, this temperature condition is
called a killing frost.
The annual cycle of air
temperature
 The
annual cycle of net radiation,
which results from the variation of
insolation with the seasons, drives the
annual cycle of air temperatures.
Land and water contrasts
◆ Land-water contrasts keep air temperatures
at coastal locations more constant than at
interior continental locations.
◆ Oceans heat and cool more slowly than
continents.
◆ The surface of any extensive, deep
body of water heats more slowly and
cools more slowly than the surface of a
large body of land when both are
subjected to the same intensity of
insolation.
Daily temperature cycle

P62 Figure 3.15
The average daily cycle of air
temperature for four different months
shows the effect of continental and
maritime location. Daily and seasonal
ranges are great at El Paso, a station in
the continental interior, but only
weakly developed at North Head,
Washington, which is on the Pacific
coast. The seasonal effect on overall
temperatures is stronger at El Paso.
Annual temperature cycle

P63 figure 3.16 Annual cycles of insolation
(a) and monthly mean air temperature (b)
for two stations at lat. 50°N: Winnipeg,
Canada, and Scilly Islands, England.

Insolation is identical for the two stations.
Winnipeg temperatures clearly show the
large annual range and earlier maximum
and minimum that are characteristic of its
continental
location.
Scilly
Islands
temperatures show its maritime location in
the small annual range and delayed
maximum and minimum.
World Patterns of air
temperature
◆ Isotherms: Lines drawn to connect
locations having the same temperature.
◆ Maps of isotherms show centers of
high and low temperatures as well as
temperature gradients.
Factors controlling air
temperature patterns
◆ Global air temperature patterns are
controlled primarily by latitude,
coastal-interior location, and elevation.
World air temperature patterns
for January and July

P65 figure
Temperatures decrease from the
equator to the poles.
◆ Large landmasses located in the
subarctic and arctic zones develop
centers of extremely low temperatures
in winter.
◆ Temperatures in equatorial regions
change little from January to July.
◆
◆ Isotherms make a large north-south
shift from January to July over
continents in the midlatitude and
subarctic zones.
◆ Highlands are always colder than
surrounding lowlands.
◆ Areas of perpetual ice and snow are
always intensely cold.
The annual range of air
temperatures
◆ The annual range increases with
latitude, especially over northern
hemisphere continents.
◆ The greatest ranges occur in the
subarctic and arctic zones of Asia and
North America.
◆ The annual range is moderately large
on land areas in the tropical zone, near
the tropics of cancer and Capricorn.
◆ The annual range over oceans is less
than that over land at the same latitude.
◆ The annual range is very small over oceans
in the tropical zone.
Global warming and the
greenhouse effect
◆ The temperature of our planet is
warming. Most scientists agree that the
human-induced buildup of greenhouse
gases has begun to affect global
climate. However, natural cycles, such
as variations in the sun’s output, still
provide strong influences.
Greenhouse gases
◆ Carbon Dioxide (CO2)
◆ Methane (CH4)
◆ Nitrous oxide (NO)
◆ Ozone (O3)
Summery
◆ The Earth’s Global Energy Balance
◆ The Path of the Sun in the Sky
◆ World Latitude Zones
◆ Composition of the Atmosphere
◆ Winds and the Global Circulation
◆ Air temperature
Thanks
for
attention !