radiation balance

1. RADIATION
BALANCE
ATMOSPHERIC
TEMPERATURE

2. THE SUN AND IT’S ENERGY
The Sun is the star located at the center
of our planetary system. It is composed
mainly of hydrogen and helium. In the
Sun's interior, a thermonuclear fusion
reaction converts the hydrogen into
helium releasing huge amounts of
energy. The energy created by the fusion
reaction is converted into thermal energy
(heat) . The solar heat energy travels
through space in the form
of electromagnetic waves (As EM waves
do not require a medium) enabling the
transfer of heat through a process known

3. WHAT IS INSOLATION
The amount of solar radiation reaching a
given area.
In simple terms – It is the incoming solar
radiation.
Insolation Varies Depending on:
Time of Year
Solar Declination
Earth-Sun Distance
Latitude
Time of day (solar zenith)
Atmoshperic Conditions (Clouds, smoke,
pollution, diffuse sky light

4. Energy Basics
 Energy Pathways and Principles
 Shortwave energy in from the Sun (ultraviolet,
visible light, and near-infrared)
 Longwave energy out from Earth (thermal
infrared)
 Transmission
 The passage of energy through atmosphere or
water
 Insolation input
 All radiation received at Earth’s surface – direct
and indirect

5. ENERGY BALANCE OF THE
EARTH
The Earth’s climate is a solar powered system. Globally,
over the course of the year, the Earth system—land
surfaces, oceans, and atmosphere—absorbs an average
of about 240 watts of solar power per square meter.
The absorbed sunlight drives photosynthesis, fuels
evaporation, melts snow and ice, and warms the Earth
system. The sun provides 99.97% of the energy
required for all physical processes that take place on
the earth and in the atmosphere
The Sun doesn’t heat the Earth evenly. Because the
Earth is a sphere, the Sun heats equatorial regions
more than polar regions. The atmosphere and ocean
work non-stop to even out solar heating imbalances
through evaporation of surface water, convection,
rainfall, winds, and ocean circulation. This coupled
atmosphere and ocean circulation is known as Earth’s
heat engine.

6. ENERGY BALANCE OF THE
EARTH
The climate’s heat engine must not only
redistribute solar heat from the equator
toward the poles, but also from the Earth’s
surface and lower atmosphere back to
space. Otherwise, Earth would endlessly
heat up. Earth’s temperature doesn’t
infinitely rise because the surface and the
atmosphere are simultaneously radiating
heat to space. This net flow of energy into
and out of the Earth system is Earth’s
energy budget.

7. ENERGY BALANCE OF THE
EARTH
The energy that Earth receives from sunlight is
balanced by an equal amount of energy
radiating into space. The energy escapes in
the form of thermal infrared radiation: like the
energy you feel radiating from a heat lamp.

8. ENERGY BALANCE OF
THE EARTH
When the flow of incoming solar energy is
balanced by an equal flow of heat to space,
Earth is in radiative equilibrium, and global
temperature is relatively stable. Anything
that increases or decreases the amount of
incoming or outgoing energy disturbs
Earth’s radiative equilibrium; global
temperatures rise or fall in response.

9. Methods of Heat Transfer
 Heat always moves from a warmer place to
a cooler place.
 Hot objects in a cooler room will cool to
room temperature.
 Cold objects in a warmer room will heat up
to room temperature.

10. Methods of Heat Transfer

11. Methods of Heat Transfer
CONDUCTION
When you heat a metal strip at one end, the heat
travels to the other end. As you heat the metal, the
particles vibrate, these vibrations make the
adjacent particles vibrate, and so on and so on, the
vibrations are passed along the metal and so is the
heat.

12. Methods of Heat Transfer
CONVECTION/ADVECTION
Convection is the transfer of heat by the
physical movement of the heated medium
itself. Convection occurs in liquids and
gases but not in solids.

13. In convection the physical mixing
involves a strong vertical motion.
In advection – the horizontal motion
dominates.

15. Methods of Heat Transfer
RADIATION
Radiation is the transfer of heat in the form
of waves through space (vacuum). Dull
black surfaces are better than white
shining ones at absorbing the radiated heat.

16. Radiation transfer from Sun to Earth.
Properties of Solar radiation: The
Sun is located at the center of our
Solar System, at a distance of
about 150 x 106 kilometers from
Earth. With a surface temperature
of 5780 K (degrees Kelvin =
degrees C + 273.15), the energy
flux at the surface of the Sun is
approximately 63 x 106 W/m2

17. Solar radiation on Earth:
As the Sun's energy spreads through space
its spectral characteristics do not change
because space contains almost no interfering
matter. However the energy flux drops
monotonically as the square of the distance
from the Sun. Thus, when the radiation
reaches the outer limit of the Earth's
atmosphere, several hundred kilometers over
the Earth's surface, the radiative flux is
approximately 1360 W/m2

18. The global heat budget is
the balance between
incoming and outgoing
solar radiation. Incoming
solar energy varies at
different times of year and
for different locations
across the globe.

19. Earth's energy budget accounts for how much energy
comes into the Earth's climate system from the Sun,
how much energy is lost to space, and accounting for
the remainder on Earth and its atmosphere. Research
to quantify changes in these amounts is required to
accurately assess global warming.
Received radiation is unevenly distributed over the
planet, because the Sun heats equatorial regions
more than polar regions. Energy is absorbed by the
atmosphere and hydrosphere and, in a process
informally described as Earth's heat engine, the solar
heating is distributed through evaporation of surface
water, convection, rainfall, winds, and ocean
circulation. When incoming solar energy is balanced
by an equal flow of heat to space, Earth is
in radiative equilibrium and global temperatures
become relatively stable.

24. The solar radiation that fills our sky can
be direct, diffused or reflected radiation.
" Direct radiation" is also sometimes
called "beam radiation" or "direct beam
radiation". It is used to describe solar
radiation traveling on a straight line from
the sun down to the surface of the earth.
"Diffuse radiation", on the other hand,
describes the sunlight that has been
scattered by molecules and particles in
the atmosphere but that has still made it
down to the surface of the earth.
Direct radiation has a definite direction
but diffuse radiation is just going any
which way.

25. Because when the radiation is direct, the
rays are all travelling in the same
direction, an object can block them all at
once. This is why shadows are only
produced when direct radiation is blocked.

26. Ratio of direct to diffuse radiation
When the sky is clear and the sun is very
high in the
sky, direct radiation is around 85% of the
total insolation striking the ground
and diffuse radiation is about 15%. As the
sun goes lower in the sky, the percent of
diffuse radiation keeps going up until it
reaches 40% when the sun is 10° above
the horizon.
Atmospheric conditions like clouds and
pollution also increase the percentage of
diffuse radiation. On an extremely

27. overcast day, pretty much 100% of the solar
radiation is diffuse radiation. Generally
speaking, the larger the percentage of diffuse
radiation, the less the total insolation.
Direct/diffuse ratio varies with latitude and
climate
The percentage of the sky's radiation that is
diffuse is much greater in higher latitude,
cloudier places than in lower latitude, sunnier
places. Also, the percentage of the total
radiation that is diffuse radiation tends to be
higher in the winter than the summer in these
higher latitude, cloudier places. The sunniest
places, by contrast, tend to have less seasonal
variation in the ratio between diffuse and
direct radiation.

28. Reflected Radiation
Reflected radiation describes sunlight that
has been reflected off of non-atmospheric
things such as the ground. Asphalt reflects
about 4% of the light that strikes it and a
lawn about 25%. However, solar panels tend
to be tilted away from where the reflected
light is going and reflected radiation rarely
accounts for a significant part of the
sunlight striking their surface.
An exception is in very snowy conditions
which can sometimes raise the percentage
of reflected radiation quite high. Fresh snow
reflects 80 to 90% of the radiation striking
it.

29. Global Insolation
"Global insolation" is the total
insolation: direct + diffuse + reflected
light.
"Normal radiation" describes the
radiation that strikes a surface that is
at a 90° angle to the sun's rays. By
constantly keeping our solar collectors
at a 90° angle with the sun, we
maximize the direct radiation received
on that day.

30. Therefore, "normal global radiation"
generally tells us what the absolutely
most sun we could get is (as discussed
earlier in this page, if all the radiation
in the sky is diffuse, you do best to just
lay your solar collectors down flat -
although in that case you aren't going
to be gathering much solar radiation
anyway).

32. When you tilt your solar panels so that the
sun's rays are hitting them at a 90° angle, you
are maximizing the amount of direct
radiation that they receive.
However, since diffuse radiation is generally
pretty equally distributed throughout the sky,
the most diffuse radiation is gathered when
your solar panels are laying down horizontally.
The steeper your solar panels are tilted, the
less of the sky they are facing and the more of
the sky's diffuse radiation they miss out on. If,
for example, your solar collectors are tilted at
a 45° angle, they are facing away from about a
quarter of the sky and would only collect about
three-fourths of the diffuse radiation in the sky.

33. Still, because direct radiation is much
more intense than diffuse radiation, the
amount of radiation missed by tilted
solar panels is generally more than
compensated for by the extra radiation
gained by tracking the sun.

34. The average temperature on the earth
is : 15 C
This average temperature is due to the
balance between incoming solar
radiation and outgoing long wave
radiation

36. 70% of the solar radiation reaches the
earth’s surface
30% is reflected back to space by
clouds, particles in the atmosphere or
snow or sand or from the surface of the
earth – this 30% is not used in the
heating of the atmosphere or the
surface of the earth.
The 70% that stays in our atmosphere
can be broken down :
1/3 Powers the hydrologic cycle
2/3 Warms to Atmosphere – the oceans
& the continents

37. When UV radiation hits the earth’s
surface
It is converted to Infrared (Heat)
It is this infrared which is heating and
keeping the atmosphere warm

39. EARTH’S ALBEDO
= 30%

40. 40
absorbed by clouds
and dust, water vapour and other gases in the atmosphere
absorbed by surface
reflected by clouds
and dust, water vapour and other gases
in the atmosphere
reflected by surface
100%
19%
26%
55%
4%
51%
SOLAR INSOLATION

41. absorbed by surface
reflected by atmosphere
reflected by surface
100%
19%
26%
55%
4%
51%
absorbed by atmosphere
solar insolation
reaches surface
TOTALALBEDO = 26 + 4
= 30%
TOTALABSORPTION = 19 + 51
= 70%
SOLAR INSOLATION

42. The proportion of radiation reflected or absorbed
depends on the object's reflectivity or albedo,
respectively.
An ideal white body has an albedo of 100% and an ideal
black body, 0%.
TOTALALBEDO = 26 + 4
= 30%

43. EARTH’S ENERGY BALANCES
ENERGY ENTERING TOP OF ATMOSPHERE (342) = ENERGY LEAVING TOP OF ATMOSPHERE(107+235)
TOTAL IN/OUT = 342
ENERGY GAINED BY ATMOSPHERE (67+350+78+24) = ENERGY LOST BY ATMOSPHERE (165+324+30)
TOTAL IN/OUT = 519
ENERGY ENTERING EARTHS SURFACE (168+324) = ENERGY LEAVING EARTHS SURFACE (24+78+390)
TOTAL IN/OUT = 492

44. Energy entering at the top of
the atmosphere = 342 W/m2
Energy leaving at the top of the
atmosphere = 107 (earths
albedo)+ 235 (cumulative infra
red radiation lost to space by
earths atmosphere & surface

45. Energy gained by the
atmosphere = 67 + 350 + 78 +
24 = 519
Energy lost by the atmosphere
= 165 + 324 + 30 = 519

46. Energy entering the earths
surface =
168 (Direct Insolation) + 324
(Back Radiation) = 492
Energy leaving earths surface =
24 + 78 + 390 = 492

47. COMPARISON BETWEEN EARTH &
VENUS
The earth has clouds-oceans & land
Venus is completely covered with a
thick layer of Sulphuric acid clouds
Earths Albedo = 30%
Venus Albedo = 70%
Insolation absorbed by earth = 70 units
Insolation absorbed by Venus = 58 units
Venus absorbs less solar radiation than
earth – so Venus should be cooler!

48. However!
Earth’s average temperature = 15 C
Venus’s average temperature = 480 C
VENUS IS HELL!

49. THE REASON!

51. SCATTERING
Insolation encounters an atmosphere of
increasing density as it travels toward
the surface. Atmospheric gases, dust,
cloud droplets, water vapour and
pollutants physically interact with the
insolation. The gas molecules re-direct
the radiation changing the direction of
the light’s movement without altering
its wave length. Scattering describes
this phenomenon and represents 7% of
The general rule is that – The shorter
the wavelength the greater the

53. scattering – the longer the wave length
the lesser the scattering.
This is the reason behind the Raleigh
Scattering – this is why the skies are
blue and why sunsets/sunrises are red.

54. REFRACTION
When insolation enters the atmosphere
– it passes from one medium to another
– from a very rare region to a very
dense region. This occurs when
insolation passes from air into water.
This causes the insolation to change
speed which also causes its direction
to shift – this is refraction. In the same
way the prism refracts the incoming
light waves.

58. VARIOUS ALBEDO VALUES

59. ALBEDO & REFLECTION
The portion of arriving energy that
bounces back into space without being
absorbed or performing any work is
called the Reflection process. Albedo is
the reflective quality.
0% is total absorption – 100% is total
reflection.
In the visible wave lengths – darker
colors have lower albedos and lighter
color have higher albedos. The angle of
the solar rays also effect albedos –
lower angles produce greater reflection

60. than do higher angles. Smooth surfaces
increase albedo where as rough
surfaces reduce it.

62. CLOUDS-AEROSOLS &
ATMOSPHERES ALBEDO

68. CHANGES IN ALBEDO

69. Clouds reflect and cool the earth and at
the same time they act as insulators –
trapping long wave radiation from the
earth and raising the minimum
temperatures. Cloud greenhouse
forcing is an increase in greenhouse
warming caused by clouds.
Industrialization is producing a haze of
pollution including sulfate aerosols,
soot & fly ash and black carbon. These
suspended aerosols in the atmosphere
act as an insolation-reflecting haze in
clear sky conditions

70. Pollution causes both an atmospheric
warming through absorption by the
pollutants and a surface cooling
through reduction in insolation reaching
the surface.
Clouds effect the heating of the lower
atmosphere in several ways –
depending on cloud type. The cloud
cover is important as well as the cloud
type, height and thickness of the cloud.
High ice crystal clouds have an albedo
value of about 50% whilst thick lower
clouds have a 90% albedo value.

71. ABSORPTION
The assimilation of radiation by
molecules of matter and its conversion
from one form of energy to another are
absorption.
The temperature of the absorbing
surface is raised in the process and
warmer surfaces radiate more total
energy at shorter wavelengths – thus
the hotter the surface – the shorter the
wave lengths emitted.

72. ENERGY BALANCE IN THE
TROPOSPHERE
The earth-atmosphere energy system
naturally balances itself in a steady
state equilibrium.

74. Several patterns are notable on the
map. Insolation decreases pole ward
from about 25 N/S. Consistent day
lengths and a high sun altitude produce
average annual values of 180-220
Watts/m2 throughout the equatorial and
tropical latitudes. In general greater
insolation of 240-280 W/m2 occurs in
low latitude deserts worldwide because
of frequently cloudless skies. Note this
energy pattern in the cloudless
subtropical deserts in both
hemispheres e.g Sahara-Gobi-Kalahari
& Australian deserts.

75. The net heating imbalance between the
equator and poles drives an atmospheric
and oceanic circulation that climate
scientists describe as a “heat engine.”
(In our everyday experience, we
associate the word engine with
automobiles, but to a scientist, an engine
is any device or system that converts
energy into motion.) The climate is an
engine that uses heat energy to keep the
atmosphere and ocean moving.
Evaporation, convection, rainfall, winds,
and ocean currents are all part of the
Earth’s heat engine.

76. Earth’s heat engine does more than
simply move heat from one part of the
surface to another; it also moves heat
from the Earth’s surface and lower
atmosphere back to space. This flow of
incoming and outgoing energy is Earth’s
energy budget. For Earth’s temperature
to be stable over long periods of time,
incoming energy and outgoing energy
have to be equal. In other words, the
energy budget at the top of the
atmosphere must balance. This state of
balance is called radiative equilibrium.

82. Regionally and seasonally the earth
absorbs more energy in the tropics and
less in the polar regions – establishing
the imbalance which drives the Global
circulation patterns.
1. Between the tropics – the angle of
incoming insolation is high and
daylight consistent – more energy is
gained than lost – Energy surpluses
dominate.
2. In the polar regions – the sun is low
in the sky, surfaces are light (ice &
snow) and reflective and up to 6
months a year no insolation is

83. received – so more energy is lost than
gained – energy deficit prevails
3. At around 36N/S a balance exists
between energy gains and losses for
the earth-atmosphere system. The
imbalance of net radiation between the
tropical surpluses and the polar deficits
drives a vast global circulation of both
energy and mass.

87. WHAT IS THE GREEN HOUSE
EFFECT?
The greenhouse effect is a process by
which thermal radiation from a
planetary surface is absorbed by
atmospheric greenhouse gases, and is
re-radiated in all directions. Since part
of this re-radiation is back towards the
surface and the lower atmosphere, it
results in an elevation of the average
surface temperature above what it
would be in the absence of the gases.

88. WHAT ARE GREEN HOUSE GASES?
A gas that contributes to the greenhouse effect by
absorbing infrared radiation.

89. When greenhouse gas molecules absorb
thermal infrared energy, their temperature
rises. Like coals from a fire that are warm but
not glowing, greenhouse gases then radiate
an increased amount of thermal infrared
energy in all directions. Heat radiated upward
continues to encounter greenhouse gas
molecules; those molecules absorb the heat,
their temperature rises, and the amount of
heat they radiate increases. At an altitude of
roughly 5-6 kilometers, the concentration of
greenhouse gases in the overlying
atmosphere is so small that heat can radiate
freely to space.

90. Because greenhouse gas molecules
radiate heat in all directions, some of
it spreads downward and ultimately
comes back into contact with the
Earth’s surface, where it is absorbed.
The temperature of the surface
becomes warmer than it would be if
it were heated only by direct solar
heating. This supplemental heating of
the Earth’s surface by the
atmosphere is the natural
greenhouse effect.

91. Why doesn’t the natural greenhouse effect
cause a runaway increase in surface
temperature?
Remember that the amount of energy a
surface radiates always increases faster than
its temperature rises—outgoing energy
increases with the fourth power of
temperature. As solar heating and “back
radiation” from the atmosphere raise the
surface temperature, the surface
simultaneously releases an increasing
amount of heat—equivalent to about 117
percent of incoming solar energy. The net
upward heat flow, then, is equivalent to 17
percent of incoming sunlight (117 percent up
minus 100 percent down).

95. The Energy Balance at
The Earths surface
What happens if all
greenhouse gases are removed
Incoming energy would decrease
Earths surface would cool and
Would emit less infrared radiation
Until the balance is restored
The cooling would stop at (0 F)

96. If all the greenhouse gases were
removed from the atmosphere – the
atmosphere would not be able to
absorb radiation emitted by the
earth so energy emitted by
greenhouse molecules would go to
zero – this in turn would drastically
reduce the incoming energy
absorbed by the earths surface.

97. The Earths surface temperature
= 15C - With greenhouse gases
Concentration of CO2 gases
Increased by 50%
Earth’s surface would heat
And emit more infrared radiation
Until balance is restored

98. The Greenhouse effect keeps the earth
warm – without it the average
temperature of the earth would be -18C.
This would mean no life on earth
because there would be no liquid water.
The Greenhouse effect is truly
important for our existence and the
existence of all living things on the
earth.
The Greenhouse effect
becomes a problem when we
humans mess with it.

100. CO2 is the biggest gas influencing the
greenhouse effect.
What will happen if we
increase the amount of
CO2 in our atmosphere?

101. MORE CO2
MORE HEAT BEING TRAPPED
HIGHER TEMPERATURES ON
EARTH

102. What will happen if the level of CO2
gases increase in the atmosphere?
1. Global warming
2. Glaciers & Icebergs will melt
3. Sea levels will rise
4. It will cause droughts
(Desertification) in one region
and extra rains in other
5. Stronger storms & extreme
events
6. Increase in ocean acidification

103. ENERGY BALANCE AT THE
EARTH’S SURFACE

105. This shows the daily pattern of
incoming short wave energy absorbed
and resulting air temperature. This is
an ideal condition for bare soil on
cloudless day in middle latitudes.
Incoming energy arrives during day
light – beginning at sunrise – peaking at
noon & ending at sunset. The shape &
height of the graph varies season &
latitude.
Within 24 hours – air temperature
generally peaks between 1500 and
1600 hours and the minimum
temperature is slightly after sunrise.

106. The interesting fact is that the
insolation curve and the temperature
curve do not align – there is a lag – The
maximum temperature does not occur
at the time of maximum insolation but
at the time when a maximum of
insolation is absorbed and emitted to
the atmosphere from the ground. The
maximum occurs when the incoming
energy begins to diminish.
The same is true for the annual
patterns of insolation & temperature –
January being colder than December &
warmest month of July after June.

109. SIMPLIFIED SURFACE ENERGY
BALANCE

111. Energy and moisture are continually
exchanged at the surface – creating a
variety of boundary layer climates.
Sensible heat transfer in the soil is
through conduction. – predominantly
downward during the day and towards
the surface at night. Energy from the
atmosphere that is moving towards the
surface is a positive (a gain) and energy
that is moving away from the surface
through sensible & latent heat is a
negative (a loss).

112. The components of the equation vary
with day length – seasons – cloudiness –
latitude so does the net radiation
received vary.

113. Latent and Sensible Heat
Latent and sensible heat are types of
energy released or absorbed in the
atmosphere. Latent heat is related to
changes in phase between liquids,
gases, and solids. Sensible heat is
related to changes in temperature of a
gas or object with no change in phase.

114. Latent heat is the energy absorbed by or released from a
substance during a phase change from a gas to a liquid or a
solid or vice versa. If a substance is changing from a solid
to a liquid, for example, the substance needs to absorb
energy from the surrounding environment in order to spread
out the molecules into a larger, more fluid volume. If the
substance is changing from something with lower density,
like a gas, to a phase with higher density like a liquid, the
substance gives off energy as the molecules come closer
together and lose energy from motion and vibration.

115. On land the higher annual values of
latent heat of evaporation (LE) occur in
the tropics and decrease towards the
pole . Over the oceans the highest LE
values are over the sub-tropical
latitudes where hot – dry air comes in
contact with the warm ocean water.

116. GLOBAL LATENT HEAT OF EVAPORATION

117. Sensible Heat
Sensible heat is the energy required to
change the temperature of a substance
with no phase change. The temperature
change can come from the absorption
of sunlight by the soil or the air
itself. Or it can come from contact with
the warmer air caused by release of
latent heat. Energy moves through the
atmosphere using both latent and
sensible heat acting on the atmosphere
to drive the movement of air molecules
which create wind and vertical motions.

118. The values for sensible heat (H) are
highest in the sub-tropics – due to vast
regions of sub-tropical deserts feature
nearly waterless surfaces – cloudless
skies and almost vegetation free
landscapes. The bulk of NET R is
expended as sensible heat in these dry
regions. Moist & vegetated surfaces
expend less in “H” and more in “LE”

119. GLOBAL SENSIBLE HEAT

121. NET RADIATION
Earth's net radiation, sometimes
called net flux, is the balance between
incoming and outgoing energy at the
top of the atmosphere. It is the total
energy that is available to influence the
climate.

122. Net Radiation
The net radiation determines whether
the surface temperature rises, falls, or
remains the same:
NET(R)= incoming solar - outgoing IR
If the net radiation > 0, surface
warms ( 0600 to 1600 Hrs)
if the net radiation < 0, surface cools
(1600 – 0600 Hrs)
This also explains why the warmest
part of the year is in July/August, not on
21 June during the summer solstice.

124. Effect of orbit's shape:
The radiation at the top of the atmosphere varies by about
3.5% over the year, as the Earth spins around the Sun.
This is because the Earth's orbit is not circular but
elliptical, with the Sun located in one of the foci of the
ellipse. The Earth is closer to the sun at one time of year
(a point referred to as perihelion) than at the "opposite"
time (a point referred to as aphelion). The time-of-year
when the Earth is at perihelion moves continuously
around the calendar year with a period of 21,000-years. At
present perihelion occurs in the middle of the Northern
Hemisphere winter. The annual average radiative solar
flux at the top of the Earth's atmosphere (=1360 W/m2) is
sometimes referred to as the Solar Constant because it
has changed by no more than a few percent over the
recent history of the Earth (last few hundred years).
There are however important variations in this flux over
longer, so-called "geological", time scales, to which the
Earth glaciation cycles are attributed.

126. The tilt of the Earth's axis and the
seasons:
If the axis of Earth was perpendicular to the
plane of its orbit (and the direction of
incoming rays of sunlight), then the radiative
energy flux would drop as the cosine of
latitude as we move from equator to pole.
However, as seen in Figure 6, the Earth axis
tilts at an angle of 23.5° with respect to its
plane of orbit, pointing towards a fix point in
space as it travels around the sun. Once a
year, on the Summer Solstice (on or about the
21st of June), the North Pole points directly
towards the Sun and the South Pole is
entirely hidden from the incoming radiation.
Half a year from that day, on the Winter

127. Solstice (on or about the 21st of December) the North Pole
points away from the Sun and does not receive any sunlight
while the South Pole receives 24 hours of continued sunlight.
During Solstices, incoming radiation is perpendicular to the
Earth surface on either the latitude of Cancer or the latitude of
Capricorn, 23.5° north or south of the equator, depending on
whether it is summer or winter in the Northern Hemisphere,
respectively. During the spring and fall (on the Equinox days,
the 21st of March and 23rd of September) the Earth's axis tilts
in parallel to the Sun and both Polar Regions get the same
amount of light. At that time the radiation is largest at the true
equator. Averaged over a full 24-hour period, the amount of
incoming radiation varies with latitude and season as shown
in Figure 7. Note that the figure combines the effect of the
change in incidence angle with latitude and time of year and
the number of hours of sunlight during the day. At the poles,
during solstice, the earth is either exposed to sunlight over the
entire (24-hours) day or is completely hidden from the Sun
throughout the entire day. This is why the poles get no
incoming radiation during their respective winter or more than
the maximum radiation at the equator during their respective
summer.

131. Lithosphere
The lithosphere is the solid, rocky crust
covering entire planet.
This crust is inorganic and is composed of
minerals. It covers the entire surface of the
earth from the top of Mount Everest to the
bottom of the Mariana Trench.
Hydrosphere
The hydrosphere is composed of all of the
water on or near the earth. This includes the
oceans, rivers, lakes, and even the moisture
in the air. Ninety-seven percent of the earth's
water is in the oceans. The remaining three
percent is fresh water; three-quarters of the
fresh water is solid and exists in ice sheets

132. Biosphere
The biosphere is composed of all living organisms. Plants,
animals, and one-celled organisms are all part of the
biosphere. Most of the planet's life is found from three
meters below the ground to thirty meters above it and in
the top 200 meters of the oceans and seas.
Atmosphere
The atmosphere is the body of air which surrounds our
planet. Most of our atmosphere is located close to the
earth's surface where it is most dense. The air of our
planet is 79% nitrogen and just under 21% oxygen; the
small amount remaining is composed of carbon dioxide
and other gases. All four spheres can be and often are
present in a single location.
For example, a piece of soil will of course have mineral
material from the lithosphere. Additionally, there will be
elements of the hydrosphere present as moisture within
the soil, the biosphere as insects and plants, and even the

133. Disturbances of Earth's radiative equilibrium, such
as an increase of greenhouse gases, change global
temperatures in response. However, Earth's energy
balance and heat fluxes depend on many factors,
such as the atmospheric chemistry composition
(mainly aerosols, and greenhouse gases),
the albedo (reflectivity) of surface properties,
cloud cover, and vegetation and land use patterns.
Changes in surface temperature due to Earth's
energy budget do not occur instantaneously, due to
the inertia (slow response) of the oceans and the
cryosphere to react to the new energy budget. The
net heat flux is buffered primarily in the ocean‘s
heat content, until a new equilibrium state is
established between incoming and outgoing
radiative forcing and climate response.

134. The cryosphere is the frozen water
part of the Earth system. Beaufort
Sea, north of Alaska. One part of
the cryosphere is ice that is found
in water. This includes frozen parts
of the ocean, such as waters
surrounding Antarctica and the
Arctic. There are places on Earth
that are so cold that water is
frozen solid.

135. Solar constant
Solar constant, the total radiation energy
received from the Sun per unit of time per
unit of area on a theoretical surface
perpendicular to the Sun’s rays and at Earth’s
mean distance from the Sun.

136. SOLAR DECLINATION

137. SOLAR DECLINATION
Solar Declination (δ)
Earth's axial tilt is: 23.45º
Solar Declination = Latitude of the sub-solar point
(where the sun is directly overhead at solar noon)
Solar Declination (δ) changes seasonally, and is
calculated by the day of year using the following
equation:
δ =23.45*cos(2*π*(JD-172)/365)Where:
JD = Julian Day (count the days from Jan.1st)

138. SEASONS

139. Earth-Sun Distance

140. Earth-Sun Distance
The sun and earth are closest during perihelion
and farthest away during aphelion. The Solar
constant is the incoming solar radiation
measured at the top of the Earth's atmosphere
on a surface that is perpendicular to the
incident rays. While the average is 1367 W/m2,
it varies due to the earth-sun distance, since
radiation intensity is proportional to the square
inverse of the sun-earth distance. This is
because the surface area (4*pi*r^2) over which
the sun's energy is distributed will increase
with r, the earth-sun distance, and therefore
since the total energy is constant, the intensity
(W/m2) must decrease.

141. LATITUDE
Insolation decreases with
increased latitude