Radiation and heat budget

1. Radiation and the Heat Budget
Email: tanvirhridoy74@gmail.com
Tanvir Ahmed
Roll – 2053221007
MESM - 2020

2. In physics, radiation is the emission or transmission of
energy in the form of waves or particles through space or
through a material medium. This includes: electromagnetic
radiation, such as radio waves, microwaves, infrared,
visible light, ultraviolet, x-rays, and gamma radiation .
Radiation is a process in which energetic particles or
energetic waves travel through vacuum, or through matter-
containing media that are not required for their propagation.
In the present context Radiation means by which Solar
Energy reaches the earth and the loses energy to outer
space.

3. The energy entering, reflected, absorbed,
and emitted by the Earth system are the
components of the Earth's radiation
budget. Based on the physics principle of
conservation of energy, this radiation
budget represents the accounting of the
balance between incoming radiation,
which is almost entirely solar radiation,
and outgoing radiation, which is partly
reflected solar radiation and partly
radiation emitted from the Earth system,
including the atmosphere. A budget that's
out of balance can cause the temperature
of the atmosphere to increase or
decrease and eventually affect our
climate. The units of energy employed in
measuring this incoming and outgoing
radiation are watts per square meter
(W/m2).
The Earth's Radiation Budget is a
concept used for understanding:
How much energy the Earth gets
from the Sun and How much
energy the Earth-system radiates
back to outer space as invisible
light.

4. INCOMING SOLAR RADIATION
Incoming ultraviolet, visible, and a limited portion
of infrared energy (together sometimes called
"shortwave radiation") from the Sun drive the
Earth's climate system. Some of this incoming
radiation is reflected off clouds, some is
absorbed by the atmosphere, and some passes
through to the Earth's surface. Larger aerosol
particles in the atmosphere interact with and
absorb some of the radiation, causing the
atmosphere to warm. The heat generated by
this absorption is emitted as longwave infrared
radiation, some of which radiates out into space.

5. ABSORBED ENERGY
The solar radiation that passes through
Earth's atmosphere is either reflected off
snow, ice, or other surfaces or is absorbed
by the Earth's surface.
Emitted LONGWAVE Radiation
Heat resulting from the absorption of
incoming shortwave radiation is emitted as
longwave radiation. Radiation from the
warmed upper atmosphere, along with a
small amount from the Earth's surface,
radiates out to space. Most of the emitted
longwave radiation warms the lower
atmosphere, which in turn warms our

6. GREENHOUSE EFFECT
Greenhouse gases in the
atmosphere (such as water vapor
and carbon dioxide) absorb most
of the Earth's emitted longwave
infrared radiation, which heats the
lower atmosphere. In turn, the
warmed atmosphere emits
longwave radiation, some of which
radiates toward the Earth's
surface, keeping our planet warm
and generally comfortable.
Increasing concentrations of
greenhouse gases such as carbon
dioxide and methane increase the
temperature of the lower
atmosphere by restricting the
outward passage of emitted
radiation, resulting in "global
warming," or, more broadly, global
climate change.

7. RADIATION AND THE CLIMATE SYSTEM
For scientists to understand climate change,
they must also determine what drives the
changes within the Earth's radiation budget.
The Clouds and the Earth's Radiant Energy
System (CERES) instrument aboard NASA's
Aqua and Terra satellites measures the
shortwave radiation reflected and longwave
radiation emitted into space accurately
enough for scientists to determine the Earth's
total radiation budget. Other NASA
instruments monitor changes in other aspects
of the Earth's climate system—such as
clouds, aerosol particles, and surface
reflectivity—and scientists are examining
their many interactions with the radiation
budget.

8. The atmospheric heat budget of the Earth
depends on the balance between insolation
and out going terrestrial radiation.
This budget has remained constant over the
last few thousand years.
If the Earth retains more energy from the Sun,
the Earth warms and emits more infrared
energy. This brings the Earth's Radiation
Budget into balance.
Scientists think of the
Radiation Budget in terms
of a see-saw or balance.
The Earth Radiation Budget is the balance between incoming energy from
the sun and the outgoing longwave (thermal) and reflected shortwave
energy from the Earth.

9. If the Earth emits more of this energy than it absorbs, the Earth cools. As it
cools, the Earth emits less energy. This change also brings the Radiation
Budget back into balance.
Basic Parts of the Radiation
Budget
•Solar Incident Energy
•Solar Reflected Energy
•Earth Emitted Energy
Solar Incident Energy :
A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth
continuously. That's more than 10,000 times the world's total energy use. And
that energy is completely renewable — at least, for the lifetime of the sun.

10. Solar Reflected Energy :
The amount of energy put out by the Sun is a constant. The incoming solar
radiation is known as insolation. The amount of solar energy reaching the Earth is
70 percent. The surface of the Earth absorbs 51 percent of the insolation. Water
vapor and dust account for 16 percent of the energy absorbed. The other 3
percent is absorbed by clouds. Of the 30 percent that is reflected back into space,
6 percent is reflected by air and dust. Clouds reflect 20 percent, and the remaining
4 percent is reflected by the surface.

11. Earth Emitted Energy :
Earth returns an equal amount of energy
back to space by reflecting some incoming
light and by radiating heat (thermal infrared
energy). Most solar energy is absorbed at
the surface, while most heat is radiated back
to space by the atmosphere.
Incoming solar radiation is absorbed by the Earth's surface, water vapor,
gases, and aerosols in the atmosphere. This incoming solar radiation is
also reflected by the Earth's surface, by clouds, and by the atmosphere.

12. The amount of energy received from the sun is determined by;
• The solar constant
-- the total radiation energy received from the Sun per unit of time per unit of
area.
-- solar constant varies slightly and affects longer term climate rather than short
term weather variations.
• The distance earth from the sun - can cause a variation of up to 6% in the
solar insolation.
• The length of day and night.
• The equator receives more energy
as solar radiation strikes the Earth,
whereas at 60 N or 60 S the angle
creates twice the area to cover and
increases the amount of atmosphere
to go through.

13. Where does incoming Solar
Radiation go?
Incoming Solar Energy can be:
• Reflected- bounced immediately
back into space so there's no effect
at all.
• Absorbed (changed into heat)-
warms the earth/atmosphere.
• Absorbed and re-radiated out to
space- incoming radiation warms the
surface temporarily.
The balance or imbalance of these :
• Controls earth surface and
atmosphere temperatures
• Drives ocean and atmosphere
circulation

14. EARTH’S GLOBAL HEAT BUDGET
Let global average solar radiation
= 100%
Reflection = 35% [31% by atm.;
4% by land & sea]
Absorption = 65% [17.5% in atm.;
47.5% by land & sea]
About half of Incoming energy absorbed by the Land and Sea
Fate of energy absorbed by land & sea
Re-radiated directly to space = 5.5%
Transferred to atmosphere = 42%
Reflection = 35% [31% by atm.; 4% by land & sea]
Absorption = 65% [17.5% in atm.; 47.5% by land & sea]
About half of Incoming energy absorbed by the Land and Sea.
Re-radiated directly to space = 5.5%
Transferred to atmosphere = 42%

15. I. Earth’s rotation: Earth’s rotation causes daily variations in
net radiation. During daytime, the net radiation is positive
while during nighttime it becomes negative because of no
incoming shortwave radiation (Rs).
II. Earth-Sun geometry: It causes annual variations in net
radiation thereby affects global radiation balance. During
winter, the amount of incoming shortwave radiation (Rs↓)
received is less which leads to less net radiation (Rn) and
the vice-versa happens during the summer.
III. Latitude: Equator receives more incoming shortwave
radiation (Rs↓) which leads to more net radiation (Rn) than
near poles.

16. IV. Altitude: With increase in altitude, there is less
atmospheric reflection/scattering/absorption which leads to
more incoming shortwave radiation (Rs↓) received at the
surface as well as less incoming longwave radiation (RL↓).
This leads to more positive net radiation (Rn) during day
than at sea level while during night it becomes more
negative than at sea level.

17. V. Surface color: Darker surface has lower albedo which leads to
lower Rs↑ and higher Rn.
VI. Clouds, dust and pollution factor: Clouds, dust, pollutants
absorb Rs↓and RL↑, and have direct radiative forcing which
varies between -0.2 to -1.1 W m-2. Under cloudy skies, daytime
Rn at surface is less positive than clear skies while it is less
negative at nighttime as cloud acts as barrier to RL↑ and
reradiates back to earth surface.
VII. Meridional Heat Transport: Rn is surplus at low latitudes (<
40° N/S) and deficit at high latitudes
(> 40° N/S). Energy is transported from the surplus to the deficit
regions (pole-ward transport) by
ocean currents warm/cold winds (sensible heat) and moisture in
air (latent heat).Thus it prevents overheating at low latitude and
over cooling at high latitude; this is known
as meridional heat transport