Insolation and heat budget

Atmosphere is open energy system.
It receives energy from both directions (earth and
sun).
Compared with sun (solar energy), earth’s energy can
be negligible.
All life processes and all exchanges of matter and
energy between the earth’s atmosphere and the
surfaces of the oceans and lands are driven by solar
energy.
The planetary circulation systems of atmosphere and
oceans are also driven by solar energy.
Water changes in various forms (liquid, solid and gas)
over the globe also driven by solar energy.
Sun is the energy source of the earth.

Emitted from sun (surface temperature 6000oC)
It is a spectrum (combination energy of different
wavelengths)
Most of it is visible light rays (short-wave)
Energy emitted by earth (surface temperature 15oC) is
terrestrial radiation (long-wave)
Higher temperature of an object emits shorter-wave of
radiation.
The radiant energy received from the sun,
transmitted in a form analogous to shortwave,
and travelling at the rate of 1,86,000 miles per second.
That it reaches earth in 8 minutes 20 seconds.

 The prime source of the energy injected into
our atmosphere is the sun.
 The sun is constantly releasing energy in all
direction. This energy is known as solar radiation.
 It is a electro-magnetic wave energy radiating from
sun, which is also called Insolation.
 All weather phenomena are affected by various
meteorology parameters which all affected by
Insolation

 incoming Solar Radiation
 Insolation is a measure of Solar Radiation
incident of a surface.
 It is the amount of solar energy received over a
given area in a given time.
 It is commonly expressed in:
kilowatt-hours per square meter per day
(kw.h/m2/day)
(or)
watts per square meter(w/m2).

 Short-wave radiation (wavelength < 0.8 micron)
– Ultra-violet, x-rays, gamma rays,
• Invisible and harmful for living organisms.
• Most of them absorbed by thermosphere and ozone layer.
– Visible lights (violet, indigo, blue, green, yellow, orange and
red).
• 90% of solar rays.
• It provides most of the heat energy to the atmosphere.
 Long-wave radiation (wavelength > 0.8 micron)
– Infrared, micro waves and radio waves
– They are also absorbed by ozone, CO2 and clouds.

Our atmosphere is transparent to radio waves, visible light, and some
infrared and UV radiation.
Atmospheric Window

Most of the radiation emitted from the sun is in the visible
part of the spectrum.

 The earth and its
atmosphere reflect part of
the solar radiation back to
space.
 Reflectivity, or albedo, is
expressed as a percentage
of the incident radiation
reaching the surface.
Reflection of sunlight depends on the type and size of
the particles as well as the wavelength

 Scattering is the process by which small
particles and molecules of gases diffuse
part of the radiation in different
directions.
 The amount and direction of scattering
depends on the ratio of the radius of the
scattering particle to the wavelength of
the energy.
 The most obvious effect of scattering in
the atmosphere is sky color.
 The only reason our sky appears blue is
because of scattering of radiation in the
shorter wave-lengths of visible light.

 Rayleigh scattering is primarily caused by oxygen and
nitrogen molecules. The effective diameters are at least 0.1
times smaller than the affected wavelengths.
 Rayleigh scattering is most influential at altitude above 4.5
km (pure atmosphere).
 The amount of Rayleigh scattering is 1/λ4
 As the result, invisible ultraviolet radiation is greatly
affected by Rayleigh scattering.
 Rayleigh scattering can be called small particle scattering.
 In visible light, blue wavelength at 0.4 μm is scattered 5
times as the red wavelength at 0.6 μm.
 This explains why the clear sky appears blue. The scattering
made blue light reach our eyes from all parts of the sky.

 Occurs when there are sufficient particles in the
atmosphere that have mean diameters from 0.1 to
10 times larger than the wavelength under
consideration.
 Mie scattering can be called large particle scattering.
 The important Mie scattering agents include water
vapor and tiny particles of smoke, dust, etc. The
influence of the Mie scattering is most affected in the
lower 4.5 km of the atmosphere.
 Mie scattering influences longer radiation
wavelengths than Rayleigh scattering.
 The wavelength of Mie scattering is between to λ4 to
λ0.

 Absorption retains incident radiation and converts it
to some other form of energy.
 Most often it changes to sensible heat, which raises
the temperature of the absorbing object.
 Gas molecules, could particles, haze, smoke, and dust
absorb part of the incoming solar radiation.
 The two most common gases in the atmosphere,
nitrogen and oxygen absorb ultraviolet radiation.

 The amount of Insolation received on the earth’s
surface is not uniform everywhere.
 It varies according to the place and time.
 When the tropical regions received maximum
annual Insolation, it gradually decreases towards the
poles.
 Insolation is more is summers and less in winters.

Solar output
Distance from the sun
Angle of solar incidence
Length of day

 Solar radiation is light energy from the Sun.
 Millions of Nuclear reaction happens across the sun every second.
 Hydrogen atoms get compressed and fuse together, creating helium.
This process is called nuclear fusion.
 It's constantly giving off a huge amount of energy and radiation.
 The core of the sun temperature , which can reach more than 15 million
degrees Celsius.
 The temperature in the photosphere is about 60000C.
 Solar output of the total solar energy sent out into space the earth
intercepts only some two thousand millionth, equivalent too a power of
1.8x1014kw.
 The energy received on a surface normal to the solar beam is about 2
cal/cm2/min (1.396kw/m2)3;this is termed the solar constant.
 There are 11 years cyclic variations of 1% in the output of solar energy.
 More energy can be received when sunspot activity is less active.

 The ever-changing distance of the earth from the sun produces more
frequent variation in our receipt of solar energy.
 Since the earth revolves around the sun in an elliptical orbit.
 The mean distance between the earth and sun is about 149.6million
km.
 Each year, on about January 3, the earth comes closer to the sun
(distance 147.3 million kilometers). This position is known as
perihelion.
 On about July 4, the earth is a little farther from the sun when the
distance becomes about 152.1 million kilometers. This position is
called aphelion.
 the receipt of solar energy on a surface normal to the beam is 7% in
January than in July.
 January world surface temperature of about 40c(70F), over those of
July.

 Angle of incidence:
It is the angle between the sun’s rays and the horizon.
Greater the angle of incidence, the more concentrated
energy, hence higher is the temperature.
Intensity of Insolation is greatest where the sun’s rays
strike vertically.
Polar regions receive the least heat per unit area.
Temperatures are maximum at low latitudes and minimum
near the poles.
Angle of incidence is affected by latitude, the time of day,
seasons and length of daytime.

 The length of daylight also affects the amount of Insolation which
received.
 At the equator the length of days and nights is 12 hours. On the
autumnal and vernal equinoxes that occur on September 23 and
March 21 respectively, the mid-day sun is overhead at the equator.
 The winter solstice (December 22) onward the length of day
increases in the northern hemisphere till the summer solstice (June
21).
 June 21 to December 22 the length of day in the northern
hemisphere decreases, and in the southern hemisphere it increases.
 the summer solstice the northern hemisphere has the longest day
and the shortest night.
 the winter solstice the southern hemisphere has the longest day, and
the northern hemisphere has the longest night.

Latitude Longest day Latitude Longest day
or night or night
0 12 hours 63.4 20 hours
17 13 hours 66.5 24 hours
31 14 hours 67.4 1 month
41 15 hours 69.8 2 months
49 16 hours 78.2 4 months
58.5 18 hours 90.0 6 months

Incoming heat being absorbed by the Earth, and outgoing
heat escaping the Earth in the form of radiation are both
perfectly balanced.
 If they were not balanced, then Earth would be getting
either progressively warmer or progressively cooler with
each passing year.
 This balance between incoming and outgoing heat is
known as Earth’s heat budget.

First let us understand the amount of solar Insolation
received by earth and atmosphere separately.
Suppose incoming solar insolation is = 100 units.
Amount lost through scattering and reflection:
a) Through Clouds - 27 units
b) By dust particles - 6 units
c) By Ice Caps and Glaciers - 2 units
Total 35 units are reflected back into space.
(known as albedo of earth)
Now, the units received by earth and its atmosphere = 100-
35 = 65 units

51 units of solar insolation is received by earth as direct
radiation which can be segregated as follows:
I. Received through direct Radiation= 34 units
II. Received as diffused day light = 17 units
Which comes out to be 51 units.

 Absorption by atmospheric gases in different
vertical zones of atmosphere - 14 units
Now 51 units + 14 units= 65 units (total solar insolation
received by earth and atmosphere)
 Out of the solar radiation received directly by
Earth i.e. 51 units, 17 units are re-radiated
back into outer space, and rest 34 units
(51-17 units) is absorbed by atmosphere in
the form of outgoing terrestrial radiation.
Which comes out to be 48 units (14+ 34 = 48).

Albedo= Reflected radiation
Incoming radiation
 A measure of the amount of radiation reflected.
 Some things reflected radiation better than others
 “dry” or “cold” snow & ice = high albedo
 Water =moderate for visible , low for infrared
 Plants =moderate for visible
 Land absorbs and releases radiative energy quicker
than water

Typical albedos of various surfaces to incoming solar radiation
Type of surface Percent reflected energy (Albedo)
Fresh Snow 75 - 95%
Old Snow 30 - 40%
Water
0° 99%
10° 35%
30° 6%
90° 2%
Clouds
Cumulus 70 - 90%
Stratus 60 - 84%
Cirrus 44 - 50%
Forest 5 - 20%
Grass 10 - 20%
Sand 35 - 45%
Plowed soil 5 - 25%
Crops 3 - 15%
Concrete 17 - 27%
Earth as a Planet 30%

 Atmosphere, Weather and Climate – Barry and R.J. Chorley
Page No: 10,11,12,13,14,15,16,17,18,19,21,27,28
 Climatology an Atmospheric Science – John E. Oliver and John J. Hidore.
Page No: 21,26,27,28,29
 https://Zolushka 4 earth.Wordpress.com/2010/08/27/understanding-heat-
budget/
 https://www.clearias.com/insolation-heat-balance/

Insolation and heat budget

More Related Content

What's hot (20)

Similar to Insolation and heat budget (20)

More from pavithrasenthilkumar5 (11)

Recently uploaded (20)

Insolation and heat budget