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Recap

When solar radiation reaches the earth, the incoming solar radiation being
 reflected
 scattered
 absorbed

When it reaches the ground, some is being reflected (shortwave radiation).

The ground converts the insolation into longwave outgoing radiation.

Recap (What’s more)

Counter-radiation by the clouds

Sensible heat transfer

Latent heat transfer

Assumptions

Scale: Global scale

Time: Long term trend

Division of Components
ATMOSPHERE
EARTH
Earth-atmosphere

Operation of Energy Budget

The incoming solar radiation
Total
Scattered to space
Scattered to ground
Reflected by cloud
Reflected from ground
Absorbed by atmosphere
Absorbed by cloud
Absorbed by ground
100
5
6
21
6
15
3
50

Income
6
100
15
3
11
21

The outgoing radiation
Total
Sensible heat transfer
Latent heat transfer
Ground radiation absorbed by atmosphere
Ground radiation to space
Radiation to the space
Counter-radiation to the ground
9
20
90
8
60
77

The outgoing radiation
8
0
77
90
20
60
18
9

Energy Budget Table

Formulate three energy budget tables according to the three different components:
 earth system
 atmospheric system
 earth-atmospheric system

Heat balance at the ground surface
Gain
Short-wave radiation from the sun 50
Counter-radiation from the atmosphere 77
The balance of gain
127
Loss
Long-wave radiation to the space 8
Long-wave radiation to the atmosphere 90
Latent heat flux to the atmosphere 20
Sensible heat flux to the atmosphere 9
The balance of loss
127

Heat balance at the atmosphere
Gain
Short-wave radiation from the sun 18
Long-wave radiation from the ground 90
Latent heat flux from the ground 20
Sensible heat flux to the space 9
The balance of gain
137
Loss
Counter-radiation to the ground 77
Long-wave radiation to the space 60
The balance of loss
137

Annual Solar Radiation at Earth Surface

Latitudinal distribution of solar radiation

The annual solar radiation received along the equator is very high but not the highest

Due to the presence of cloud cover ( ITCZ)

Inter-tropical Convergence Zone

Between 10 o -20 o N and S, there receive most solar radiation

The angle of incidence is high

Lack of cloud cover

Latitudinal distribution of solar radiation

At high latitudes, there is less radiation

Because the angle of incidence is low

High albedo because of snow cover

More insolation in Northern Hemisphere

Because there is more land surface and less cloud cover

Global Distribution of Short Wave
Radiation

Latitudinal Distribution of Annual Solar
Radiation

Global Distribution of Long Wave
Radiation

Global Distribution of Net Radiation

Annual Net Radiation

Difference between Figure 2.13 and 2.15
 Fig. 2.13 shows annual solar radiation but Fig. 2.15 shows the net radiation
 Annual solar radiation considers incoming solar radiation only
 Net radiation is nthe difference between incoming solar radiation and outgoing solar radiation.

TWO characteristics in spatial variation
 The net radiation amount of ocean is greater than land at the same latitude.
 Net radiation decreases with increasing latitude .

Difference between S. Hemisphere and
N. Hemisphere
 The net radiation amount at equivalent latitudes in the S. Hemisphere is more than the N. Hemisphere
 because there are more ocean,
 then there is more cloud cover.

Variation in Average Annual Net
Radiation

Variation in Average Annual Net
Radiation
 At nearly all latitudes, net radiation of the earth surface is above zero.
 Energy deficit is experienced at most latitudes of the atmomsphere system and stable over latitudes.
 The net radiation of the earth-atmosphere system is the combination of earth surface and atmosphere system
 Energy Surplus in between 0 o and 40 o N & S
 Energy Deficit in regions higher than 40 o N & S

Seasonal and latitudinal effect on Energy
Budget
Summer Winter Total surplus surplus surplus
Equator
Around 20 o surplus
35 o -40 o N&S surplus
Polewards of about
65 o N&S deficit deficit deficit deficit surplus balance deficit

Relaxation of Assumptions

Relaxation of Assumptions

Illustration of the atmospheric energy budget

Description
 Incoming solar radiation may be reflected and absorbed by clouds. Scattered and absorbed by atmosphere, reflected and absorbed by earth’s surface
 Short-wave solar radiation reflected by clouds and earth’s surface may go back to space
 Short-wave solar radiation scattered by atmosphere may go either to space or to the earth’s surface

Description
 Radiation (both short-wave and long-wave) absorbed by clouds and atmosphere will eventually go to space or the earth’s surface in form of long-wave radiation
 Radiation (both short-wave and long-wave) absorbed by earth’s surface will go back to space or atmosphere in form of log-wave radiation; or may be dissipated through latent heat loss or sensible heat loss to atmosphere

Heat transfer
 Short wave radiation from the sun received by the earth leaves the atmosphere in the form of long-wave radiation and heated up the atmosphere
 For the earth as a whole, the amount of short wave-radiation received will be equal to the amount of long-wave radiation lost as to keep the earth at the same temperatures in the long run

Heat transfer
 The amount of short wave radiation received by the earth varies greatly along latitude and between seasons because of the earth’s spherical shape, the inclination of the axis, different amount of cloud cover and albedo of the earth’s surface
 The amount of long wave radiation leaving the atmosphere at different latitude does not vary as great as the amount received and thus resulting surplus of heat in the lower latitudes and a deficiency of heat in the higher latitudes.

Heat transfer
 To maintain an equilibrium, surplus heat from the low latitudes is transported to high latitude
 Heat from lower altitudes is transport to higher altitudes
 Both horizontal and vertical transfer are involved
 Atmospheric processes such as air circulation, condensation and precipitation are involved

Heat transfer
 Since air is a poor conductor, conduction is unimportant in the atmosphere, but it is important in the ground
 The low viscosity of air and its consequent ease of motion makes convection the chief method of atmospheric heat transfer
 Heat energy transferred by radiation becomes sensible heat only when absorbed by water vapour, carbon dioxide or ozone

Energy budget it tropical rainforest TRF
 Due to high angle of incidence there is high incoming solar radiation, causing hot climate
 Albedo of forest-covered surface is low
 Small variation in length of daytime leads to little seasonal variation of incoming solar radiation producing uniform climate, small annual range of temperature and even distribution of precipitation

Energy budget it tropical rainforest TRF
 Large amount of radiation absorbed by earth’s surface, causing intense convection (latent heat loss), resulting abundant precipitation throughout the whole year
 About 20% incoming solar radiation reflected by clouds. Preventing extreme high temperature in daytime

Energy budget it tropical rainforest TRF
 More than half of long-wave radiation from the earth’s surface absorbed by clouds and then re-radiated back to earth’s surface, keeping warm temperature in night time
 Therefore, daily temperature range is also small

Energy budget of Tundra (Polar region)