Radiation balance (budget) of the Earth surface and the atmosphere

B

Definition

R I B

I

Difference between absorbed and emitted by a body radiation is called balance of radiative energy (radiation balance – R) of the body.

We know sufficiently well about the R of the Earth surface and R of the Earth as a whole planet. However, we know a little about the radiation balance of separate layers of the atmosphere.

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Radiation balance of the Earth surface

Income part		Outlay part
•Absorbed fraction of the		The Earth surface
direct SR	1 r I '	radiation B0

•Absorbed fraction of the scattered SR 1 r i

•A fraction of atmospheric radiation BA

R 1 r I ' 1 r i BA B0

B *

R 1 r I' i B *

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Radiation balance of the surface influences:

• Temperature regime in the soil and the surface layer of the atmosphere.

•Processes of fog and frost formation.

•Air mass transformation.

Radiation balance varies depending on latitude, time of the year and day, and weather conditions.

Radiation balance can be calculated for various time intervals: minutes, hours, days, weeks etc.

It can be positive ( income exceeds outlay) and negative (the body emits more energy than absorbs)

Radiation balance is subject for annual and diurnal variations.

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Annual and diurnal variations of the radiation balance of the Earth surface.

R			For a location at
			60°N latitude
			June
6	noon	18	t
			April
			October

An important feature of the radiation balance is its transfer via 0. Usually, it happens at the time when Sun altitude reaches 10 -15°. In case of snow cover existence it occurs at the Sun altitude 20 - 25°. This means that the time interval with positive radiation balance becomes much shorter.

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Some particularities of the radiation balance annual variation

Annual variation of the radiation balance depends on latitude and type of underlying surface.

Tropical area: radiation balance is always positive.

Antarctic area: radiation balance is always negative due to large value of the surface albedo.

At 60° latitude: radiation balance is positive 6 – 8 months a year.

In arctic area there are some places where radiation balance (average for a year) is positive. It is valid for the places with snow and ice free surfaces for at least 2 months. The Sun shines here 24 hours at summer months.

Question: Where radiation balance is larger on ocean or on land at the same altitude and weather conditions?

Answer: On ocean, since water surface albedo is less than that of land

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Radiation balance depends on Sun altitude, albedo and cloudiness.

R...a ho b		Parameters “a” and “b” depends on albedo of
		the underlying surface.
r%	10 - 20	20 - 30	50 - 60	60 - 70	80 - 90
a W/m²	9,1	8,4	6,3	4,9	2,8
b°	10,0	9,8	7,4	7,4	8,5

Cloudiness impact

When R>0, cloudiness causes the net and effective radiation decrease. But the net radiation decrease is much stronger. Therefore, the radiation balance decreases at cloudiness condition.

When R<0, cloudiness causes the effective radiation decease and, hence, decrease of radiation balance absolute value.

	Conclusion: cloudiness always decreases the radiation balance	6
	absolute value

Radiation balance of the atmosphere

Income part	Outlay part
•The Earth surface radiation	•Radiation directed toward the
absorbed by the atmosphere Ua	Earth surface BA
•Direct and scattered SR absorbed	•Radiation into space B
by the atmosphere Qa

RA Ua Qa BA B

B

Ua 1

P B0

Surface

radiation

Qa

Ua B0

PB0

Transmission

Ua

function

Part of the surface radiation that goes

into the space

B* B0 BA

BA

BA B0 B *

RA Ua Qa BA B

	Ua B0 PB0						BA B0 B *
	RA B0 PB0 B Qa B0 B *
				U			Calculations done with this formula
	RA B * Qa U
							have shown that the RA values are
							negative over whole globe.
	φ°	0 - 10				20 - 30			40 - 50		60 - 70
	RA W/m²	-101				-109			-80		-93

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Radiation balance of the Earth as a whole planet

We’ll discuss the balance of radiative energy in a vertical column including active layer of soil ( water) and the atmosphere.

Incoming part RE I0! 1 rE U Outgoing part

Every unit of time the Earth receives the amount of SR equal to the
product of the solar constant			I0* by the area of the Earth cross
section	R2	i. e. R2 I0*

Due to Earth rotation this energy is distributed over the all surface of the globe that is 4 R2

R	2	*	*				Near equator RE>0 over the whole
		I0		I0	0,343 kW	m2	year. In the middle latitudes RE>0
4 R2			4				is observed only in summer.

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Cloudiness impact on RE value

R

E

I!

1 r U

0

E

Cloudiness increases albedo rE .

U

rE

RE

U

Cloudiness diminishes U∞ value

U∞

RE

At nights, when I0! 0 , RE U

At clear sky RE 0

At cloudy weather

RE 0

RE

Clear

RE

Cloudy

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