Effective radiation

Содержание

1. Effective radiation
2. Difference between Earth’s surface own radiation B0
3. In some rare cases, the effective radiation may turn out to be negative (B*
4. Effective radiation and water vapor in the
5. Application of Angstrem’s formulaHere, e1 is water
6. Let’s denoteA=0,18 and D=0,25 (dimensionless quantities); c=0,95
7. Cloudiness impact on counter and effective radiationEffective
8. Counter (earthward) flux from the cloud layerZ
9. At overcast conditionThis formula suggests that at overcast ER decreases since the quantity in brackets
10. Let’s transform the ratioDecomposing into raw and restricting our self with only first member, we obtain
11. Thus, ER at overcast condition depends on
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Difference between Earth’s surface own radiation B0 and absorbed by the surface the long wavelength atmospheric back radiation is called effective radiation of the Earth surface.UsuallyThereforeandIt means that through the long

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Слайд 1Effective radiation
Notations
Short wavelength radiation
Terrestrial Rad.

Atmospheric counter Rad.

Earth’s surface absorbs rad.
Atmosphere

absorbs some terrestrial radiation
The flux of atmospheric counter radiation

is amount of long wavelength radiation coming from the atmosphere in a unit of time on a unit of area of the Earth surface.

Since the surface is not ABB, it absorbs just a part of incoming radiation

Effective radiationNotationsShort wavelength radiationTerrestrial Rad.Atmospheric counter Rad.Earth’s surface absorbs rad.Atmosphere absorbs some terrestrial radiationThe flux of atmospheric

Слайд 2Difference between Earth’s surface own radiation B0 and absorbed by

the surface the long wavelength atmospheric back radiation is called

effective radiation of the Earth surface.

Usually

Therefore

and

It means that through the long wave radiation the surface always looses the energy.

Difference between Earth’s surface own radiation B0 and absorbed by the surface the long wavelength atmospheric back

Слайд 3In some rare cases, the effective radiation may turn out

to be negative (B*

the surface becomes very cold.

Effective radiation has an important bearing
on the temperature regime of the Earth surface.

It plays a significant role in radiation frost and
fog formation and in snow melting.

In some rare cases, the effective radiation may turn out to be negative (B*

Слайд 4Effective radiation and water vapor in the atmosphere
Effective radiation greatly

depends on:
the water vapor content in the atmosphere
presence

of cloudiness. It decreases with increase of the water vapor content.

Increase of humidity results in increase of BA value, and, hence, decrease of B* value.

Air temperature at the level z1

Absorption coefficient

Value z1 is arbitrary chosen quantity, it can be equal to 2 meters. Coefficient “a” specifies emissivity of the atmosphere, depends on humidity, amount and altitude of the cloudiness.
The increase of water vapor pressure and cloud amount results in coefficient “a” growth up.

Effective radiation and water vapor in the atmosphereEffective radiation greatly depends on: the water vapor content in

Слайд 5Application of Angstrem’s formula
Here, e1 is water vapor pressure at

the level z1, are empirical constants.
Combining formulas
We obtain
Effective

radiation in cloud free atmosphere

Let’s add

Application of Angstrem’s formulaHere, e1 is water vapor pressure at the level z1, are empirical constants.

Слайд 6Let’s denote
A=0,18 and D=0,25 (dimensionless quantities); c=0,95 if e1 in

hPa
There is also well known Brent’s formula
“e” in hPa

Let’s denoteA=0,18 and D=0,25 (dimensionless quantities); c=0,95 if e1 in hPaThere is also well known Brent’s formula“e”

Слайд 7Cloudiness impact on counter and effective radiation
Effective radiation depends upon

following factors
Cloudiness thickness
Cloudiness altitude
Cloudiness form
Cloud amount

To understand the essence of

the impact, an example will be considered.
Initial conditions are: overcast, cloud base height is a few hundred meters.
Notation: T0 is the surface temperature, T1 is air temperature in shelter, Tk is air temperature at the cloud base.
At these conditions: ; ; within the layer from the surface up to the cloud base.

Numerous influencing factor combinations make theoretical approach to the problem to be very complicated or even not possible.

Cloudiness impact on counter and effective radiationEffective radiation depends upon following factorsCloudiness thicknessCloudiness altitudeCloudiness formCloud amountTo understand

Слайд 8Counter (earthward) flux from the cloud layer

Z cloud base height
The

energy loss when passing the layer 0 - Z
Radiation of

the layer 0Z

Since clouds, air and surface are not ABB factor δ is to be introduced

The cloudiness radiation that reaches the surface

Effective radiation at cloud free condition

Counter (earthward) flux from the cloud layerZ cloud base heightThe energy loss when passing the layer 0

Слайд 9At overcast condition
This formula suggests that at overcast ER decreases

since the quantity in brackets

Слайд 10Let’s transform the ratio
Decomposing into raw and restricting our self

with only first member, we obtain

Слайд 11Thus, ER at overcast condition depends on following factors;
1. Air

temperature (T1).
2. Stratification of the atmosphere (γ).
3. Cloud base

height (Zk)

4. Humidity of the atmosphere

At overcast condition T0≈T1

Angstrem’s formula

A=0,18; D=0,25; c=0,95 (e in hPa)

If n=±1 (10 points)

Thus, ER at overcast condition depends on following factors;1. Air temperature (T1).2. Stratification of the atmosphere (γ).

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