Environmental Engineering Reference
In-Depth Information
and under the above conditions
α
D
0.24 km/K. Next, since
„
ω
T
,wehave
1
1
dF
du
D
2
l
„
ω
3
uT
2
dT
dz
dT
dz
α
F
,
"
2
l
1
#
1
2
d
2
F
du
2
D
„
ω
3
uT
2
dT
dz
dT
dz
α
F
.
Correspondingly, we obtain the criterion
"
l
1
#
1
2
„
T
2
dT
dz
dT
dz
5
18
α
1,
which allows us to ignore the second term in parentheses in (3.97) and allows us
to represent the radiative flux in the form of blackbody radiation (1.61). The maxi-
mum of the left-hand side of this criterion corresponds to a large temperature gra-
dient and is 5(
2
0
; this value is 0.04 for the photosphere parameters above.
Thus, one can use the equilibrium relation (1.61) for the radiative flux
j
ω
at a given
frequency for any linear dependence of the temperature on the altitude.
Taking into account a temperature variation, we have for the altitude of a layer
z
ω
)
2
/18
„
ω
ε
that is responsible for emission at a given frequency
2
l
ln
h
σ
det
(
ω
)
σ
max
i
2
l
3
ε
0
T
2
z
ω
D
z
max
3
1
dz
,
α
D
.
(3.101)
dT
α
Note that the measured value
j
E
ω
varies in time, and these formulas allow us to
determine the current temperature of the photosphere boundary and its gradient
on the basis of measurement of the spectrum
j
E
ω
for solar radiation at the posi-
tion of Earth. Thus, if we assume the temperature of the solar atmosphere to be a
smooth function of the height, we reduce the problem of the radiation from a plas-
ma of variable temperature to a problem of a constant temperature for the radiating
plasma. To solve this problem, it is necessary to use two parameters of the solar at-
mosphere:
N
H
(
T
0
)and
dT
/
dz
, where the temperature
T
0
is close to the effective
temperature of the radiation. Hence, two parameters of the solar atmosphere must
be introduced into the problem for the determination of radiation fluxes from the
photosphere and the spectrum of its radiation is similar to the blackbody spectrum.
3.3.8
Excitations in a Photoresonant Plasma
An examination of the propagation of resonant radiation in an excited gas shows
a strong absorption near the center of the spectral line. This means that resonant
radiation can be transformed into excitation of the gas. This is a property used
as a diagnostic technique for the analysis of gases and flames. The optogalvanic
method [68, 69] is based on measurement of a current through an excited or ionized
