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Ta b l e 1 The “best average” values of the k 1 , k 2 ,and k 3 coefficients in Eq. ( 15 ), as presented by
Rüeger ( 2002a , b )
k 1 (K/hPa) k 2 (K/hPa) k 3 (K 2 /hPa)
375 ppm CO 2 77.6890 71.2952 375463
392 ppm CO 2 77.6900 71.2952 375463
For k 1 two values are given corresponding to two different carbon dioxide concentrations: 375 ppm
(2004 level, used by Rüeger ( 2002a , b ) and 392 ppm (2012 level)
( 2002a , b ) assumed a carbon dioxide concentration of 375 ppm (2004 level). Table 1
also shows k 1 for a carbon dioxide concentration of 392 ppm (2012 level). The con-
centration of carbon dioxide also shows an annual variation of about 5 ppm, meaning
that k 1 will have an annual variation of about 2
10 4 K/hPa. This variation is neg-
.
8
·
ligible for all practical purposes.
Using Eq. ( 12 ) it is possible to rewrite Eq. ( 15 )as
R
M d ρ +
p w
T
k 3 p w
k 2
Z 1
w
T 2 Z 1
N
=
k 1
+
=
N h +
N w ,
(16)
w
where k 2 =
k 1 M M d
k 2
and:
R
M d ρ,
N h =
k 1
(17)
p w
T
k 3 p w
k 2
Z 1
T 2 Z 1
N w =
+
.
(18)
w
w
N h is called the hydrostatic refractivity and N w the wet (or non-hydrostatic) refrac-
tivity. The hydrostatic refractivity depends only on the total density of air, while the
wet part depends only on the partial pressure of water vapor and the temperature.
Figure 2 shows examples of vertical profiles of N h and N w . While the hydrostatic part
Fig. 2 Examples of vertical profiles of the hydrostatic andwet refractivity. The profiles are calulated
using radiosonde data from Vienna, Austria
 
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