Table 8. Observed and various modeled values of the longwave
radiation balance (B, top number) and incoming longwave
radiation (Fdn, bottom number) in W/m2.
Cloud amount
0-10
0-2
8-10
744 Observations
110 Observations
283 Observations
Mean
Std
Mean
Std
Mean
Std
ISW Observations*
15.0
18.2
42.8
5.5
3.4
6.3
198.4
33.6
154.2
13.5
228.3
19.0
Brunt, eq 7
41.1
19.4
72.2
5.8
21.5
3.8
171.7
34.6
123.9
12.0
203.1
17.6
Marshunova, eq 9
44.7
9.4
59.2
3.8
35.5
3.3
171.6
27.7
139.7
14.1
193.0
20.6
Maykut, eq 10
27.3
11.1
38.7
3.4
14.8
4.8
189.4
27.2
160.6
13.0
214.1
17.9
Satterlund, eq 11
33.4
16.3
59.6
4.3
17.0
2.9
179.5
32.6
136.5
15.0
207.6
18.2
KL&A, eq 12
23.5
14.8
38.8
3.4
6.5
6.3
193.2
30.6
160.6
13.0
222.5
19.2
* The observations are from Ice Station Weddell in May 1992. "Mean" is the
average value for the indicated cloud amount; "Std" is the standard devi-
ation of the values in that category.
where n is again the fractional total cloud amount, and aK and bK are empirical
coefficients. As in Maykut and Church's parameterization, these aK and bK coeffi-
cients implicitly include humidity effects.
Knig-Langlo and Augstein obtained aK = 0.765 and bK = 0.22 on the basis of
visual observations of cloud amount and measurements of incoming longwave
radiation with an Eppley PIR pyrgeometer at two polar stations (Ny-lesund,
7056'N, 1156 E; and Georg von Neumayer, 7039'S, 815'W). KL&A's ε* differs
from Maykut and Church's by its stronger dependence on cloud amount.
New test of the longwave parameterizations
We obtained new data for evaluating the five parameterizations described above
during the drift of the Russian-American Ice Station Weddell (ISW) in the western
Weddell Sea from February to June 1992 (Andreas et al. 1992, Claffey et al. 1995).
During this period, in the center of a drifting 1-km-wide ice floe, we made con-
tinuous, hourly averaged measurements of the components of the longwave
radiation budget and the usual meteorological variables with both Russian and
American sensors. The radiation measurements, in particular, showed good agree-
ment among the various instruments (Claffey et al. 1995).
Table 8 lists some of the statistical results of measurements and calculations for
all of the observations made in May 1992 on ISW. We focus on May because we
have data for the entire month and because the shortwave components--which
might complicate our measuring and interpreting the longwave radiation--were
small. Because cloud amount at ISW had a U-shaped distribution (Fig. 4), Table 8
treats the radiation values for clear (02) and overcast (810) skies separately,
regardless of other weather conditions.
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