total water flux to the ocean has spatial patterns
that are highly unrealistic. McWilliams (1996)
points out that with such unrealistic forcing, it is
no surprise that the model’s salinity field is also
unrealistic. The result is that the use of salinity, the
next best observationally known ocean quantity
after temperature, has been greatly limited as a
means of identifying and correcting physical errors
in ocean models.
6.2.4 Direct ocean estimates of
freshwater transport
Direct estimates of oceanic freshwater transport
are an independent means of measuring the freshwater exchange between the ocean and atmosphere, and so have the potential to address some
of the problems outlined above. In order to be of
use, however, the strengths and limitations of
these estimates need to be clearly examined.
SECTION 6 LARGE-SCALE OCEAN TRANSPORTS
478
50° E
100°
150°
200°
250°
300°
350°
80°S
60°
40°
20°
0°
20°
40°
60°
80°N
80°S
60°
40°
20°
0°
20°
40°
60°
80°N
1000
1000
10 00
10 00
10 00
Mean Annual EP Flux
2 5 0
250
2 5 0
25 0
2 5 0
2 5 0
500
50 0
500
5 0 0
500
Standard Deviation of EP Flux
(a)
(b)
Fig. 6.2.1 Average (a) and standard deviation (b) of an ensemble of 13 estimates of E–P over the oceans based on
the products in Table 6.2.1.The contour interval is 250 mm yr
91
, with the zero contour dotted.