Geoscience Reference
In-Depth Information
The online data of
Ardhuin
et al.
(
2009a
) provide swell height
H
1
at distance 4000 km
from the slow-moving limited-area storm and the attenuation rate
measured over the
subsequent 11000 km. Expression
(7.92)
does not have distance to the stormwhich is effec-
tively implied to be a point-source and have an infinite power at
x
α
0. Therefore,
(7.92)
was first used to estimate distance
x
0
from this fictitious point-source such that the resulting
wave height is
H
1
:
=
2
3
1
k
2
H
1
.
8
10
3
x
0
=
(7.93)
Such inferred distance is then used to obtain what would be the wave height 11000 km
down the path, based on
(7.92)
:
3
4
10
3
1
H
B
=
)
.
(7.94)
k
2
(
x
0
+
11000000
This wave height is then compared to the estimate obtained from
H
1
and the decay rate
α
:
H
A
=
H
1
exp
(
−
11000000
α).
(7.95)
The results of
(7.94)
-
(7.95)
are compared with each other in
Figure 7.26
(asterisks).
Attenuation rates of
(7.94)
are, on average 2.5 times larger than those of
(7.95)
estimated
by
Ardhuin
et al.
(
2009a
). In the top panel,
H
B
points are always below the one-to-one
1
0.5
0
0
0.5
1
1.5
2
H
A
, m
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
x 10
−7
α
Figure 7.26 (top) Swell height
H
B
(7.94)
, estimated by means of decay described by
(7.92)
,versus
height
H
A
(7.95)
based on the experimental decay rate
α
(7.60)
of
Ardhuin
et al.
(
2009a
); (bottom)
Ratio
H
B
/
H
A
versus
α
. In both subplots, asterisks correspond to the empirical coefficient
(7.84)
and
circles to
(7.96)
, and the solid line indicates the one-to-one ratio
Search WWH ::
Custom Search