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Fig. 14.1
The ROMS CCS
domain and bathymetry
et al. 2009
). The ocean surface fluxes were derived using the bulk formulations
of
Liu et al.
(
1979
)and
Fairalletal.
(
1996a
, b). However, historical COAMPS
analyses are not available prior to 1999, so in the case of the 31 year reanalysis
described in Sect.
14.4.2
, a combination of 6 hourly fields from the ECMWF ERA40
and ERA Interim projects were used, along with the cross-calibrated, multiplatform
(CCMP) ocean wind product of
Atlas et al.
(
2011
). In either case, the surface forcing
fields obtained represent the background surface forcing,
f
b
, for 4D-Var introduced
in Sect.
14.2.1
.
The model domain has open boundaries at the northern, southern, and western
edges, and at these boundaries the tracer and velocity fields are prescribed, while
the free surface and vertically integrated flow are subject to
Chapman
(
1985
)and
Flather
(
1976
) boundary conditions respectively. The prescribed open boundary
solution was taken from the Simple Ocean Data Assimilation product (SODA)
of
Carton and Giese
(
2008
) in the case of the reanalyses of Sect.
14.4
, and from
the
World Ocean Atlas 2005
(WOA05) in the case of the near real-time system
of Sect.
14.5
. In either case, these fields represent the background open boundary
conditions,
b
b
, for 4D-Var introduced in Sect.
14.2.1
.
A sponge layer was also used adjacent to each open boundary where viscosity
increased linearly from
m
2
s
1
in the interior to
m
2
s
1
at the boundary over a
4
400
distance of 100 km.
The observations assimilated into the model were collected by various platforms,
and will be described in more detail in Sects.
14.4
and
14.5
. To reduce data
redundancy, all observations of the same state variable within each model grid
cell, over a 6 h time window, were combined to form “super observations,” and
the standard deviation of the observations that contribute to the super observation in
each grid cell was used as an estimate of the error of representativeness.
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