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Polcoms
Ocean model |
Assimilation |
Computing resources |
References
| Ocean model |
The
Polcoms model is described by Holt and James (2001). Particular
features of the model include: incompressible, hydrostatic, Boussinesq
approximation, free surface, use of an Arakawa B-grid, hybrid vertical
co-ordinate (for improved near-surface vertical resolution in deeper
water with sigma co-ordinate in shelf seas), the Piecewise Parabolic
Method advection scheme (for long term maintenance of sharp gradients),
and interpolation onto horizontal surfaces for calculation of the
pressure gradient term. The vertical mixing scheme is Mellor-Yamada
level 2.5 with an algebraic mixing length, and including Craig and
Banner (1994) representation of turbulence induced by surface waves. A
simple convective adjustment is applied to mix unstable vertical
density gradients. The present Met Office Atlantic Margin model runs
with POLCOMS V4 and this does not include the tidal potential body
force. However this forcing term is included in POLCOMS V5 and the Met
Office Atlantic Margin model will upgrade to POLCOMS V5 during 2005.
The Atlantic Margin Model covers the domain 40oN to 65oN and 20oW to
13oE, and has 34 levels (32 wet levels) using the hybrid s-coordinate.
In water shallower than 150m the vertical coordinate is sigma. For the
Atlantic Margin model, tidal boundary forcing with harmonics for both
elevation and depth-mean currents is applied using 9 harmonics. (Q1,
O1, K1, MU2, N2, M2, L2, S2, M4)
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| Assimilation system |
There
is no direct data assimilation in the model system. However
observations of SST are used to generate the SST analysis used by the
NWP model that provides the surface heat forcing, and there is a weak
relaxation towards this SST analysis implied in the calculation of heat
fluxes applied to POLCOMS.
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| Computing resources |
The Met Office has an NEC SX6 with 30 nodes. The POLCOMS shelf seas
modelling system currently uses less than 1% of this resource. |
| References |
- Craig,
P.D.; Banner, M.L. Modeling wave-enhanced turbulence in the ocean
surface layer. Journal of Physical Oceanography, [Boston MA], VOL. 24,
NO. 12, pp. 2546-2559; 1994
- Holt, J.T.; James, I.D. An s coordinate density evolving
model of the northwest European continental shelf 1, Model description
and density structure, Journal of Geophysical Research, Oceans, VOL.
106, NO. C7, pp. 14,015-14,034; 2001
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