Evaluation of methods for estimating the internal pressure in
sigma-coordinate ocean models using measurements from the Norwegian
Trench and the Skagerrak
Inge K. Eliassen and Jarle Berntsen
Abstract
A three dimensional sigma-coordinate model has been implemented for
an extended North Sea with 20 km horizontal resolution and for a subarea
including the central North Sea, the Skagerrak and the Norwegian trench
with 4 km horizontal resolution. The models are forced with hindcast
atmospheric forcing, 4 components of the tide and river runoff and run
for the period from 15 January 1990 to 24 June 1990.
Model results are produced with six different methods for estimating the
internal pressure and compared to measurements taken across a transect
from the Norwegian coast to the Orkneys and to measurements from
repeated hydrographical transects across Skagerrak taken in 1990.
The main conclusions are that the model results are relatively robust to the
choice of internal pressure method and the observed fields are at least as well
represented when sigma-coordinate based methods are used to estimate the
internal pressure instead of z-coordinate based methods. Furthermore, no
evidence is found to support that it is essential to satisfy the hydrostatic
consistency condition when using sigma-coordinate based methods for
estimating the internal pressure.
Keywords: Ocean models, sigma-coordinates, internal pressure,
the North Sea, the Skagerrak, evaluation