186 Kikuro Miyakoda
10.3 Nested techniques
10.3.1 Eta-coordinate
li and Vemekar (1997) developed a nested climate model, which will be
described later. They used an eta-coordinate model. One of the disadvantages of
the cr-coordinate is that the surface is not horizontal, so that horizontal diffusion is
not correct if diffusion is computed on a sigma surface, (though Blumberg and
Mellor (1987) included a correction of this effect in their cr coordinate model). In
addition there is some difficulty in utilizing the observations for the initial conditions (conversion from p to cr surface). For this reason, the 11-coordinate was introduced by Mesinger (1984). 11 is defined by
_ PrfZs)
11s - PrfO)
(24)
where Prf (Zs) is a suitably defined reference pressure as a function of mountain
height, Zs. They are permitted to take only a discrete set of values, chosen so that
mountains are constructed from the three-dimensional grid boxes in the model, (see
Fig. 10.1).
~----~--~-----;---~~~~2
:
j ;
• u •• T ••• ~ • • T • _. ~ •• T ' " ~ • . T •.. U·
:
:
Fig. 10.1 A schematic picture of representing mountains using the eta coordinate (24)
10.3.2 Horizontal grids
One of the characteristics in the Mediterranean coupled system is that forecasts
can utilize the effect of the small-scale ocean eddies, which have long time scales
(more than several months). One of the GCMs applied to the Mediterranean Sea
was "the curvilinear orthogonal grid" model (Mellor 1991; Zavatarelli and Mellor
1995).
As is seen in Fig. 10.2, the oceanic grid can be irregular, while the atmospheric
grid should be quite regular, because of the reasons mentioned in section 10.2. In
order to couple the oceanic model of the curvilinear grid with the atmospheric
model of the regular grid, care is needed. Examples of the smooth and soft interac-
10.3 Nested techniques
10.3.1 Eta-coordinate
li and Vemekar (1997) developed a nested climate model, which will be
described later. They used an eta-coordinate model. One of the disadvantages of
the cr-coordinate is that the surface is not horizontal, so that horizontal diffusion is
not correct if diffusion is computed on a sigma surface, (though Blumberg and
Mellor (1987) included a correction of this effect in their cr coordinate model). In
addition there is some difficulty in utilizing the observations for the initial conditions (conversion from p to cr surface). For this reason, the 11-coordinate was introduced by Mesinger (1984). 11 is defined by
_ PrfZs)
11s - PrfO)
(24)
where Prf (Zs) is a suitably defined reference pressure as a function of mountain
height, Zs. They are permitted to take only a discrete set of values, chosen so that
mountains are constructed from the three-dimensional grid boxes in the model, (see
Fig. 10.1).
~----~--~-----;---~~~~2
:
j ;
• u •• T ••• ~ • • T • _. ~ •• T ' " ~ • . T •.. U·
:
:
Fig. 10.1 A schematic picture of representing mountains using the eta coordinate (24)
10.3.2 Horizontal grids
One of the characteristics in the Mediterranean coupled system is that forecasts
can utilize the effect of the small-scale ocean eddies, which have long time scales
(more than several months). One of the GCMs applied to the Mediterranean Sea
was "the curvilinear orthogonal grid" model (Mellor 1991; Zavatarelli and Mellor
1995).
As is seen in Fig. 10.2, the oceanic grid can be irregular, while the atmospheric
grid should be quite regular, because of the reasons mentioned in section 10.2. In
order to couple the oceanic model of the curvilinear grid with the atmospheric
model of the regular grid, care is needed. Examples of the smooth and soft interac-