Advanced Research WRF (ARW) Technical Note - MMM - University ...

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U U U U U
V V
V V V V V V
U U U U U U U
V V V V V V
U U U U U U U
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V V V V V V
U U U U U U U
V V
V V V V V V
U U U U U U U
V V V V V V
U U U U U U U
U U
V V V V V V
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V V V V V V V V
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Figure 7.3: Arakawa-C grid staggering for a portion of a parent domain and an imbedded nest
domain with a 3:1 grid size ratio. The solid lines denote coarse grid cell boundaries, and the
dashed lines are the boundaries for each fine grid cell. The horizontal components of velocity
(“U” and “V”) are defined along the normal cell face, and the thermodynamic variables (“θ”)
are defined at the center of the grid cell (each square). The bold typeface variables along the
interface between the coarse and the fine grid define the locations where the specified lateral
boundaries for the nest are in effect.
ratios.
7.2 Nesting and Staggering
The ARW uses an Arakawa-C grid staggering. As shown in Fig. 7.3, the u and v components
of horizontal velocity are normal to the respective faces of the grid cell, and the
mass/thermodynamic/scalar variables are located in the center of the cell.
The variable staggering has an additional column of u in the x-direction and an additional
row of v in the y-direction because the normal velocity points define the grid boundaries.
The horizontal momentum components reflect an average across each cell-face, while
each mass/thermodynamic/scalar variable is the representative mean value throughout the cell.
Feedback is handled to preserve these mean values: the mass/thermodynamic/scalar fields are
fed back with an average from within the entire coarse grid point (Fig. 7.3), and the horizontal
momentum variables are averaged along their respective normal coarse grid cell faces.
The horizontal interpolation (to instantiate a grid and to provide time-dependent lateral
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