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In the horizontal, the Arakawa-C grid is used. In the vertical, the Charney-Phillips grid - see graphic below.
The levels of the winds are on the full levels, also called "momentum levels" , and the ones for the scalar fields (like temperature and humidity) are on the half levels, also called "thermodynamic levels". The are alternating with the lowest model level being a thermodynamic level, the highest a momentum level. See also wiki about model levels.
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