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Dependent on the scientific objectives of the model experiment not all variables will require nudging. As a minimum it is recommended to use vorticity, divergence and temperature.
In this context disk space usage should also be a consideration as an increasing number of nudged variables will result in larger forcing files. At T255L60 forcing files that contain all 9 variables require 70 MB for each time step (grid point file 47 MB, spectral file 23 MB).
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