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If need be the Yin-Yang grid can get split into the two LAM grids with the command: yydecode.Abs
And the two LAM grids can get put back together with the command: yyencode.Abs
For more information about the Yin-Yang grid in GEM have a look at the following publication:
Qaddouri, A., & Lee, V. (2011). The Canadian Global Environmental Multiscale model on the Yin‐Yang grid system. Quarterly Quarterly Journal of the Royal Meteorological Society. Royal Meteorological Society (Great Britain), 137(660), 1913–1926. https://doi.org/10.1002/qj.873
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