CAM-SE works with data stored at Gauss-Lobatto-Legendre (GLL) nodes. These nodes can be interpreted in several ways shown in the three grids below. In all three grids, the GLL nodes are the same (the green dots in the figure). Internally, the dycore uses the CAM-SE native grid connectivity, but the rest of CAM and ACME has no knowledge of the grid connectivity and only sees data at GLL nodes and their associated area weight. The other other types of connectivity are not used within the model, but are sometimes used by pre- and post-processing tools.
CAM-SE Native Grid
Here is a low-resolution CAM-SE grid. This is a "ne4np4" grid, meaning that it has 4x4 spectral elements in each cube face (the "ne" value), and each spectral element has a grid of 4x4 (the "np" value) Gauss-Lobatto points inside it. The blue lines show the edges of the spectral elements. The green dots show the Gauss-Lobatto-Legendre (GLL) nodes. CAM-SE is collocated, meaning that all variables (U,V,T, etc...) are carried around on the GLL nodes. CAM physics is computed in columns at GLL nodes. Each column has a Gauss-Lobatto weight associated with it, which is also that columns area. The sum of these weights is 4pi (the area of the unit sphere). One can see from the figure that GLL nodes are not quite equally spaced - they cluster at the edges of the spectral elements.
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