It's been a while since I was a grad student but I think the raw station/radiosonde data is interpolated into a grid format before it's put into the standard models.
This was also in the article. It splits the sphere surface in to 1M grids (not actually grids in the cartesian sense of a plane, these are radial units). Then there's 37 altitude layers.
So there's radial-coordinate voxels that represent a low resolution of the physical state of the entire atmosphere.
So there's radial-coordinate voxels that represent a low resolution of the physical state of the entire atmosphere.