The grid system is a rectangular Arakawa staggered B grid (Bryan 1969) containing T-cells and U-cells. In order to visualize this arrangement, it will be helpful to refer to Figs 16.2, 16.3, and 16.4 which depict grid cells within horizontal and vertical surfaces. Within each T cell is a T grid point which defines the location of tracer quantities. Similarly, each U cell contains a U grid point which defines the location of the zonal and meridional velocity components.