A vertical coordinate for atmospheric models that changes from one standard coordinate (for instance, the terrain-following sigma coordinate system) to another coordinate system as a function of height. For instance, hybrid coordinates allow a model to accrue the benefits of pressure or isentropic coordinates in the upper model layers where the use of a terrain-following coordinate is disadvantageous while avoiding technical difficulties associated with the use of a nonterrain following coordinate near the ground. See isentropic vertical coordinate, height vertical coordinate, vertical coordinate system.