CoachA general circulation model (GCM) is a numerical model of the atmosphere, of the ocean, or of both coupled, that solves the equations of motion, continuity and energy of a fluid on the rotating Earth — for the atmosphere, with the hydrostatic approximation, the “primitive equations” — on a three-dimensional grid covering the globe, stepping forward in time. Its dynamical core is the part that solves these equations for the motions the grid resolves. A parameterisation represents the effect on the resolved variables of a process smaller than a grid cell — clouds, convection, turbulence, gravity waves — by a formula in the resolved variables, with parameters that the modellers choose.
