An
atmospheric model is a
mathematical model constructed around the full set of
primitive dynamical equations which govern atmospheric motions. It can supplement these equations with
parameterizations for
turbulent diffusion,
radiation, moist processes (
clouds and
precipitation),
heat exchange,
soil, vegetation, surface water, the
kinematic effects of
terrain, and convection. Most atmospheric models are numerical, i.e. they discretize equations of motion. They can predict microscale phenomena such as
tornadoes and
boundary layer eddies, sub-microscale turbulent flow over buildings, as well as synoptic and global flows. The horizontal domain of a model is either
global, covering the entire
Earth, or
regional (
limited-area), covering only part of the Earth. The different types of models run are thermotropic,
barotropic, hydrostatic, and nonhydrostatic. Some of the model types make assumptions about the atmosphere which lengthens the time steps used and increases computational speed.