### Resolved Dynamical Processes

To directly simulate processes in Earth’s climate system, we need to create a set of equations using the fundamental laws of physics. These are called the equations of motion or primitive equations, and are used by both climate and NWP models. These equations balance forces acting in three dimensions, conserve mass, and track the temperature of each grid box. There are also equations that track the amount of moisture and other trace products that move in and out of grid boxes.

To solve these equations for Earth, we create a grid structure on which to make the calculations. This structure involves vertical columns of air sliced into horizontal layers over the full Earth for global models, or a portion of it for regional models. Finally, we solve the equations at the center point of each model grid box, at fixed, predetermined time intervals.

Early climate and weather models had grid cells that measured 300-400 km on a side. As of 2012, the NWP models have grid boxes as small as 1.5 km on a side or even a little less. Climate models are now run at a resolution as high as about 50 km. Text Note: To learn more about the primitive equations, see the COMET module *Impact of Model Structure and Dynamics*.