prize1-7, Exercise 2: What a model does

Model answer:

Numerical weather prediction divides the atmosphere into a three-dimensional grid and uses the laws of physics (fluid motion, conservation of energy and mass, the behaviour of gases and water) to step the measured starting state forward in time, box by box. A model can only show features larger than a few grid boxes, so a single thunderstorm, which is smaller than a coarse box, cannot be resolved and has to be handled by simplified rules called parametrisations.