Don Jones studies partial differential equations (PDEs) associated with geophysical fluids. That is, equations resulting from the modeling of the atmosphere, ocean, and interiors of planets. The primary mathematical tools employed come from a branch of mathematics called functional analysis. The analysis is used, in part, to validate, rigorously, the models possess the physical properties engineers and physicists expect. This approach often yields surprising properties of the solutions to the equations and suggests new algorithms for approximating the models.