1.   Before we look at the average quantities most often used to examine the more detailed structure of the velocity field, we consider briefly an alternative representation.

2.   The mean and fluctuating parts of the velocity field thus individually satisfy the usual form of the continuity equation.

3.   Using Cartesian coordinates with z vertical, a velocity field of the form together with temperature and pressure perturbations of similar form are superimposed on the equilibrium configuration.

4.   In experiments on convection, particularly free convection, measurements of the temperature field are usually both easier and more accurate than measurements of the velocity field.