In order to clarify theoretically the accuracy of method for posing a computational boundary condition at an outflow point in numerical time integration of advective equation by means of the centered finite difference scheme in space, we use the analytical method adopted by Matsuno (1964) who computed and examined the amplitude of reflective computational mode occurred at the boundary to satisfiy the artificial condition by the physical progressive wave.
The result shows that the amplitudes of reflective waves in preferred methods which are tested numerically and proposed by the author in the previous paper (1962) are one order of magnitude or more less than those in other methods.