Publisher Summary The special class of motions that occur in the vicinity of the equator, where both components of the Coriolis term in the shallow-water equations vanish, are discussed in the chapter. The equatorial zone is found to be a waveguide just as is a coastal region. For studying tropical dynamics, the shallow-water equations are derived for a sphere, so that effects of variations in the Coriolis parameter are included in the equations. The calculations of dynamic response in the equatorial region are done by using an approximation called the “equatorial beta plane.” In this approximation, the Coriolis parameter is taken to be the product of a constant (called β) and the distance from the equator. This approximation can usefully be applied over the whole of the tropics and hence over a fair proportion of the earth's surface. Different types of waves that can propagate in the equatorial waveguide include an equatorial Kelvin wave, trapped gravity waves, and planetary waves.