Upper-level waves in the westerlies in midlatitudes usually move from west to east, in part as a result of advection (a process in which the airflow transports a property of the atmosphere [warmth, cold, etc.] downstream) and in part as a result of propagation, which acts in the opposite direction, toward the west. Rossby showed that to a good approximation, c = U – β / (2π/L)2, (4) where c is the phase speed of the waves, U is the speed from west to east of the component of upper-level wind due to uniform flow, β is the meridional, or ...(100 of 37038 words)