Atmospheric flows feature length scales from 10−5 to 105 m and timescales from microseconds to weeks or more. For scales above several kilometers and minutes, there is a natural scale separation induced by the atmosphere's thermal stratification, together with the influences of gravity and Earth's rotation, and the fact that atmospheric-flow Mach numbers are typically small. A central aim of theoretical meteorology is to understand the associated scale-specific flow phenomena, such as internal gravity waves, baroclinic instabilities, Rossby waves, cloud formation and moist convection, (anti-)cyclonic weather patterns, hurricanes, and a variety of interacting waves in the tropics. Single-scale asymptotics yields reduced sets of equations that capture the essence of these scale-specific processes. For studies of interactions across scales, techniques of multiple-scales asymptotics have received increasing recognition in recent years. This article recounts the most prominent scales and associated scale-dependent models and summarizes recent multiple-scales developments.
