The atmosphere in movement

Abstract

Let us reexamine this atmosphere, presented as calm and immobile in the first chapter but in reality in constant movement over a very large range of scales. Some winds are relatively stable and well established; others appear quite random and are the source of serious conundrums for meteorologists. A relatively methodical observation thus appears necessary to extract the main properties: we shall begin with the largest scales; namely, those with horizontal dimensions of the same order of magnitude as the radius of Earth (6730 km) and that encompass the entire thickness of the troposphere (8 to 15 km). The circulation of air on these scales in fact structures movement within the atmosphere on the whole. We shall see later that oscillations on more modest scales can explain seasonal phenomena, such as monsoons, or random phenomena, such as the back and forth between high- and low-pressure zones. On scales approaching 500 to 1000 km, we shall focus on the mechanisms that drive significant meteorological phenomena, such as cyclones and low-pressure zones, which are remarkable in their rather precise organization. On smaller scales, we shall examine periodic spatial fluctuations, such as lee waves, or periodic as in the diurnal thermal winds. However, the violent intermittent events that often occur in the atmosphere, such as thunderstorms, tornadoes, or the whims of precipitation, are reserved for the next chapter.

You think, then, that aerostatic science has said its last word?

Not at all! Not at all! But we must look for another point in the case, and if we cannot manage to guide our balloon, we must at least try to keep it in favorable aerial currents.

(Jules Verne, Five Weeks in a Balloon)