Atmospheric Motion

Abstract

Wind, whether it occurs on a local scale or spans vast regions, arises from the natural inclination to balance temperature and pressure differentials induced by varying solar heating across different areas of the Earth. Hence, a variety of forces come into play to set the air in motion. The observation of air movement dates back to various historical periods, but it was not until the eighteenth century that British scientist George Hadley (1686–1768) made significant strides in comprehending and describing this phenomenon. However, even Hadley fell short of fully grasping the intricate relationship between global air movement and the Earth’s rotation. As air strives to equalize pressure disparities by moving from areas of high to low pressure, the Earth’s rotation compels it to alter its trajectory by a certain degree. It was not until 1835 that French scientist Gustave Gaspar Coriolis elucidated the magnitude and dependence of this deviation, providing a comprehensive theory of relative motion. Subsequently, in 1836, this theory found practical application, primarily through the work of Poisson, in understanding motions observed relative to the Earth. Local air movements, such as those between land and sea, arise as a result of the endeavor to equalize variations stemming from contrasting properties of water and land in response to received heat. During the daytime, the land heats up more rapidly than the adjacent water, causing the air above the heated ground to warm and ascend. In response, the cooler air above the water moves toward the “vacated” space above the land. Conversely, at higher altitudes, the air circulates in the opposite direction. This regulated air circulation manifests itself distinctly, particularly during summer when we experience it firsthand along the coast. Similar patterns occur in regions where the topography shields certain areas from direct solar radiation, such as wider valleys, giving rise to what is known as a valley or mountain circulation.

Today, we possess a comprehensive understanding of these phenomena. However, approximately 250 years ago, a complete comprehension of these mechanisms eluded us. It was during this time that French scientist Jean le Rond Dalamber (1717–1783) made a significant contribution by highlighting that solar radiation solely influenced the heating of the soil rather than being the primary driver of wind formation. Dalamber introduced the notation for “partial derivatives,” which would prove instrumental in further advancements in the field.

In 1926, Lewis Richardson made a notable observation regarding atmospheric movements, highlighting their wide-ranging nature, spanning from scales encompassing thousands of kilometers down to minuscule millimeter scales. Richardson eloquently expressed this phenomenon, capturing its essence: “Great eddies have little eddies, which derive their energy from the large eddies; and small eddies have smaller eddies, and so on, down to the scale of viscosity.”