Gravity Waves in the Sky: Nature's Rippling Masterpiece

3. Atmospheric Conditions Conducive to Gravity Wave Formation

Gravity waves in the atmosphere must be formed under particular conditions to align and produce a delicate equilibrium allowing these amazing occurrences. One of the most often occurring situations for the generation of gravity waves is steady air over steep terrain. The topography's force upward of the air generates a disturbance capable of spreading as a gravity wave. Under the appropriate conditions, this phenomena—known as mountain wave or lee wave—can span hundreds of kilometres downwind of the mountain range and produce a sequence of standing waves in the atmosphere that can last hours or even days. Strong temperature inversions are yet another favourable environment for the development of gravity waves. A stable stratification in the atmosphere results from an inversion—that is, from a layer of warm air atop a layer of cooler air. By serving as a waveguide, this steady layering lets gravity waves travel horizontally across great distances. Often linked with high-pressure systems, inversions can be especially widespread in winter or in places like valleys or coastal areas impacted by cool sea air. Gravity waves can also be produced by atmospheric fronts—where two air masses with different densities and temperatures interact. Unstable interactions between these air masses can produce wave-like disturbances spreading across the atmosphere. Strong convective activity—that linked with thunderstorms or extreme heating of the Earth's surface—can also produce gravity waves by means of strong updrafts that perturb the surrounding air. These convectively produced waves can be rather important in moving momentum and energy within the atmosphere, so affecting local as well as more general weather patterns.