One of the most powerful defensive charms known to wizardkind, the Patronus can also be used as a messenger between wizards. As a pure, protective magical concentration of happiness and hope (the recollection of a single talisman memory is essential in its creation) it is the only spell effective against Dementors.
The wave visible above the level of the water is in fact only part of the wave; the wave extends down through the water column to the ocean floor as well. Waves start out in the deep, open ocean as relatively vertical in shape, Presnell said. As a wave travels toward the shore, though, the bottom part of the wave drags along the ocean floor. The upper part of the wave above the water line starts to move faster than the rest of the wave. As the ocean depth decreases closer to shore, the drag on the wave's bottom becomes stronger, and the upper part of the wave begins to tilt forward.
In fluid dynamics, wind waves, or wind-generated waves, are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They result from the wind blowing over an area of fluid surface. Waves in the oceans can travel thousands of miles before reaching land. Wind waves range in size from small ripples, to waves over 100 ft (30 m) high. When directly generated and affected by local winds, a wind wave system is called a wind sea. After the wind ceases to blow, wind waves are called swells. More generally, a swell consists of wind-generated waves that are not significantly affected by the local wind at that time.