raindrop

A water drop that forms and grows inside a cloud and falls from it, whose diameter ranges between 0.5 and 6 mm (extending to 10 mm [=1 cm] under very particular favorable conditions). The lower value marks the boundary between a drizzle drop and a raindrop. As for the upper one, for a long time it was thought that there could be no raindrops with a larger diameter, as those 6 mm were considered the theoretical limit to their growth, such that, for larger values, the drop would inevitably have to split into two or more smaller drops, as the balance between the water's surface tension and internal pressure broke down. In 2004, researchers at the University of Washington (USA) measured, using a laser-based instrument installed on an aircraft, a couple of drops of 8.8 mm in diameter at two different locations within the tropical realm. That finding suggests the existence of giant raindrops, up to a centimeter in diameter, inside clouds where the liquid water content is very high. They are the result of multiple collisions between smaller drops.