Are raindrops really shaped like teardrops?

Settled in 1904 by Established through early 20th-century fluid-dynamics studies of falling drops (e.g. P. Lenard, 1904) and refined through later aerodynamic modeling.

Small raindrops (below about 1 mm) are held essentially spherical by surface tension, which minimizes surface area for a given volume. As drops grow larger and fall faster, aerodynamic pressure from the air rushing past flattens their undersides into a shape more like a hamburger bun or kidney bean, with a rounded top (where surface tension still dominates) and a flattened, sometimes slightly concave, bottom (where air pressure dominates); this balance of surface tension versus aerodynamic pressure was worked out through early 20th-century fluid-dynamics studies and has been repeatedly confirmed with modern high-speed imaging. Above roughly 4-5 mm in diameter, the flattening becomes unstable and the drop breaks apart into smaller droplets, setting a natural upper size limit for raindrops.

Nearly every visual depiction of a raindrop is wrong, and the real shape is a direct, visible readout of the tug-of-war between surface tension and aerodynamic drag.

Explanations that circulated

• Raindrops are shaped like a classic pointed teardrop, narrow at the top and rounded at the bottom
• Raindrop shape is irrelevant to their fall speed or splash pattern

References

• The Physics of Falling Raindrops in Diverse Planetary Atmospheres, K. Palumbo, K. Battaglia, et al. (review of raindrop shape physics), arXiv preprint, 2021