Rain-induced subsurface turbulence measured using image processing methods

Rain-induced turbulence results in a relatively thin "mixed layer" at the water surface which is very important for heat and gas exchange processes at the air-sea interface and is intimately related to the rain splash products, which in turn, strongly affect radar remote sensing signals. Fluid dye, digital particle image velocimetry, and ultrasonic sounding techniques have been used in experimental tanks to investigate the subsurface turbulence caused by single and multiple raindrops impinging on a water surface. Typical eddies 10-15 mm in diameter, that have evolved from ring vortices, could be measured. The thickness of the rain-induced mixed layer was found to be 15 cm for a moderate rain rate and showed homogeneous turbulence.