Light rain recorded just below the surface. The sound is similar to a wind chime. Sound courtesy of Sonatech, Inc., http://www.sonatech.com
Rainfall produces a loud distinctive signal. There are two different sound waves produced by a drop of rain. One is the sound from the raindrop hitting the ocean surface; the other is from the sound radiated from bubbles trapped underwater during the splash. For most raindrops, the sound produced by the bubble is louder. Raindrops of different sizes produce different sounds. Small raindrops (0.8-1.2mm) are loud and heard between 10-25 kHz. Medium raindrops (1.2-2.0mm) are quiet. Large (2.0-3.5mm) and very large (>3.5mm) raindrops trap larger bubbles, which produce sound frequencies as low as 1kHz.
The unique characteristics of these sounds help researchers identify and measure raindrop size, rainfall rate, and other features of rainfall over the ocean. This can help meteorologists, oceanographers, and climatologists and is useful in the study of climate change.
Rain can be a source of underwater noise. Even common occurrences such as heavy rain can increase noise levels by up to 35 underwater dB across a broad range of frequencies (from several hundred Hertz to greater than 20,000 Hz). Extreme rain events produce very loud signals, sometimes as much as 50 underwater dB above the background noise level.
