By placing hydrophones on deep ocean moorings, the team can listen to the ocean and determine when it is raining, how hard it is raining and even what type of rain is falling. This is because different size raindrops produce different sounds underwater. Raindrops produce two types of sound underwater. One is the slapping sound as the drop strikes the water surface, and the second is a distinct ring from air bubbles trapped underwater by the splash. For most raindrops, the sound of the bubble is, by far, the louder sound.
Small raindrops are especially good at trapping air bubbles underwater and are surprisingly loud.
Nystuen has used the Acoustic Rain Gauges in conjunction with other scientific experiments, which have taken place in the North Atlantic Ocean, the South China Sea and the central tropical Pacific Ocean. The results of the collaborative studies are promising. This is because the formation of a raindrop releases energy into the air. This energy or heat release is one of the primary sources of energy driving atmospheric circulation. Understanding the global patterns of distribution and intensity of rainfall is needed to improve weather and climate forecasting.