Estimation of rain amount over global oceans using ambient sound recorded on Argo floats relating to global water cycle studies

Rain over the ocean is a central process in the global freshwater cycle. The freshening of the ocean surface due to rain can be seen in global maps of sea surface salinity, where areas with high precipitation are broadly coincident with areas of low salinity and regions of high salinity occur in regions with low precipitation and high evaporation. The transfer of water from these evaporating regions to the precipitating regions drives the global water cycle, and understanding its dynamics is essential in determining how weather patterns will respond to changes in global climate. Rain is difficult to measure over the ocean due to its spatial and temporal variability and the limitations imposed by rain gauges when mounted on moving platforms. However, the loud and distinctive underwater sound generated by raindrops on the ocean surface can be used to detect and quantify rainfall and to track climate change impacts. The work here will focus on deriving time series of rain rate with temporal resolution on the order of minutes using ambient noise recorded by Passive Aquatic Listener (PAL) on both Argo floats and deep ocean moorings (Nystuen, J., Atmos. Oceanic Tech, 13, 74–84, 1996). [Work supported by NOAA and NASA.]