Intense and Small Freshwater Pools From Rainfall Investigated During Spurs-2 on 9 November 2017 in the Eastern Tropical Pacific Journal of Geophysical Research: Oceans

During the second Salinity Processes in the Upper Ocean Regional Study (SPURS-2) 2017 tropical Pacific cruise, two drifters were deployed on 9 November. The drifters measured temperature and salinity in the top 36 cm, wave spectra, and the noise of rain drops. During a short nearly circular survey with a 1.8-km radius around the drifters, the R/V Revelle measured air-sea fluxes, as well as temperature and salinity stratification in the top 1 m from a towed surface salinity profiler (SSP). A C-band weather radar measuring rain rate within 1- to 100-km range of the ship observed discrete rain cells organized in a system moving from the southeast to the northwest. Some of the intense rain cells were small scale (1 km in diameter or less) with short lifetimes yet dropped more than 5 cm of water in half an hour near the drifters, whereas the ship measured short rain episodes totaling 1.3 cm of rainfall mostly accompanied by very low wind. The data indicate a large spatial heterogeneity in temperature and salinity, with near-surface freshening of up to 9 psu measured at different times by the two drifters (separated by less than 500 m) and by the SSP. The drifters indicate deepening of the fresh and cool surface layer during the rain which then thinned during the following 40 min with very low wind speed (<2 m/s). Patchy surface-trapped cold and fresh layers were also observed by the SSP east of the drifters. The high spatial and temporal variability of rainfall and surface-trapped fresh pools is discussed.