Diurnal cycle of rainfall and surface salinity in the western Pacific warmpool

The diurnal cycles of rainfall and surface salinity in the western equatori al Pacific were computed for the period August 1991-December 1994 using hou rly data from the Tropical Atmosphere Ocean (TAO) mooring array enhanced fo r the Coupled Ocean Atmosphere Response Experiment (COARE). The analysis sh ows preferential rainfall during predawn hours. Nighttime mixing typically caused the predawn rainfall to mix downward into higher salinity subsurface waters. In contrast, afternoon rainfall, although weaker, generally produc ed a stable shallow layer of very low salinity. Consequently, sea surface s alinity (SSS) exhibited a weak diurnal cycle, with anomalously low salinity in the late afternoon and anomalously high salinity at night. At 1 m depth , the SSS diurnal cycle anomalies were similar to 0.005 psu. Although nearl y two orders of magnitude less than the SSS standard deviation for this reg ion, the anomalies were significant at the 95% confidence level.