Near-surface variability of temperature and salinity in the near-tropical ocean: Observations from profiling floats

Upper ocean measurements of temperature and salinity obtained from profiling floats equipped with auxiliary surface temperature and salinity sensors (STS) are presented. Using these instruments, high vertical resolution (10 cm) measurements in the near-surface layer were acquired to within 20 cm of the sea surface, allowing for an examination of the ocean's near-surface structure and variability not usually possible. We examine the data from 62 Argo-type floats equipped with STS units deployed in the Pacific, Atlantic, and Indian Oceans. The vertical variability of temperature and salinity in the near-surface layer is characterized for each of these regions. While observations show the upper 4 m of the ocean are well mixed most of the time, this homogeneity is interrupted by significant and often short-lived warming/cooling and freshening events. In addition to the presence of barrier layers, a strong diurnal signal in temperature is observed, with salinity exhibiting somewhat weaker diurnal variations. The magnitude of the upper ocean diurnal cycle in temperature and salinity is largest in areas with light winds and heavy precipitation and was found to decay rapidly with depth (approximate to 50% over the top 2 m). Storm events, validated from meteorological data collected from nearby TAO moorings and the Tropical Rainfall Measuring Mission (TRMM) satellite, show downward mixing of rainfall-derived freshwater to 10 m depth over only a few hours. Turner angle calculations show instability following these events. Key Points <list id="jgrc20941-list-0001" list-type="bulleted"> <list-item id="jgrc20941-li-0001">Upper ocean temperature and salinity is well mixed the majority of the time <list-item id="jgrc20941-li-0002">Diurnal cycles decay with depth