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Abstract In conditions of low winds and high insolation, near-surface stratification develops in the ocean that is typically referred to as a diurnal warm layer (DWL). These layers can have a substantial effect on sea surface temperature and air–sea fluxes yet are rarely accounted for in modern global models due to their small vertical scale. Here, we present collocated measurements of vertical temperature and turbulence structures in large DWLs made from a Lagrangian float featuring a robotic lead screw temperature/salinity (T/S) profiler and pulse-to-pulse coherent ADCP as well as a comprehensive suite of meteorological observations above the ocean surface, yielding novel observations of the response of large DWLs to variability in wind and solar forcing at subhourly time scales. Comparison between the observations and a hierarchy of upper-ocean models reveals the importance of an accurate solar heating parameterization and suggests a modification to the critical bulk Richardson number used by default in theK-profile parameterization. Comparison to a simple scaling for DWL evolution highlights its potential as a means of incorporating DWL effects into global-scale modeling, and a new extension to the scaling is developed to remedy its inaccuracy in cases of wind decrease. None of the models tested are able to reproduce the observed response to sudden insolation loss on one of the stations. Significance StatementThis study presents measurements of warm layers of water that can develop on the ocean surface on a calm, sunny day. These layers are widespread in the ocean and change the relationship between the ocean and the atmosphere, but they are hard to include in large models because they are so shallow. By comparing first-of-their-kind observations of these warm layers made by our drifting buoy with several types of physical models, we improve our understanding of them and chart a realistic path toward their inclusion in global models. 

Abstract Rainfall alters the physical and chemical properties of the surface ocean, and its effect on ocean skin temperature and surface heat fluxes is poorly represented in many air‐sea interaction models. We present radiometric observations of ocean skin temperature, near‐surface (5 cm) temperature from a towed thermistor, and bulk atmospheric and oceanic variables, for 69 rain events observed over the course of 4 months in the Indian Ocean as part of the DYNAMO project. We test a state‐of‐the‐art prognostic model developed by Bellenger et al. (2017,https://doi.org/10.1002/2016JC012429) to predict ocean skin temperature in the presence of rain, and demonstrate a physically motivated modification to the model that improves its performance with increasing rain rate. We characterize the vertical skin‐bulk temperature gradient induced by rain and find that it levels off at high rain rates, suggestive of a transition in skin‐layer physics that has been previously hypothesized in the literature. We also quantify the small bias that will be present in turbulent sensible heat fluxes parameterized from ocean temperature measurements made at typical “bulk” depths during a rain event. Finally, a wind threshold is observed above which the surface ocean remains well‐mixed during a rain event; however, the skin temperature is observed to decrease at all wind speeds in the presence of rain.