The Response of Ocean Skin Temperature to Rain: Observations and Implications for Parameterization of Rain-Induced Fluxes

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.