Numerical output used for diagnostics in Gasparin et al.

The diurnal cycle in the equatorial Atlantic strongly influences temperature, currents, and heat exchange between the ocean and atmosphere. However, studying these daily changes is challenging because conditions vary rapidly, complicating the collection of sufficient observations and the validation of ocean models. To address this, ten specially programmed Argo floats were deployed in the equatorial Atlantic in 2021 and 2022. Combined with tropical moorings and a regional model, these observations provide new insights into how daily temperature cycles vary by location and season—especially during the formation of the Atlantic cold tongue, a region of cooler water that develops in the tropical Atlantic during boreal summer. The model captures the evolution of the diurnal warm layer but underestimates its depth and deepening rate. Still, the model reveales that the daily downward heat transfer increases by 50% under strong winds compared to weak winds. However, background ocean conditions also play an important role. For instance, same wind speeds can produce deeper and stronger mixing of heat at 10°W than at 0°. These characteristics of the diurnal heat flux may influence how heat is transferred to the deeper ocean, potentially helping to reduce known biases in climate models and improve predictions of climate variability.