Three‐Dimensional Ocean Surface Layer Response to Atmospheric Cold Pools and Diurnal Heating in the Trade Wind Regime

Abstract In the tropical ocean, diurnal heating and the formation of atmospheric convection cells associated with local precipitation events, cold pools and wind bursts, have been shown to impact air‐sea exchange and the structure of the ocean surface layer. Here, we present results from a high‐resolution process study based on idealized ocean simulations, forced by realistic, ultra high‐resolution atmospheric Large Eddy Simulations in the trade wind zone. By explicitly resolving small‐scale features associated with atmospheric convection, we are able to study their impact on the ocean surface layer and parameterized air‐sea fluxes. We find that in our study area, the oceanic heat loss is, unexpectedly, reduced in the presence of cold pools by on average 30 W due to the higher air humidity, weaker mean winds, and increased cloud cover. Our results also show that the total non‐solar heat flux is dominated by the diurnal cycle of the trade winds, rather than by diurnal heating. In the ocean surface layer, local wind bursts, rain layers, and cloud shading induce a strong lateral variability of Diurnal Warm Layers (DWLs), questioning the local applicability of available DWL bulk parameterizations. From a series of numerical tracer experiments, we identify a new shear‐dispersion mechanism, induced by the diurnal jet, that is reflected in an extreme anisotropy of horizontal dispersion with diffusivities of order 10–100 .