Convection and heat transfer in island (warm) wakes

The interaction between the incoming winds with high mountainous islands produces a wind-sheltered area in the leeward side, known as the atmospheric wake. In addition to weaker winds, the wake is also characterized by a clearing of clouds, resulting in intense solar radiation reaching the sea surface. As a consequence, a warm oceanic wake forms on the leeward side. This phenomenon detectable from space can extend 100 km offshore of Madeira, where the sea surface temperature can be 4⁰C higher than the surrounding oceanic waters. This study considers in-situ, remote sensing, and ocean circulation model data, to investigate the effects of the warm wake in the vertical structure of the upper ocean. To characterize the convective layer (25-70m) developing within the oceanic wake, 200 vertical profiles of temperature, salinity and turbulence were considered, together with the computation of the Density Ratio and Turner-angle. In comparison to the open-ocean water column, wake waters are strongly stratified with respect to temperature although highly unstable. The vertical profiles of salinity show distinct water parcels that sink and/or rise as a response to the intense heat fluxes. During the night, the ocean surface cools, leading to the stretching of the mixed layer which was replicated by the ocean circulation model. In exposed, non-wake regions however, particularly in the southeast and north coast of the island, the stretching of the mixed layer is not detectable.