On the Upper-Ocean Vertical Eddy Heat Transport in the Kuroshio Extension. Part II: Effects of Air-Sea Interactions
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AbstractEncountering of energetic ocean eddies and atmosphere storms makes the winter Kuroshio extension a hotspot for air-sea interactions. This second part investigates the regulation of vertical eddy heat transport QT in the winter Kuroshio extension mixed layer by different types of air-sea interactions, including the atmosphere synoptic forcing, eddy thermal feedback resulting from eddy-induced surface heat flux anomalies, and eddy current feedback from eddy currents imprint on wind stress.Atmosphere synoptic forcing modulates intra-seasonal variation of QT by boosting its component contributed by the turbulent thermal wind balance during strong cooling events associated with intense winds. In addition, the magnitude of QT is influenced by the direction of synoptic wind stress primarily via , with the latter exhibiting enhancement both in the downfront- and upfront-wind forcing. Enhanced by the downfront-wind forcing is attributed to increased turbulent vertical viscosity and front intensity caused by the destabilizing wind-driven Ekman buoyancy flux, whereas interaction of uniform wind stress with smaller turbulent vertical viscosity at the front center than periphery (a so-called internal Ekman pumping) accounts for the increased in the upfront-wind forcing. The eddy thermal feedback reduces QT significantly through weakening the fronts. In contrast, the eddy current feedback exerts negligible influences on QT, although it weakens eddy kinetic energy (EKE) evidently. This is due to the much reduced effect of eddy current feedback in damping the fronts compared to EKE and also due to the compensation from Ekman pumping induced by the eddy current feedback.
