Heat transfer patterns of marine heatwaves with distinct vertical structures in the southwestern East Sea (Japan Sea)

Abstract Recent studies have shown that marine heatwaves (MHWs) with similar surface signals can have distinct subsurface vertical structures; however, the processes associated with these differences remain an open question. MHW heat budgets have predominantly been examined at the mixed-layer scale, and the components of oceanic forcing in the subsurface have received less attention. We classified MHWs in the southwestern East Sea by their vertical structures and analyzed the associated heat transfer patterns. By applying K-means clustering to MHW events identified from detrended sea surface temperatures, we categorized the vertical structures into four types: subsurface-intensified, deep, shallow, and subsurface-reversed. We then analyzed the heat budget of each type by decomposing the lateral heat flux into dynamical (associated with velocity anomaly) and thermodynamical (associated with temperature anomaly) components. In the shallow type, the net surface heat flux term contributed most to the warming. In the subsurface-intensified and deep types, the dynamical component contributed more to the warming than the thermodynamical component, particularly in the subsurface-intensified type. In the subsurface layer, however, the thermodynamical component exerted a cooling effect, partially offsetting the dynamical warming. This study demonstrates that the dynamical and thermodynamical contributions to the lateral heat flux vary substantially among MHW types.