Diurnal Sea Surface Temperature Warming Along the Kuroshio off Taiwan Under Easterly Wind Conditions

We carry out the Lagrangian diurnal warm layer (DWL) observations, supplemented by satellite products, along the strong Kuroshio east of Taiwan, where the boundary terrain modifies the winds and the advection effect is significant. The synoptic easterly wind bifurcates as it encounters Taiwan's coast, forming the southward‐blowing and the northward‐blowing branches in the southern and northern regions of the bifurcation, respectively. The two branches produce areas with enhanced and weakened apparent wind speed relative to the northeastward flowing Kuroshio. The DWL can reach 5 m in the south of the bifurcation due to the shear instability‐induced mixing. Sea surface temperature (SST) enhancement occurs around and in the north of the wind bifurcation, where the solar heat is only trapped in the upper 2 m due to the absence of instability, forming inhomogeneous SST along the Kuroshio. The synoptic wind variations and Kuroshio advection further modulate the location of SST enhancement. Plain Language Summary Sea surface temperature could change in a day due to solar heating over the top few meters, where a thin surface warm layer is created. This layer's thickness and mean temperature are related to solar heating and wind speed. The wind blowing works like a stick stirring the surface water to spread the surface heat from the sun to the deeper ocean and, therefore, affect the thickness of the upper ocean's warm layer. However, the warm layer and its associated surface temperature variation exist only in the weak to moderate wind (0–4 m s−1). In the region of a strong current, such as the western boundary current, the moving speed of surface water (1–2 m s−1) is comparable to the wind speed suitable for warm layer formation. It is essential to use the wind speed that the surface waters “feel” as they move to evaluate the warm layer. We found that the above effect has resulted in the asymmetric sea surface warming along the Kuroshio in response to the daily solar heating. Key Points Lagrangian observations and satellite remote sensing reveal inhomogeneous diurnal surface temperature warming along the Kuroshio path Inhomogeneous diurnal surface warming is due to terrain‐induced bifurcated wind and the strong Kuroshio flow speed The critical wind speed of ∼2 m s−1 relative to the current determines whether the solar heat could transfer deeper via shear instability