The formation and dynamics of the cold-dome off northeastern Taiwan

The cold-dome off northeastern Taiwan is commonly observed by remote-sensing of Sea Surface Temperature (SST) and in-situ observation. The recent remote-sensing SST and subsurface Argo profiles were analyzed to investigate possible formation mechanisms and dynamics. The observed time series of SST anomaly suggested that the surface cold-dome occurred more frequently in summer, including an unusual contribution due to the cold water residual associated with typhoon events. Subsurface hydrographic features from Argo float data indicated that the near-shore thermocline can be lifted up about 85 m by Kuroshio dynamics, and the cold saline deep water (100 m deep off northeastern Taiwan) can only result from subsurface Kuroshio. We examined the possible formation mechanisms using a duo-grids North Pacific Ocean model (DUPOM) with a horizontal resolution of 1/8° for the East Asian Seas and 1/4° for the remaining North Pacific. The model reproduced several cold-dome formation events and displayed typical cold-dome features. Further analysis shows that the geostrophic component of Kuroshio transport is the main contributor to the cold-dome formation (57.4% of the total isotherm uplift) and dominates seasonal occurrence of the cold-dome. The contribution resulting from the associated cyclonic eddy is only 3.3% of the total isotherm uplift. Additional sensitivity tests suggested that the remaining contribution (39.6% of the total isotherm uplift) is mainly due to the topographically controlled upwelling in this region. Moreover, the local boundary Ekman transport may enhance the surface appearance of the cold-dome, but plays only a minor role.

Research highlights
► Investigate the possible formation mechanisms of the cold-dome observed northeastern Taiwan.
► Geostrophic Kuroshio dynamic along the coast dominates the formation of cold-dome.
► The isotherm uplift across Kuroshio contributes mostly to the seasonal variability.
► Wind stress and Ekman layer dynamics is not important in fact.