Classification and 3-D distribution of upper layer water masses in the northern South China Sea

Using the Sigma‐Pi Diagram to Analyze Water Masses in the Northern South China Sea in Spring

“…These water mass centers are illustrated in Figure 7b as brown triangles (the ZDW is also ignored). There are several differences and similarities between our results and those of Zhu et al (2019). For example, in the surface layer, surface-subsurface mixed layer, and subsurface-intermediate mixed layer, the fuzzy cluster and TSSN analysis did not distinguish the water sourcing from the NSCS or from the WPO.…”

“…Comparatively, on the surface of 25.7 kg/m 3 corresponding to the subsurface-intermediate layer, there are no clear intrusion features, revealing either homogeneous characteristics of water masses or a relatively weak east-west movement of water masses in this layer. Moreover, some high potential spicity patches can be detected in the central NSCS on the 22.9 and 24.5 kg/m 3 surfaces, which could be the signature of nonlinear Rossby eddies propagating into the NSCS through the Luzon Strait from the WPO (e.g., Cheng et al, 2014;Hu et al, 2012;Xie et al, 2016;Zheng et al, 2011Zheng et al, , 2017Zhu et al, 2019). The WPUW can traverse westward through the Luzon Strait and mix with the SUW, resulting in a subsequent decrease in its potential spicity, but it still has higher potential spicity than the local water.…”

“…Using the same CTD data set in this work, Zhu et al (2019) utilized the fuzzy cluster and TSSN analysis to classify the water masses in the upper layer (above 300 m) into six types: ZDW, surface water, surface-subsurface mixed water, SUW, WPUW, and subsurface-intermediate mixed water. These water mass centers are illustrated in Figure 7b as brown triangles (the ZDW is also ignored).…”

“…In addition, the similarity is often estimated by the squared Euclidean distance based on the normalized T and S differences between points. To improve the practicability of fuzzy cluster analysis, Zhu et al (2019) introduced the T-S similarity number (TSSN) to further quantify the water sample by specifying the boundaries between the water masses. Apart from the T-S-based or fuzzy cluster methods, Li et al (2006) proposed the spiciness index parameter (b), which is nondimensional and simplified from the definition given by Flament (2002).…”

“…The small dots in the same color mean that they belong to the same water mass. The brown triangles in (b) indicate the water mass centers classified by the fuzzy cluster and TSSN analysis (fromZhu et al, 2019).…”