Upper Ocean Thermal Structure in the Western North Pacific from Satellite Altimetry

Using >38,000 Argo temperature profiles, a linear regression method for the western North Pacific (i.e., REGWNP) is developed. Then, >7,000 in situ profiles are used to assess accuracy of REGWNP-derived UOTS. The results show that REGWNP is able to produce rather reliable UOTS. During the typhoon season, the rms difference for the depth of 20°C isotherm (D20), depth of 26°C isotherm (D26), UOHC and averaged temperature of the upper 100 m (T100) is less than 30 m, 20 m, 20 kJ cm-2, and 1.5°C, respectively. Also, it is found that REGWNP outperforms the traditional two-layer approach and is comparable to a sophisticated full ocean model for producing real-time UOTS field. Based on the sea surface height anomaly (SSHA) record between 1993 and 2010, the long-term changes in ocean conditions in the western North Pacific main typhoon intensification region are investigated. It is found that the activity of warm eddies enhanced while cold eddies weakened. In terms of subsurface variability, D20, D26 and UOHC increased by 9-17%, meanwhile, T100 warmed by 0.16-0.35°C over the 18 years period. Furthermore, it is also found that the total area of positive SSHA (≧ 10 cm) features substantially increased while negative SSHA (≦ -10 cm) features deceased. These results suggest that the western North Pacific ocean conditions are becoming more favorable to typhoon intensification.