Acknowledgements

This study is supported by the National Natural Science Foundation of China (Grant No. 41876209) and by the State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences (Project No. LTO 1908). Much of the work reported in this chapter is the outcome of Xi-Yu Xu during his visit in Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS), Observatoire Midi-Pyrénées, France. Anny Cazenave and Florence Birol, the collaborators of Xi-Yu Xu in Legos, are gratefully acknowledged for their substantial help and insightful advice.
