Distribution of seasonal signals in the deep South China Sea

The upper South China Sea (SCS) circulation is characterized by seasonal variability due to the monsoon, and in fact, some studies have shown that the deep SCS circulation could also vary seasonally. Based on SODA product, this study presents the distribution of seasonal signals at 2100 m in the deep SCS by the method of harmonic analysis. Seasonal signals are evident in most areas, sufficient to explain more than 20% of the total variation. The amplitude pattern of U displays a four-core structure on the meridional band of 114 degrees -118 degrees E, and high amplitudes of V are located in the middle basin. The annual harmonics of U along 12.75 degrees N have several char-acteristics: notable seasonal signals in the deep ocean, phase isolines that slope downward to the west implying upward and westward phase propagation, and amplitude maxima that are parallel to phase isolines. These features suggest that seasonal signals in the deep SCS originate from the upper ocean and the vertically prop-agating Rossby waves provide a mechanism.