Temporal and spatial variabilities of sea surface heights in the northeastern South China Sea

Analyses of sea surface height anomalies (SSHA) from Jan. 1993 to Dec. 2001 measured by TOPEX/ Poseidon (T/P) satellite altimetry indicate that there are two energy highs of SSHA fluctuations on both sides of the Luzon Strait. The highs centered at (19.5° N, 119.5° E) and (22.0° N, 124.0° E) respectively, are separated by a low energy band in the Strait. Empirical Orthogonal Function (EOF) analysis on the “Far Field” suggests that fluctuations of these two areas are mutually independent. EOF analysis on the “Near Field” shows that SSHA oscillation in the northeastern South China Sea (SCS) is dominated by seasonal variations accompanied with significant intra-seasonal and inter-annual fluctuations. Among which, EOF1 and EOF2 reflect 66.7% of the total variance. They are both seasonal but showing three months difference in phase. The basic pattern of EOF1 appears to be the seasonal SSHA oscillation centered at (18.0° N, 119.0° E) northwest off Luzon Island, which shows maximums (minimums) in August/September (January/February) and mainly reflects the seasonal variation of steric heights of the deep SCS basin and its corresponding circulation adjustments. The basic pattern of EOF2 is featured by seasonal seesaw of sea surface elevation in the SE-NW direction, which imaged the Ekman adjustment of sea surface height (SSH) in the northeastern South China Sea (NESCS) driven by the monsoons. Our analyses also reveal that intra-seasonal variation is an important component of SSHA fluctuation of the NESCS, which reflects the frequent occurrence of mesoscale processes west to the Luzon Strait. Moreover, inter-annual variations appear in all major EOF modes.