Technical Note: Mean sea level variation in the Singapore Strait from long-term tide data

Winds over the South China Sea (SCS) are primarily responsible for the observed variability in sea level anomalies (SLAs) in the Singapore Strait (SS). The present study focuses on remote forcing contributing to local mean sea level changes in the SS in seasonal and inter-annual scales, and relating the long term mean sea level variation to El Ni\~no/ENSO. As Tanjong Pagar (TP) tide station in the SS has nearly 23.5 yr (1984-2007) of time series data with less data gaps, this data was subject to harmonic and sea level analyses. The mean sea level changes suggest that the fluctuations are quasi-periodic. Rising and falling of sea level is noticed atleast 7 times in a period of 15 yr, with 3 distinct sharp falls (1984-1987, 1989-1992 and 1995-1996) and 4 sharp rises (1987-1988, 1992-1993, 1994-1995 and 1997-1999). These sea level falls are related to El Ni\~no events. When we segregated the results into 2 time spans, we find that from 1984 to 1999 the sea level was on the rising trend in spite of sharp falls, and from 1999 to 2007 on gradual falling trend. More or less similar trend was observed by other researchers for the SCS with altimetry data. During the El Ni\~no periods of 1987 and 1992, the inter-annual MSL variability is the highest, of the order of 7 cm. In one of the events, sea level recovered from a fall of 60 mm (in 1987) to a rise of 40 mm (in 1988). During 1992 to 1999, sea level was continuously on rising trend (from -50 mm to +60 mm), except in one year (1995-1996). The analysis shows a MSL rise rate of 15.7 mm yr-1, which is very closer to MSL in the SCS. The average rate of sea level rise around Singapore as shown by the Tanjong Pagar tidal station is 1.6 mm yr-1, and this matches with the global sea level rise.