Storm surges in the Singapore Strait due to winds in the South China Sea

Abstract

Among the semi-enclosed basins of the world ocean, the South China Sea (SCS) is unique in its configuration as it lies under the main southwest-northeast pathway of the seasonal monsoons. The northeast (NE) monsoon (November-February) and southwest (SW) monsoon (June-August) dominate the large-scale sea level dynamics of the SCS. Sunda Shelf at the southwest part of SCS tends to amplify Sea Level Anomalies (SLAs) generated by winds over the sea. The entire region, bounded by Gulf of Thailand on the north, Karimata Strait on the south, east cost of Peninsular Malaysia on the west, and break of Sunda Shelf on the east, could experience positive or negative SLAs depending on the wind direction and speed. Strong sea level surges during NE monsoon, if coincide with spring tide, usually lead to coastal floods in the region. To understand the phenomena, we analyzed the wind-driven sea level anomalies focusing on Singapore Strait (SS), laying at the most southwest point of the region. An analysis of Tanjong Pagar tide gauge data in the SS, as well as satellite altimetry and reanalyzed wind in the region, reveals that the wind over central part of SCS is arguably the most important factor determining the observed variability of SLAs at hourly to monthly scales. Climatological SLAs in SS are found to be positive, and of the order of 30 cm during NE monsoon, but negative, and of the order of 20 cm during SW monsoon. The largest anomalies are associated with intensified winds during NE monsoon, with historical highs exceeding 50 cm. At the hourly and daily timescales, SLA magnitude is correlated with the NE wind speed over central part of SCS with an average time lag of 36-42 h. An exact solution is derived by approximating the elongated SCS shape with one-dimensional two-step channel. The solution is utilized to derive simple model connecting SLAs in SS with the wind speeds over central part of SCS. Due to delay of P. Tkalich (&)

The forced and free response of the South China Sea to the large-scale monsoon system

“…We do not give the solutions for the velocities (Tkalich et al, 2011). Again, the integration constants are found by imposing the boundary conditions at the two side walls and the matching conditions at x=0 where continuity of transport is required.…”

“…However, frequent events of extreme SLAs produced by different mechanisms have been recorded (Tkalich et al, 2011). In this work we have two major objectives.…”

A storm surge forecasting system for the Singapore Strait

“…During the south-west (SW) monsoon from June to August, the SLA is 0.15-0.2 m lower than the annual mean. Tkalich et al (2012) explained this observed mechanism as shown Tkalich et al (2012) pointed out that the intensified wind over SCS is the most important factor determining the observed variability of SLAs in the Singapore Strait. Local SLA magnitude is correlated with the wind speed of NE monsoon over the central part of SCS ( Fig.…”

“…To further assess the accuracy of the system as a whole, we computed the total root mean square error (RMSE) of sea level using the formula (e.g. Luu et al, 2011;Tkalich et al, 2012)…”

“…2) with an average time lag of 36-42 h. The mechanism of rising and falling sea levels in the Singapore Strait for the shorter timescale (hours to days) is physically similar to that of the seasonal phenomenon. Tkalich et al (2012) further derived an empirical relationship to estimate the storm surge heights measured in the Singapore Strait as a function of the wind observed at the central part of SCS. The simple algebraic equation allows for a quick estimate of the storm surge height in the Strait.…”