Response of internal solitary waves to tropical storm Washi in the northwestern South China Sea

Z H Xu,B S Yin,Y J Hou

doi:10.5194/angeo-29-2181-2011

Abstract

Abstract. Based on in-situ time series data from an array of temperature sensors and an acoustic Doppler current profiler on the continental shelf of the northwestern South China Sea, a sequence of internal solitary waves (ISWs) were observed during the passage of tropical storm Washi in the summer of 2005, which provided a unique opportunity to investigate the ISW response to the tropical cyclone. The passing tropical storm is found to play an important role in affecting the stratification structure of the water column, and consequently leading to significant variability in the propagating features of the ISWs, such as the polarity reversal and amplitude variations of the waves. The response of the ISWs to Washi can be divided into two stages, direct forcing by the strong wind (during the arrival of Washi) and remote forcing via the near-inertial internal waves induced by the tropical storm (after the passage of Washi). The field observations as well as a theoretical analysis suggest that the variations of the ISWs closely coincide with the changing stratification structure and shear currents in accompanied by the typhoon wind and near-inertial waves. This study presents the first observations and analysis of the ISW response to the tropical cyclone in the South China Sea.

Highlights

Internal solitary waves (ISWs) are commonly observed all over the world ocean, especially on the continental shelves (Liu et al, 1998; Ramp et al, 2004), in the marginal seas (Klymak et al, 2006) and straits (Vlasenko and Hutter, 2002)
With respect to the varying amplitudes of the ISWs, we caculate the environment conditions for our observational cases (Table 1) and find that the absolute values of nonlinear coefficient α, which are sensitive to the stratification structure of the water column, are obviously in close relation with the amplitude variations of the ISWs
The tropical storm Washi is found to lead to significant response of the ISWs in the South China Sea (SCS)

Summary

Introduction

Internal solitary waves (ISWs) are commonly observed all over the world ocean, especially on the continental shelves (Liu et al, 1998; Ramp et al, 2004), in the marginal seas (Klymak et al, 2006) and straits (Vlasenko and Hutter, 2002). They usually arise from the steepening of the strong internal tides (Lien et al, 2005; Mihanovicet al., 2006; Xu et al, 2011). All variables are examined in a 6 day period surrounding the arrival and departure of Washi (28 July–2 August)

Objectives

Discussion

Conclusion