Abstract
Analysis of sea-level observations demonstrates that Typhoons Mawar (2017) and Mangkhut (2018) induced seiches in both Dapeng Bay and Daya Bay near Shenzhen of China, with periods varying from about 3.5 to 4.0 h. Typhoon Mawar (2017) also generated seiches with a period of about 1.2 h. Seiches with such periods in the two bays have not been reported in the past. In this study, we investigate the main processes affecting seiches over these coastal waters using a nested-grid ocean circulation modeling system. The modelled results of typhoon-induced seiches agree well with observations, which indicates that the seiches after the passage of typhoons are dynamically free waves generated by the storm-induced accumulation of water bodies in the two bays. Model sensitivity experiments show that wind directions have an important influence on the type and characteristics of seiches. When the wind stress causes the water body to accumulate in a cross-bay direction, seiches in a closed water body are generated. When the wind stress causes the water body to accumulate in an along-bay direction, seiches in a semi-closed water body are produced. Because of the irregularity of the bathymetry and coastline and variability of wind directions, these two types of seiches can exist simultaneously in the two bays.
Highlights
Seiches are oscillations in a closed or semi-closed water body, such as lakes or coastal bays [1]
We examine model results in idealized experiments using a wind pulse to determine different kinds of seiches, i.e., those with characteristics of both “closed water body” and “semi-closed water body”, coexist over the coastal waters off Shenzhen due to changes in wind directions
Observations and model results were used in this study to investigate characteristics of seiches over the coastal waters off Shenzhen, China
Summary
Seiches are oscillations in a closed or semi-closed water body, such as lakes or coastal bays [1]. Wu et al [3] compared seiches in Daya Bay off Shenzhen and Haizhou Bay off Lianyungang City of Jiangsu Province and argued that the amplitudes and periods of seiches in these two bays are significantly different. They suggested that the main reason for these differences may be due to different sizes, shapes and depths of the two bays, but they did not examine the influence of these factors on seiches in detail in the two bays. Most previous studies on seiches over coastal waters off Shenzhen focused mainly on periods and amplitudes of seiches without systematic investigations of the generation mechanisms and influencing factors of seiches.
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