Effect of Wind Speed and Direction on Summer Tidal Circulation and Vertical Mixing in Hong Kong Waters

Abstract

KUANG, C.P.; LEE, J.H.W.; HARRISON, P.J., and YIN, K.D., 2011. Effect of wind speed and direction on summer tidal circulation and vertical mixing in Hong Kong Waters. Journal of Coastal Research, 27(6A), 74-86. West Palm Beach (Florida), ISSN 0749-0208.In subtropical coastal waters around Hong Kong, a well-mixed water body is usually observed after typhoons or strong easterly wind events in summer. A calibrated three-dimensional (3-D) hydrodynamic model for the Pearl River Estuary (Delft3D) was applied to study the physical hydrography of Hong Kong waters and its relationship with wind events in the summer wet season. The general 3-D hydrodynamic circulation and salinity structure in the partially mixed estuary are presented here. The effect of wind on vertical mixing was studied for two representative wind directions (NE and SW) and three wind speeds (5, 7.5, and 10 m/s). The computations show that: (i) in general, in the summer wet season, the river plume moves into the western waters of Hong Kong due to the SW monsoon winds, and the current flow is mainly from W/SW to E/NE in the southern Hong Kong waters; the salinity vertical profile indicates that the water is strongly stratified; (ii) a strong SW wind pushes the river plume into a narrow band and decreases the salinity of the surface water in the estuary and its neighboring region; it may also enhance the mixing in the upper layer of water column, but the whole water body is still stratified; and (iii) a strong NE wind pushes the river plume westward away from Hong Kong waters, and more saline coastal waters enter Hong Kong waters; the water only becomes vertically well mixed after a 10 m/s NE wind blows for 5 d, but wind speeds of 5 and 7.5 m/s do not result in the same extent of mixing. We also examined the role of wind in an episodic storm event in August 2003. The strong SE wind from 23 to 26 August strongly mixed the water column. The moderate to weak NE wind during 16-20 August and the spring tide also contributed to the vertical mixing.www.JCRonline.org ADDITIONAL INDEX WORDS: Hydrodynamic modeling, water quality, environmental hydraulics, monsoon windinduced water transport, Hong Kong, Pearl River Estuary, wind mixing.

Summer monsoon–induced upwelling dominated coastal sea surface temperature variations in the northern South China Sea over the last two millennia

“…A stronger ASM leads to intensification of wind-induced upwelling, which, subsequently, decreases the coastal SSTs of northern SCS (e.g. Kong et al, 2015; Kuang et al, 2011; Liu et al, 2013). Moreover, an enhanced upwelling also promotes vertical mixing of nutrient-rich subsurface waters that allows favorable conditions for haptophyte production (Villanueva et al, 1998) and would thereby explain higher C 37 concentrations (Figure 3b).…”

“…Chen et al, 2017; Jiang and Wang, 2018; Jing et al, 2009; Kong et al, 2015). Furthermore, investigations of three nearby cores in the Mirs Bay (Kong et al, 2015) have indicated that regional SST variations over the past four centuries, as mainly controlled by changes in coastal upwelling, are able to reflect the ASM intensity (Kuang et al, 2011; Liu et al, 2013).…”

Exploring the Influence Mechanism of Meteorological Conditions on the Concentration of Suspended Solids and Chlorophyll-a in Large Estuaries Based on MODIS Imagery

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Study of the wind drag coefficient during the storm Xaver in the German Bight using data assimilation

“…Sigma coordinate is used for vertical grid in 3-D simulations. Delft3D FLOW is widely used in the coastal hydrodynamic research (Jiao, 2014;Kuang et al, 2016;Wang et al, 2017b). The wave model for the study is the module WAVE of Delft3D.…”