Tidal Mixing Signatures in the Hong Kong Coastal Waters from Satellite-Derived Sea Surface Temperature

R Susanto,Adam Devlin,Jiayi Pan

doi:10.3390/rs11010005

Abstract

Tidal mixing in the coastal waters of Hong Kong was investigated using a combination of in situ observations and high-resolution satellite-derived sea surface temperature (SST) data. An indicator of tide-induced mixing is a fortnightly (spring-neap cycle) signature in SST due to nonlinear interactions between the two principal diurnal and the two principal semi-diurnal tides. Both semi-diurnal and diurnal tides have strong tidal amplitudes and currents near Hong Kong. As a result, both the near-fortnightly (Mf) and fortnightly (MSf) tides are enhanced due to nonlinear tidal signal interactions. In addition, these fortnightly tidal signals are modulated by seasonal variability, with the maximum seasonal modulation of fortnightly tides occurring during the monsoon transition periods in May and October. The largest fortnightly signals are found in the southwestern part of the Pearl River estuary. Tidal constituent properties vary by space and depth, and high-resolution SST plays a pivotal role in resolving the spatial characteristics of tidal mixing.

Highlights

The Hong Kong coastal waters are part of the South China Sea (SCS), which is the largest marginal sea in Southeast Asia (Figure 1)
Various tidal phenomena in the SCS have drawn attention because of their complicated characteristics and have been the focus of many diverse oceanographic studies. These tidal studies can be summarized into three themes: (a) analysis of harmonic constants based on limited tide gauge station data or mooring data in the SCS (e.g., [3,4,5,6] and references therein), (b) analysis of results based on 2D or 3D numerical models and data assimilation [2,7,8,9,10,11,12], and (c) analysis of altimeter data in the SCS (e.g., [13,14]) to obtain the tidal constituents
It is hypothesized that tidal mixing can lower sea surface temperature (SST) as cooler subsurface water is mixed into the surface layer and that the tidal mixing can lower SST as cooler subsurface water is mixed into the surface layer and that the cooling would be proportional to the intensity of the mixing

Summary

Introduction

The Hong Kong coastal waters are part of the South China Sea (SCS), which is the largest marginal sea in Southeast Asia (Figure 1). Various tidal phenomena in the SCS have drawn attention because of their complicated characteristics and have been the focus of many diverse oceanographic studies These tidal studies can be summarized into three themes: (a) analysis of harmonic constants based on limited tide gauge station data or mooring data in the SCS (e.g., [3,4,5,6] and references therein), (b) analysis of results based on 2D or 3D numerical models and data assimilation [2,7,8,9,10,11,12], and (c) analysis of altimeter data in the SCS (e.g., [13,14]) to obtain the tidal constituents. No previous studies have been reported on the extraction of nonlinear tidal interactions and tidal mixing signatures from a combination of satellite sea surface temperature (SST) data and in situ measurements in the Hong

Objectives

Methods

Results