华南不同类型热带风暴驱动下珠江口表层悬沙分布趋势

本文利用1949—2014年的华南热带风暴数据和1960—2014年珠江入海流量等, 统计分析风暴作用期间珠江口的风强迫和珠江入海水沙强迫特征, 结果表明, 热带风暴对珠江口的风强迫和水沙强迫因台风距珠江口的距离、强度等因素的影响有显著差异。依据水沙及风强迫的强度, 将热带风暴对珠江口的影响简单分成四类: 中风中水沙驱动型、中风高水沙驱动型、强风中水沙驱动型及强风高水沙驱动型。利用MODIS (moderate-resolution imaging spectroradiometer)一级数据和已建立的珠江口表层悬沙指数反演模型, 挑选2002—2010年风暴影响期间无云天气的MODIS影像, 反演珠江口悬沙分布, 分析表层悬沙对四种不同来水来沙及风强迫型风暴的响应特征。结果显示, 中风中水沙型风暴驱动下, 珠江口整体含沙量偏低, 其悬沙扩散及时间变化受控于潮流的强弱; 中风高水沙型风暴驱动下, 八大口门特别是磨刀门浅滩、伶仃洋西滩的含沙量高于其他海域, 其高含沙水体向南偏西方向扩散输运; 强风中水沙风暴驱动下, 河口表层悬沙分布及扩散受主导风向的影响, 在强东北风驱动下, 伶仃洋西侧浅滩含沙量因台风浪的掀沙作用高于湾内大部分海域, 高含沙水体向西南侧扩散; 强风高水沙风暴驱动下珠江河口湾含沙量偏高, 水体一片浑浊, 河口悬沙随偏南风驱动下的沿岸流向东侧输运、扩散。

Surface suspended sediment distribution of Pearl River estuary under tropical storms with different wind and river discharge forcing

In this study, the data of tropical storms, CFSR gridded wind during 1949~2014, and Pearl River discharge were used to analyze wind forcing and runoff forcing on the Pearl River estuary (PRE) under tropical storm. The results show that the wind and runoff forcing varied with location and strength of the storm, and can be classified into four types: storm I with medium wind and runoff forcing on PRE, storm II with medium wind and high runoff forcing, storm III with strong wind and medium wind, and storm IV with strong wind and high runoff forcing. According to the selected moderate-resolution imaging spectroradiometer (MODIS) imaging with fine and no cloudy during tropical storms in South China, existing empirical formula between the water reflectance of MODIS band 1 and suspended sediment concentration (SSC) was used to retrieve the surface SSC in the PRE during storms, and the corresponding spatial diffusion of SSC was studied. We find that under four types of storms with different wind and runoff forcing, the responses of SSC in the PRE were different. The SSC was low under storm I, and suspended sediment diffusion was mostly controlled by tidal current. Under storm II, the higher SSC was shown in the Modaomen Estuary shoal and Lingdingyang west shoal than the other areas, which was mostly transported southwesterly. Under storm III, the distribution and diffusion of suspended sediment were influenced by the dominant storm wind, so that under strong NE wind, Lingdingyang west shoal sediment was resuspended by relatively larger waves for the largest wind fetch in the Lingdingyang estuary, higher SSC was presented and transported to the southwest under longshore current. The response of the PRE to storm IV was that the water body was muddy and the SSC was high in the whole PRE than under normal condition; and under southerly storm wind, the high SSC was diffused to the east