长江口湍流剖面的观测与分析

OBSERVATION AND ANALYSIS OF TURBULENCE VERTICAL PROFILE IN THE CHANGJIANG RIVER ESTUARY

小尺度湍流过程对河口物质输运与能量交换至关重要。受传统观测方法的限制,河口浅水区域的剖面观测资料至今较为匮乏,进而限制了湍流过程的研究。为此,采用新型5波束声学多普勒流速剖面仪(Nortek Signature 1 000 kHz AD2CP)在长江口开展湍流剖面观测,获取高频、低噪的高质量湍流剖面数据,并与声学多普勒点式流速仪(acoustic doppler velocimeters,ADV)同步观测的数据进行对比。结果表明,通过AD2CP与ADV获得的近底部边界层摩阻流速u*、拖曳系数C_(d)、雷诺应力S_(R)等特征参数基本一致,底摩擦与波浪能量为河口区域湍动能的主要输入源。湍流垂向结构存在显著的非局地平衡,即温盐等斜压作用引起的浮力通量、对流项以及强波浪作用影响的脉动压力做功、黏性输运等因素可能为长江口湍流非局地平衡的主因。

Small-scale turbulence process is critical to material transport and energy exchange in estuaries.Due to the limitation of traditional observation methods,observation of turbulence vertical profiles in relatively shallow areas is scarce,which limits the study of estuarine turbulence processes.In this study,a 5-beam Signature 1000 kHz acoustic Doppler current profiler(Nortek Signature 1000 kHz AD2CP)was used to observe the turbulence vertical profiles in the Changjiang(Yangtze)River estuary,and low-noise,high-frequency turbulence parameters vertical profiles were obtained.The data were compared with the synchronous observation results from an Acoustic Doppler Velocimeter(ADV).The comparison shows that the most crucial parameters of the near-bottom boundary layer,such as friction velocity u*,drag coefficient C_(d),and Reynolds stress S_(R),obtained by AD2CP and ADV are basically consistent.Bottom friction and wave energy are the main sources of turbulent kinetic energy.Non-local equilibrium is found in turbulence vertical structure.The buoyancy flux caused by temperature and salinity gradient,convection,pulse pressure work,and viscous transport caused by strong wave action are the main factors of the non-local equilibrium of turbulence vertical structure in the Changjiang River estuary.