一个小型热带河口羽流的季节性变化与洪水事件影响下的特征与动力分析

doi:10.11978/2016106

摘要/Abstract

摘要：

小河口与大河口的羽流特征具有显著的不同, 其更多地受风、径流的变化所控制。文章以海南博鳌万泉河口为例, 研究其河口羽流的季节性变化特征, 以及洪水对河口羽流的影响。采用动量平衡方法, 分析了万泉河口羽流的动力特征。结果表明, 万泉河口羽流具有显著的季节性变化, 羽流的扩展路径与范围主要受径流和风的控制, 夏季时以向外海与向上游方向(相对于开尔文波的传播方向)扩展为主, 而冬季时则向下游扩展。夏季的羽流范围大于冬季。一次近2天的洪水可极大地影响羽流的范围及盐度大小, 盐度减小1‰的范围可达300km²。但洪水过后, 在风与潮汐的混合作用下, 河口近岸的盐度可较为快速地恢复到洪水前水平。在羽流的远场区域, 流速切线方向主要为压强梯度力与摩擦力的平衡, 而在法线方向则为地转平衡; 在近场切线方向主要为平流项、压力梯度项与摩擦力项的平衡, 而法线方向则主要为压强梯度力与离心力之间的平衡, 科氏力项可忽略不计, 这与中纬度大河口的近场动力特征具有明显不同。

关键词: 河口羽流, 小河口, 季节性变化, 洪水事件, 动量平衡, 海南

Abstract:

A small river plume is distinctly different from a large river plume, more controlled by the variation of river discharge and wind. Taking the Wanquan River plume in Hainan as an example, we focus on the seasonal variation of a small river plume and its response to a river flood event in this study. The dynamics of the plume is investigated through momentum balance analysis. The results indicate that the spreading of the Wanquan River plume features a conspicuously seasonal variability, with the spreading direction being mostly downstream during winter, and being offshore or upstream during summer. The spreading extent is the largest in August and the smallest in December and January. A two-day flood event can greatly increase the plume extent; however, the effect of this river flood quickly disappears, with a recovery time in the order of 3 days. The momentum balance shows the balance in the far-field region is mostly a geostrophic one in the normal direction, while it is dominated by pressure gradient and friction in the stream-wise direction. In the near-field region, the Coriolis force is negligible in the normal direction, which is greatly different from that in the mid-latitude river plume.

Key words: small river plume, seasonal variation, flood event, momentum balance, Hainan

中图分类号:

P731

赵军鹏, 李溢涵, 龚文平. 一个小型热带河口羽流的季节性变化与洪水事件影响下的特征与动力分析[J]. 热带海洋学报, 2017, 36(4): 67-76.

Junpeng ZHAO, Yihan LI, Wenping GONG. The seasonal and sporadic variation of the spreading of a small tropical river plume and its associated dynamics[J]. Journal of Tropical Oceanography, 2017, 36(4): 67-76.

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