NUMERICAL EXPERIMENTS TO EVALUATE EFFECT OF EXTERNAL FORCES ON TEMPERATURE STRATIFICATION IN LAKE KASUMIGAURA, JAPAN
NUMERICAL EXPERIMENTS TO EVALUATE EFFECT OF EXTERNAL FORCES ON TEMPERATURE STRATIFICATION IN LAKE KASUMIGAURA, JAPAN
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发表时间：
2020
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通讯作者：
Wang Yueyi
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作者：
Wang Yueyi
霞浦湖是日本第二大湖泊，湖水浅，富营养化程度高。虽然在以往的研究中，湖流的变化已被揭示的现场观测，数值模拟，以进一步揭示外力对湖流的影响，并探讨温度分层和藻类水华现象。本文采用非结构化网格并行计算的近岸海洋模式SUNTANS模拟湖流。非结构化网格的水平分辨率约为200米，垂直方向分为30层。模拟结果表明，SUNTANS能较好地再现湖泊的观测数据，并能较好地模拟明显的日分层现象。通过对不同个例的对比分析，温度随时间变化的差异表明了风的驱动作用和太阳辐射对层结形成的重要贡献。粒子追踪的结果显示，表面分布的藻华和风力条件之间有很强的关系。风力驱动与地形条件相结合，导致颗粒倾向于被复杂的海岸线捕获，并积聚在湖的北方。据推测，这一趋势是这些地区经常发生藻华的原因之一。
Lake Kasumigaura is the second largest lake in Japan, and it is shallow and highly eutrophic. Although variations in lake current have been revealed by field observations in previous research, numerical simulations should be adopted to further reveal the influence of external forces on the lake flow, and investigate the phenomena of temperature stratification and algal blooms. An unstructured grid, parallel computing coastal ocean model, SUNTANS, is utilized for modeling lake currents in this study. The horizontal resolution of the unstructured grid is approximately 200 m, and 30 layers are split vertically. The simulation results demonstrated that SUNTANS could reproduce observations in the lake and had a good performance for modeling the obvious diurnal stratification. Through a comparison of results of different cases, the difference in the temporal temperature change would indicate the driving effect of wind and the significant contribution of insolation to the formation of stratification. Particle-tracking results showed a strong relationship between the surface distribution of algal blooms and the wind condition. Wind driving combined with topographic conditions led to a tendency for particles to become trapped by a complicated shoreline and accumulate on the northern part of the lake. This trend was inferred to be one of the reasons why algal blooms often occur in those areas.