A Numerical Simulation of Residual Circulation in Tampa Bay. Part II: Lagrangian Residence Time
A Numerical Simulation of Residual Circulation in Tampa Bay. Part II: Lagrangian Residence Time
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DOI：
10.1007/s12237-008-9085-0
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发表时间：
2008-09
影响因子：
2.7
通讯作者：
S. Meyers;M. Luther
中科院分区：
文献类型：
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作者：
S. Meyers;M. Luther
拉格朗日保留和冲洗检查平流中性浮力点粒子内的环流场产生的数值海洋模式的坦帕湾。拉格朗日停留时间的大的时间变化被发现在边界条件的现实变化。研究了两个90天的时间段。第一层（P1）的特征是淡水流入量少，斜压环流弱。第二层（P2）淡水入流量大，斜压环流强;在这两个时间段的开始，686，400个颗粒均匀地释放在整个海湾中。在三个不同的空间尺度上研究了与颗粒分布和冲刷有关的问题：（1）整个海湾的尺度，（2）海湾内的四个主要区域，（3）单个模型网格单元的尺度。粒子数随时间变化的两个简单理论模型N（t）与海洋模型中的粒子数相吻合。当考虑整个海湾时，理论模型显示出合理的代表N（t），允许直接计算全湾停留时间：P1为156天，P2为36天。然而，这些简单模型的准确性随着空间尺度的减小而降低。这可能是由于粒子可以以任何顺序从一个区域退出、重新进入或重新分布到另一个区域。所考虑的域越小，这种交换过程就越占主导地位。因此，需要修改“非当地”情况下的停留时间定义。在选择了合理的定义，并删除潮汐和天气信号，在每个网格单元在P1的停留时间被发现在空间上从几天到90天，计算的限制，平均停留时间为53天。对于P2，总体空间格局更均匀，停留时间平均值为26天。
Lagrangian retention and flushing are examined by advecting neutrally buoyant point particles within a circulation field generated by a numerical ocean model of Tampa Bay. Large temporal variations in Lagrangian residence time are found under realistic changes in boundary conditions. Two 90-day time periods are examined. The first (P1) is characterized by low freshwater inflow and weak baroclinic circulation. The second (P2) has high freshwater inflow and strong baroclinic circulation. At the beginning of both time periods, 686,400 particles are released uniformly throughout the bay. Issues relating to particle distribution and flushing are examined at three different spatial scales: (1) at the scale of the entire bay, (2) the four major regions within the bay, and (3) at the scale of individual model grid cells. Two simple theoretical models for the particle number over time,N(t), are fit to the particle counts from the ocean model. The theoretical models are shown to representN(t) reasonably well when considering the entire bay, allowing for straightforward calculation of baywide residence times: 156 days for P1 and 36 days for P2. However, the accuracy of these simple models decreases with decreasing spatial scale. This is likely due to the fact that particles may exit, reenter, or redistribute from one region to another in any sequence. The smaller the domain under consideration, the more this exchange process dominates. Therefore, definitions of residence time need to be modified for “non-local” situations. After choosing a reasonable definition, and removal of the tidal and synoptic signals, the residence times at each grid cell in P1 is found to vary spatially from a few days to 90 days, the limit of the calculation, with an average residence time of 53 days. For P2, the overall spatial pattern is more homogeneous, and the residence times have an average value of 26 days.