Ventilation rates estimated from tracers in the presence of mixing
Ventilation rates estimated from tracers in the presence of mixing
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DOI：
10.1175/2006jpo3471.1
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发表时间：
2007-11-01
影响因子：
3.5
通讯作者：
Waugh, Darryn W.
中科院分区：
文献类型：
--
作者：
Hall, Timothy M.;Haine, Thomas W. N.;Waugh, Darryn W.
分析了通风、渡越时间分布和瞬态示踪剂预算之间的密切关系。为了表征从混合层到内部海洋的对流扩散运输的通量，我们采用了累积通风率分布，Phi（τ），定义为返回之前在内部至少停留时间τ的水的单向质量通量。单向（或总）通量与净平流通量（通常称为俯冲速率）形成对比，后者不包含混合的影响，而形成速率仅取决于平流和扩散混合的净影响。随着τ减小，Phi（τ）增加，包含越来越多的单向通量。一般来说，Φ是τ的快速变化函数（它在小τ处发散），并且没有可以评估Φ以完全总结对流扩散通量的单个停留时间。为了调和最近一项大气环流模式研究中形成率估计值之间的差异，使用了φ（τ）。然后，氯氟烃数据被用来绑定Phi（τ）的副热带模态水和拉布拉多海水在北大西洋。作者表明，忽视扩散混合会导致虚假行为，例如地层中明显的时间依赖性，即使传输稳定也是如此。
The intimate relationship among ventilation, transit-time distributions, and transient tracer budgets is analyzed. To characterize the advective-diffusive transport from the mixed layer to the interior ocean in terms of flux we employ a cumulative ventilation-rate distribution, Phi(tau), defined as the one-way mass flux of water that resides at least time tau in the interior before returning. A one-way (or gross) flux contrasts with the net advective flux, often called the subduction rate, which does not accommodate the effects of mixing, and it contrasts with the formation rate, which depends only on the net effects of advection and diffusive mixing. As tau decreases Phi(tau) increases, encompassing progressively more one-way flux. In general, Phi is a rapidly varying function of tau( it diverges at small tau), and there is no single residence time at which Phi can be evaluated to fully summarize the advective-diffusive flux. To reconcile discrepancies between estimates of formation rates in a recent GCM study, Phi(tau) is used. Then chlorofluorocarbon data are used to bound Phi(tau) for Subtropical Mode Water and Labrador Sea Water in the North Atlantic Ocean. The authors show that the neglect of diffusive mixing leads to spurious behavior, such as apparent time dependence in the formation, even when transport is steady.