Dispersion in deep polar firn driven by synoptic-scale surface pressure variability
Dispersion in deep polar firn driven by synoptic-scale surface pressure variability
复制标题
天气尺度表面压力变化驱动的极地深处的色散
DOI：
10.5194/tc-10-2099-2016
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
J. Severinghaus
中科院分区：
文献类型：
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作者：
C. Buizert;J. Severinghaus
抽象的。通常，有三种机制的积雪空气输送区分：分子扩散，平流和近地面对流混合。在这里，我们确定并描述了第四种机制，即分散驱动的天气尺度表面压力变化（或气压泵）。我们使用已发表的气相色谱实验的积雪样品，以获得沿流分散性的积雪，并结合联合收割机这种分散性与动态的空气压力传播模型迫使表面气压时间序列估计的大小分散混合的积雪。我们表明，分散主导的混合内的积雪锁定区。在不同极地的积雪空气样品中测量的痕量气体浓度证实了分散混合的发生。包括分散混合在一个积雪空气传输模型表明，我们的理论估计有正确的数量级，但可能高估了真正的分散。我们进一步表明，强大的气压泵，如在法律圆顶网站，可能会减少重力富集的δ 15 N-N2和其他示踪剂低于重力平衡，质疑锁定深度的传统定义为深度的δ 15 N富集停止。最后，我们认为86 Kr过量可能可以作为该地点过去天气活动（或古风暴）的代表。
Abstract. Commonly, three mechanisms of firn air transport are distinguished: molecular diffusion, advection, and near-surface convective mixing. Here we identify and describe a fourth mechanism, namely dispersion driven by synoptic-scale surface pressure variability (or barometric pumping). We use published gas chromatography experiments on firn samples to derive the along-flow dispersivity of firn, and combine this dispersivity with a dynamical air pressure propagation model forced by surface air pressure time series to estimate the magnitude of dispersive mixing in the firn. We show that dispersion dominates mixing within the firn lock-in zone. Trace gas concentrations measured in firn air samples from various polar sites confirm that dispersive mixing occurs. Including dispersive mixing in a firn air transport model suggests that our theoretical estimates have the correct order of magnitude, yet may overestimate the true dispersion. We further show that strong barometric pumping, such as at the Law Dome site, may reduce the gravitational enrichment of δ15N–N2 and other tracers below gravitational equilibrium, questioning the traditional definition of the lock-in depth as the depth where δ15N enrichment ceases. Last, we propose that 86Kr excess may act as a proxy for past synoptic activity (or paleo-storminess) at the site.