Transport timescales and tracer properties in the extratropical UTLS
Transport timescales and tracer properties in the extratropical UTLS
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DOI：
10.5194/acp-10-7929-2010
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发表时间：
2010-01-01
影响因子：
6.3
通讯作者：
Boenisch, H.
中科院分区：
文献类型：
--
作者：
Hoor, P.;Wernli, H.;Boenisch, H.
对北方半球平流层最低层（LMS）的季节性后向轨迹进行了综合分析，以探讨对流层-平流层输送（TST）的时空结构及其对LMS的影响。特别是，我们解释了自最后TST（t（TST））的LMS的化学组成的渡越时间的基本作用。根据我们的结果，LMS的结构可以用一个t（TST）< 40天的层在当地对流层顶周围形成一个窄带来表征。这层延伸约30 K以上的本地动力对流层顶，对应于对流层顶过渡层（ExTL）确定CO。超出这一层的LMS显示了一个相对明确的分离标记为一个aprupt过渡到较长的t（TST）表示不太频繁的混合和对流层空气的一小部分。因此，LMS构成了一个区域的两个明确定义的制度对流层的影响。这些特征主要表现在对流层的不同传输时间和对流层空气的不同比例。一氧化碳（CO）反映了t（TST）的这种结构，因为它的有限寿命大约为三个月。另一方面，水汽等值线并不唯一地指示TST，并且与t（TST）无关，而是由空气包的拉格朗日冷点（LCP）确定。大多数来自LMS的后向轨迹在热带和亚热带经历了LCP，TST通常发生在轨迹遇到LCP后20天。因此，从CO和H_2O推导的ExTL性质提供了完全不同的信息传输和特定的TST的LMS。
A comprehensive evaluation of seasonal backward trajectories initialized in the northern hemisphere lowermost stratosphere (LMS) has been performed to investigate the factors that determine the temporal and spatial structure of troposphere-to-stratosphere-transport (TST) and it's impact on the LMS. In particular we explain the fundamental role of the transit time since last TST (t(TST)) for the chemical composition of the LMS. According to our results the structure of the LMS can be characterized by a layer with t(TST)< 40 days forming a narrow band around the local tropopause. This layer extends about 30 K above the local dynamical tropopause, corresponding to the extratropical tropopause transition layer (ExTL) as identified by CO. The LMS beyond this layer shows a relatively well defined separation as marked by an aprupt transition to longer t(TST) indicating less frequent mixing and a smaller fraction of tropospheric air. Thus the LMS constitutes a region of two well defined regimes of tropospheric influence. These can be characterized mainly by different transport times from the troposphere and different fractions of tropospheric air.Carbon monoxide (CO) mirrors this structure of t(TST) due to it's finite lifetime on the order of three months. Water vapour isopleths, on the other hand, do not uniquely indicate TST and are independent of t(TST), but are determined by the Lagrangian Cold Point (LCP) of air parcels. Most of the backward trajectories from the LMS experienced their LCP in the tropics and sub-tropics, and TST often occurs 20 days after trajectories have encountered their LCP. Therefore, ExTL properties deduced from CO and H2O provide totally different informations on transport and particular TST for the LMS.