A Lagrangian perspective of the tropopause and the ventilation of the lowermost stratosphere
A Lagrangian perspective of the tropopause and the ventilation of the lowermost stratosphere
复制标题
DOI：
10.1029/2006jd008295
复制
发表时间：
2007-09
影响因子：
--
通讯作者：
G. Berthet;J. G. Esler;P. Haynes
中科院分区：
文献类型：
--
作者：
G. Berthet;J. G. Esler;P. Haynes
大尺度分析风场驱动的后轨迹用于研究北半球对流层顶区域对流层到平流层的输送（TST），以及这种输送的地面源，根据每条轨迹最后离开大气边界层的位置（对数压力高度z* < 1 km）来定义。到达对流层顶区域的轨迹在前一个固定时间段（通常为30天）内到达边界层的比例chi（BL）由每条轨迹的最终等效纬度和势温的函数确定。对于一系列潜在温度表面（类似于300-380 K）， chi（BL）显示在温带有一个陡峭的梯度，表明运输的部分可渗透屏障可以被识别为“拉格朗日对流层顶”。“chi（BL）在同等纬度和潜在温度以及季节时间尺度上的变化为对流层顶屏障的相对位置和渗透率提供了一种新的测量方法。在北部夏季温带平流层下层（类似370-410 K）存在一个“通气层”等细节是非常明显的。在这一层的正下方（340-370 K），对流层顶的输送屏障相对较强，而在340 K以下，对流层顶的可渗透性更强。因此，可以区分主要在340 K以下的最下层平流层通风的“温带”TST和发生在370-410 K通风层的“热带”TST。尽管喜马拉雅高原等高架区域也被认为是重要的，但温带TST的边界层源区域与以前确定为温带气旋温暖传送带环流中深部锋面隆起源的区域相对应。热带TST有不同的源区，这些源区与热带西部太平洋和夏季北部的印度次大陆等活跃的深对流区有关。总的来说，发现源区域在地理上是局部的，从而得出结论，受方法的限制，特定区域的微量气体排放比其他地方更有可能被输送到平流层的最底层。文中提到了寿命极短的卤化物种对评估臭氧耗损的影响。
Back trajectories driven by large-scale analyzed wind fields are used to investigate troposphere to stratosphere transport (TST) in the Northern Hemisphere tropopause region, as well as the surface sources for such transport, defined in terms of the locations where each trajectory last left the atmospheric boundary layer ( log pressure height z* < 1 km). The proportion chi(BL) of those trajectories arriving in the tropopause region that have visited the boundary layer within the previous fixed time period ( typically 30 days) is determined as a function of each trajectory's final equivalent latitude and potential temperature. For a range of potential temperature surfaces ( similar to 300-380 K), chi(BL) is shown to have a sharp gradient in the extratropics indicative of a partial permeable barrier to transport that can be identified as a "Lagrangian tropopause.'' Variations in chi(BL) with equivalent latitude and potential temperature and on seasonal timescales are shown to provide a novel measure for the relative location and permeability of the tropopause barrier. Details such as the presence of a "ventilated layer'' in the northern summer extratropical lower stratosphere ( similar to 370-410 K) are clearly apparent. Directly below this layer ( 340-370 K) the tropopause barrier to transport is shown to be relatively strong, whereas below 340 K it is again more permeable. A distinction can therefore be made between "extratropical'' TST that primarily ventilates the lowermost stratosphere below 340 K and "tropical'' TST that occurs into the 370-410 K ventilated layer. The boundary layer source regions for extratropical TST are shown to correspond to those regions previously identified as sources for deep frontal uplift in the warm conveyor belt circulations of extratropical cyclones, although elevated regions such as the Himalayan plateau are also seen to be important. Tropical TST has different source regions associated with regions of active deep convection such as the western tropical Pacific and, in the northern summer, the Indian subcontinent. The source regions are, in general, found to be geographically localized, leading to the conclusion that subject to the limitations of the methodology, trace gas emissions in specific regions are substantially more likely to be transported to the lowermost stratosphere than elsewhere. The implications for the assessment of ozone depletion by very short lived halogenated species are mentioned.