Seasonal differences of vertical-transport efficiency in the tropical tropopause layer: On the interplay between tropical deep convection, large-scale vertical ascent, and horizontal circulationes
Seasonal differences of vertical-transport efficiency in the tropical tropopause layer: On the interplay between tropical deep convection, large-scale vertical ascent, and horizontal circulationes
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DOI：
10.1029/2011jd016992
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发表时间：
2012-03-03
影响因子：
4.4
通讯作者：
Yang, Qiong
中科院分区：
文献类型：
--
作者：
Bergman, John W.;Jensen, Eric J.;Yang, Qiong
冬季和夏季的差异，在低纬度地区的空气从边界层到平流层下部的运输进行了研究与合奏的后轨迹计算，跟踪包裹从380 K等熵表面的对流detrainment在热带对流层顶层（TTL）在2006-2007年冬季和2007年夏季。轨道的水平位移是从再分析数据计算的;潜在温度位移是从观测到的云、水汽、臭氧和温度变化的辐射加热率计算的;位置的对流消散是由对流云的卫星观测确定的。较弱的上升流在TTL在北方夏季与冬季相比，既减缓了通过TTL的上升，并提高了高度阈值，对流detrainment必须超过为了上升发生，限制注入新的空气进入平流层在夏季。此外，与对流活动相关的反气旋环流有助于垂直运输的TTL通过最强的上升流区域引导detrained空气包裹。这些特征联合收割机使印度次大陆上空与季风有关的对流成为夏季新空气的主要来源。相比之下，冬季来源分布在南部大陆和西太平洋。这些季节性差异意味着夏季进入热带平流层的空气比冬季进入的空气更古老，但污染程度可能更高。虽然在TTL的数据采样差，很难验证我们的结果，他们是支持有利的比较与以前的研究的TTL，敏感性测试，揭示了重要的动力学影响地面平流层运输，和动力相互作用的鲁棒性，系统地关联深对流与反气旋环流和强辐射加热的TTL。敏感性实验表明，上述季节性差异是敏感的强大的“大尺度”（全球空间尺度和季节性时间尺度）扰动。特别是，垂直运动场的不确定性限制了我们得出明确结论的能力。然而，轨迹统计是不敏感的小尺度扰动，令人鼓舞的暗示，我们的结果主要是与这些功能的流通是最有可能是强大的。
Winter-summer differences in the transport of air from the boundary layer to the lower stratosphere at low latitudes are investigated with ensembles of back trajectory calculations that track parcels from the 380 K isentropic surface to their convective detrainment in the tropical tropopause layer (TTL) during the winter of 2006-2007 and summer of 2007. Horizontal displacements for the trajectories are calculated from reanalysis data; potential temperature displacements are calculated from radiative heating rates derived from observed cloud, water vapor, ozone, and temperature variations; and the locations' convective detrainments are determined by satellite observations of convective clouds. Weaker upwelling in the TTL during boreal summer compared with that of winter both slows the ascent through the TTL and raises the height threshold that convective detrainment must surpass in order for ascent to occur, restricting the injection of new air into the stratosphere during summer. In addition, anticyclonic circulations associated with convective activity contribute to vertical transport in the TTL by guiding detrained air parcels through regions with the strongest upwelling. These features combine to make monsoon-related convection over the Indian subcontinent the dominant source of new air during summer. In contrast, winter sources are spread over the southern continents and the western Pacific Ocean. These seasonal differences imply that air entering the tropical stratosphere during summer is older but might nevertheless be more polluted than air entering during winter. While poor data sampling in the TTL makes it difficult to validate our results, they are bolstered by favorable comparisons with previous studies of the TTL, by sensitivity tests that reveal important dynamical influences on surface-to-stratospheric transport, and by the robustness of dynamical interactions that systematically associate deep convection with anticyclonic circulations and strong radiative heating in the TTL. Sensitivity experiments suggest that the aforementioned seasonal differences are sensitive to strong "large-scale" (on global space scales and seasonal time scales) perturbations. In particular, uncertainties in the vertical motion fields constrain our ability to draw definitive conclusions. However, trajectory statistics are not sensitive to small-scale perturbations, with the encouraging implication that our results are primarily associated with those features of the circulation that are the most likely to be robust.