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Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period

机译：观测到的2002年至2010年全球平流层大气平均年龄的时间演变

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An extensive observational data set, consisting of more than 10~6 SF_6 vertical profiles from MIPAS measurements distributed over the whole globe has been condensed into monthly zonal means of mean age of air for the period September 2002 to January 2010, binned at 10° latitude and 1-2 km altitude. The data were analysed with respect to their temporal variation by fitting a regression model consisting of a constant and a linear increase term, 2 proxies for the QBO variation, sinusoidal terms for the seasonal and semi-annual variation and overtones for the correction of the shapes to the observed data set. The impact of subsidence of mesospheric SF6-depleted air and in-mixing into non-polar latitudes on mid-latitudinal absolute age of air and its linear increase was assessed and found to be small. The linear increase of mean age of stratospheric air was found to be positive and partly larger than the trend derived by Engel et al. (2009) for most of the Northern mid-latitudes, the middle stratosphere in the tropics, and parts of the Southern mid-latitudes, as well as for the Southern polar upper stratosphere. Multi-year decrease of age of air was found for the lowermost and the upper stratospheric tropics, for parts of Southern mid-latitudes, and for the Northern polar regions. Analysis of the amplitudes and phases of the seasonal variation shed light on the coupling of stratospheric regions to each other. In particular, the Northern mid-latitude stratosphere is well coupled to the tropics, while the Northern lowermost mid-latitudinal stratosphere is decoupled, confirming the separation of the shallow branch of the Brewer-Dobson circulation from the deep branch. We suggest an overall increased tropical upwelling, together with weakening of mixing barriers, especially in the Northern Hemisphere, as a hypothetical model to explain the observed pattern of linear multi-year increase/decrease, and amplitudes and phase shifts of the seasonal variation.
机译：由2002年9月至2010年1月期间，由MIPAS分布在全球各地的超过10〜6个SF_6垂直剖面组成的广泛的观测数据集，被浓缩成月平均空气年龄的纬向平均值，并以10°纬度划分和1-2公里的高度。通过拟合由常数和线性增加项，QBO变化的2个代理，季节性和半年度变化的正弦项以及校正形状的泛音组成的回归模型，对数据的时间变化进行了分析。到观察到的数据集。评估了中层SF6耗尽的空气的沉陷和混入非极性纬度对中纬度绝对空气年龄及其线性增加的影响，发现该影响很小。发现平流层空气平均年龄的线性增加是正的，并且部分地大于Engel等人得出的趋势。 （2009年）适用于大多数北半球中纬度地区，热带中部平流层，南部中纬度的部分地区以及南极平流层。在最低和最高的平流层热带地区，南部中纬度地区和北极地区发现了空气年龄的多年下降现象。对季节变化幅度和相位的分析为平流层区域之间的耦合提供了参考。特别是，北中纬平流层与热带之间耦合良好，而北最北纬中平流层则解耦，从而确认了Brewer-Dobson环流的浅分支与深分支的分离。我们建议整体上升的热带上升，以及混合障碍的减弱，尤其是在北半球，作为一种假设模型来解释观测到的线性多年增长/下降以及季节性变化的幅度和相移的模式。

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