QUANTifying stratospheric circulation Impacts on Tropospheric Emission Estimates (QUANTITEE)

最近的研究表明，最重要的一种含氯氟烃（CFC）的排放，CFC-11自2012年左右开始再次增加，这意味着对平流层臭氧层的潜在严重威胁。然而，由于平流层环流的变化，对氟氯化碳排放量的估计往往存在很大的不确定性，而平流层环流的变化又没有在目前的大气模型和再分析中得到充分的约束。此外，限制平流层环流模式和观测平流层模式变化的方法有限，本项目的目标是加强了解平流层传输的年际至十年期变化对对流层长寿命痕量气体变化的影响，重点是氟氯化碳。出于这个原因，我们将评估和进一步改进新的方法，推导平流层年龄的空气光谱，通过平流层的过境时间分布，这是一个有利的诊断平流层运输。第一步，将在模型环境中进行方法评估。三种不同的方法计算年龄谱的化学物种的混合比进行比较，基于（i）的谱的逆高斯参数化，（ii）改进的参数化，和（iii）直接反演方法。通过与平流层化学拉格朗日模型（CLaMS）中（精确）脉冲法计算的模型年龄谱进行比较，将对所有三种方法进行仔细的“概念证明”。在第二步中，这些方法将用于对在平流层收集的空气样品进行高分辨率现场痕量气体测量，既使用更传统的飞机采样器，也使用基于AirCores的新技术。因此，年龄谱的计算将结合新的年龄谱模拟技术和新的观测，提供前所未有的限制平流层传输的变化。通过对由不同气象再分析，包括最新产品（ERA 5）和较老产品（ERA-Interim、MERRA-2、JRA-55）驱动的模拟所产生的模型年龄谱进行比较，将能够评估平流层传输变化表示的可靠性。最后，运输可变性（例如，将分析与准两年期振荡有关的大气环流（QBO），并将对平流层下部痕量气体成分和对流层趋势的影响进行量化。经过改进的对流层预算推断方法将成为科学界的一个传统工具，可用于更好地限制许多长期存在的臭氧消耗物质和温室气体的未来排放。

Recent studies have provided evidence that emissions of one of the most important chlorofluorocarbons (CFCs), i.e., CFC-11, have started to increase again since around 2012, implying a potentially severe threat to the stratospheric ozone layer. However, estimates of CFC emissions are prone to large uncertainty caused by changes in the stratospheric circulation which, in turn, are insufficiently constrained in current atmospheric models and reanalyses. Moreover, the methodologies to constrain the representation of stratospheric circulation patterns and variations in stratospheric models with observations are limited.The goal of this project is to enhance the understanding of the impacts of inter-annual to decadal variability in stratospheric transport on tropospheric variations of long-lived trace gases, with focus on CFCs. For this reason, we will evaluate and further improve novel methods for deducing stratospheric age of air spectra, the transit time distribution through the stratosphere which is an advantageous diagnostic for stratospheric transport. In a first step, the method evaluation will be carried out in a model environment. Three different methods for calculating age spectra from mixing ratios of chemical species will be compared, based on (i) an inverse Gaussian parameterization of the spectrum, (ii) an improved parameterization, and (iii) a direct inversion approach. A careful “proof of concept” will be carried out for all three methods by comparison to model age spectra calculated with the (exact) pulse method in the Chemical Lagrangian Model of the Stratosphere (CLaMS). In a second step, the methods will be applied to high-resolution in-situ trace gas measurements on air samples collected in the stratosphere, both with the more conventional aircraft samplers and a new technique based on AirCores. Hence, age spectra will be calculated from a combination of new age spectra simulation techniques and novel observations, providing unprecedented constraints on variations of stratospheric transport. A comparison to model age spectra from simulations driven by different meteorological reanalyses, including newest (ERA5) and older products (ERA-Interim, MERRA-2, JRA-55), will allow assessing the reliability of the representation of stratospheric transport variations. Finally, transport variability (e.g., related to the QBO) will be analyzed and the effects on trace gas composition in the lower stratosphere and on tropospheric trends will be quantified. The improved methods to infer tropospheric budgets will be a legacy tool for the scientific community to better constrain future emissions of many long-lived ozone-depleting substances and greenhouse gases.