1998–2016 ozone trends in the lower stratosphere (LS) are examined using the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) and related NASA products. After removing biases resulting from step-changes in the MERRA-2 ozone observations, a discernible negative trend of −1.67±0.54 Dobson units per decade (DU/decade) is found in the 10-km layer above the tropopause between 20°N and 60°N. A weaker but statistically significant trend of −1.17±0.33 DU/decade exists between 50°S and 20°S. In the Tropics, a positive trend is seen in a 5-km layer above the tropopause. Analysis of an idealized tracer in a model simulation constrained by MERRA-2 meteorological fields provides strong evidence that these trends are driven by enhanced isentropic transport between the tropical (20°S–20°N) and extratropical LS in the past two decades. This is the first time that a reanalysis dataset has been used to detect and attribute trends in lower stratospheric ozone.
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机译：使用现代时代研究与应用第2版回顾性分析（MERRA-2）和相关的NASA产品，检查了平流层下部（LS）1998-2016年的臭氧趋势。消除由MERRA-2臭氧观测值的阶跃变化引起的偏差后，在对流层顶上方20 km和20°C之间的10 km层中发现了可识别的负趋势，每十年十进制的-1.67±0.54 Dobson单位（DU /十年）。 60°N。在50°S和20°S之间存在一个较弱但统计学上显着的趋势，即-1.17±0.33 DU /十年。在热带地区，对流层顶上方5公里处有一个积极的趋势。在MERRA-2气象领域约束下的模型模拟中对理想示踪剂的分析提供了有力的证据，表明这些趋势是由过去二十年来热带（20°S–20°N）和温带LS之间等熵传输增强所驱动的。这是首次使用再分析数据集来检测和归因于平流层下部臭氧的趋势。
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