资源环境科技发展态势分析平台

Total columns of the trace gases nitric acid (HNO₃) and hydrogen chloride (HCl) are sensitive to variations in the lower stratospheric age of air (AoA), a quantity that describes transport timescales in the stratosphere. Analyses of HNO₃ and HCl columns from the Network for the Detection of Atmospheric Composition Change (NDACC) spanning 77^oS to 79^oN have detected changes in the extratropical stratospheric transport circulation from 1994 to 2018. The HNO₃ and HCl analyses combined with AoA from a simulation using the MERRA2 reanalysis show that the southern hemisphere (SH) lower stratosphere has become 1 month/decade younger relative to the northern hemisphere, largely driven by the SH transport circulation. The analyses reveal multi‐year anomalies with a 5‐7 yr period driven by interactions between the circulation and the Quasi Biennial Oscillation (QBO) in tropical winds. This hitherto unrecognized variability is large relative to hemispheric transport trends and may bias ozone trend regressions.