Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results

Abstract. We analyze Aura Microwave Limb Sounder (MLS) monthly zonal mean time series of ClO and HOCl between 50∘ S N to estimate upper stratospheric trends in these chlorine species from 2005 through 2020. compare observations those the Whole Atmosphere Community Climate Model version 6 (WACCM6), run under specified dynamics configuration. The model sampling follows MLS coverage space local time. use 5 daytime profiles similarly binned 32 1.5 hPa. For HOCl, we offline product derived daily radiances rather than averaged level-2 profiles; is scientifically useful 10 2 hPa, means are separated into day night for comparison WACCM6. find good agreement (mostly within ∼ %) climatological distributions climatology 2005–2020. climatology, however, underestimates by about 30 %. This could well be caused a combination fairly large systematic uncertainties both model-assumed rate constant formation retrievals themselves. versus latitude pressure agree quite with MLS. MLS-derived near-global 7 hPa −0.73 ± 0.40 % yr−1 −0.39 0.35 2σ uncertainty estimates used here. corresponding decreases somewhat faster observed (although difference not statistically significant), trend values −0.85 0.45 −0.64 0.37 HOCl. Both data results point consistent past satellite ground-based microwave data. As discussed past, other (in particular, positive CH4 H2O) can lead decrease that total inorganic chlorine. Regarding HO2 as function time, which partially offsets decreasing active provide additional confirmation effectiveness Montreal Protocol its amendments, have led early stages an expected long-term ozone recovery effects ozone-depleting substances.