Abstract
Abstract. Constituent evolution for 1990–2015 simulated using the Global Modeling Initiative chemistry and transport model driven by meteorological fields from the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) is compared with three sources of observations: ground-based column measurements of HNO3 and HCl from two stations in the Network for the Detection of Atmospheric Composition Change (NDACC, ∼ 1990–ongoing), profiles of CH4 from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS, 1992–2005), and profiles of N2O from the Microwave Limb Sounder on the Earth Observing System satellite Aura (2005–ongoing). The differences between observed and simulated values are shown to be time dependent, with better agreement after ∼ 2000 compared with the prior decade. Furthermore, the differences between observed and simulated HNO3 and HCl columns are shown to be correlated with each other, suggesting that issues with the simulated transport and mixing cause the differences during the 1990s and that these issues are less important during the later years. Because the simulated fields are related to mean age in the lower stratosphere, we use these comparisons to evaluate the time dependence of mean age. The ongoing NDACC column observations provide critical information necessary to substantiate trends in mean age obtained using fields from MERRA-2 or any other reanalysis products.
Highlights
The composition of the stratosphere is changing in response to changes in ozone-depleting substances (ODSs), nitrous oxide (N2O) and methane (CH4) with consequences for the ozone layer, stratospheric circulation, stratosphere–troposphere exchange and climate
The first step towards meeting these goals is to examine the relationships between tracer and reservoir species and the mean age as produced by simulations using the GMI chemistry transport model (CTM) and the Goddard Earth Observing System chemistry–climate model (GEOSCCM) (Sect. 4.1)
Reanalysis data sets such as Modern-Era Retrospective analysis for Research and Applications (MERRA)-2 depend on the data assimilation system, its general circulation model and the data sets that are ingested by the system
Summary
The composition of the stratosphere is changing in response to changes in ozone-depleting substances (ODSs), nitrous oxide (N2O) and methane (CH4) with consequences for the ozone layer, stratospheric circulation, stratosphere–troposphere exchange and climate. ODSs (primarily chlorine- and bromine-containing compounds) are decreasing due to cessation of their production as a result of the Montreal Protocol and its amendments. These man-made compounds are greenhouse gases (Ramanathan, 1975). The stratospheric climate is changing in response to composition change, as increased greenhouse gases both cool the stratosphere and accelerate the stratospheric circulation (Butchart and Scaife, 2001). Both decreases in ODSs and cooling due to the increase in greenhouse gases cause ozone to increase by reducing ozone loss. The net ozone layer response is a combination of photochemical and dynamical changes, as well as feedbacks in ozone heating and photochemistry that link them
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