The stratospheric Brewer–Dobson circulation inferred from age of air in the ERA5 reanalysis

Abstract. This paper investigates the global stratospheric Brewer–Dobson circulation (BDC) in ERA5 meteorological reanalysis from European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is based on simulations of mean age air, including full spectrum, with Lagrangian transport model CLaMS (Chemical Model Stratosphere), driven by winds and total diabatic heating rates. ERA5-based results are compared to preceding ERA-Interim reanalysis. Our show a significantly slower BDC than ERA-Interim, manifesting weaker rates higher air. In tropical lower stratosphere, 30 %–40 % ERA5, likely correcting bias ERA-Interim. At 20 km Northern Hemisphere (NH) values around upper margin uncertainty range historical tracer observations, indicating somewhat slow–biased BDC. trend over 1989–2018 period negative throughout as climate models predict response warming. However, decrease not linear but steplike, potentially caused multi-annual variability or changes observations included assimilation. During 2002–2012 period, shows similar hemispheric dipole pattern increasing NH decreasing Southern (SH). Shifts spectrum peak residual transit times indicate that differences circulation. particular, shallow branch accelerates both reanalyses, whereas deep decelerates