TY  - JOUR
A1  - Ploeger, Felilx
A1  - Diallo, Mouhamadou Mountaga
A1  - Charlesworth, Edward
A1  - Konopka, Paul
A1  - Legras, Bernard
A1  - Laube, Johannes Christian
A1  - Grooß, Jens-Uwe
A1  - Günther, Gebhard
A1  - Engel, Andreas
A1  - Riese, Martin
T1  - The stratospheric Brewer–Dobson circulation inferred from age of air in the ERA5 reanalysis
T2  - Atmospheric chemistry and physics
N2  - This paper investigates the global stratospheric Brewer–Dobson circulation (BDC) in the ERA5 meteorological reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is based on simulations of stratospheric mean age of air, including the full age spectrum, with the Lagrangian transport model CLaMS (Chemical Lagrangian Model of the Stratosphere), driven by reanalysis winds and total diabatic heating rates. ERA5-based results are compared to results based on the preceding ERA-Interim reanalysis. Our results show a significantly slower BDC for ERA5 than for ERA-Interim, manifesting in weaker diabatic heating rates and higher age of air. In the tropical lower stratosphere, heating rates are 30 %–40 % weaker in ERA5, likely correcting a bias in ERA-Interim. At 20 km and in the Northern Hemisphere (NH) stratosphere, ERA5 age values are around the upper margin of the uncertainty range from historical tracer observations, indicating a somewhat slow–biased BDC. The age trend in ERA5 over the 1989–2018 period is negative throughout the stratosphere, as climate models predict in response to global warming. However, the age decrease is not linear but steplike, potentially caused by multi-annual variability or changes in the observations included in the assimilation. During the 2002–2012 period, the ERA5 age shows a similar hemispheric dipole trend pattern as ERA-Interim, with age increasing in the NH and decreasing in the Southern Hemisphere (SH). Shifts in the age spectrum peak and residual circulation transit times indicate that reanalysis differences in age are likely caused by differences in the residual circulation. In particular, the shallow BDC branch accelerates in both reanalyses, whereas the deep branch accelerates in ERA5 and decelerates in ERA-Interim.
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/73781
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-737813
SN  - 1680-7324
N1  - This research has been supported by the Helmholtz Association (grant no. VH-NG-1128; Helmholtz Young Investigators Group A–SPECi).

The article processing charges for this open-access publication were covered by the Forschungszentrum Jülich.
N1  - ERA5 and ERA-Interim reanalysis data are available from the ECMWF (for ERA5 via https://apps.ecmwf.int/data-catalogues/era5/?class=ea, last access: 15 April 2021, Hersbach et al., 2020; for ERA-Interim via https://apps.ecmwf.int/archive-catalogue/?class=ei, last access: 15 April 2021, Dee et al., 2011). The CLaMS model data used for this paper may be requested from the corresponding author (f.ploeger@fz-juelich.de)
VL  - 21
IS  - 11
SP  - 8393
EP  - 8412
PB  - EGU
CY  - Katlenburg-Lindau
ER  -