How robust are stratospheric age of air trends from different reanalyses?
<p>An accelerating Brewer–Dobson circulation (BDC) is a robust signal of climate change in model predictions but has been questioned by trace gas observations. We analyse the stratospheric mean age of air and the full age spectrum as measures for the BDC and its trend. Age of air is calculated...
| Main Authors: | , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-05-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/6085/2019/acp-19-6085-2019.pdf |
| Summary: | <p>An accelerating Brewer–Dobson circulation (BDC) is a robust signal
of climate change in model predictions but has been questioned by
trace gas observations. We analyse the stratospheric mean age of air and
the full age spectrum as measures for the BDC and its trend. Age
of air is calculated using the Chemical Lagrangian Model of the
Stratosphere (CLaMS) driven by ERA-Interim, JRA-55 and MERRA-2
reanalysis data to assess the robustness of the representation of
the BDC in current generation meteorological reanalyses. We find
that the climatological mean age significantly depends on the
reanalysis, with JRA-55 showing the youngest and MERRA-2 the
oldest mean age. Consideration of the age spectrum indicates that
the older air for MERRA-2 is related to a stronger spectrum tail,
which is likely associated with weaker tropical upwelling and stronger
recirculation. Seasonality of stratospheric transport is robustly
represented in reanalyses, with similar mean age variations
and age spectrum peaks. Long-term changes from 1989 to 2015 turn
out to be similar for the reanalyses with mainly decreasing mean age
accompanied by a shift of the age spectrum peak towards shorter
transit times, resembling the forced response in climate model
simulations to increasing greenhouse gas concentrations. For the
shorter periods, 1989–2001 and 2002–2015, the age of air changes are
less robust. Only ERA-Interim shows the hemispheric dipole pattern
in age changes from 2002 to 2015 as viewed by recent satellite
observations. Consequently, the representation of decadal
variability of the BDC in current generation reanalyses appears less
robust and is a major uncertainty of modelling the BDC.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |