The role of tropical upwelling in explaining discrepancies between recent modeled and observed lower-stratospheric ozone trends
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Published:2023-03-17
Issue:5
Volume:23
Page:3347-3361
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Davis Sean M.ORCID, Davis NicholasORCID, Portmann Robert W.ORCID, Ray EricORCID, Rosenlof KarenORCID
Abstract
Abstract. Several analyses of satellite-based ozone measurements
have reported that lower-stratospheric ozone has declined since the late
1990s. In contrast to this, lower-stratospheric ozone was found to be
increasing in specified-dynamics (SD) simulations from the Whole Atmosphere
Community Climate Model (WACCM-SD) despite the fact that these simulations
are expected to represent the real-world dynamics and chemistry relevant to
stratospheric ozone changes. This paper seeks to explain this specific
model and observational discrepancy and to more generally examine the
relationship between tropical lower-stratospheric upwelling and lower-stratospheric ozone. This work shows that, in general, the standard
configuration of WACCM-SD fails to reproduce the tropical upwelling changes
present in its input reanalysis fields. Over the period 1998 to 2016,
WACCM-SD has a spurious negative upwelling trend that induces a positive
near-global lower-stratospheric column ozone trend and that accounts for much of
the apparent discrepancy between modeled and observed ozone trends. Using a
suite of SD simulations with alternative nudging configurations, it is shown
that short-term (∼ 2-decade) lower-stratospheric ozone trends
scale linearly with short-term trends in tropical lower-stratospheric
upwelling near 85 hPa. However, none of the simulations fully capture the
recent ozone decline, and the ozone and upwelling scaling in the WACCM
simulations suggests that a large short-term upwelling trend
(∼ 6 % decade−1) would be needed to explain the
observed satellite trends. The strong relationship between ozone and
upwelling, coupled with both the large range of reanalysis upwelling trend
estimates and the inability of WACCM-SD simulations to reproduce upwelling
from their input reanalyses, severely limits the use of SD simulations for
accurately reproducing recent ozone variability. However, a free-running
version of WACCM using only surface boundary conditions and a nudged quasi-biennial oscillation
produces a positive decadal-scale lower-stratospheric upwelling trend and a
negative near-global lower-stratospheric column ozone trend that is in
closest agreement with the ozone observations.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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