Antarctic ozone trends and Southern Hemisphere
precipitation, evaporation and extreme changes
Ariaan Purich, Seok-Woo Son and Jacques Derome
Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, Québec, Canada
Global Environmental and Climate Change Centre, Montréal, Québec, Canada
Methodology
Introduction
Changes in stratospheric ozone (Figure 1) have previously been linked to Southern Hemisphere (SH) circulation changes [2]. For instance, the effects of ozone depletion have been linked to a rising extratropical tropopause
height, a poleward intensification of the extratropical westerly jet, a poleward shift in storm tracks and a poleward
expansion of the Hadley cell (Figure 2) [3, 4].
Although model studies have been undertaken to
investigate SH circulation variability and trends,
the impact of stratospheric ozone depletion and
recovery on the SH hydrological cycle still remained to be determined.
By examining CMIP3 models for trends in precipitation and
evaporation in the 20th and 21st centuries, we show that
stratospheric ozone forcing plays an important role in SH
extratropical precipitation changes during austral-summer.
Figure 1: Antarctic minimum total ozone [1]. Ozone levels declined
rapidly in the latter part of the 20th century but are predicted to recover
in the 21st century.
Figure 2: Schematic of ozone impact on the troposphere [4].
Daily data from the CMIP3 20C3m and A1B experiments
are analysed for changes in precipitation and evaporation.
Models (listed in Table 1) are divided into two groups:
• Ten models which incorporated ozone depletion (recovery) in the 20th (21st) century; and
• Nine models which prescribed climatological ozone in
both past and future climates.
Table 1: CMIP3 models used in this study.
Ozone depletion and recovery
CCSM3.0 (NCAR, USA)
CSIRO-Mk3.0 (CSIRO, Australia)
CSIRO-Mk3.5d (CSIRO, Australia)
ECHAM5/MPI-OM (MPI, Germany)
GFDL-CM2.0 (NOAA, USA)
GFDL-CM2.1 (NOAA, USA)
INGV-SXG (INGV, Italy)
MIROC3.2(hires) (CCSR, Japan)
MIROC3.2(medres) (CCSR, Japan)
PCM1.1 (NCAR, USA)
Climatological ozone
BCCR-BCM2.0 (BCCR, Norway)
CGCM3.1(T47) (CCCma, Canada)
CGCM3.1(T63) (CCCma, Canada)
CNRM-CM3 (CNRM, France)
ECHO-G (MIUB, Germany, Korea)
GISS-AOM (NASA, USA)
INM-CM3.0 (INM, Russia)
IPSL-CM4 (IPSL, France)
MRI-CGCM2.3.2 (MRI, Japan)
Model simulated trends: mean precipitation and evaporation
Multimodel-means for each group are compared. Since
ozone forcing has impacts on austral-summer (DJF) climate, DJF differences between the two groups of models
can be attributed to ozone forcing. Although not shown,
no significant differences are found between the two groups
during austral-winter when ozone is inactive.
It is found that stratospheric ozone forcing modifies SH
precipitation (Figure 3). Dipolar trends in extratropical
precipitation are enhanced by ozone depletion in the 20th
century and weakened by ozone recovery in the 21st century. Here, only the extratropics are shown, as tropical and
subtropical trends are noisy and largely insignificant.
Long-term trends are assessed using decadal-differencing.
The difference between 1990–1999 and 1961–1970 climatologies represents the 20th century change, reflecting the
impact of ozone depletion. The difference between 2056–
2065 and 1990–1999 climatologies reflects the 21st century
change, in association with ozone recovery.
In contrast to the annular-like trends of precipitation,
evaporation shows relatively weak trends in the extratropics, which lack organisation. These results indicate
that Antarctic ozone forcing modulates long-term trends
in freshwater flux to the surface (or equivalently, precipitation minus evaporation) by affecting precipitation trends.
Figure 3: DJF precipitation and evaporation trends. Hatching denotes
where the multimodel-mean trend is greater than or equal to one standard deviation of the trends of different models within that group.
Model simulated trends: different precipitation intensities
Ozone induced changes in mean precipitation are mostly
due to changes in light precipitation (1–10 mm day−1)
(Figure 4 and Figure 5). Changes in very light precipitation
(0.1–1 mm day−1) are in the opposite sense to mean precipitation changes. No ozone impacts are found in moderate
to heavy precipitation (>10 mm day−1) or 99th percentile
changes.
Although not shown, other extreme precipitation indicators
such as 95th percentile precipitation and seasonal maximum
five-day consecutive precipitation are also examined and no
ozone impacts are found.
Figure 4 (left): DJF trends in very light, light, moderate to heavy and
99th percentile precipitation. Hatching as per Figure 3. Note that very
light precipitation panels have a different colour scale.
Figure 5 (right): Individual and multimodel-mean zonal-mean DJF
precipitation climatology and trends, plotted versus latitude relative to
the jet location. GPCP v2 observational climatology is shown in black.
Note the varying y-axis scales.
Conclusions
Stratospheric ozone is found to have a statistically significant impact on austral-summer precipitation
trends, primarily through changes in light precipitation (1–10 mm day−1). The influence of ozone forcing is
evident in both high and mid-latitudes, in both the 20th and 21st centuries. No significant impacts are, however, found in
subtropical precipitation changes and in other seasons. As ozone forcing alters precipitation through dynamic effects, its
impact on extreme precipitation trends is found to be minimal, consistent with previous studies that showed thermodynamic
control of extratropical extreme precipitation changes [5]. Results further suggest that ozone depletion has likely contributed
to the observed freshening of the Southern Ocean by increasing freshwater flux in high latitudes.
Correspondance: [email protected]. A.P. is supported by a Stephen and Anastasia Mysak Graduate Fellowship, a GEC3 Travel Grant and an IAMAS Conference Grant.
References
[1] WMO (2011), Scientific Assessment of Ozone Depletion: 2010.
[2] D.W.J. Thompson and S. Solomon (2002), Science, 296, 895–899.
[3] S.-W. Son, N.F. Tandon, M.P. Lorenzo and D.W Waugh (2009), Geophys.
Res. Lett., 36, L15705.
[4] S.-W. Son et al. (2010), J. Geophys. Res., 115, D00M07.
[5] S. Emori and S.J. Brown (2005), Geophys. Res. Lett., 32, L17706.