Download What controls polar stratospheric temperature trends?

What controls polar stratospheric
temperature trends?
Diane Ivy, Susan Solomon, Harald Rieder, Lorenzo Polvani
(paper in preparation)
Stratospheric Climate Change
Antarctic Ozone Hole
REVIEW ARTICLE
NATURE GEOSCIENCE DOI: 10.1038/ NGEO1296
•
Caused pronounced coolinga in the lower
stratosphere in austral spring
b Simulated 500 hPa Z (Gillet & Thompson, 2003)
Observed 500 hPa Z
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7.5
60
60
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45
45
4.5
30
30
3
15
15
1.5
0
0
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–15
–15
–1.5
–30
–30
–3
–45
–45
–4.5
–60
–60
–6
–75
–75
–7.5
Ozone depletion has resulted in a seasonal
strengthening of the polar vortex and shifting of
the tropospheric jet (positive trend in the SAM)
•
c Simulated surface pressure (Polvani et al., 2011)
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Influenced Southern Hemisphere surface climate
Figure 2 | Signature of the ozone hole in observed and simulat ed changes in the austral summertime circulation. a, Observed composite dif erences
between the pre-ozone-hole and ozone-hole eras in mean December–February (DJF) 500-hPa Z from the NCEP-NCAR Reanalysis. b, Simulated
dif erences in 500-hPa Z between the pre-ozone-hole and ozone-hole eras from the experiments in ref. 30. c, As in b, but for surface pressure from the
experiments in ref. 33. The contour interval is 5 m in a and b, and 0.5 hPa in c. Values under 10 m (a and b) and 1 hPa (c) are not contoured.
REVIEW ARTICLE
NATURE GEOSCIENCE DOI: 10.1038/ NGEO1296
a
b
Ozone
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−500
100
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A
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2010
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S
O
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J
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Month
M
A
M
J
2030
2050
Winter
2070
2090
Greenhouse gases
2
d (2011) Nature Geoscience
Simulated Z (Polvani et al., 2011)
Thompson et al.
30
Simulated Z (Gillett & Thompson, 2003)
−500
M
0
b
300
500
J
Past Future
1
−2
1970
Std deviations
300
1,000
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Pressure (hPa)
Pressure (hPa)
−90
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Ozone-depleting substances
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Z from observations
Std deviations
a
Past Future
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0
−1
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−2
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Summer
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2010
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Winter
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2090
Stratospheric Climate Change
Arctic Stratosphere
Solomon et al. (2014) PNAS
Antarctic Temperature Trends
How to reconcile?
Obsvd T trends are
generally smaller than
models.
Here we show a way to
interpret the
data/model
comparisons in a new
way.
Stratospheric Temperatures
Roles of Radiation and Dynamics
http://www.ccpo.odu.edu
Stratospheric Temperatures
Dynamical contribution to stratospheric temperatures and trends
Newman et al. (2010) JGR
Two ways to analyze contributions to dT/dt
- use eddy heat flux to get dynamical term and
treat radiative terms as a residual
Bohlinger et al. (2014) ACP
- use radiative information and treat dynamical
term as a residual
Stratospheric Temperatures
Dynamical contribution to stratospheric temperatures and trends
Newman et al. (2010) JGR
Residual
Bohlinger et al. (2014) ACP
Bohlinger et al. (2014) ACP
Stratospheric Temperatures
Radiative contribution to stratospheric temperatures and trends
Parallel Offline Radiative Transfer Model
• Radiative code of NCAR’s CAM4 (Community Atmosphere
Model)
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Fixed Dynamical Heating Calculation
Data
• MERRA Reanalysis
•
•
•
•
3 Additional Ozone Databases
BDBP (Hassler et al., 2009)
SPARC (Cionni et al., 2011)
RW07 (Randel and Wu, 2007)
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Include increased long-lived GHGs
Model Forcings
Radiative and Dynamical Temperature Trends
Arctic Trends in the Lower Stratosphere
•
Estimates agree well with
results presented in
Bohlinger et al. (2014)
•
Most notable difference is
Bohlinger estimates
stronger radiative cooling
trend in winter
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Dynamical warming in
winter, indicates
increased wave activity
•
Summer trends are due to
radiation
•
Error bars on radiative
trends are relatively small,
reflect uncertainty on
ozone trends (but
checking H2O is TBD)
Bohlinger et al. (2014) ACP
Radiative and Dynamical Temperature Trends
Arctic and Antarctic in the Lower Stratosphere
•
Cooling trend in Antarctic
spring - mainly radiative
•
Cooling trend in Arctic
spring – dynamical
•
Cooling in Arctic summer
– radiative
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Cooling in Antarctic
summer – radiation and
dynamics
Historical Temperature Trends
Arctic and Antarctic
•
Strong cooling in both
hemispheres
• Antarctic confined to
lower stratosphere
• Arctic cooling first
appears in mid and upper
stratosphere
•
Warming trend above Antarctic
cooling
Radiative and Dynamical
Temperature Trends
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Peak in radiative cooling
associated with ozone lags by
one month
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Cooling in the Antarctic is largely
radiative due to ozone depletion
•
Cooling in the Arctic is dynamical
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Dynamical “Warming above the
cooling” is seen in both
hemispheres and isn’t confined
to just mid-stratosphere
•
•
Acts to weaken the
radiative cooling – big
effect in Antarctic summer
Influence on strat/trop
coupling
Some Key Points
•
Estimated the radiative and dynamical contributions to polar stratospheric
temperature trends – lower stratospheric results are similar to those using the eddyheat flux
•
Radiative approach can be used over a broad range of altitudes (at least up to 10
mbar); depends mainly on accuracy of knowledge of ozone and T trends
•
Arctic summer and fall seasons are close to radiative equilibrium; temperature trends
are result of radiative cooling associated with ozone depletion (and increased
greenhouse gases)
•
Dynamical changes are evident in both hemispheres:
• Arctic: Strengthening of BDC in winter and in weakening in spring
• Antarctic: Strengthening of BDC in spring and summer; dynamical response to
Antarctic ozone hole, the Antarctic dynamical response acts to weaken the
radiative cooling.
• Warming above the cooling is an indicator of circulation changes – value as a
diagnostic
Additional slides, not for presentation
Stratospheric Climate Change
Antarctic Ozone Hole
•
Large ozone depletion event in austral spring
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Ozone depletion occurs as heterogeneous
chemistry on polar stratospheric clouds
Stratospheric Climate Change
Arctic Stratosphere
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Temperatures on the threshold for
polar stratospheric cloud formation
•
Coldest winters are getting colder
•
Implications for future ozone loss
Solomon et al. (2014) PNAS
Rex et al. (2006) GRL
Stratospheric Climate Change
Comparison of Models
•
CCMVal-1 gave stronger tropospheric
response than CCMVal-2 but much of
that traced to a single model
Son et al. (2010) JGR
•
CCMVal-2 shows similar results as AR4
models
•
Models aren’t able to capture the
seasonality in Arctic winter/spring
trends and overall cool too much
compared to lower stratospheric
temperatures
Wang et al. (2012) JGR
Stratospheric Temperatures
Dynamical contribution to stratospheric temperatures
Newman et al. (2010) JGR
Radiative Temperature Trends
Arctic and Antarctic in the Lower Stratosphere
2648
Q. Fu et al.: Seasonal dependence of tropical lo
515
•
Fu et al. (2010) used eddyheat flux to estimate the
dynamical contribution to
trends in Arctic and Antarctic
(1980-2008)
•
Antarctic radiative trend
peaks in November
•
Arctic radiatve trend peaks
in March
Fu et al. (2010) ACP
516
517
518
519
520
•
Antarctic fall and Arctic
summer and fall trends are
similar at -0.5 K/decade
Figure 7. MSU lower-stratospheric temperature (T ) trends due to the radiative forcing in the SH
4
Fig. 7. MSUo lower-stratospheric
temperature
(T4 o) trends due to the
high latitudes (40 S-82.5oS) (dashed line), NH high latitude (40oN-82.5
N) (dotted line), and the
radiative forcing
in
the
SH
high
latitudes
(40◦ S–82.5◦ S) (dashed
o
o
o
o
high latitudes (40 N-82.5 N and 40 S-82.5
S) (solid ◦line) for 1980-2008 versus month.
◦
line), NH high latitude (40 N–82.5 N) (dotted line), and the high
latitudes (40◦ N–82.5◦ N and 40◦ S–82.5◦ S) (solid line) for 1980–
2008 versus month.
and June in the illuminated regions of the SH high latitudes
(Fig. 4). But we cannot explain the minimum cooling in
February when there is more ozone depletion with more solar
illumination than March-May. Therefore we conclude that
our method using the NCEP/NCAR reanalysis data may underestimate the radiative cooling
in February and thus the dy26
namic cooling in this month may be an artifact. Note that the
derived dynamic trend is near-zero if we substitute the radiative cooling in February with that in March or with the aver-
dynamic and radiative
− 0.32 K/decade, respec
Figure 6 indicates th
latitudes (dotted line)
becomes large in Dece
(0.44 K/decade). As a
March (− 0.20 K/decade
the dynamic warming in
Since there is no ozo
expect much less season
T4 trends there (see dot
radiative cooling in the
The minimum cooling i
July, is partly because o
Figure 7 indicates more
itudes in February and
we note a similar ozon
in February and March
May (Fig. 8), suggesting
of radiative cooling, an
cooling in the same amo
The solid line in
radiatively-induced SH
pected from the analysi
of these trends in the firs
small.
4.3
Coupling of tropi
dynamical T4 tre
The contribution of the
Radiative and Dynamical Temperature Trends
Arctic Trends in the Lower Stratosphere
•
Winter trends are subject to
large uncertainties and are
sensitive to end-year
•
Dynamical cooling in February
•
Stronger radiative cooling with
trends ending in 2000
•
Summer trends are robust and
are driven by radiation
Consistent trend patterns in the SH winter and spring are
502
Figure 5. (a) MSU observed lower-stratospheric temperature (T4) trend pattern in units of
Fig. 5. (a) MSU observed lower-stratospheric temperature (T4 )
also found regardless of the ending years used (e.g., 1980–
503
K/decade for 1980-2008 in southern hemisphere high latitudes in September. (b) T4 trend pattern
trend pattern in units of K/decade for 1980–2008 in southern hemi1995, . . . , 1980–2001, . . . , 1980–2008), indicating that the
504
attributed to the trend of the BDC. (c) T4 trend pattern difference between (a) and (b). (d ) Time
sphere high latitudes in September. (b) T4 trend pattern attributed
observed trend patterns in Fig. 4 are not unduly influenced
505
series
of thetrend
observed
T4 temperature
averaged
over difference
southern hemisphere
high(a)
latitudes
to the
of the
BDC. (c)anomaly
T4 trend
pattern
between
by the effect of unusual years such as 2002. Figure 4 also
506
in September
linear trend
withofthethe
95%observed
confidence interval.
(e ) Time series
of the T4
and (b). and
(d)itsTime
series
T4 temperature
anomaly
shows trend patterns of observed total ozone in SH high lat507
temperature
attributed
to the variation
of the BDC high
and itslatitudes
linear trend.
Time series of
(d)-(e)
averaged
over southern
hemisphere
in(f)September
and
itudes, which along with the T4 patterns, will later be used
508
andits
itslinear
linear trend.
(a), (b),
and95%
(c), yellow/red
colorsinterval.
indic ate positive
trendsseries
and blue
trendInwith
the
confidence
(e) Time
ofcolors
in the discussions of our derived T4 trends due to radiative
the Tnegative
attributed to the variation of the BDC and its lin509
indicate
trends.
4 temperature
ear trend. (f) Time series of (d)–(e) and its linear trend. In (a), (b),
forcing and BDC changes.
510
and (c), yellow/red colors indicate positive trends and blue colors
A regression of gridded monthly-mean T4 data is perindicate negative trends.
formed upon the corresponding eddy heat flux index time
510
series for each month. The regression map represents the
patterns of temperature anomalies that are associated with
changes in the eddy heat flux index. The attribution of the T4
24
trend to changes in the BDC strength is thus obtained by multiplying the regression maps by the linear trend in the eddy
heat flux index.
As an example, Fig. 5 shows the observed September T4
trend pattern in a, the contributions to the T4 trend due to the
changes in the BDC in b, and the difference in c. The corresponding time series of the mean T4 temperature anomalies over SH high latitudes are shown in d, e, and f, which
represent the total, dynamical, and radiative components of
T4 anomalies, respectively. We see that the large dynamic
warming of 0.59 K/decade largely cancels the radiative cooling of − 0.62 K/decade, leading to a near-zero T4 total trend. 511
Note that the slight warming in c might be related to the 512 Figure 6. MSU lower-stratospheric temperature ( T4) trends due to the changes in the BDC in the
Fig. 6. MSU lower-stratospheric temperature (T ) trends due to
change of the polar planetary waves that have little direct im- 513 SH high latitudes (40 oS-82.5oS) (dashed line), NH high latitude (40 oN-82.54 oN) (dotted
line), and
the changes in o the BDC
in the SH high latitudes (40◦ S–82.5 ◦ S)
the high latitudes (40 N-82.5oN and 40oS-82.5oS) (solid
line) for 1980-2008 versus month.
pact on the area-mean trend. LFSW2009 showed that the 514 (dashed
line), NH high latitude (40◦ N–82.5◦ N) (dotted line), and
September temperature change on the decadal timescale is
the high latitudes (40◦ N–82.5 ◦ N and 40◦ S–82.5◦ S) (solid line)
largely driven by changes in ozone concentration and BDC.
for 1980–2008 versus month.
The T4 trend contributions due to the changing BDC and
radiative forcing, averaged over SH high latitudes (40◦ S–
derived dynamic trend however is negative (− 0.14 K/decade)
82.5◦ S), versus the month of the year, are shown in Figs. 6
in February.
and 7 (dashed line), respectively. The dynamic contribution
to the trend has a maximum warming of 0.63 K/decade in
The radiative contributions to the trends (Fig.7) have large
October, and is positive from May through November, as
cooling in the SH spring and early summer related to the
2650
Q. Fu et al.: Seasonal dependence of tropical lower-stratospheric temperature trends
indicated
in Fig. 4. It is near zero in December,
January, 535 ozone hole (see Fig. 4). The second maximum cooling in
531
March, and April, which is also consistent with Fig. 4. The
May may be explained by more
25 ozone depletion than April
Dynamical Temperature Trends
Arctic and Antarctic in the Lower Stratosphere
•
Dynamical trends show
similar seasonality as Fu et
al. (2010)
•
Fu et al. (2010) found a
strengthening of BDC SH
cell in July - November;
strengthening of NH cell in
DJF and weakening in
MAM
Atmos. Chem. Phys., 10, 2643–2653, 2010
www.atmos-chem-phys.net/10/2643/2010/
536
Fu et al. (2010) ACP
Historical Temperature Trends
Warming above the cooling
•
Dynamical response to Antarctic ozone
hole; enhanced gravity wave
propagation (Calvo et al., 2012).
•
Warming above cooling modeled in
chemistry climate models
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Not seen in GCMs with prescribed
ozone
Young et al. (2013) JGR
•
Young et al. (2013) suggests “warming
above cooling" is a benchmark for
models representation of middle
atmospheric dynamics
Radiative and Dynamical Temperature Trends
Arctic Upper Troposphere
•
Arctic summer trends in the lower stratosphere are driven changes in radiative
cooling associated with ozone depletion; these trends extend down to 250hPa
Radiative and Dynamical Temperature Trends
Antarctic Upper Troposphere
•
•
Antarctic summer trends in the lower stratosphere are driven changes in
radiative cooling associated with ozone depletion and dynamical warming
Lowermost stratospheric and upper tropospheric trends are driven by
radiation