JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D21305, doi:10.1029/2005JD005798, 2005

Effects of atmospheric sphericity on stratospheric chemistry
and dynamics over Antarctica
Jun-ichi Kurokawa,1 Hideharu Akiyoshi,2 Tatsuya Nagashima,2 Hirohiko Masunaga,3Teruyuki Nakajima,4 Masaaki Takahashi,4 and Hideaki Nakane2
Received 25 January 2005; revised 18 July 2005; accepted 8 August 2005; published 4 November 2005.

[1] Atmospheric sphericity is an important factor that must be considered in order toevaluate an accurate ozone loss rate in the polar stratosphere. The built-in plane-parallel
radiative transfer scheme of a nudging chemical transport model (CTM) and an
atmospheric general circulation model (AGCM) with coupled chemistry is modified by apseudospherical approximation. The plane-parallel atmosphere radiative transfer version(PPA version) is compared with the pseudospherical atmosphere radiative transfer
version (SA version) for both the nudging CTM and AGCM. The nudging CTM canisolate the chemical effects for a given dynamical field, while the interaction among thechemical, radiative, and dynamical processes can be studied with the AGCM. The present
analysis focuses on Antarctica during an ozone hole period. In the ozone loss period
over Antarctica, ozone starts to decrease earlier and minimum value of total ozone
becomes lower in the SA versions of both the nudging CTM and the AGCM than in thecorresponding PPA versions. The ozone mixing ratio decreases earlier in the SA version
because of an earlier increase of ClO concentration initiated by the upward actinic flux atsolar zenith angles greater than 90. Dynamics plays an important role as well as thechemical processes. During the ozone recovery period, the ozone distribution becomesalmost the same in the SA and PPA versions of the nudging CTM, while in the AGCM theozone amount in the SA version remains at lower values compared to those of the PPA
version. In the AGCM, a decrease of ozone over Antarctica enhances the latitudinal
gradient of temperature and thus strengthens the polar vortex in the SA version. A
resultant delay of the polar vortex breakup causes the delay of the ozone recovery. For the
AGCM, ensemble runs are performed. The ensemble experiment exhibits large ozone
variances after the middle of December, when the ozone recovery is dynamicallycontrolled. Most ensemble members of the AGCM show a delay of the polar vortex
breakup in the SA version, while a few members show opposite results. In the latter
members, the polar vortex breakup is strongly affected by the enhanced EP flux from thetroposphere around 100 hPa, which causes the variances in the ozone recovery period.
Most members, however, do not show large statistical variances; that justifies theconclusions from the ensemble means.
Citation: Kurokawa, J., H. Akiyoshi, T. Nagashima, H. Masunaga, T. Nakajima, M. Takahashi, and H. Nakane (2005),
Effects of atmospheric sphericity on stratospheric chemistry and dynamics over Antarctica, J. Geophys. Res., 110, D21305,
doi:10.1029/2005JD005798.

1. Introduction[2] In order to evaluate an accurate ozone loss rate in thepolar stratosphere, atmospheric sphericity is an importantfactor that must be considered because the ozone hole starts
1

Fujitsu FIP Corporation, Tokyo, Japan.
National Institute for Environmental Studies, Tsukuba, Japan.
Department of Atmospheric Science, Colorado State University, Fort
Collins, Colorado, USA.
4
Center for Climate System Research, University of Tokyo, Tokyo,
Japan.
2
3

Copyright 2005 by the American Geophysical Union.
0148-0227/05/2005JD005798$09.00

at the end of the polar night, when solar zenith angles(SZAs) are greater than 90. The effects of atmosphericsphericity have been studied using multidimensional models
with radiative transfer schemes for a spherical atmosphereor with a pseudospherical approximation. The performanceof such schemes has been justified by many previous
studies [Lary and Pyle, 1991a, 1991b; Lary et al., 1991;
Perner et al., 1991; Dahlback and Stamnes, 1991; Dvortsov
et al., 1992; Müller et al., 1994; Rattigan et al., 1996;
Chipperfield et al., 1998; Kylling et al., 2003].
[3] Recently, the effects of atmospheric sphericity on the
dynamics and chemistry of the global lower stratospherehave been studied by Lamago et al. [2003] with a coupledchemistry-climate model. They performed calculations with

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and without photolysis for SZAs between 87.5 and 93.
Photolysis rates for SZAs less equal than 87.5 were
calculated using the method of Landgraf and Crutzen[1998], while those for larger SZAs were computed using
an empirical formula, where the photolysis rates were
multiplied by a correction factor [Levy, 1974; Röth, 1992,
2002]. They showed that in the polar Southern Hemisphere,
total ozone was reduced by about 20% in the simulation
with photolysis for SZAs between 87.5 and 93 because
ozone destruction started earlier (at larger SZAs), andtherefore the loss period became longer. They also showedthat a cooling of the polar lower stratosphere (at 50 hPa) of
up to 4K was caused by a chemical-radiative-dynamical
coupling response to the solar flux at large SZAs.
[4] We have developed (1) a three-dimensional stratospheric model with fully interactive chemistry based on theCenter for Climate System Research (CCSR)/National Institute for Environmental Studies (NIES) Atmospheric General Circulation Model (AGCM) [Numaguti, 1993;
Numaguti et al., 1995, 1997; Takigawa et al., 1999;
Nagashima et al., 2002] and (2) a nudged version of themodel (hereafter, a nudging chemical transport model(CTM)) that assimilates the observed wind and temperaturefields into the CCSR/NIES AGCM using nudging methods[Akiyoshi et al., 2002a, 2002b, 2004]. In these models,
photolysis rates are calculated using the actinic flux from aplane-parallel radiative transfer scheme. The actinic flux inthe plane-parallel scheme is accurate enough when SZAs
are small, but the error becomes larger as SZAs approach90. Furthermore, the plane-parallel scheme does not treat
actinic flux at SZAs larger than 90.
[5] In this paper, the effects of the sphericity of theatmosphere are incorporated by modifying the planeparallel scheme with a pseudospherical approximation forradiative transfer calculations. This modified scheme isintroduced to both the nudging CTM and the AGCM withcoupled chemistry. In the nudging CTM, the dynamical
fields are specified by observations and therefore thechemical effects of the atmospheric sphericity for a given
dynamical field can be isolated. In the AGCM with coupledchemistry, on the other hand, ozone changes affect thetemperature and circulation interactively and therefore theeffects of atmospheric sphericity on the interactions among
the chemical, radiative, and dynamical processes can bestudied. The present analysis focuses on Antarctica during
an ozone hole period.
[6] Section 2 briefly describes the procedure for extension of the plane-parallel radiative transfer scheme for large
SZAs. The models and the layouts of the experiments aredescribed in section 3. The results of the nudging CTM
and the AGCM with coupled chemistry are analyzed in
section 4 and discussions are presented in section 5. Finally,
section 6 gives the conclusions of this paper.

2. Extension of the Plane-Parallel Radiative
Transfer Scheme for Photolysis Rate
Calculations at Large SZAs
[7] The nudging CTM and the AGCM with coupledchemistry calculate photolysis rates using the actinic flux
calculated in the radiative transfer scheme of the models.
The original radiative transfer scheme of the models is a

D21305

two-stream discrete ordinates method assuming a planeparallel atmosphere [Nakajima and Tanaka, 1986; Nakajima
et al., 2000; Numaguti, 1993; Numaguti et al., 1995, 1997].
The computation of the fluxes involved in the photolysis rate
calculations is done in six spectral bins (200.0 – 217.4,
217.4 – 232.6, 277.8 – 289.9, 289.9 – 303.0, 303.0 – 317.5,
and 317.5 – 689.7 nm). The concentrations of chemical
species calculated in the models are used in the radiativetransfer scheme. The background aerosol concentration in
the troposphere is assumed to be 1.0  10 – 12 cm3/cm3 and isassumed to be zero in the stratosphere.
[8] In the models, photolysis rates are calculated asfollows [Akiyoshi, 1997]:
Ji ðZ Þ ¼

X

j ðZ; lÞl ilji ðZ; lÞ ¼ I  ðZ; lÞ þ I þ ðZ; lÞ  si ðl; T ðZ ÞÞ  qi ðlÞ  ;hcwhere Ji(Z) is the spectrally integrated photolysis rate ofchemical species i at altitude Z, ji(Z, l) is that in spectral
bin l, I  ðZ; lÞ represents the downward () and upward(+) actinic flux at altitude Z in spectral bin l, si(l, T(Z))
is the absorption cross section of species i at temperature
T(Z) at Z in spectral bin l, qi(l) is the quantum yield ofspecies i in spectral bin l, h is Planck’s constant, and c isthe velocity of light. Note that the interval of the lastspectral bin (317.5 –689.7 nm) is too large to calculate
accurate photolysis rates. In this spectral bin, photolysis
rates are calculated using weighted mean cross sections ofchemical species. The weighted mean absorption crosssections were calculated using the monochromatic solar
flux at the top of the atmosphere as weighting factors[Akiyoshi, 1997]. Wavelengths of less than 200 nm are notconsidered in the radiative transfer schemes of the models.
Thus the photolysis rates in the Schumann-Runge band
are calculated with the parameterization developed by
Minschwaner et al. [1993] and Allen and Frederick[1982].
[9] The nudging CTM and the AGCM with coupledchemistry with the plane-parallel scheme have reproduced
realistic seasonal and day-to-day variations and global
distributions of chemical compounds in the stratosphere[Takigawa et al., 1999; Akiyoshi et al., 2002a, 2002b,
2004; Nagashima et al., 2002]. However, the optical pathof direct solar incidence in the plane-parallel scheme isoverestimated everywhere, especially when SZAs are close
to 90, which results in the underestimation of photolysis
rates. Moreover, plane-parallel approximation cannot treat
the solar direct radiation at SZAs greater than 90.
[10] In order to overcome these deficiencies, the planeparallel radiative transfer scheme is modified using a
pseudospherical approximation as follows: (1) The upward
solar direct radiation at SZAs greater than 90 is added.
(2) The single-scattering phase function for the upward
solar direct radiation is added. (3) The Chapman function
is modified to consider the atmospheric sphericity withthe method of Dahlback and Stamnes [1991] and is used
for both the downward and upward solar direct radiation.
Then, downward and upward actinic fluxes at vertical

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D21305

D21305Figure 1. Geometry of direct sunlight used to calculate the Chapman function in a spherically layered
atmosphere. (a) SZAs q0 < 90 and (b) SZAs q0  90.
optical depths t = t(Z) in spectral bin l are obtained
depending on the value of SZA, q0, as follows:

function is given as follows using the formulation of
Dahlback and Stamnes [1991]:

For q0 < 90

For q0 < 90I  ðt; lÞ ¼ Fdiffuse
þ I0 echðt;q0 Þchðt; q0 Þ ¼

Xp



Dsj
Dtj
j¼1
Dhj



For q0  90þI þ ðt; lÞ ¼ FdiffuseDsjchðt; q0 Þ ¼
Dtj
j¼1
Dhj
 


XL1
Dsj
DsL
þ2
Dt
þ
Dt
j
L
j¼pþ1
Dhj
DhL
Xp

For q0  90I  ðt; lÞ ¼ FdiffuseþI þ ðt; lÞ ¼ Fdiffuse
þ I0 echðt;q0 Þ ;where Fdiffuse
is the diffuse component of the downward() and the upward (+) solar flux, I0ech(t,q0) is the directcomponent of the solar flux, and ch(t, q0) is the Chapman
function, which represents the optical path of direct solar
incidence through a spherical atmosphere. The Chapman

where Dtj is the plane-parallel optical depthpof
each layer j,
ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
2  OG2 
Dhj = rj  rj+1, and
Ds
=
AB
=
GB

GA
=
OB
j
qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
pﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
2
2
2
2
2
2
2
OA  OG = rj  rp sin q0  rjþ1  rp sin2 q0 (seeFigure 1). L is the deepest layer in the atmosphere where theattenuation of the direct beam must be considered.
[11] The diurnally averaged photolysis rates of Cl2O2
at the winter solstice by the new scheme are shown in

Figure 2. A latitude-height cross section of the diurnally averaged photolysis rates of Cl2O2 at the
winter solstice calculated with the new pseudospherical scheme.
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94.23

1.416  1071.880  108
1.937  1074.037  101093

1.019  x1051.355  1061.464  1052.585  108D21305Figure 2. The results generally agree with those of Lary andPyle [1991a]. The photolysis rates of Cl2O2, HOCl, HOBr,
and H2O2 at local noon at 80S, 50 hPa, and SZAs from 70
to 94.23 are also presented in Table 1. The maximum SZA
is 94.23 at 80S and 50 hPa. In the new scheme, the solar
direct radiation at SZAs greater than 90 is considered
except where the model grid is in the shadow of the earth.
Therefore the maximum SZA for a given grid box in thisscheme depends on its latitude and altitude.

92
91

2.083  1042.769  1053.027  1045.115  107
1.691  1032.248  1042.457  103
4.152  106

1.052  103
1.398  104
1.532  1032.574  10689

1.531  1032.030  1042.226  1033.746  106

88

90

[12] In this work, we use two types of three-dimensional
stratospheric chemical models. One is a nudging CTM andthe other is an AGCM with coupled chemistry. The chemical scheme for the nudging CTM includes gas phasechemical reactions of Ox, HOx, NOx, hydrocarbons, ClOx,
and BrOx, and heterogeneous reactions on nitric acidtrihydrate (NAT), water ice, and supercooled ternary solution (STS) polar stratospheric clouds [Akiyoshi et al., 2004].
On the other hand, the scheme for the AGCM is slightly
simplified to circumvent the large computation time required for the ensemble experiment. In particular, it does notinclude bromine chemistry or heterogeneous reactions on
STS [see Takigawa et al., 1999; Nagashima et al., 2002].
However, the strength of ozone destruction by bromine
species is much smaller than that by chlorine species over
Antarctica and the time evolution of ozone destruction rate
due to bromine species is similar to that due to chlorine
species, especially in the ozone loss phase (see Figure 13).
Therefore omitting these aspects of chemistry in the AGCM
does not reduce the validity of the results and conclusions of
this paper. Both models have 34 vertical atmospheric layersthat extend from the surface to about 80 km with a horizontal
resolution T21 (longitude  latitude 5.6  5.6).
[13] In the nudging CTM, observed wind and temperaturefields are assimilated into the AGCM by adding the nudging
terms to the time tendency equations for zonal windvelocity, meridional wind velocity, and temperature,ab

J(Cl2O2):Cl2O2 + hn ! ClOO + Cl, sec1.
J(HOCl):HOCl + hn ! OH + Cl, sec1.
c
J(HOBr):HOBr + hn ! OH + Br, sec1.
d
J(H2O2):H2O2 + hn ! 2OH, sec1.

2.144  1032.848  1043.072  1035.475  1062.660  1033.533  1043.661  1037.510  106
J(Cl2O2)aJ(HOCl)bJ(HOBr)cJ(H2O2)d3.400  1034.517  1044.678  1039.799  10685ðx  xobs Þ=t;

80Photolysis Rates for Each SZA Greater Than 70

7.576  105
1.007  105
1.099  1041.865  107

3. Model Description and Numerical Experiments

70

Table 1. Photolysis Rates of Cl2O2, HOCl, HOBr, and H2O2 at Local Noon at 80S, 50 hPa, and Solar Zenith Angles (SZAs) From 70 to 94.23, Calculated by the Spherical Radiative
Transfer Version

D21305x ¼ u; v; and T;

where u is the zonal wind velocity; v is the meridional windvelocity; T is the temperature; x are the model calculated
values of u, v, and T; xobs are the observed values of u, v, andT; and t is the timescale of the nudging. Then, the u, v, and T
values in the nudging CTM tend to approach observed
values with a timescale of t. A timescale of one day is used
for this study. Below 10 hPa, the European Centre for
Medium-Range Weather Forecast (ECMWF) analysis data
are used. Above 10 hPa, where no ECMWF data exist, themonthly and zonal mean zonal wind and temperature data of
the Committee on Space Research (COSPAR) International
Reference Atmosphere 86 (CIRA1986) [Rees et al., 1990]
are used. The meridional wind above 10 hPa is not nudged
but is calculated by the continuity equation in the model (seeAkiyoshi et al. [2004] for details).
[14] We perform the integration of the nudging CTM andthe AGCM with coupled chemistry both with the planeparallel and the pseudospherical radiative transfer schemes.
The runs of the nudging CTM are performed from 1 January
to 31 December 1999 using the same initial and surface
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Figure 3. Time evolution of (a) the total ozone at Syowa
Station and (b) the zonal mean total ozone over 80S
simulated by the nudging CTM and observed by TOMS andthe Dobson spectrophotometer (DOBSON SPM) at thestation from June to December 1999. Solid and dashed lines
indicate the calculated results from the PPA and SA
versions, respectively; the open squares denote the TOMS
observations; and the diagonal crosses denote the Dobson
spectrophotometer observations. The horizontal dashed line
indicates the ozone hole criterion of <220 D.U.
boundary conditions. The initial conditions are preparedby a spin-up run by the nudging CTM with the planeparallel scheme under conditions typical of the 1990s. The
boundary conditions are obtained from World MeteorologicalOrganization (WMO) [1999] surface concentration of CFCs
and greenhouse gases. For the AGCM with coupled chemistry, the 24 different initial conditions for 1 January areprepared from the outputs of spin-up runs under conditions
typical of the 1990s using the AGCM with the planeparallel scheme. Then ensemble runs are performed for a
14-month period from 1 January to the end of February of
the following year. The surface boundary conditions for the
AGCM are also specified by WMO [1999].

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zonal mean total ozone at the slightly higher latitude of80S is also compared with TOMS in Figure 3b. The
nudging CTM successfully simulates the variation andminimum value of the total ozone during the ozone loss
phase as well as during the ozone recovery phase. In thisand the next subsection, the effects of atmospheric sphericity on the chemistry and dynamics are studied in detail at
80S. This latitude is located sufficiently far from the model
boundary of both the polar vortex and the South Pole.
[16] The difference in the time evolution of the zonal
mean total ozone between the SA and PPA versions is seen in
Figure 3b. In the SA version, onset of the ozone hole (definedas the region of total ozone values less than 220 D.U.) in
August shifts to earlier dates, and the minimum value of totalozone becomes lower in comparison with the PPAversion. On
the other hand the variation and the absolute value in therecovery phase are almost the same between the two models
versions. A similar feature is also seen in Figure 3a. Thesebehaviors are clearly shown in Figure 4, where the differencein the zonal mean total ozone between the SA and PPA
versions (SA minus PPA) at 80S is plotted. The difference
starts to increase at the beginning of July, continues toincrease until the end of August, and then diminishes rapidly
by the end of September.
[17] In order to understand these features of the totalozone during the ozone hole period, the temporal evolutionof the ozone mixing ratio simulated by the SA and PPA
versions at 80S and 50 hPa from 1 June to 31 December
1999, and the difference between the SA version and the PPA
versions (SA minus PPA) are shown in Figures 5a and 5b.
The ozone amount at 50 hPa contributes largely to the totalozone, and the difference between the SA and PPA versions
is evident at this altitude. Figures 5c and 5d show the ClO
mixing ratio, and the photolysis rates of Cl2O2. It is wellknown that Cl2O2 photolysis plays a dominant role in polarozone loss.
[18] Both the time evolution of the ozone mixing ratio in
Figure 5a and the difference between the SA and PPA
versions in Figure 5b show similar variations to those of
total ozone. Figure 5c shows an earlier increase of the ClO
mixing ratio in the SA version, which corresponds to an
earlier increase of the photolysis rate of Cl2O2 shown in
Figure 5d. The SZA at local noon at 80S reaches 90 on

4. Results
4.1. Effects of Atmospheric Sphericity on Polar
Chemistry: Results From the Nudging CTM Simulation[15] A comparison of the simulated and observed time
evolution of total ozone during the Southern Hemisphereozone hole period of 1999 is shown in Figure 3. Figure 3ashows the time evolution of the total ozone at Syowa
Station (69S 39.5E) calculated with the plane-parallel
atmosphere version (hereafter, the PPA version) and thepseudospherical atmosphere version (hereafter, the SA version) of the radiative transfer schemes. Observations by the
Total Ozone Mapping Spectrometer (TOMS) and the Dobson spectrophotometer at the station are also shown. The

Figure 4. Time evolution of the zonal mean total ozone
difference between the SA and PPA versions (SA minus
PPA) of the nudging CTM over 80S from June to
December 1999.

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D21305ozone compared to the PPA version. These results are consistent with the work of Lary and Pyle [1991a, 1991b], whosuggested the importance of Cl2O2 photolysis at SZAs greaterthan 90 for polar ozone loss.
[19] After the ClO mixing ratio in the PPA version reaches
a maximum on the middle of September, the difference in theozone mixing ratio between the SA and PPA versions
diminishes rapidly, as seen in Figure 5a and 5b. During theozone recovery phase after the end of September, thedifference in the ozone amount is very small. This suggeststhat the ozone variation in the recovery phase is mainly
controlled by dynamical processes because the dynamical
fields of the nudging CTM are the same in the SA and PPA
versions.
[20] Note that the difference both in the total ozone andthe ozone mixing ratio between the SA and PPA versions
already exists during the polar night, i.e., before the onset ofthe ozone hole. The reason is discussed in section 5.1.

Figure 5. Time evolution of (a) the zonal mean ozone
mixing ratio at 80S and 50 hPa, (b) the difference between
the SA and PPA versions (SA minus PPA), (c) the zonal
mean ClO mixing ratio, and (d) the photolysis rates of Cl2O2
at local noon simulated by the nudging CTM from June to
December 1999. Solid and dashed lines in Figures 5a, 5c,
and 5d indicate the calculated results from the PPA and SA
versions, respectively.
28 August. Therefore the rapid increase of the ClO mixing
ratio starts just after 28 August in the PPA version. On theother hand, the ClO mixing ratio in the SA version starts toincrease on 18 August by the upward actinic flux at SZAs
greater than 90. As a result, the onset of ozone destruction
starts earlier and thus the ozone destruction continues longer
in the SA version, which reduces the minimum value of total

4.2. Effects of Atmospheric Sphericity on Chemical,
Radiative, and Dynamical Coupling Processes of the
Polar Stratosphere: Results From the AGCM
Ensemble Experiments
4.2.1. Chemistry[21] Figure 6 shows the ensemble mean difference in thetemporal distribution of the zonal mean total ozone between
the SA and PPA versions (SA minus PPA). The dark shaded
area and light shaded area indicate the 99% and 95%
statistical significance levels, respectively, by the t-test.
The total ozone around Antarctica in the SA version islower by 20 –40 D.U. than that in the PPA version from
September to the following January.
[22] The temporal variations of the zonal mean totalozone at 80S, the difference between the SA and PPA
versions (SA minus PPA), the ozone mixing ratio, and the
ClO mixing ratio at 80S and 50 hPa in the ensemble meansfrom 1 June to the end of February of the following year are
shown in Figures 7a – 7d. In the ozone loss phase similar
results to those from the nudging CTM are obtained. The
earlier onset of ozone reduction and the smaller minimum

Figure 6. Time-latitude cross section of the zonal mean total ozone difference in the ensemble mean
between the SA and PPA versions (SA minus PPA) of the AGCM from January to February of thefollowing year. The dark and light shaded areas show the regions where the differences are statisticallysignificant at the 99% and 95% levels by the t-test, respectively. Smoothed results by 7-day running mean
are plotted.
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Figure 7. Time evolution of (a) the zonal mean total ozone
at 80S, (b) the difference between the SA and PPA versions(SA minus PPA), (c) the zonal mean ozone mixing ratio at
80S and 50 hPa, (d) the zonal mean ClO mixing ratio, and(e) the zonal mean temperature in the ensemble mean
simulated by the AGCM from June to February of thefollowing year. Solid and dashed lines in Figures 7a and7c – 7e indicate the calculated results from the PPA and SA
versions, respectively. The horizontal dashed line in
Figure 7a indicates the ozone hole criterion of <220 D.U.

D21305value of the ozone amount in the SA version compared to
the PPA version are evident in Figures 7a – 7c. Figure 7d
indicates that the earlier decrease of ozone in the SA version
is caused by the earlier increase of ClO, same as the case of
the nudging CTM. In the SA version, the ClO mixing
ratio suddenly decreases after the middle of October. Samefeature is seen around the South Pole as shown in Figure 8,
where the time-latitude cross section of the zonal meandifference of the ensemble mean ClO mixing ratio between
the SA and PPA versions (SA-PPA) at 50 hPa is plotted. In
this region, O3 mixing ratio in the SA version of the AGCM
becomes almost zero after the middle of October and thenCl starts to react with CH4.
[23] After the total ozone minimum, the behavior of theozone variation is different from the results of the nudging
CTM. The total ozone in the SA version maintains its values
lower than those of the PPA version until the end of thesimulation, despite the decrease of the ClO mixing ratio.
This behavior during the ozone recovery phase cannot be
explained by ozone chemistry alone.
[24] Note that, similar to the nudging CTM, the differencein the ozone value between the SA and PPA versions alreadyexists during the polar night. The reason of this is the same as
for the nudging CTM (see section 5.1 for details).
4.2.2. Radiation and Dynamics[25] In the AGCM with coupled chemistry, polar ozone
loss can change the meteorological fields through a changeof the radiative energy balance. Actually, the temperaturesin the SA version remain cooler than those in the PPA
version after the ozone minimum as shown in Figure 7e,where the temporal evolution of the ensemble means oftemperature at 80S and 50 hPa is plotted.
[26] In order to understand this feature, the zonallyaveraged thermal balance in the lower stratosphere isinvestigated. The zonally averaged thermal balance is givenby@T¼ Qdiabatic þ Qdynamical ;@tFigure 8. Time-latitude cross section of the zonal mean difference of the ClO mixing ratio in theensemble mean between the SA and PPA versions (SA minus PPA) of the AGCM at 50 hPa in theSouthern Hemisphere from June to February of the following year. Smoothed results by 7-day runningmean are plotted.
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ð1Þ

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Figure 9. Time evolution of the three terms of the thermalbalance equation (equation (1)), zonally averaged at 80S
and 50 hPa in the ensemble mean simulated by (a) the PPA
version and (b) the SA version of the AGCM from June to
February of the following year. Solid, short-dashed, andlong-dashed lines indicate the temperature tendency @T@t ,the dynamical heating Qdynamical, and the diabatic heating
Qdiabatic, respectively. Smoothed results by 10-day runningmean are plotted.
where @T@t is the temperature tendency, Qdiabatic is the net
diabatic heating, and Qdynamical is the dynamical heating.
The temporal variation of each term of (1) at 80S and
50 hPa is plotted in Figures 9a and 9b for the PPA and SA
versions, respectively. These results are obtained from theD21305ensemble means using a 10-day running mean. The net
diabatic heating term in the SA version is smaller than thatin the PPA version in September, October, and at the
beginning of November, corresponding to the maximum
difference of ozone concentration at this time (seeFigure 7c). The smaller diabatic heating in the SA version
is caused by the decreased shortwave radiation absorption
by ozone molecules due to the larger ozone destruction.
This leads to a smaller temperature tendency and hence thelower temperature in the SA version. The increase of the
dynamical heating term starts after the middle of Novemberin the PPA version, while that in the SA version is delayed
about 10 days. These results suggest that some differencesin the dynamical fields between the SA and PPA versions
occur owing to the different extent of the ozone depletion.
[27] Figure 10 shows the difference of the zonal mean
zonal wind in the ensemble mean between the SA and PPA
versions (SA minus PPA) over 64S, where a zonal windmaximum exists. The zonal mean zonal wind of the upper
stratosphere in the SA version is larger than that in the PPA
version from the middle of October to the end of January of
the following year. This indicates that the onset of thewesterly wind deceleration is delayed and therefore theduration of the polar vortex is longer in the SA version.
[28] The stronger polar vortex in the SA version is causedby the larger latitudinal gradient of temperature, resulted
from the smaller net diabatic heating due to the larger polarozone depletion in the SA version. A resultant delay of thepolar vortex breakup prevents the transport of ozone-rich air
masses at lower latitudes into the polar region. This is apossible reason that the ozone recovery over Antarctica isdelayed in the SA version.
4.2.3. Variances of the Ensemble Experimentsin the Ozone Recovery Phase[29] In sections 4.2.1 and 4.2.2, only the results of theensemble means are described. However, after the middle ofDecember, large ozone variances are shown over Antarctica(see Figure 6), when the ozone recovery is dynamicallycontrolled. In this section, all ensemble members are examined to investigate whether each member actually shows the

Figure 10. Time-height cross section of the zonal mean zonal wind difference in the ensemble mean
between the SA and PPA versions (SA minus PPA) of the AGCM over 64S from June to February of thefollowing year. The shaded areas represent the difference values over 5 m s1. Smoothed results by 7-day
running mean are plotted.
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D21305Figure 11. Time evolution of the zonal mean total ozone at 80S and zonal mean zonal wind at 64S
and 50 hPa of typical ensemble members 5, 8, 11, and 16 in the PPA version (solid line) and in the SA
version (dashed line) of the AGCM.
variances that are expected from the statistical theory in theozone recovery period.
[30] In all members, there are strong correlations between
the zonal mean total ozone increase and the zonal mean
zonal wind deceleration during the ozone recovery phase.
This indicates that dynamical processes certainly play animportant role in the ozone recovery period. Most ensemble
members show that the polar vortex breakup and ozone

recovery processes are delayed in the SA version of themodel, which is expected from the effects of atmosphericsphericity on the chemical, radiative, and dynamical processes in the stratosphere, as described in previous section.
Figure 11 shows the typical time evolution of the zonal
mean total ozone at 80S and the zonal mean zonal wind at
64S and 50 hPa in the SA and PPA versions (for ensemble
members 5, 8, 11, and 16). However, four unusual cases

Figure 12. Same as Figure 11 but for the unusual ensemble members 9, 12, 18, and 21.
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Figure 13. Time evolution of the zonal mean ozone
destruction and production terms at 80S and 50 hPa in the
SA version (solid lines) and the PPA version (symbols) of
the nudging CTM from January to December 1999. Black,
red, dark blue, dark green, pink, and dark yellow colors
indicate the ozone destruction rates due to Ox, HOx, NOx,
the ClO-ClO cycle, the BrO-ClO cycle, and the ozone
production rate due to oxygen photolysis, respectively.
(ensemble members 9, 12, 18, and 21) are found, where thetotal ozone recovery and the polar vortex breakup occur
earlier in the SA version, as seen in Figure 12.
[31] If these unusual cases are ignored, the total ozone
difference in the ensemble means between the SA and PPA
versions becomes statistically significant at the 95% level
until the middle of January of the following year (notshown). Therefore the large variance in the ozone recovery
period is caused by the unusual behavior of a few ensemble
members, which most members do not show. These results
justify the hypothesis from the ensemble means that thechemical, radiative, and dynamical coupling processes inthe stratosphere, described in previous section, mainly
explain the delays of the polar vortex breakup and theresultant ozone recovery over Antarctica in the SA versionof the AGCM. Further analysis of the unusual cases is
described in section 5.2.

D21305tion and production terms at 80S and 50 hPa in the SA andPPA versions of the nudging CTM is plotted in Figure 13.
The ozone destruction rates due to Ox, HOx, and NOx
processes are calculated following the method of Fahey etal. [2000]. The ‘‘2J[Cl2O2]’’ and ‘‘2k[ClO][BrO]’’ represent the ozone destruction terms of the ClO-ClO and ClOBrO cycles, respectively, and the ‘‘2J[O2]’’ represents theozone production term. From mid-February to the onset ofthe polar night (mid-April), the NOx, HOx, and Ox cycles
are the main contributors to the ozone destruction, and thecontribution of the ClOx and BrOx cycles are negligible. In
the SA version, the ozone destruction terms of the NOx,HOx and Ox cycles are slightly larger and continue a little
longer than those in the PPA version before the onset ofpolar night. This is due to the actinic flux at SZAs larger
than 90 and is the reason for the initial increase of thedifference.
[34] For the investigation of the latter increase of thedifference, which starts at the beginning of July, a passive
tracer ozone experiment using the SA version of thenudging CTM is executed. In the experiment, the chemicalchange of ozone is ignored at and to the south of 80S andat 50 hPa from 20 June, slightly before the latter increase of
the difference starts. Figure 14 shows the temporal evolution of the ozone mixing ratio in the original experiment andthe passive tracer ozone experiment. The difference between
the solid and dotted lines in Figure 14 represents the effectof local chemical ozone destruction at and to the south of80S and at 50 hPa. Just after 18 August, the difference
begins to increase because the upward actinic flux initiatedthe local photochemical ozone loss (see section 4.1). Before
the end of the polar night, on the other hand, there arealmost no differences between the experiments and thepassive tracer ozone experiment already shows the larger
decline in ozone concentration compared to the PPA version. All these results indicate that the time evolution ofozone at 80S and 50 hPa is affected by the advection of
low-ozone concentration air masses from lower latitudes

5. Discussion
5.1. Analysis of the Different Time Evolutions of Polar
Ozone Between the SA and PPA Model Versions Before
the End of the Polar Night[32] In sections 4.1 and 4.2 we indicated that the differences in the total ozone at 80S and the ozone mixing ratio
at 80S and 50 hPa between the SA and PPA versions
already existed even before the end of the polar night. In the
nudging CTM these differences started to increase frommid-February to mid-April and then remained almost constant until the end of June. After that, at the beginning ofJuly, the difference started to increase again and reached amaximum at the end of August. The situation was almost
the same in the AGCM.
[33] In order to investigate the initial increase of thedifference, time evolution of the zonal mean ozone destruc-

Figure 14. Time evolution of the zonal mean ozone
mixing ratio at 80S and 50 hPa from June to December
1999 in the original experiment and the passive tracer ozone
experiment using the SA version of the nudging CTM. Solidand dashed lines indicate the results from the original
experiment and the passive tracer ozone experiment,
respectively. Ozone is assumed to be a passive tracer atand to the south of 80S and at 50 hPa from 20 June.

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D21305Figure 15. Time evolution of the vertical component of the EP flux averaged over 40 – 80S and at
100 hPa in the PPA version (solid line) and the SA version (dashed line) of the AGCM. (left) Typicalcases (5, 8, 11, and 16) and (right) unusual cases (9, 12, 18, and 21).
and higher altitude, where ozone destruction processes startearlier because of the actinic flux at SZAs greater than 90.
5.2. Analysis of the Statistical Variances of theEnsemble Experiments in the Ozone Recovery Phase[35] The Eliassen-Parm (EP) flux for the eight ensemble
members in Figures 11 and 12 is calculated in order toinvestigate what causes the behavior of the zonal mean totalozone and the zonal mean zonal wind in the unusual cases.
Figure 15 shows the time evolution of the vertical component of the EP flux averaged over 40 – 80S and 100 hPa
for the eight ensemble members. In the unusual cases
shown in the right column of Figure 15, the magnitude of
the EP flux in the SA version becomes larger than that in
the PPA version just before the total ozone in the SA
version rapidly rises (see also Figure 12 around 20 Octoberin 9, around 25 December in 12, around 5 November in 18,
and around 15 December in 21). The EP flux at this level
expresses the wave flux from the troposphere into thestratosphere. Therefore, in the SA version of the unusual
members, the wave flux from the troposphere into thestratosphere dominantly controls the timing of the ozone
recovery, overwhelming the effects of the atmosphericsphericity on the modeled radiation field in the Antarctic
stratosphere. In the typical cases, on the other hand, thecorrelation between the EP flux enhancement and the ozone
rise in the SA version is not as clear as that in the unusualcases. For example, the EP flux enhancement in the SA
version is found around 20 October and 10 November in 11
and around 5 October in 16, but the total ozone amount in
the SA version did not exceed that in the PPA version justafter these dates (see Figure 11). The EP flux at 200 hPa is
also examined and a very similar result is found (notshown).

[36] In most cases, the polar vortex breakup is delayed in
the SA version because of the chemical-radiative-dynamical
coupling effects of the atmospheric sphericity in the stratosphere. However, the analysis of each ensemble member
shows that the increased wave flux from the troposphereis sometimes a more effective determinant of the timing of
the polar vortex breakup than the effects of atmosphericsphericity in the stratosphere.
5.3. Influence of Neglecting Refraction and Heating
Due to the Solar Radiation Flux at SZAs Larger
Than 90°[37] The new radiative transfer scheme does not include
the two factors, namely, refraction and the heating effects of
the radiation flux at SZAs larger than 90. Neglecting theseprocesses may have an influence on Antarctica during theozone hole period [Lary and Balluch, 1993; Balluch andLary, 1995; Herman et al., 1995; Swartz et al., 1999;
Trentmann et al., 2003; Uhl and Reddmann, 2004].
[38] By considering the effects of refraction, maximum
SZA at the edge of the polar twilight region becomes larger
by about 1 at 50 hPa (i.e., the apparent SZA is 1 less),which would make the onset of the ozone loss occur several
days earlier. Furthermore, the refraction effects increase theoptical transmittance and may strengthen the ozone destruction due to photochemical catalysis [Uhl and Reddmann,2004]. Thus the introduction of refraction will enhance theeffects of atmospheric sphericity.
[39] With respect to heating rates, Lary and Balluch[1993] suggested that ignoring the heating effects at SZAs
larger than 90 might lead to the large latitudinal heating
rate gradient and misrepresent the structure of the generalcirculation, particularly in the region close to the polar night(and polar day). Furthermore, it may be possible that the

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increased temperature in the polar stratosphere by theheating due to the solar radiation flux at SZAs larger than90 prevents heterogeneous chemistry and attenuates further
ozone loss. However, the radiative heating at SZAs larger
than 90 may have a dominant effect only in the period
before the radiation flux at SZAs smaller than 90 reaches.
Therefore the effect on the timing of polar vortex breakup
might be limited. These possibilities must be examined
carefully in a future study.

6. Conclusions[40] The effects of atmospheric sphericity are incorporated
into the CCSR/NIES nudging CTM and AGCM withcoupled chemistry. The plane-parallel radiative transfer
scheme of both models is modified using a pseudosphericalapproximation. We perform the integration of the nudging
CTM and the ensemble runs of the AGCM with coupledchemistry for both the SA and PPA versions. The chemical
processes and coupling effects of the chemical, radiative,and dynamical processes over Antarctica during an ozone
hole period are analyzed.
[41] In the SA versions of both the nudging CTM and theAGCM, the onset of an ozone loss over Antarctica shifts toearlier dates, and the minimum value of the total ozone
becomes lower in comparison with the corresponding PPA
versions. The earlier reduction in the ozone mixing ratio in
the SA version is caused by an earlier increase of the ClO
mixing ratio, which is initiated by the upward actinic flux at
SZAs greater than 90. During the ozone recovery period,
however, the ozone distribution becomes almost the same in
the SA and PPA versions of the nudging CTM, while in the
AGCM the ozone amount of the SA version remains atlower values compared to that of the PPA version.
[42] In the SA version of the AGCM, the larger ozone
loss over Antarctica makes the diabatic heating smaller andtemperatures lower in comparison with the PPA version.
This enhances the latitudinal gradient of temperature andthus strengthens the polar vortex in the SA version. These
processes cause the delayed ozone recovery over Antarctica
by preventing the transport of ozone-rich air masses fromlower latitudes into the polar region.
[43] In the AGCM ensemble experiment, there are large
ozone variances after the middle of December, when theozone recovery is controlled dynamically. Most ensemble
members show the delay of the polar vortex breakup in the
SA version, but a few members show opposite results. In thelatter members, the polar vortex breakup in the SA version
is strongly affected by the enhanced wave flux from thetroposphere, which causes the variances in the ozone
recovery period. Most members, however, do not show
large statistical variances, that justifies the conclusions fromthe ensemble means.
[44] Acknowledgments. The authors thank the late A. Numaguti andother members for the development of the CCSR/NIES AGCM, T. Imamura
for useful discussions, and anonymous reviewers for helpful comments.
Computations were made on a NEC SX-6 computer at CGER (Center for
Global Environmental Research) of the NIES. The GFD-DENNOU library
and GTOOL were used for drawing the figures. This work was supportedby the Global Environmental Research Fund of the Ministry of theEnvironment (MOE) of Japan and by a grant-in-aid for scientific researchfrom the Ministry of Education, Culture, Sports, Science and Technology(MEXT) of Japan (16540405).

D21305

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H. Akiyoshi, T. Nagashima, and H. Nakane, National Institute forEnvironmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan.
(hakiyosi@nies.go.jp; nakane@nies.go.jp; nagashima.tatsuya@nies.go.jp)
J. Kurokawa, Fujitsu FIP Corporation, TIME24 BLDG., 2-45 Aomi,
Koto-Ku, Tokyo 135-8686, Japan. (kurokawa@fip.fujitsu.com)
H. Masunaga, Department of Atmospheric Science, Colorado State
University, Fort Collins, CO 80523, USA. (masunaga@atmos.colostate.
edu)
T. Nakajima and M. Takahashi, Center for Climate System Research,
University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568,
Japan. (teruyuki@ccsr.u-tokyo.ac.jp; masaaki@ccsr.u-tokyo.ac.jp)

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