We have studied the development of the austral ozone hole using a 3-D spectral chemical transport model at R15 resolution for the period 15th September to 15th October, 1991. The model is driven by objectively analyzed wind fields obtained from the Canadian Meteorological Center and uses the chemical module developed by Kaminski (1992). Although extensive processing of NO(y) and Cl(x) occurs within the model, the ozone hole that develops appears shallow and ephemeral. Analysis of the results indicate that the meridional transport of ozone is sufficient to overwhelm the substantial chemical depletion that does occur. We suggest that the low resolution objectively analyzed data used is unable to capture the essential isolated nature of the vortex

Beagley, S. R.

Kaminski, J. W.

Mcconnell, J. C.

Mcfarlane, N.

Sandilands, J. W.

English

NASA Technical Reports Server

N95- 11023
MODELLING STRATOSPHERIC POLAR OZONE
USING OBJECTIVE ANALYSIS
J. IV. Sandilands 1,j. W. Kamiriski 2, J.C. McConnell 1,2.a
S.R. Beagley 3, and N. McFarlane 4
XDepartment of Physics, York University,
2Centre for Research in Earth and Space Science, York University,
3Department of Earth and Atmospheric Science, York University,
4Atmospheric Environment Service,
North York, Canada
Abstract
We have studied the development of the austral ozone
hole using a 3-D spectral chemical transport model at R15
resolution for the period 15th September to 15th October,
1991. The model is driven by objectively analyzed wind
fields obtained from the Canadian Meteorological Cen-
tre and uses the chemical module developed by Kaminski
(1992). Although extensive processing of NO v and Clz
occurs within the model the ozone hole that develops ap-
pears shallow and ephemeral. Analysis of the results in-
dicate that the meridional transport of ozone is sufficient
to overwhelm the substantial chemical depletion that does
occurs. We suggest that the low resolution objectively an-
alyzed data used is unable to capture the essential isolated
nature of the vortex.
Introduction
The formation of the Antarctic polar ozone hole in the
austral spring is a complex process involving temperatures
sufficiently cold for polar stratospheric clouds (PSCs) to
form, and dynamics that lead to the chemical isolation of
the polar vortex (eg. Solomon, 1990). PSCs provide the
surfaces upon which heterogeneous chemistry proceeds to
produce the precursors of ozone destruction. Due. to this
complex interaction of chemistry and dynamics, we have
used a three dimensional model to study the evolution of
ozone during this period.
This study uses the York University global spectral
stratospheric chemical transport model (CTM) (Kamifiski,
1992) with a R15 truncation (corresponding to 48 longi-
tudes by 40 latitudes in grid space). It uses objectively
analyzed wind fields as the source of the driving meteo-
rology to solve the continuity equation
OX___j_= -_.V)¢i +V(K.V)XI+ Pi _ L,X, (1)
Ot m
where Xi is the mixing ratio of the i'th species, Pi is
the chemical production term, Li is the chemical loss fre-
---+
quency, - V • X7 Xi is the advection term, _7(K • _TXi) is
the diffusion term, and m is the number density of the
atmosphere.
The version of the model used for this experiment has
been reduced from the previous 26 vertical levels to 15 ex-
tending from the surface to 10 mb, the height at which the
objective analysis stops. A leapfrog numerical scheme in
spectral space, and a finite difference scheme in the verti-
cal are employed to integrate the model's continuity equa-
tion forward in time. The chemistry in the model consists
of 49 reactions (which include gas phase, heterogeneous
and photochemical reactions) and 21 species. Seven trac-
ers are used: O_, CI_, NO2, CH4, N20, H20, and O3-
passive. The passive tracer undergoes no chemistry, just
transport. Note that the chemistry has no brominated
species included, which means that the model will under-
estimate ozone destruction. This will be added to the
chemistry at a later time. A 30 minute dynamical time
step and a 1.5 hour chemical time step are used to calcu-
late the species future concentrations.
Objectively analyzed meteorological fields axe obtained
from the Canadian Meteorological Centre (CMC) and are
the source of the meteorology for the model. Fields in-
cluded in the objective analysis are divergence, vortic-
ity, temperature and surface pressure at 00, 06, 12, and
18Z. The CMC operational global spectral model (Ritchie,
1991) wasrun at R15 resolution in the Analysis Cycle and
the zero hour forecast was used. These objective analysis
fields are then interpolated to the model dynamical time
step.
The CTM was integrated over the 30 day period, from
September 15 to October 15, 1991 to study the conver-
sion of HCI and CINO3 to active chlorine and the den-
itrification of the polar stratosphere using the following
heterogeneous reactions
5O8
https://ntrs.nasa.gov/search.jsp?R=19950004610 2020-06-16T11:33:08+00:00Z
TOMS DarivedCe4umn Ozone (IX/)
1_1'74 O_l.l_l Column Orone (OUJ
O6v 274.ell • Oc_ I , 19ql
6 lie I_-- I_ 1_*g¢
4e( 1
• 1641£
./..
I -GM---- 18$
_IIV 168W
41W i41g
lleW
Figure 1. Column ozone amounts for October 1, 1991 for
TOMS and the model at OOZ.
CIONO2(g) + HCI(s) ---*CI_ + HNO3(s)
N2Os(g) + HCl(s) --* CINO_(g) + HNO3(s)
CIONO2(g) + H20(s) _ HOCI(g) + HNO3(s)
N2Os(g) + H20(s) ---* 2HNO3(s)
In the model, heterogeneous chemistry proceeds when the
temperatures are sufficiently cold (< 195K for type I PSCs
and < 190 for type II) for the production of PSCs. The
initial conditions for the chemistry were taken from a pre-
vious experiment run on the 26 level CTM (Kamifski,
1992) that used the two-dimensional fields of Garcia and
Solomon (1983). The initial ozone fields applied did not
exhibit an ozone hole at the beginning of the model run.
Due to the large volume of data generated over the course
of one model month, October 1st, 1991 has been chosen
as the one day concentrated on for the analysis, given the
brief nature of this communication.
Analysis
Figure 1 compares the model column 03 with the TOMS
data for October 1, 1991. Many of the features observed in
the collar surrounding the ozone hole are reproduced with
the model's wind fields. However, the depth of the hole is
far from being reproduced. The lowest amount during the
first 3 days of October is 134 DUs compared to the 122
DU for the TOMS minimum. However, the model atone
depletion has neither the temporal nor spatial extent that
is usually associated with an "ozone hole". At the end
of the model run on October 15 the lowest total column
ozone value is 227 DUs while the TOMS value for the
same period is 139 DUs. Interestingly enough, the model
stratosphere experiences two warmings, one on Sept. 25th
and another on October 10th, suggesting that the polar
vortex is breaking down. Indeed, a time series of total
column ozone over the pole shows the hole decreasing in
size as ozone rich air from lower latitudes replaces it due
to meridional transport into the vortex.
Figure 2 shows the major zonally averaged individ-
ual components of production and loss of odd oxygen
for both inside (73 ° S) and outside (51 ° S) the vortex.
The two production terms considered for Ox axe 02+hv,
and HO_+NO. There are six loss terms: O+Oa, O+NOa,
O+CIO, On+OH, Oa+HO_, and CI202+hv. Because of
the presence of heterogeneous reactions in the vortex, we
would expect to see the conversion of unreactive forms
of chlorine to more reactive forms, and denitrification of
the stratosphere, and this is indeed the case. Outside the
vortex there is approximate photochemical steady state
(PCSS) down to about 30 mb and extensive production
of ozone via photolysis of 0_. The major odd-oxygen loss
processes are due to NO_ + O, O + CIO, and O + 03.
Within the vortex, O2 photolysis is greatly reduced as is
the loss due to O + NO2 due to denitrification. Below
30 mb the main ozone losses are due to hv + C1202, O
509
Ox Chemical Prod/Loss Terms Inside Vortex
Latitude=73S Date-Oct/I/91 (Zonal Aversles)
llio ...... '..t,,I ........ Ix ' ', .... '/'1 ' ''/"J 2
"_.... '. / ,'\ ...'"ll I
Cl_O_+hw "-... 'z , t/" ,/
"--...I',,' ,."//"
/'f" "N3, , 'it- - - - -"J"J,' ""-1g <.,_+,,o ___f ""_'t
! k'f"-.-" :"/ i
V"-,""_×o+o, L" i
'"'1 ./".. . ._o_+ott/I-" "'-.. ,'r - ---./
' "--,2 ;' / /2xO+CIO I / "-'¢'\ / /
_. \..I 03+H02-_/'I .\,,/ /'/
3ee.o-_ _ , L,_ml ...... .t' , , , ,/_,ht" , , ,,,,,
1 eE.e2 1 e(+13 1 eE+o4 10E+_'_ I ._E+O+
cm-Is-L
is o-_
3I. O
.,0
P
1
lSl.i.
300. I
1 .IE*O2
Ox Chemical Prod/LosI Terms Outside Vortex
Latltude-51S Date-Oct/I/eL (Zonal AveraleI )
\ ........ I ........ i\ ...... ',"y' " 7'"b' '/ ..... "I
'\ ',,. I ,_ i /,_./ !
"" ""..,I // ./ 2xO+NO2
"_ 2xo+o_...,'X/ .:(/
', ,,',I,\"!/"o,+_v
_ / ..11 Iii r
', ,,/ ; / I
,'/I I",03+HO,
..,£.2" ', ! I "- o_+on
...Z, ', I !
.,/"/_ ',/ I
." / ' i
.. t / H02+ /, /
'/ / i
> _ %o+c,o / "/
t i i llt,l.J 'Xl **_LII_J * l l,NliH. 1 Jlln.
1 .0[*13 1 .@1E*$4 1 IIE-@5 I K+I6 1 I[-I7
cm-ls-i
Figure 2. Twenty four hour averaged odd-oxygen produc-
tion and loss rates (cm -3 s -1) for (a) inside (73 ° S) and
(b) outside (51 ° S) the vortex.
30.0
,.0
t_
I@o.0
Continuity Equation Components Inside Vortex
Lastitude-738 Data=Oct/I/91 (Zone[ AverageI)
"-'-t'- ..... .'/'1
>--/-_L. 1
c ," l, 'q
...... --:--......L ,,,;I
.-" D /; _/
../ , _ /' /
\ ............ _ /,' ,,1
• _ _ ......... ..=:1,,, ,,J
\.- .................. /, ,,'/
--,'_.. ..... ,f:;-';/
• _ -"---.y-" /" A
.......... --,,--- /.;-_
_!_ @ • i t Iliiitl 1 i lilllll_ I 1_1 lilllil l I ItllIII i I llIlJ
1 OE-Ib 1 0E-15 1.0E-14 1 0E-13 1 0E-12 1.0E-11 1 0E-10
@-I
Continuity Equation Components OutIide Vortex
Latitude-SiS Date=Oct/i/g! (Zonll AveraleI _
,,,.. :L ......, ,,._ ...., ,, ......, ;.; ......
'> I/
I.- d
• C ..,<
_- _._-.. I .-_'-" /( .
z -'"" "'"< / _ "
:_ _ " / "-
II/ /__, '"
1 @E-14 1 @E-13 I @E-12 1 IE-11 I OE-1I
s-!
Figure 3. The zonally averaged dynamical and net chem-
ical components [or Oz for the version of the continuity
equat.ion described in the text for (a) inside (73 °) and (b)
outside (51 °) the vortex. Units are s -] and averaged over
one day. The terms A, B, C, D, E, and F, are described
in the text.
510
+ CIO and OH + 03 with a combined loss rate of ap-
proximately 6.25 x 10 s cm -3 s -1 at 50 mb which is about
6.25 x 101° ozone molecules cm -a day -1 or about 1.2%
per day. Thus, if this persisted for a period of about a
month, we might expect a 30-40% decrease in the ozone
column (even if bromine chemistry were added this would
only add an additional 10% (cf Henderson et al., 1990)).
However, the net loss is much less than this as can be seen
in Figure 1.
The reason for the lack of decrease of ozone is shown in
Figure 3 which shows the various dynamical and net chem-
ical components of the continuity equation. The labelled
curves of the figure are as follows. A is the negative of hor-
izontal advection term, B is the vertical advection term, C
is the horizontal diffusion term, D is the total mixing ratio
tendency, E is the total Ox chemical production term, and
F is the total Oz chemical loss term. Outside the vortex at
l0 mb the chemistry terms are larger than the dynamical
terms. But in the 30-100 mb region the dynamical terms
dominate the chemistry. Inside the vortex the dynamical
terms are between 5 to 10 times larger than the chemical
terms at all heights. At these latitudes the main terms are
the horizontal and vertical advection terms which are in
approximate balance: the chemical loss is superimposed
on this dynamically active situation. Thus, in spite of
extensive ozone loss the transport from lower latitudes in
the model dominates the vortex ozone budget. This exces-
sive transport may be a consequence of the inadequacies
of the low resolution CMC objectively analyzed data in
being unable to correctly provide a description of the im-
portant vortex dynamics during the period (cf. Kamlnski
et al., 1992). In particular, the transport resulting from
the two previously mentioned model warmings needs to
be more critically examined to assess the accuracy of the
CMC data in describing the temperature and wind evo-
lution during these events.
Conclusions
At the Symposium we had anticipated that the problem
resided in the temperature fields being too warm. Even
though we have found that there was indeed a tempera-
ture error with the CMC stratospheric temperatures this
is clearly not directly (in terms of heterogeneous chem-
istry) the major problem. The problem in simulating the
generation of the ozone hole lies with the excessive trans-
port of ozone which may in part be due to the temperature
field (which is used to provide the forecast field at 6 and
18Z, when radiosonde data is not available).
The zonal average temperatures near the beginning
and at the end of the run suggest that the temperatures
from the objective analysis might be too warm by as much
as 5 degrees (Dr. H. Ritchie, private communication,
1992). This implies that the winds are also effected, as
they are derived from the temperature. As an aside, the
temperature problems in the stratosphere have since been
investigated and fixed by CMC. Also the warming rates
might be too high, as at 10 mb over the south pole there
is a warming of almost 40K in 25 days. These points seem
to suggest that the objective analysis itself doesn't accu-
rately reflect the dynamical processes over the southern
hemisphere. The major problem may be the low resolu-
tion at which the CMC objectively analyzed data have
been used and further work will investigate this effect.
Acknowledgements
The authors wish to thank the Atmospheric Environment
Service of Environment Canada, and the Natural Science
and Engineering Research Council of Canada for their
continuing support. In addition, we also would like to
thank Dr. H. Ritchie of RPN, Dorval for useful discus-
sions regarding the objective analysis program of CMC,
and Dr. S. Solomon for providing the 2-D initial fields.
References
Garcia, R.R., and S. Solomon, A Numerical Model of the
Zonally Averaged Dynamical and Chemical Structure of
the Middle Atmosphere, Journal of Geophysical Research,
88, 1379-1400, 1983. Henderson, G.S., W.F.J. Evans and
J.C. McConnell, Effects of Initial Active Chlorine Con-
centrations on the Arctic Spring Depletion, Journal of
Geophysical Research, 95, 1899-1908, 1990.
Kamifiski, ,1.W., Study of Stratospheric Chemistry Us-
ing a Three-Dimensional Spectral Chemical Transport
Model, Ph D. Thesis, York University to be submitted,
1992.
Kamifiski, J.W., J.C. McConnell and J.W. Sandilands,
Calculations of Arctic Ozone Chemistry Using Objectively
Analyzed Data in a 3-D CTM, These Proceedings, 1992.
Ritchie, H., Application of the semi-Lagrangian method
to a multilevel spectral primitive--equations model, Q. J.
R. Meteorol. Soc., 117, 91-106, 1991.
Solomon, S., Progress Towards a Quantitative Understand-
ing of Antarctic Ozone Depletion, Nature, 347, 347-354,
1990.
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