A three-dimensional chemical transport model (CTM) (Kaminski, 1992) has been used to study the evolution of the Arctic ozone during the winter of 1992. The continuity equation has been solved using a spectral method with Rhomboidal 15 (R15) truncation and leap-frog time stepping. Six-hourly meteorological fields from the Canadian Meteorological Center global objective analysis routines run at T79 were degraded to the model resolution. In addition, they were interpolated to the model time grid and were used to drive the model from the surface to 10 mb. In the model, processing of Cl(x) occurred over Arctic latitudes but some of the initial products were still present by mid-January. Also, the large amounts of ClO formed in the model in early January were converted to ClNO3. The results suggest that the model resolution may be insufficient to resolve the details of the Arctic transport during this time period. In particular, the wind field does not move the ClO(x) 'cloud' to the south over Europe as seen in the MLS measurements

Kaminski, J. W.

Mcconnell, J. C.

Sandilands, J. W.

English

NASA Technical Reports Server

N95- 11019
Calculations of Arctic Ozone Chemistry
Using ObJectively Analyzed Data in a 3-D CTM
by
J.W. Kami_ski 1 J.C. McConnell la,a j. iV. Sandilands 3
1Centre for Research in Earth and Space Science,
2Department of Earth and Atmospheric Science,
aDepartment of Physics,
York University, North York, Ontario, Canada
Abstract
A three-dimensional chemical transport model (CTM)
(Kaanifiski, 1992) has been used to study the evolution of
the Arctic ozone during the winter of 1992. The continu-
ity equation has been solved using a spectral method with
Rhomboidal 15 (R15) truncation and leap-frog time step-
ping. Six hourly rneteorological fields from the Canadian
Meteorological Centre global objective analysis routines
run at T79 were degraded to the model resolution. In ad-
dition, they were interpolated to the rnode] time grid and
were used to drive the model from the surface to 10 mb.
In the model, processing of CI_ occurred over Arctic lati-
tudes but some of the initial products were still present by
mid-January. Also, the large amounts of CIO formed in
the model in early January were conw!rted to CINO3. The
results suggest that the model resolution may be insuffi-
cient to resolve the details of the Arctic transport during
this time period. In particular, tile wind field does not
move the CIO, 'cloud' to the south over Europe as seen in
the MLS measurements.
Introduction
Although the dynamical situation during the Arctic
winter is less stable than that in Antarctica and the tem-
peratures are not as cold, Polar Stratospheric Clouds (PSC'
type I and type II PSCs do form (eg. GRL, 1990). Also, air
remains in the vortex sutticiently long that there may be
extensive processing (eg., McConnell et al., 1991) so that
CI_ may be converted to active forms of chlorine within
extensiw' regions of the polar vortex. This has clearly
been observed during the Arctic Airborne Stratospheric
Expedition (AASE) during the winter of 1989/90 where
enhanced levels of ttrO and (JlO were observed along with
some denitrification ((',Ill,, 1990). l"u,ther, the microwave
limb sounder (MLS) inslrume,lt on hoard the lrAIIS satel-
lite has observed extensive _clouds' of C10 oww northern
latitudes and as far south as the Mediterranean (Waters
et el., 1992).
In this note we present the results of an attempt to sim-
ulate the dynamics and chemistry of Arctic stratosphere,
and in particular the formation of the ClO 'cloud' observed
over Northern Europe during the 1991/1992 winter (eg.
Waters et al., 1992). The York Chemical Transport Model
(CTM) (Kamifiski, 1992) was run in an off line mode from
December 15th to January 22nd. The CTM was driven
by the objectively analyzed wind and temperature data
generated by tile Canadian Meteorological Centre (CMC)
global spectral model (l/itchie, 1991) run in the Analysis
Cycle (zero hour forecast at 00Z, 06Z, 12Z, and 18Z was
used). The CMC's global objective analysis (OA) stops
at I0 rob. The upper level temperature fields are inverted
from satellite observations (T()VS), and the wind fields
are derived from temperature.
The chemistry in the model consists of 49 reactions
(which includes gas phase, heterogeneous and photochem-
ical reactions) and 21 species. The following heteroge-
neous reactions were included
C1ONO_(g) + ttCl(s) --, C12 + ItNO3(s) (1)
N2Os(g) + ItCl(s) _ CINO2(g) + ttNO_(s) (2)
CIONO_(g) + tt_O(s) --_ tlOCl(g) + HNOa(s) (3)
N2Os(g) + lt20(s) --_ 2tlNOa(s) (4)
and were activated by temperature switches. For T < 195
K the reactions (1) and (2) were activated, while for
T < 190 K the reactions (3) and (4) were added. Al-
though this does not simulate the details of the effects
of processing by type I and lI PSCs it should produce
the correct general conw_rsion from inactive tbrms of CI,
to active forms, CIO_. We define ('1_, = C10_ + IIC1 +
CINO3 and C10_ = CI + 2C12 + (110 + IIOCI + CINOe
+ 2C1_O_.
Seven tracers are used: O_, CIr., NO> Ctt.I, N20, f120
and passive- O3. Tim passive tracer ),as the mixing ratios
of the initial Oa field and provides a ineasurc of Ihe cf
fects of transport without ('}lemistry and is thus l,articu-
larly useful for comparing wilh the chemically aclive ():_
field. In addition, it provides a useful ('beck for the mass
492
https://ntrs.nasa.gov/search.jsp?R=19950004606 2020-06-16T11:32:56+00:00Z
conservationpropertiesof the code. For this experiment
a half-hour dynamical time step (required by the CFL
condition) and a 1.5 hour chemical time step are used to
calculate the species concentrations. The chemical time
step of 1.5 hours was selected in order to adequately sim-
ulate the diurnal behaviour of the Arctic chemistry. The
chemistry solver is stable and previous experiments have
indicated that much longer time steps could be used. The
J values are evaluated by means of a look-up table at
each chemical time step. A two dimensional look-up ta-
ble is generated using combinations of the logarithm of 02
and 03 optical thickness, and temperature, depending on
the d value. Currently we allow the d value look-up ta-
bles to have a rnaximum error of about 5% as compared
with those generated by a detailed wavelength integration
method (cf. Henderson et al., 1987).
The CTM employs a spectral solution to the conti-
nuity equation (eg. Williamson et al., 1987) and was
run with Rhomboidal 15 (R15) truncation, correspond-
ing to 48 longitudes by 40 latitudes in grid space. A
leapfrog scheme in spectral space, and a finite difference
scheme in the vertical are used to integrate the continuity
equation. The initial conditions, representative for mid-
December, were generated by a two-dimensional zonal
average model of the middle atmosphere that was sup-
plied by Dr G. Brasseur of NCAR (Brasseur et al. 1990).
The model was run from 15th December, 1991 to 22nd
January, 1992. Since this is a short note and the results
are extensive we have chosen to concentrate on the out-
put for a single day and a single pressure level, viz. the
30 mb surface on the 16th January, 1992.
Analysis and Conclusions
It is quite clear from a preliminary comparison of the
model Oz data with the TOMS Oz that the dynamical
field rapidly imposes its main features in a relatively short
period. A comparison between the model active and pas-
sive ozone and the TOMS ozone field is shown in Fig-
ure 1 for the 16th January, 1992. It can be seen that
many of the features exhibited by the TOMS ozone are
reproduced by the model. Noteworthy are the highs over
eastern North America and eastern Asia and the low over
the eastern Atlantic. There are several locations where
the detail is not good. However, considering the limited
resolution of the model and the fact that it presents a
snapshot whereas the TOMS data represent the ozone
field gathered over a day we consider the agreement quite
reasonable. Since the effects of chemistry in the polar re-
gions are marginal over this short time period what we
are seeing in the model is largely the effects of transport.
This is also seen in a comparison of the active and passive
ozone fields in Figure 1. At low latitudes the difference
between the passive and active ozone is due to the ef-
fect of substantial ozone generation, as expected, due to
photolysis of 02. The effect of ozone depletio_ at boreal
latitudes is not immediately evident and still requires fur-
ther quantification. We note that the model ozone highs
are within 5% of the TOMS data.
At the beginning of the simulation the temperature
is sufficiently cold to form PSC type I and the hetero-
geneous reactions listed above are activated. During the
second week of January, 1992 the boreal temperatures are
warmer than 195 K and there is no further formation of
active chlorine. Figure 2 shows time series of the percent
volume of air within each layer that has (a) temperatures
less than 190 K, (b) temperatures less than 195 K and (c)
temperatures less than 200 K for latitudes greater than
50 ° N. It shows quite dramatically the evolution of the
processing in the model. The 200 K temperature was in-
cluded because the CMC temperatures in this region of
the stratosphere for this period of the ka-ecast were prob-
ably up to 5 degrees too wlrm (Dr H. Ritchie, private
communication, 1992; this problem with the stratospheric
temperatures has now been cot'v_ted).
Although the processing has finished by the 16th of
January it takes several weeks for the processed air to
be reconverted back to HC1 and CINOs (eg. Henderson
et al., 1990). This is indicated in Figure 3 which shows
the fields for HCI, CIO_, and CINO3 on the 30 mb level
for 00Z on the 16th January, 1992. Figure 3a shows that
a large region of HCI has been completely processed to
active chlorine and has not been reformed. At the time of
the snapshot the hole in the HCI field is over Greenlasrd
and northern Europe. Other regions with low values are
due to transport effects which are immediately apparent
in the CI_ field (not shown). Furthermore, we note that
there as almost no PCS type II activated in the model.
The active chlorine field, C10_, is shown in Figure 3b.
It is similar in shape to the processed HCI hole, but some-
what smaller and this is significant as illustrated later.
The peak CIO_ mixing ratio is 3.6 ppb. The C1Offi it
composed mainly of CINO2, HOC1 and C12 with peak
mixing ratios ,,_ 2.2 ppb (over Greenland), ,,_ 0.45 ppb
over Scandinavia and _ 0.6 ppb over Greenland, respec-
tively. C1_O2 and CIO are relatively small components
of the C10_ field. The fact that CINO_, HOCI and Ci2
predominate, indicates that the air in this region has not
seen the sunlight otherwise it would have been processed
into CIO and C1202. Given that the MLS measurements
of Waters et al. (1992) show several ppb of C10, our re-
suits indicate that there may be serious problems with
the dynamical field run at R15.
The missing CI_ between the HCI hole and the CIO,
'cloud' is found as CINOs and is shown in Figure 3c. It
appears as a collar of CINOa around the CIO_ 'cloud' with
the highest values ,-_ 3 ppb occurring over northern Russia
and with mixing ratios _ 1 ppb around the collar. What
appears to have occurred is tl_ HCI has been processed
and the products photolyzed to form C|O. This has then
reacted with the NO2 present in the model to form CINOs.
493
Figure1. a)Active,b)passiveandc) TOMScolumnozoneforthe 16th
January, 1992
a) b) c)
30
2O
10
3O
_n
tO
2O
10
2O
10
151_¢
a = 0.0148
a : 0.0221
a = 0.0331
a = 0.0493
20_10
-t
3O
2O
10
3O
2O
I0
15Dc¢ 22Doc22Due 29De¢ 5Jan 12Jan IIJan 29Dec 51_ 12lm lSJan
"I'mw T'wae
30
30
I0
2O
I0
20
l0
ISDec Z2 I_e¢ 29Dec 5Jan 12Jan |il Jmm
Figure 2. Time series showing the percent volume of air that has a) temper-
atures less than 190 K, b) temperatures less than 195 K and c) temperatures
less than 200 K for latitudes greater than 50 ° N (time sries are shown for 4
model levels).
b) :)
Figure 3. a) The ttCI mixing ratios on the 30 mb surface for 00Z on the 16th
January 1992 using tile CTM showing the region of reduced mixing ratios
due to processing simulated by the model; b) CIOx c) C1NOa.
494
WenotethatwehavenotincludedanyprocessingofN_Os
in themodelto HNOsbystratosphericaerosolswhich
wouldoccuratalltemperatures.Thiswouldremoveany
N205formedinthemodelandsotheNO_.Wefindthat
N205mixingratiosare-_ 1-3 ppb in the polar region
(> 50 ° N) and NO_ values are < 2.5 ppb. However, this
would be adequate to convert any free C10 to CINO3
on a time scale of a day. The edge of the C1NOa collar
reaches as far south as northern France. This is about
1 model grid point further north than measured by the
MLS instrument for earlier dates. Again, we suspect that
this is due to the limitations of the R15 simulation and
possibly poor representation of the N205 as mentioned
_,bove.
Waters, J.W., L. Froidevaux, W.G. Read, L.S. Elson, E.F.
Fishbein, T. Lungu, D.A. Flower, R.F. Jarnot, Strato-
spheric C10 and O3 measured by the Upper Atmosphere
Research Satellite (UAI{S) Microwaw_ lamb Sounder (MLS)
experiment. Quardenial Ozone Symposium, 1992.
Williamson, I).L., J.T. Kiehl, V. Ramanathan, R.E. Dick-
inson, J.J. Hack, Description of NCAR Community Cli-
mate Model (CCM1), NCAR/TN 285+STR, Boulder, Col-
orado, USA, 1987.
Acknowledgments
This work was supported by the Atmospheric Environ-
ment Service of Environment Canada and by the Natural
Science and Engineering Research Council of Canada. We
wish to thank Dr G. Brasseur for the use of his 2-D model
output used in the development of the initial conditions.
Dr H. Ritchie of RPN in Dorval was very helpful in dis-
cussing the use of the CMC spectral forecast model.
References
Brasseur, G., M.H. Hitchman, S. Walters, M. Dymek, E.
Falise, and M. Pirre, An interactive chemical dynamical ra-
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J. Geophys. Res., 95, 5639-5655, 1990.
G.R.L., Geophys. Res. Left., 17, 313-564, special issue,
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Henderson G.S., J.C. McConnell, and W.F.J. Evans, The
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Henderson, G.S., W.F.J. Evans, J.C. McConnell and E.M.J.
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495


Calculations of Arctic ozone chemistry using objectively analyzed data in a 3-D CTM

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