20 Dec 1991 - quirement of these models therefore is a good simulation of total ozone. ... Units are in parts per billion by volume (ppbv), parts per million by volume (ppmv), and parts per trillion by .... q'â¢--â¢o-⢠may be ....... ,4 xx;ith tho oetâ¢mato nf â¢-â¢nltnn [1 qqfll .... these. The number of 14C atoms lost per unit time is equal to.
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 96, NO. D12, PAGES 22,559-22,572,DECEMBER 20, 1991
The Influence of Dynamics on Two-Dimensional Model Results'
Simulations of 14CandStratospheric AircraftNOx Injections CHARLES H. JACKMAN
AND ANNE
R. DOUGLASS
Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland KURT
F. BRUESKE
Research and Data Systems Corporation, Greenbelt, Maryland STEPHEN
A. KLEIN
Department of Atmospheric Science, Seattle, Washington
A two-dimensional(2D) photochemicalmodel (latitude range from -85 ø to + 85ø and altitude range from the ground to 0.23 mbar (about 60 km)) has been used to investigate the influence of dynamics on model results. We tested three representationsof atmospherictransport to simulatetotal ozone and
14Camounts afternuclear testsintheearly1960s. Wealsosimulated threescenarios ofNOx injections from a proposed fleet of stratospheric aircraft and their effects on ozone. The three dynamical formulations used were Dynamics A, a base dynamics used in previous work with this model' Dynamics B, a strongcirculation dynamics discussedby Jackman et al. [ 1989a]' and Dynamics C, the
dynamicsusedby Shia et al. [1989].The advectivecomponentof the stratosphereto tropospheremass
exchange rate(advective strat/trop exchange rate(ASTER)) is largestfor Dynamics B (5.8 x 1017k1 17 1
yr-)and smallest forDynamics C(1.4 x 10 kgyr-),with the ASTER forDynamics A(2.4 x 10lq 1
14
kg yr- ) beingbetweenthesetwo extremes.Simulationsof both total ozone and C were worst with
Dynamics B. Simulations of totalozonewerebestwithDynamics A andfor 14CbestwithDynamics C. This illustrates the difficulty of simultaneously modeling constituents with different altitude and
latitudedependencies.Ozone depletionfrom NO x injectionsof stratosphericaircraft showeda strong sensitivity to dynamics. Generally, if eddy diffusion is not changed, then a large ASTER leads to reducedozonelosswhile a smallASTER leadsto increasedozone lossfrom a given stratosphericNOx injection.
1.
INTRODUCTION
Pyle, 1980; Garcia and Solomon, 1983; Ko et al., 1984;
Two-dimensional (2D) models are used extensively to study the middle atmosphere. These 2D models, while particularly suitable for assessmentstudies [World Meteorological Organization (WMO), 1990], are also used in a variety of other applications to understand atmospheric behavior [e.g., Garcia et al., 1984;Russell et al., 1984;Ko et al., 1986; Tung and Yang, 1988; Gray and Pyle, 1989; Legrand et al., 1989; Jackman et al., 1991]. Measurements of some species are especially useful to check the photochemistryof 2D models(e.g., OH and HO2) while measurements of other species (e.g., CFC13 and N20) are more useful to check the transport (advection and diffusion) of 2D models. Many stratosphericconstituentsare controlled by both transport and photochemistry, thus if there is a disagreement between model and measurement, it is often very difficult to decide which model aspect (transport or photochemistry) is in error. Stratospheric 2D models are used primarily to assessand predict total ozone levels in the atmosphere. A major requirementof these modelstherefore is a good simulationof total ozone. Several 2D models have achieved a reasonably good qualitative representation of the total ozone seasonal behavior when comparedto total ozone measurements[e.g., Copyright 1991 by the American Geophysical Union.
Stordal et al., 1985;Jackman et al., 1989a, b; Yang et al., 1991]. While a reasonable simulation of present-day total ozone amounts is a required condition of 2D models, good simulationsof ozone do not necessarilyimply good simulations of other atmospheric constituents. Other atmosphericconstituentswhich provide checks on the model dynamics include inert tracers. The radioactive
isotope14Chasa half-lifeof 5730years[Warneck,1988,p. 573]. Although recent observational [Tans et al., 1990] and modeling [Shia et al., 1989] evidence has cast doubt on the relative importanceof the oceansas a loss of carbon (relative to the continents), we have assumed that the oceans are the only significantmeans for surface loss of carbon and hence
14C.Carbon14 is rapidlyconvertedto 14CO2whichis photochemically inactive in the troposphere and stratosphere. The remainder of this paper is divided into seven sections. We discussthe atmosphericmodel employed in our research
and the three dynamicalformulationsin section2. Comparison of model
simulations
of total
ozone
for
the
three
dynamicalformulationswith total ozone mappingspectrometer (TOMS) measurementsare given in section 3. Baseline
modelsimulations of 14Cfor a nonperturbed atmosphere are discussedin section 4. We present model predictions of the
time-decay of 14Camounts fromnuclearexplosions in the
Paper number 91JD02510.
early 1960sin section5. Model assessmentsfor the changein
0148-0227/91/91JD-02510505.00
ozoneassumingNOx injectionsby stratosphericaircraft are 22,559
22,560
JACKMAN ETAL' MODEL SIMULATIONS OF14CANDNOxINJECTIONS TABLE 1. Lower BoundaryConditionsfor All TransportedSpeciesin Total Ozone Simulations Given in Figure 1 and for C1x PerturbationsDiscussed Perturbed
Species
Type of Boundary
1980 Value,
Value,
Condition,Units
Clx • 2.5 ppbv
Clx • 8.2 ppbv
300 1.6 100
360 3.2 100
N20 CH 4 CO
mixing ratio, ppbv mixing ratio, ppmv mixing ratio, ppbv
H 2 CH3OOH
flux,cm-2 s
mixing ratio,•pbv
500 0.0
CH3C1 CH3CC13 CC14 CFC13 CF2C12
mixing ratio, pptv mixing ratio, pptv mixingratio, pptv mixing ratio, pptv mixing ratio, pptv
700 100 100 170 285
0.1
500 0.0 700 100 100 800 2200
Ox
deposition velocity,cm s-1
HNO3
mixing ratio, pptv
90
90
0.1
NOy(wO HNO3) C1x
mixing ratio,•ptv flux, cm -2 s
10 0.0
10 0.0
Units are in partsper billionby volume(ppbv), partsper millionby volume(ppmv), and partsper trillion by volume (pptv).
given in section 6, while discussion and conclusions are presented in section 7.
same data set as the residual circulation.
The smallest values
allowed inthestratosphere are2 x 109 cm2 s-1. TheKyz representthe ratio of the mixing on isentropicsurfacesto the
2.
MODEL DESCRIPTION AND DYNAMICAL
FORMULATION
The 2D model used in this study is describedby Douglass et al. [1989] and applied in an assessmentof the atmosphere for a chlorine perturbation in Jackman et al. [1989a]. The model vertical coordinate is between the ground and 0.23 mbar (approximately 60 km), equally spacedin log pressure, with about a 2 km grid spacing,and the horizontal coordinate is from 85øSand 85øN with a 10ø grid spacing.The lower boundary conditions for the year 1980 are given in Table 1 for the modelbackground:•2.5 parts per billion per volume (ppbv) Clx input at the ground. Simulationsof other years include different lower boundary conditions and will be discussedbelow. The upper boundary conditions were assumed to be zero flux for all species. Reaction rates and photodissociation cross sections are taken from DeMore et al. [1987] and given by Douglass et al. [1989]. Three different dynamical formulations, Dynamics A, B, and C, were used in the model calculations.Both Dynamics A and B are describedand appliedto a chlorineperturbation
mixingonpressure surfaces andarecomputed fromtheKyy values and the potential temperature [Newman et al., 1988;
Jackman et al., 1988].TheKyyvaluesin thetroposphere are taperedup to the largestvaluesof 2 x 10•0 cm2 s-• at the ground.The vertical eddy diffusionKzz is assumedto be
smallin thestratosphere (2 x 103cm2 s-l), increasing with decreasing altitudefromthetropopause to 1 x 105cm2 s-• at the ground.
The Dynamics B residual circulation is also computed from heatingrates and temperaturesin the methodformulated by Dunkerton [1978]. Heating rates are taken from Rosenfield et al. [1987] for pressuresless than 100 mbar and from Wei et al. [1983] for pressures from 100 mbar to the ground. The temperatures and eddy diffusion parameters
Kyy, Kyz, and Kzz are the sameas discussed abovefor Dynamics A. Thus this transport differs from Dynamics A only in the residual circulation between the ground and 100 mbar.
The residual circulation and diffusion for Dynamics C is taken from $hia et al. [1989]. The transport coefficientsare bined circulation" and the "strong circulation," respec- originally given by Yang et al. [1990] for their isentropic2D tively. Dynamics C is describedby $hia et al. [1989]. When model. Yang et al. computed the diabatic circulation from usedto simulatethe behaviorof •4C, the three different the NMC 1980 temperature field and self-consistentlydeterdynamical formulations produce medium, large, and small mined the isentropic diffusion coefficients by solving the advective mass exchange from the stratosphereto the tro- momentum equation. Shia et al. have converted this isenposphere. tropically derived transport formulation to a 2D model with The Dynamics A residual circulation is computed using a pressure grid. Shiaet al. havealsospecified Kyy in the heatingrates and temperaturesin the methodformulatedby troposphere as 1 x 10•0 cm2 s- • and have fixed stratoDunkerton [ 1978].Heating rates are taken from Rosenfieldet spheric Kzzat 1 x 102cm2 s-• andtropospheric Kzzas1 x al. [ 1987]for pressureslessthan 100mbarandfrom Dopplick 105 cm2 s-•. [1974, 1979] for pressures from 100 mbar to the ground. Dynamics C has a circulation grossly similar in many Temperatures are defined from a 4-year average (1979-1983) respects to the circulation of Dynamics A. There are, of National MeteorologicalCenter (NMC) data for pressures however, subtle but important differences in the magnitude greater than 0.4 mbar and from COSPAR International of the vertical and meridional winds. The stratospheric ReferenceAtmosphere(CIRA) (1972)for pressureslessthan vertical and horizontal diffusionare quite differentbetween 0.4 mbar.The horizontal eddydiffusion coefficients (Kyy) Dynamics C and those used in Dynamics A and B. Vertical were derived from the flux and gradientof potentialvorticity diffusion(Kzz) in DynamicsC is lower thanthat in Dynamics using NMC temperatures [Newman et al., 1988] from the A andB by a factorof 20. The Kyyin DynamicsC havea by Jackman et al. [1989a] and are referred to as the "com-
JACKMAN ETAL ' MODELSIMULATIONS OF 14CANDNOx INJECTIONS
K•,•, (109cmz s-j) - Dyn A,B - March
60 •_.
_
_
50 '•'
1.0
/ 10.0
2oo
10< _
1000.0-9o-o-o
60
o
In a time-averagedglobal domainthe residualcirculation can be usedto provide at least a crude estimateof the mass exchangebetween the stratosphereand the troposphere. Consider a stratosphericvolume bounded below by the
K• (109 cmz s-j) - DynC - March o.1[_ .....
•
and seasons.
As an illustration of the differences between the different
values of eddy diffusion in Table 2.
90
LATITUDE(DEG)
v
latitudes
March from DynamicsA-B and C in Figures l a and lb, respectively.Fairly largedifferences asfunctionsof latitude and altitude are obviouswhen comparingthe two dynamical representations. It is impossible to discuss completelyall the dynamicaldifferencesin DynamicsA, B, and C. We do, however, summarizethe referencesused to representthe three dynamical formulationsas well as some relevant
30 -•
100.0 - •/•
tropospheric valuesover one grid box. Tropopauseheights in DynamicsA and B comparedwith DynamicsC, while mostlythe same,do showonegridbox differencesat certain
dynamical representations, we plot Kyy for the monthof
40 D
-
22,561
tropopause,aboveby the 50 mbar surface,and extending from 30ø to 90øN. The vertical mass flux through the
tropopause, Ftrop,is calculated according to
1.o
p0w* cos 2f 90øN
Ftrop= 2•rre
zl.O•
o.o
d 30øN
30
700 DU above80øN
-60
-90
0
60
1 20
1 80
240
300
360
for days 15-135),muchgreaterthan shownin TOMS data; DAY OF YEAR and (3) the southernhemisphereoff-the-polemaximumas Fig. 2. Total ozone from (a) TOMS and model simulationswith observedin the TOMS datais not predictedby the model. (b) DynamicsA, (c) DynamicsB, and (d) DynamicsC. Contour A modelsimulationwith DynamicsC doesa respectable intervals are spacingsof 20 Dobson units.
JACKMAN ETAL ' MODELSIMULATIONS OF 14CANDNOx INJECTIONS
22,563
job of representing total ozonewhencomparedwith TOMS 14Cin and out of the oceanapproximatelycancelsuchthat data (compareFigures 2a and 2d). The first two major the net flux of 14Cat the ocean-airinterfaceis only 0.05 -+ 0.015 of the flux of 14Cinto the ocean. Recent studies(modelingby Shia et al. [1989] and data and measurementinclude (1) the southern hemisphereoff- analysisby Tans et al. [1990]) have suggestedthat the the-polemaximumis not predictedby the model but is continentsmay be responsiblefor the largestlossesof CO2 observed in the TOMS data and (2) southern hemisphere from the atmosphere.We have investigatedthis suggested polarozoneamountsare muchlowerin the TOMS datathan land surface loss in a series of model sensitivity studies. predicted by the model. Althoughwe do not discussthesemodelexperimentsin any Model simulationsusingDynamics A give a slightlybetter detail,we notethatourcomputations of 14Carein better overall total ozone representationthan model simulations agreementwith observations when our surfacelossis only usingDynamicsC. Model simulationsusingthe large AS- dependenton the oceans.Furthermore,the stratospheric TER of Dynamics B show a poor representationof total resultsare relatively insensitiveto the boundarycondition
features noted in the TOMS data are again simulated using
DynamicsC in the model. Differencesbetweenthe model
ozone when compared to TOMS data.
on time scales of our model simulations (a few years). We
thereforeonly use the oceancomponentof surfacelossin our model for 14C. Since our troposphericdynamicsis controlledby eddy Radioactive isotope14Cis produced naturallyby galactic diffusion(seeTable2), our modelresultsshouldbe usedwith cosmicraysbut alsocanbe injectedinto the atmosphere by cautionwhentryingto addressissuesthat may be dependent
4. BASELINE MODELSIMULATION OF 14C
nuclearexplosions. Since•4C appearsin gaseous form onthetropospheric dynamics. Ourmodel simulations of •4C (almostalwaysas 14CO2), it is thought to be quitesuitable do not supportthe continentalcarbonsink,however,we do
for useas a tracer [List and Telegadas, 1969;Johnstonet al., 1976; Johnston, 1989].
not believe that our model computationsnecessarilyrefute the continental
carbon sink either.
Forthemodeling of isotope14C,threephysical processes In our modelthe net loss of •4C over oceansis included
(production,radioactiveloss,and surfacedepositionveloc- via a deposition velocity.The netchangein concentration of ity) needto be included.Radioactivelossis the simplestof
these.Thenumberof 14Catomslostperunittimeis equalto
14Cperunittimein thelowestgridboxof eachlatituderange
is equal to 0.05 (vd/AZ)cnfo, where Vd is the deposition In 2/rl/2,Nx is thenumber of 14Catoms velocity,AZ is the heightof the lowestbox in our grid (=2
ANx,whereA = present, and rl/2 is the half-lifeof 14C.Production and
km),Cnistheconcentration of 14Cinthatbox,andfo isthe
surface depositionvelocity are discussedin the ensuing fraction of the Earth's surface in that latitude bin covered by
paragraphs.
The naturalcontinuous production of 14Cby galactic
oceans.
The observedabundanceof natural •4C is 74 x 105
cosmicrays posesan uncertaintyfor modeling.High energy air)or 3.57x 10-16in mixingratio[Telegadas, particles(of the orderof MeV to GeV) reactwith N 2 and02 atoms/(gm
of its longhalf-life,•4Cis assumed to be to form14Camongotherproducts. Most 14Cis produced 1971].Because
near the poles where cosmicray activity is most intense. uniformlymixedthroughoutthe atmosphere.With a fixed Extensive direct measurements of the production do not input productionrate (as given above) and the known
of natural•4C, our 2D modelcan be usedto exist; consequently,the calculatedproductionrates have a abundance calculate what depositionvelocity is neededto maintainan large uncertainty.Two estimatesof the globalproduction
witha background •4Cof 74 x 105atoms/(gm rate of 14Cexist' 3.5 x 1026 atoms/yr[Lingenfelterand atmosphere
has74 x 10514Catoms/(gm Ramaty,1970]and2.9 x 1026atoms/yr[Lal andPeters, air).Thusourinitialcondition 1967];however, latitude versusaltitudeprofiles(in kilometers or millibars)of productionrates are not in the literature
air) everywherein the atmosphere,and the model is integratedforward with a specificdepositionvelocity to see
cosmicrays, theseprofileswere assumedto be identicalto
the northern hemisphere troposphere. Most measurements
whetheror not74 x !05 14C' atnmq/(gm air) is maintained in
thoseof radioactive isotope7Be [Bhandariet al., 1966] of •4C are in the northernhemispheretroposphere[Telegaare comparedin scaled to giveanannualproduction of 3 x 1026atoms/yr. das, 1971],thus modeland measurements The biospherecycles its carbon content with the atmo- thisregion.Severalrunswith differentdepositionvelocities sphereon time scalesof a few years; surfacedeposition were necessaryto find the value of the depositionvelocity processesare thoughtto be responsiblefor controllingthe that maintains this background level. Our modelindicatesthat the background•4C is not carboncycle on muchlongertime scales.Until recently,it was believed [e.g., Warneck, 1988] that the long term uniformlymixed but variesby about 10% and is dependent abundance of •4C in the atmosphere is determined by the on the local intensity of cosmicrays. To achieve a backabundance of 74 x 105•4Catoms/(gm air) in the lossof 14Cto the oceanswhosecarboncycletime scaleis of ground the order of thousandsof years and comparable to the northernhemispheretroposphererequiresan oceandeposi-
half-lifeof •4C, 5730years.At the ocean-airinterfacethe tionvelocityof 6.7 x 10-3 cm/s,a numberin goodagreeof Liss[1988]of 5.6 -+ 1.4 x 10-3 amountof •4C that entersthe oceanis proportionalto the mentwiththe estimate amount in the atmosphereabove the ocean, and the amount
cm/s.Thecorresponding meanlifetimeof 14Catomsin the
of •4Cthat entersthe atmosphere fromthe oceanis propor- atmospherebeingtransferredto the mixedlayer of the ocean equalto themeanlifetime of •2Catomsor tionalto the amountof •4Cin the mixedlayerof the ocean. (approximately On the basis of measurements of the actual amounts of CO2) is 6.2 years, in rough agreementwith an average natural 14Cin both the mixed layer of the oceanand the lifetime of 7 years derived from 12 other investigations atmosphere,Oeschgeret al. [1975]concludethat the flux of [Warneck, 1988, p. 574].
22,564
JACKMAN ETAL.'MODEL SIMULATIONS OF14CANDNOxINJECTIONS Latitude
4O 35
3O 25
2O
- 0)
31øN -
October
1963
Latitude 31øN - January 1964
4O
"'•
i
i
i
i
35
-
3O
_
25
_
_
2O
_
15
_
10
•'•CData(Johnston, 1989) ........
15 10
[l•
DynamicsA) Base
I
0
I
240
480
I
720
1200
0
Excess •4C(105 atoms/ gmof dryair)
i
i
i
_
Dynamics C)Shia etal.(1989)
I
I
240
480
I
720
I
960
1200
Excess •4C(105atoms/ gmof dryair)
Latitude 31øN - January 1965
4O
Dynamics B)Strong
J!
I
960
...• .... Dynomic•A) Base89) _
•iI
DynamicsB) Stroh9 DynamicsC) Shia et al. (1989)
Latitude 31øN - January 1966
4O
i
'\ \
/,:' /
35
35
5O
5O
??
\
25
25
2O
,;' ,I,' /,"
2O
I,/ ••.•' '/
15
_
I•"" •
10
Data (Johnston, 1989)_ DvnomicsA• Bose
........
•
} o
Dynamics B)Strong
15
I
480
I
720
/
-
•,,,
-
10
•'•CData (Johnston, 1989)
........
_ I
960
1
1200
-
/
Dynamics C)Shiaet al.(1989)
I
240
/,,'
/
/
o
240
DynamicsA) Base DynamicsB) Strong DynamicsC) Shio et ol. (1989) I
480
I
720
_
I
96O
1200
Excess •4C(105atoms/ gmof dryair) Excess•4C(10s atoms/ gmof dr)/(]Jr) Fig.3. Excess 14Cmeasurements andmodel simulations at 31øN at fourdifferent times'(a) October 1963, (b)
January 1964,(c) January 1965,and(d) January 1966.Initial14Cdistribution in (a) forOctober1963(shortdashed, dashed-dotted, and longdashedcurvesfor the modelsimulations) is takenfrom Johnston[1989].The solidcurve represents the balloondata((a), (b), (c), and(d)), whilethe shortdashed,dashed-dotted, andlongdashedcurves
represent themodel simulation of 14C forDynamics A, B,andC,respectively, in(b), (c),and(d).Theunitsarein l0s ]4Catomspergramof dryair. MODEL SIMULATIONSOF 14CPRODUCED BY NUCLEAR
14C,whileit resides intheatmosphere, byradioactive decay
EXPLOSIONS
(•'•/2 = 5730 years) is fairly simpleand small on a few-year time scale when compared to the lossesof the other noted Carbon 14 was producedin large quantitiesby every tracers. Thereforeit is believedthat if the startingamountof abovegroundnuclear test carried out by the United States 14C,the 14Cproduced by nuclear and the Soviet Union in the late 1950sand early 1960s.The •4C(inthiscase,excess
is known,then •4Cis one of the besttracersof concentration of •4C was monitored by the Healthand explosions) Safety Laboratory (HASL) program of the U.S. Atomic Energy Commissionfor several years during and after the testingperiod [Telegadas,1968, 1971;Telegadasand List,
motion in the atmosphere.Becauseit appearsin gaseous form in the atmosphere,gravitationalsettlingplaysno role. Chemical models should be able to model the short term as
1969]. The subsequentdecay in concentrations of •4C well as the long term behavior of this tracer. Our test of tryingto modelthe decayof theexcess•4Cfrom providesa stringenttest of 2D models.Johnston[1989] has consists
recentlyadvocated thistestfor ]4CandrecentlyKinnison October 1963 to January 1967. October 1963 is chosen [1989] and Shia et al. [1989] detailed their successfulmod-
becausethis month is six monthsafter the last nucleartest,
elingof nuclearexplosion-produced •4C.
andthus•4Cwaspresumed to haveachieved zonalsymme-
For studiesof the lower stratosphereand upper tropo- try. January 1967 is chosen as the cutoff date because this is sphere,severalgases(e.g., N:O, CH4, CFC13,CF2C12, immediatelyprior to the resumptionof aboveground testing HNO3, 0 3, and•4C)havebeenemployed astracers to test with the Chinesedetonationof a 3 MT nuclearexplosionin
the transportin models.There are propertiesof •4C that approximately April of 1967. make it particularly well suited to transport tests. All of Carbon 14 data exist for four latitudes, 31ø, 70ø, and 9øN thesetracers have an atmosphericsink and/or sourcewhich and 42øS.We compare model resultsto measurementsfor all can lead to problems in interpreting the agreement/ these latitudes (see Figures 3, 4, 5, and 6). disagreementbetween model and measurements.The lossof Our initial conditions for October 1963 are taken from the
JACKMAN ETAL' MODELSIMULATIONS OF 14CANDNOx INJECTIONS Latitude
4O
70øN -October
i
i
i
1963
22,565
Latitude 70øN - January 1964
4O
i
i
i
i
I
\ 35
35
3O
3O
25
25
2O
2O
15
15
'- ci-•.•_.•__ ' •.•-/'
/
10
•4C Data (Johnston, 1989) _
10
•'• •' ....... Dynamics A)Base , / . •/ •.z' ...... Dynamics B)Strong
........ Dynamics ...... DynamicsA) B) Bose Strong
/
Dynamics C)Shia etal.(1989)
'
I
0
I
240
480
I
I
720
960
:• • "• '
\x '\ \ \, \
i
\
20
15
15
/
0
240
i
i
! _
/',;' I /,/
I
-
,/
/'"/>
-
/,," /
/...' /
:)•'"
10
10
I
1200
/','
2O
/!/ :•!
i
,,
25
.......
960
/,,
,,
•
720
-d)
5O
25 /:
480
Latitude 70øN - January 1966
4O 35
3O
DynamicsC) Shia et al. (1989) I I
I
Excess•4C(10s atoms/ gm of dry air)
Latitude 70øN - January 1965
35
.... I
240
o
1200
Excess•4C(10s atoms/gm of dry air) 4O
.•
•CData (Johnston, 1989) _
DynamicsA) Bose
!i
Dynomios B)Strong Dynomics C) Shia etal./•989 )
I
480
......
I!
I
I
72_0
960
1200
Excess•C (•0 • otoms/gm of dry oir)
0
240
Dynamics B)Strong
_
Dynamics C) Shio etel. (1989) I I
I
480
720
960
1200
Excess14C(10s (]toms/ gm of dry
Fig.4. Excess 14Cmeasurements andmodel simulations at70øNatfourdifferent times: (a) October 1963,(b) January 1964, (c)January 1965, and(d)January 1966. Initial•4Cdistribution in(a)forOctober 1963 (short dashed, dashed-dotted, andlongdashed curves for themodelsimulations) is takenfromJohnston [1989].Thesolidcurve represents theballoon data((a), (b), (c), and(d)), whiletheshortdashed, dashed-dotted, andlongdashed curves
represent themodel simulation of•4C forDynamics A,B,and C,respectively, in(b),(c),and (d).Theunits arein105 •4Catomsper gramof dry air.
Johnston[1989] analysisof the experimentalmeasurements centrationof 14Cin the mixedlayer of the oceanincreased
for September to Novemberof 1963contained in Telegadas t l,l•bllgkl, • [• / •1ß These initial conditions•,8IlOl ............. ua•h•udotted, and long dashedcurves) are given in Figure 3a compared to measurements (solidcurve).Because thegreatestabundances of excess•4Clie in the lowerstratosphere at northernpolarlatitudesfor October1963and mostof the
only 10%overbackground levelsduringthisperiod;hence
successive months, modeling of excess•4Crigorously tests
Figures3b, 3c, and 3d show model simulations and measurements of excess•4C(abovethe background of 74 x 105•4Catoms/(gm air)) in Januaryfor the years1964,1965,
thedynamics of thelowerstratosphere at northernmiddleto high latitudes.
We used the three dynamicalformulationsin modeling
oceanrepresents onlya smallerrorin themodeling. Onshort timescales,changes in themodelingof the troposphere have only a smalleffecton the modelingof the stratospheric abundancesof excess•4C.
and1966, respectively. TheDynamics A simulation of •4C
•4C. In proceeding we integrated forwardin timethe total givesa fairlyreasonable representation of the tropospheric amountof •4C (excessplusnaturallyoccurring background abundanceof •4C but seriouslyunderestimates the abun•4C),includingthe naturalproduction, radioactive loss,and danceof •4C in the lower stratosphere(see short dashed loss at the ocean-atmosphereinterface. For the ocean-
curvein Figures3b, 3c, and3d). The solidcurvein Figure atmosphere interfaceour initial assumption was that the 3 showsthis resultfor the balloonmeasurements of •4C
back flux of •4C from the ocean did not increaseand stayed
atthelevelnecessary to maintain thebackground •4C.This
[Johnston, 1989].
Simulationof •4C with DynamicsB (see dashed-dotted curve in Figures3b, 3c, and 3d) is even worsein compartheocean certainly increased astheconcentration of •4Cin ison to measurementsthan the simulation with Dynamics A. the mixedlayer of the oceanincreased,is a reasonable one. For example,datafrom Tans[1981]indicatethat the con- Carbon14 is transportedout of the stratospherewith Dy-
assumption, whilenot strictlytrue sincethe backfluxfrom
22,566
JACKMAN ETAL.'MODELSIMULATIONS OF14CANDNOxINJECTIONS Latitude
9øN -
October
1963
Latitude 9øN - January 1964-
40
40 ,
\
35
35 30 25
25
20
2O
]5
15
._
•'!'"'
10
•4CData (Johnston,1989)
]0
-b)
30
-.•
_
I1•
Dynamics A) Base Dynamics B) Strong DynamicsC) Shia et el. (1989)
1 60
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Fig. 5. Excess14Cmeasurements andmodelsimulations at 9øNat four differenttimes:(a) October1963,(b) January1964,(c) January1965,and(d) January1966.Initial 14Cdistribution in (a) for October1963(shortdashed, dashed-dotted, and long dashed curves for the model simulations) is taken from Johnston [1989]. The solid curve represents the balloon data ((a), (b), (c), and (d)), while the short dashed, dashed-dotted, and long dashed lines
represent themodelsimulation of 14CforDynamics A, B, andC, respectively, in (b), (c), and(d). Theunitsarein 105 14Catomspergramof dryair. namics B much more quickly than indicated by the measurements.
Resultsfor 14Cat latitudes70øand 9øN and 42øSare shown for the same months and years in Figures 4, 5, and 6 as were shown for 3 IøN in Figure 3. At 70øN, model results indicate better agreement in the stratosphere with Dynamics C than with either Dynamics A or B (see Figures 4c and 4d). The tropospheric results at 70øN are not quite as clear, although Dynamics B tends to transport more to the troposphere than is observed (see, e.g., dashed-dotted curve in Figure 4b). The model versus measurement results at 9øN show Dynamics A and B to be better representationsthan Dynamics C in the stratosphere in January 1964 and January 1966 (Figures 5b and 5d), whereas Dynamics C provides a better repre-
more consistent with those that are measured. Dynamics C has a smaller ASTER than either Dynamics A or B (see discussion in section 2). Dynamics C also has a sharper
transition in eddydiffusioncoefficients (KyyandKzz)at the tropopausethan do Dynamics A and B (see Table 2).
Kinnison[1989]founda bettersimulationof 14Cwith a sharper transition in eddy diffusion at the tropopause. We ran a model sensitivity experiment in which Dynamics A was used with the sharper transition at the tropopause from Dynamics C. Carbon 14 was slightly better simulated in this modified Dynamics A simulation, but we conclude from this model experiment that the magnitude of the advective component of the strat/trop exchange rate is even more important than the severity of the eddy diffusion transition at the
sentation of 14Cin the stratosphere in January1965(Figure 5c). Generally,thetropospheric observations of •4Cat 9øN
tropopause.
are better simulated with Dynamics C (see Figures 5b, 5c, and 5d). Carbon 14 in both the stratosphereand the troposphere is better represented at 42øS with Dynamics C than with either Dynamics A or B (see Figures 6b, 6c, and 6d). Given the above discussion for latitudes 31ø, 70ø, 9øN and
eddydiffusion (bothKyyandKzz)wastakenfromDynamics
We also ran a model sensitivity experiment in which the
C combined with the advective field from Dynamics A. This
modelexperiment gave14Cresultsthatshowed betteragree-
ment with measurementsthan those achieved with Dynamics A, but the agreement with measurements is not as good 42øS,we conclude that 14Cis bestsimulated withDynamics as that achieved with Dynamics C.
C. The amountof 14Cin the stratosphere staysat levels
Theseresultsfor 14Cimplythatbothadvection andeddy
JACKMAN ETAL.'MODELSIMULATIONS OF14CANDNOxINJECTIONS Latitude
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is included in simulations with an imposed sulfate aerosol layer, then strataspheric aircraft may increase ozone. This provocative result indicates that we still do not totally understand nor are we able to indisputably predict with present-day models the effects of strataspheric aircraft on ozone. More laboratory work and model simulations are necessaryto help quantify the influence of these high-flying aircraft.
100.0 10
