J. Laurent, M.P. Lemaitre, J. Besson, and A. Girard

GEOPHYSICAL RESEARCH LETTERS, VOL. 12, NO. 10, PAGES 667-670, OCTOBER 1985

OBSERVATIONS OF MIDDLE ATMOSPHERIC CH 4 AND N20 VERTICAL DISTRIBUTIONS BY THE SPACELAB 1 GRILLE SPECTROMETER

C. Muller, J. Vercheval, M. Ackerman, and C. Lippens Belgian Institute for Space Aeronomy, B-1180 Brussels, Belgium

J. Laurent, M.P. Lemaitre, J. Besson, and A. Girard

Office National d'Etudes et de Recherches A•rospatiales, France

Abstract. Methane and nitrous oxide have been to the launch date and orbit inclination the observed by limb absorption spectrometry using sunset occultations were all performed at middle

the Spacelab One grille spectrometer. The CH, • Northern latitudes while the sunrises were ob-

band is obsserved with a 0.1 cm- resolutio• served at high Southern latitudes. Two observa- to 80 km while N_O can be seen up to 52 km in tions of CH• and one of N20 were successfully

strong lines of its vR band. The values are performed, aI1 in sunset mode, thus taking place

compared, where possibl•, with previous observa- at Northern latitudes: 34øN for N20 and 27øN for

tions and are in agreement with rocket determina- both CH• observations.

tions. The two CHa observations were performed in two

wavelengths idter•als : the v• Q branch spanning

Introduction 3010. to 3020 cm-- covering t•e most intense CHa

features and the • band manifold around 2978.8 Methane and nitrous oxide are known to be cm--. For N20 , the {hoosen interval was from 2205 atmospheric minor constituents for about forty to 2212 cm-1 and was including the strong R 2, years [Adel, 1938; Migeotte, 1948]. The interest in their observation has been driven mainly in R•, P2' P-' P" and P • N O lines. The choice these intJerva•s responded 2 to a need to detect of

the last years by their role as tracers of these two constituents at the highest possible stratospheric and mesospheric transport, they altitude. Typical spectra are shown on Figures 1 have no presently known production above ground and 2, showing the growth of the lines with de-

level; also they are important in themselves as creasing limb altitudes. CH 4 was observed in i•

sources of nitric oxide and hydrogen in the upper Q branch from 80 to 25 km and in the 2978.8 cm atmosphere [Brasseur and Solomon, 1984] Moreover, manifold from 80 TO 35 km; N^0 was seen from

the recent evidence of their increase in the last about 52 to 28 km. Both o•servation_• being

centuries [Rasmussen and Khalil, 1984] has led to performed at a resolution close to 0.1 cm . speculate on their effects on radiative transfer

and photochemistry. Inversion of spectra

CH has been previously observed from air-

craft• and balloons [Ackerman et al., 1977, 1978; The spectroscopic data were taken from the

Farmer et al., 1979; Borghi et al., 1983; Ehhalt AFGL line parameters table, 1982 edition [Rothman et al., 1983; Rinsland et al., 1984] as well as et al., 1983] while the atmospheric model used

N20 [Ehhalt et al , 1983; Borghi et al , 1983; was the mid-latitude spring-fall U.S. standard

Rlnsland et al., •982; Farmer et al., •980 and atmosphere which was found in reasonable agre-

references therein]. Methane has also been ement (around 5% in temperature) with the corres- observed at higher altitudes by means of sampling ponding meteorological lower stratospheric satel- rockets [Ehhalt et al., 1972, 1975]; these

results being completed by the satellite data of Jones and Pyle (1984).

Space observation of nitrous oxide was per- formed too using the Nimbus 7 pressure modulated cell SAMS radiometer [Jones and Pyle, 1984] up to the stratopause levels; the purpose of the space- lab grille spectrometer was to extend these ob-

servations up to the altitude wher_e 1these species

become undetectable at the 0.1 cm instrumental resolution.

Observation

The grille Spectrometer and its operation from November 28 to December 4, 1983 have already been described [Lema•tre et al., 1984]. it is a solar absorption limb sounding spectrometer and was first flown during the Spacelab One flight. Due Copyright 1985 by the American Geophysical Union.

Paper number 5L6615.

0094-8276/85/005L-66155 02 . 00

3000

2500 2500

2000

1500

1000 500

3012 301 3016 3018

WAVENUNBER (cm -1)

Fig. 1. Solar spectra showing the telluric CH Q

branch obtained at two different limb altitu4de

during sunset.

667

668 Muller et al.: Observations of Middle Atmospheric CH 4 and N20

• 1400

e

v v v V '

• 600[

• 200• N20 q3 P lines

206 220? 2208 2209 2210 2211

WAVENUMBER {cm -1)

Eig. 2. •olap 8peetpa showing tellupie N•O line8 obtained at two diffepent limb altitudes z duping

sunset;

lite •ounding8 EPlanet, pep•onal communication,

198q].

The aeeupaey of the moleeulap papametep8 i8

vepy high fop N20 of which 8ingle line8 ape ob- 8epved but 8till could be imppoved fop CH• EToth

et al., 1981] a8 •ome line• pemain unp•olved blend8 even at the 8peetpal quality of fundamen-

tal labopatopy wopk; in the wopst CH• eases, a

20% eppop on absolute line 8tpength8 p•main8 pos- sible.

The invepsion was made using an onion peeling technique fitting calculated equivalent line width8 and obsepved one8 by an itepative ppoee88 using a Voigt line shape, the altitude pe8olution being 2 km. The pesult8 wepe simultaneously

55

50

45,

N20

ß This work

43øN

ß SAMS

(40ø_50ø N

40

lxl lx10 -• lx10 -?

35

30

25

107 108 109 1010

N20 NUMBER DENSITY (mo[.cm -3)

obtained vertical distributions are shown on Fi-

gures 3 for CH, and 4 for N20 while numerical

results and observational conditions are pre- sented in Tables 1 and 2.

The results are indicated in concentrations which are the measured quantities because for ab- sorption measurements, the model dependence of the derived number densities is much lower than the dependence of the conversion to mixing ratios. In the case where these data should be used in comparison with theoretical models, we would suggest that the modelers use the pressures and temperatures actually derived in their theo- retical computations, as long as they correspond to the time and location of the observations.

The error on the measurements of equivalent widths range from 20% on the top of the distribu- tion to lower values in the botton where the ab- sorptions are the strongest; however, due to

80

60

• •o

<r '

., T,s _

q-.' Ehhat• ef a[ (1975) 30øN •••• .

•Ackerman ef a[ (1977)43øN • • '

2010• 10 • 109 1010 1011 012 8Lrong non-lineariLie8 in •he absorption, Lhe un- [H• NUHBER DENSITY (molcm -3) eerLainLie8 _{Zn order} Lo determine on Lhe quobed a precise densities erroP are higher. bar, Lhe

Fig. 3. Obtained CHq vertical dis•ribuLions. 8ynLheLie 8peeLrum program was used and Triangle8 and eiPele• correspond r•ee•ively Lo shown •ha• eoneenLra•ion8 differing by 15%

Lhe CH• Q branch and Lhe 29•8.8 em CH mani- •hose indicated on figure 3 and q would have led fold. •rror bar8 ape + 15% of Lhe in•ieaLed Lo 8ignifieanLly differenL spectra in all Lhe ob-

values. These daLa are compared wiLh Lhe upper 8ervaLion altitude range and Lhu8 + 15% become8 8LraLospherie and me8ospherie average observa- ouP LenLa•ive error bar. These daLa could also be tion8 of Jone• and Pyle (198q) and EhhalL eb al. 81ighLly modified, e•peeially in LheiP boLLom

(1972, 1975). paP•, if more Pef•nemenb wa• •o alLeP

results are compared with the upper stratospheric average observations of Jones and Pyle (1984).

checked by simulating the observed spectra by

synthetic ones adjusted by trial and errors. The Fig. 4. Obtained ^{Errorbars are + 15%} oNtO ^the vertical ^indicated distribution. ^{values. The}

Muller et al.: Observations of Middle Atmospheric CH 4 and N20 ⁶⁶⁹

TABLE 1 : CH 4 vertical distribution.

-1

Altitude CH 4 Q branch CH 4 2978.8 cm

27.5 7 x 10 11

32.5 2.8 - 3.36 x 10

37.5 1 - 1.11 -

42.5 5 x 1010 5 x 1010

47.5 2 - 2 -

52.5 1 - 7.5 x 109

57.5 3.7 x 10 9 2.85 -

62.5 2 - 1.25 -

67.5 1 - 5 x 108

72.5 5.4 x 108 2.1 -

11

Latitude 27 ø N 27 ø N

Longitude 176 ø W 161 0 E

Time (GMT) 3h 47m 5h 16m

(1983, Dec. 3)

represented for the corresponding latitudes on Figure 3 and the 32øN rocket data of [Ehhalt et al., 1972, 1975]. These three data sets show satisfactory agreement with the data presented here above 40 kin, the Jones and Pyle (1984) vertical distribution agreeing down to 27 km altitude. It should be stated here that the SAMS data are zonal averages and annual means. Between 35 and 40 km altitude, two balloon data sets have been published by Ackerman et al. (1977) and Farmer 'et al. (1980) using infrared spectrometry in the • band, respectively at 43øN and 30øS;

Farmer et 3al. (1980) publish also a 32øN profile

limited to 37 km which is lower by 25% than the 30 ø S profile but still higher than the upper limit of Ackerman et al. (1977). The latitude gradients suggested by these balloon data sets are in contradiction with the Jones and Pyle (1984) results where the higher latitudes mixing ratio are actually higher than the mid-latitudes values. SAMS data [Jones and Pyle, 1984] show in this respect a very complex structure with marked seasonal variations and an equatorial maximum coupled with a tropical minimum followed by again an increase toward the higher latitudes.

In the nitrous case, there is a good agreement in the whole range of our observation with the corresponding Jones and Pyle (1 984) average,

* Error bars are + 15% of the indicated concen- other measurements are limited to the 35 km

trations. - altitude with the exception of two values re-

ported by Ehhalt et al. (1975) : (3 + 7) ppb for the 40-50 km altitude range and (0.3 • 7) ppb for cantly the orbit parameters of the first Spacelab the 42-62 km altitude range; the upper limits in- mission, parameters used in these determinations clude the present determinations. There is agree- are still those communicated directly by NASA ment in the 28-35 km range between the here orbit engineers during the flight and immediately reported values and the in situ or infrared mea- after landing; their correctness was already surements [Schmeltekopf et al., 1977; Farmer et

checked in the case of CO 2 determination from the al., 1980]; the Jones and Pyle (1984) data being,

grille spectrometer spectra Obtained together with the CH data [Lippens et al., 1984] where a

constant CO• mixing ratio was observed up to 98 TABLE 2 : N20 vertical distribution

km and has • now been confirmed by the latest release of flight data tapes.

Discussion and conclusion

Altitude (km) Concentration (cm -3)

6.3 x 1010

3,8 - 1.9 - 1.05 -

6.8 x 109

4.2 - 2.1 -

8.1 x 108

4.7 - 2.3 -

4.25 x 107

Latitude 43 ø N

28

The two CHa vertical distributions obtained at

the same latitude but at 23 ø longitude difference 30

and separated by lh 30m give the same values be- 32 low 50 km but at higher altitudes they show a di-

vergence reaching a factor of 2 at 75 km. The 34

origin of this difference cannot be explained 36

now, the discrepancy• is too high to be attributed 38

to errors in the AFGL line parameters. Two possi-

bilities are left: first, deviations from a ri- 40

gorous Voigt profile cannot be completely exclU- 42

ded in the mesosphere and secondly, a short term

spatial and temporal variability of mesospheric 44

methane cannot a priori be ruled out. This pro- 47

blem will be addressed during the next flight of

the grille spectrometer, in late 1986, where more 52 CH runs will be scheduled in several spectral

intervals.

Few other CH• and NAO observations have been

performed at aititudes higher than 35 km and those are compared on Figure 3 and 4 with our ob-

Longitude 154 ø N servations. Until now, no models spanning the Time (GMT) 2H 42m entire middle atmosphere have been published and (183, Nov. 30)

no comparison with model data will be attempted.

For CH 4, observations are up to about 55 km the * Error bars are + 15% of the indicated concen-

SAMS data of Jones and Pyle (1984), which are trations.

6?0 Muller eta!.: Observations of Middle Atmospheric CH 4 and N20

on their lower altitude values at the upper limit CO, CO_, N20, H_O, HC1 and HF at Northern and of other measurements. Southern mld-la•itu•des, J., Geophys. Res., 85,

A second flight of the instrument is scheduled 1621-1632, 1980.

on the Spacelab Earth ObservatiOns Mission 1/2 •in Jones, R.L. and J.A. Pyle, Observations of CH 4

late 1986, while the CH 4 • Q branch will again and Nl•n ¸ by the Nimbus 7 SAMS-A comparaison

be observed, other P mani ld will b•l included; with situ data and two-dimensionsal numeri-

N_O will be observed in the 2240 cm spectral cal model calculations J Geophys. Res. 89 interval in order to enhance the instrumental 5263-5279, 1984.

signal to noise ratio and to be able to detect it Lema•tre, M.P., J. Laurent, J. Besson, A. Girard,

at higher altitudes. C. Lippens, C. Muller, J. Vercheval, M.

Ackerman, Sample performance of the grille

Acknowledgments. This work has been made pos- spectrometer, Science, 225, 171-172, 1984.

sible by the close cooperation of the European Lippens, C., Co Muller• J. Vercheval, M. Ackerman Space Agency (ESA) and NASA in the Spacelab J. Laurent, M.P. Lema•tre, J. Besson and A.

program and by the dedicated work of individuals Girard, Trace constituents measurements de- too numerous to be named here at several centers duced from spectrometric observations on-board of both agencies. Thanks are also due to the en- Spacelab, Ad.v. Space Res., 4, 75-79, 1984.

gineering staffs of ETCA (Belgium), CNES (France) Migeotte, M., Spectroscopic evidence of methane and ERNO (Germany) who contributed to the design

and integration of-the instrument.

References

Ackerman, M., D. Frimout and C. Muller, Strato-

spheric CH 4, HC1 and ClO and the chlorine

ozone cycle, Nature, 269, 226-227, 1977.

Ackerman, M., D. Frimout, C. Muller and D.J.

Wuebbles, Stratospheric methane measurements

and predictions, Pur. and App•. Geophys., 117,

367-380, 1978.

Adel, A., Further detail in the rock-salt prisma-

tic solar spectrum, Astrophys. J., 88, 186- 188, 1938.

Borghi, R., A. Girard, J. Laurent, N. Louisnard and D. Carlolie, Comparaison entre les r•- sultats d'un module unidimensionnel et des r•- sultats de mesures stratosph•riques de CH ,

H_O et des oxydes d'azote, Rev. Phys. Ap., 1•,

2•9-237, 1983. m

Brasscur, G. and S. Solomon, Aeronomy of the mid-

in the earth's atmosphere, Phys. Rev., 73, 519-520, 1948.

Rasmussen, R.A. and M.A.K. Khalil, Atmospheric methane in the recent and ancient atmospheres:

concentrations, trends and interhemispheric

gradient, J. G. eophys. Res., 89, 11599-11605,

1984.

Rinsland, C.P., A. Goldman, F.J. Murcray, D.G.

Murcray, M.A.H. Smith, R.K. Seals, J.C. Larsen

and P.L. Rinsland, Stratospheric N20 mixing

ratio Profile from high resolution balloon- borne solar absorpti_o• spectra and laboratory spectra near 1880 om , Appl. Opt., 2•1, 4341- 4355, 1982.

RinSland, C.P., A. Goldman, V. Malathy Devi, B.

Fridovich, D.G.S. Snyder, G.D. Jones, F.J.

Murcray, D.G. Murcray, M.A.H. Smith, R.K.

Seals, M.T. Coffey and W.G. Mankin, Simulta-

neous stratospheric measurements of H2o, HDO, and CH 4 from balloon-borne and aircraft infra-

red soIar absorption spectra and tunable diode laser laboratory spectra of HDO, •J. Geophys.

dle atmosphere. chemistry and Physics of the Res,, 89; 7259-7266, 1984.

stratosphere and mesosphere. 441 pp.,•' D. Rothman, L.S., R.R. Gamache, A. Barbe, A. Goldman Reidel Publ. Cy., Dordrecht-Holland, 1984. J.R. Gillis, L.R. Brown, R.A. Toth, J.M. Flaud Ehhalt, D.H., L.E. Heidt and E.Ao Martell, The

concentration of atmospheric methane between 44 and 62 kilometers altitude, J. Geophys.- Res., 77, 2193-2196, 1972.

Ehhalt, D.H., L.E. Heidt, R.H. Lueb and E.A.

Martell, Concentrations of CH 4, CO, CO 2, H20

and N_O in the upper stratosphere, J. Atm.

Sci., •__•2, 163-169, 1•75.

Ehhalt, D.H., U. Schmidt, E.P. Roeth, On the tem- poral variance of stratospheric trace gas con- centration, J. Atm. Chem., 1, 27-51, 1983.

Farmer, C.B., O.F. Raper, B.D. Robbins, R.A. Toth and C. Muller, Simultaneous spectroscopic mea-

surements of stratospheric species .' 03 , CH 4,

and C. Camy-Peyret, A.F.G.L. Atmospheric ab- sorption line parameters compilation: 1982 edition, Appl. Opt., 22, 2247-2256, 1983.

Schmeltekopf, A.L;, D.L. Albritton, P.J. Crutzen, P.D. Goldman, W.J. Haarop, W.R. Henderson, J.R. McAfee, M. Mc Farland, H.I. Schiff, T.L.

Thomson, D.J. Hoffman and N.T. Kjome, Strato- spheric nitrous oxides profiles at various latitudes, J. Atm. Sci., 34, 729-736, 1977.

(Received June 14, 1985;

Revised July 29, 1985;

accepted July 31, 1985)