- Email: [email protected]
Validation of SAGE II data inversions by the European correlative experiments
Adv. Space Rex. Vol. 7, No. 3, pp. (3)227—(3)236, 1987 Printed in Great Britain. All rights reserved.
0273-1177/87 $0.00 + .50 Copyright © COSPAR
VALIDATION OF SAGE II DATA INVERSIONS BY THE EUROPEAN CORRELATIVE EXPERIMENTS J. Lenoble Laboratoire d’Optique Atmospherique, Université des Sciences et Techniques de Lille Flandres Artois, U.F.R. de Physique, 59655 Villeneuve d’Ascq Cédex, France
ABSTRACT
An European program of correlative experiments has been organized in order to validate SAGE II data during three periods of observation over Europe (November 1984, April 1985, October 1985). About ten groups from France, Belgium, Germany and Italy were participating. The correlative data are lidar aerosol profiles, soundings of ozone profiles, and balloon observations, including limb photographies, polarimetric measurements of the aerosol scattered light and nitrogen dioxide extinction measurements. Results of the comparisons between SAGE II inverted data and correlative data are presented. The analysis of the aerosol correlative observations with the SAGE II four aerosol channel data, in term of profile and size distribution is perfectly consistent and provide a good indirect validation. The NO 2 comparison shows a good agreement between SAGE II and correlative data. INTRODUCTION The Stratospheric Aerosol and Gas Experiment II (SAGE II) is a seven channel occultation experiment /1/. It is expected to provide ozone, nitrogen dioxide, water vapor content profiles, and aerosol extinction profiles at four wavelengths. SAGE II is flown on the Earth Radiation Budget Satellite (ERBS) with a 610 km circular orbit at 57° inclination. It observes sunsets and sunrises, with a tangent point shifting approximately between BO°Sto 80°N in about a month; 15 events per day (sunset or sunrise) distant of about 24° in longitude are recorded in a narrow latitude band. A programme of correlative experiments, aiming at the validation of SAGE II data has been developped in Europe. The three main periods of observations were November 1984, April 1985, September—October 1985.About ten groups from Belgium, France, Germany and Italy were participating in these validations. The first two sections present the analysis of SAGE II products and the organization of the European correlative experiments, with the available data. The third section is devoted to the problem of the aerosol retrieval, including their vertical profile and their size distribution. The fourth section presents the comparison results for the ozone and the nitrogen dioxide profiles. ANALYSIS OF SAGE II DATA The raw radiances are converted into transmittances, averaged over 1 km; they are given with their standard deviation versus the tangent height, on the SAGE II PROFILE tapes provided by NASA to the users. The tapes contain also the meteorological data, which are used to compute and to correct the Rayleigh contribution to the measured transmissions. We will leave out of this discussion the 940 nm channel, because no water vapor measurements have been made during the European experiments, and because its inversion needs a particular treatment for the gaseous line transmission. In the six other channels (1020 nm, 600 nm, 525 nm, 453 nm, 448 nm, 385 nm) the extinction due to aerosols, O3~ or NO2 varies slowly within the filter widths (about 3 nra for 453 and 448 nm, and 20 nm for the other channels); the inversion is straightforward and leads to the vertical profiles of the extinction coefficients a(X) for the six channels. Error bars on o(X) are evaluated from the experimental error on the transmission and from the expected error on the Rayleigh correction /2/. At 1020 nm the extinction is only due to aerosols. In the 600 nm channel, the main contribution is due to the ozone absorption, at least above 20 km; below this level the aerosol correction becomes large and the results are of poor quality. The two narrow channel transmission ratio gives (o(.448) — o(.453)J, which is mainly due to NO , with a small correction for 0 and aerosols, above 25—30 km; at lower levels the aeroso~contribution is too large to al~ow a good retrieval of NO2. The 03 and NO2 extinction profiles can be converted into number density profiles, given the absorption cross sections.
(3)227
(3)228
J. Lenoble
With the necessary 03 and NO
2 corrections, the aerosol extinction coefficient profiles are obtained at 525 nm, 453 ns, and 385 nra; however between 25—30 km, the commanding role in extinction shifts from aerosols to NO2, making the results dubious, for both components. Whereas the aerosol extinction profile at 1020 nra can be retrieved down to 3 km from the ground in cloudless atmospheres, the short wavelength profiles are limited, by the increasing Rayleigh contribution, at respectively about 10, 12 and 14 km. The conversion of aerosol extinction into number density needs the knowledge of the aerosol size distribution n(r), which can be sought from the spectral variation of the extinction c,aer(X). However a direct inversion of the experimental data is not feasible, because of the rather large errors on the three short wavelength channels; a smoothing of the data has been introduced, using the best fit approximation 5~’(X) = 9~ 2 (1) 9~n o 0aer(10) — a ZnX — B(2~nX) This means that we will be able to derive two parameters of the size distribution (to be chosen and related to a and B). An inversion algorithm has been developed at the Laboratoire d’Optique Atmosphérique de Lille (LOA) in order to derive the extinction profiles from the transmission profiles. The comparison of the results with the extinction derived at Langley Research Center (LaRC) and given on the SAGE II PROFILE tapes is generally good (Figures 1—9—10), with some exceptions in the altitude ranges, where the data have to be considered with caution, as explained above. EUROPEAN CORRELATIVE EXPERIMENTS The list of the participants to the European correlative experiments is given in table 1, with the geographical position of the ground stations. The balloon experiments were launched from Aire sur l’Adour by the french Centre National d’Etudes Spatiales. Three major coordinated experiments have been organized for SAGE II validation: i/ in November 1984, during the two periods when SAGE II was observing sunsets at the latitudes of Europe, i.e. 10—14 November and 26—30 November; ii/ in April 1985, from 20 April to 23 April (sunsets); iii/ in September—October 1985, with the MAP—GLOBUS NO experiment starting on 19 September , just after the sunset observations of SAGE II on 15218 September and an aerosol—ozone experiment during the sunrise observations of SAGE II on 12—14 October. A few other individual observations of ozone or aerosol backscattering have been performed during SAGE II passages over Europe and are available for further validations. The balloon polarimetric experiment has been flown again in coincidence with a SAGE II sunset observation on 21 April 1986. Ozone soundings During the three periods ozone Komhyr—ECC sondes were launched from Garmisch— Partenkirchen and Ozone Brewer Mast sondes from Aire sur l’Adour, Hohenpeissenberg, Observatoire de Haute Provence (OHP) and Uccle; from previous comparisons it is expected that the Brewer Mast sondes give values slightly larger in the troposphere and slightly smaller in the stratosphere than the Komhyr—ECC sondes. All the ozone data have been transmitted to the experiment coordina~r~nd converted into extinction coefficients at 600 nm, using a cross section of 4.84.10 cm , for comparison with SAGE II data. Lidar soundings Lidar backscattering aerosol profiles have been obtained during the three main periods with a ruby lidar (694 nm) at Garmish—Partenkirchen and with a Nd YAG lidar (532 nra) at Florence, Frascatti and OHP. In order to compare with the SAGE II extinction profiles at 1020 mm, the aerosol backscattering profiles have to be converted into extinction, using an aerosol model. It has been checked that the conversion is not very sensitive to the exact size distribution, but can be fixed by an effective radius rff defined by reff
=
r3 n(r)dr
/ 1
r2 n(r)dr
(2)
The model chosen, which may vary with altitude, must be compatible with the spectral variation of the SAGE II extinction coefficient and with the other correlative observations.
SAGE II Data Inversions
(3)229
Balloon experiments Three instruments were flown on correlative experiment programme.
balloons
from
Aire
sur
l’Adour
during the
SAGE
II
Limb camera. Photographies of the earth limb at 840 nm, 440 nm and 375 nm were taken with the camera of the Institut d’Aéronomie Spatiale de Belgique (IASB) on 10 November 1984, and 22 April 1985. The radiance profiles at 30°scattering angle were inverted at the lASS in order to provide aerosol extinction profiles at the three wavelengths; the two shortest wavelengths are very close to SAGE II channels 450 ns and 385 nm, allowing a direct comparison. Infrared polarimeter. The radiance and the degree of polarization at 850 mm and 1650 nm are recorded scanning in an horizontal plane for various altitudes. The instrument built by the LOA was flown on 10 and 28 November 1984, on 22 April 1985, and on 12 October 1985. The radiance at 850 nm and 30° scattering angle is inverted to provide the extinction coefficient; the conversion of extinction at 850 nm to extinction at 1020 nm is not very sensitive to the aerosol model. The polarization diagram allows a retrieval of the size distribution /3/. occultation spectrometer. The occultation spectrometer of the Service d’Aéronomie (SA) was flown on 20 April 1985. The data were analysed at the SA, and results provided to the coordinator as a NO 2 number density profile. In order to compare with SAGE II data, they were con~rt~d into an extinction coefficient profile at 448 rim using the cross section 5.73 10 cm . The MAP—GLOBUS NO experiment has been described elsewhere /4/ and the data are presently analysed by the participants. Only the SAGE II data for November 1984 and April 1985 have been received till now, from NASA. The main results of the comparison for these two periods will be presented in the next sections. AEROSOL During the April 1985 experiment the aerosol layer was very homogeneous and stable; the five SAGE II aerosol profiles over the experiment zone were very similar for all channels. The average of these five profiles at 1020 mm is shown in figure 2. This is a very advantageous situation for validation purpose and we will focus most of our discussion on this case. In November 1984, the aerosol layer was more variable, especially in mid—November, and we will present only some typical results. Comparison between SAGE II and lidar data The backscattering profile obtained at Garmisch—Partenkirchen on 21 April is of good quality up to 30 km; it has been converted into extinction coefficient, using various log normal (LND) aerosol size distributio~s: n(r)
1
exp
=
/~ir~no
r~ L
nra 2 2~n o
1
J
the effective radius rff defined previously is related to the mode radius rm by reff
=
r
exp
(
5q2 ~ ~.n o)
;
(4)
we will use also the effective variance 2O) — 1 (5) Vff exp (in Some of the extinction profiles deduced from the lidar profile are presented in figure 3; it appears that the conversion factor from backscatttering to extinction is mainly sensitive to ref and does not depend much on the variance of the size distribution. The extinction profile varies slightly with the model, as long as r is larger than 0.2 I~m, but it becomes strongly model dependent for smaller particles. ~e best agreement between lidar and SAGE II profiles is found for a model with r around 0.35 3~m for altitudes smaller than 20—21 km and for a model with rf around O.X~~Amabove 22—23 km. A transition layer between 20—23 km corresponds apparently a very rapid change of the particle sizes. Figure 4 compares the SAGE II profile averaged from the five profiles (figure 2), to the lidar profile converted into extinction with an aerosol effective radius of 0.35 pm for the lower levels and of 0.10 pm for the higher levels; the error bars on the lidar profiles correspond only to the statistical fluctuations.
(3)230
J. Lenoble
On 30 November 1984 a lidar profile was obtained at Frascatti in very close coincidence to the SAGE II observation; the result of the comparison is presented in figure 5. The aerosol size distribution deduced from the spectral variation of extinction The lidar comparison suggests a decrease of the aerosol size with altitude, wich should reflect on the spectral distribution of the extinction coefficient as observed by SAGE II. For the sake of simplicit~, 0aer(1•02) has been taken as the value at 1.00 pm, and the best fit curve to aer (X)/ae (1.00), defined by equation (1) has been forced to pass by 1; this seems justified because the measure is of better quality in the 1020 mm channel than in the short wavelength channels. As can be seen in figure 6 the experimental points are generally very close to the fitting curve. A rough comparison with LND models shows that the experimental curves correspond approximately to LND size distributions with r ~ = 0.35 pm at 15 km, r ~ = 0.28 pm at 20 km, r ~ between 0.15 and 0.10 pm at 25 km an~r ~ between 0.10 I 0.05 ~m at 28 km. This confiFms the results found previously: in ord~ér to find agreement between the SAGE II profile and the lidar profile, we had to make the conversion of backscattering into extinction using an aerosol model with r ~ decreasing from about O.35pm below 20 km to about 0.10 1jn above 23 km. A more detaile~analysis can be sought, using a diagram of the coefficients a andBof equation (1). Figure 7 exhibits the behaviour of (a,B ) for LND aerosol models with various Vff and rff. For a given variance, a increases when the effective radius decreases, whereas B is mainly sensitive to the variance and decreases for large variances. The knowledge of a arid B from experimental data allows on the diagram of figure 7 an approximate determination of the two parameters of a LND size distribution, i.e. V and r , orG and r • For a bimodal size distribution, more eff and they eff cannot be deauced from the only knowledge of a and 8. parameters are necessary However B decreases very fast when two LND size distributions are mixed together, increasing from zero the contribution of one mode. Therefore very low or even negative values of B could suggest the presence of a bimodal size distribution. The average of a and B~ for the five SAGE II events of April, with their standard deviations at various altitudes, are plotted on figure 7. Despite the large dispersion of the points, the results on figure 7 confirm the general decrease of the aerosol sizes, accompanied by an increase of the variance when the altitude increases: z z z z z
= = = = =
16—18 20—21 22 km 23—24 25—27
km km km km
rff rff reff rff rff
.35 .28 .22 .15 .05
pm pm pm pm to,lO pm
vff Vff
veff Vff Vff
.15 to .20 .15 .17 .30 .30
Balloon borne polarization measurement The infrared polarimeter RADIBAL was flown on a CNES balloon from Aire sur l’Adour on 22 April 1985. Measurements of the degree of polarization at 850 nm and 1650 nm were made during the ascent between 15—22 km and 27—30 km. Unfortunately the instrument broke down at this level and no measurements were recorded during the descent, when the gondolla should have been more stable, and the sun lower on the horizon. In order to reduce the influence of the small oscillations of the gondolla, the data are cumulated for three rotations. The contribution of the solar radiation reflected from the ground and the lower atmosphere, has been taken care of, assuming an albedo of 0.20 at 850 nm and 0.15 at 1650 nm, which were the values measured beginning of May 1984 in the same conditions of clear sky. No direct inversion of the data has been tried, but the measured polarization has been compared with the polarization computed using the SAGE II extinction profile at 1020 nra, and the aerosol size distribution deduced from SAGE II spectral extinction. The results are presented for various altitudes between 15 km and 21.5 km in figure 8, and the agreement is very good; the model used (curves a)are LND with Ve f 0.17 (0=1.48) and reff = 0.37 pm (r5 0.25 pa) at 15 km, r5ff=O.29 pm (rm 0.20 pm) a~ove. During the American SAGE II validation experiment, direct in situ measurements of the aerosol size distribution have been made, and the extinction computed from these size distributions have been compared with the SAGE II extinction values. A good agreement was found at 1020 nra, but at the short wavelengths the SAGE II values seem larger than the computed ones, by approximately a factor 2 at 385 nm /5/. We do not have in situ size distributions available to try the same comparison. But we have checked if the conclusion of Oberbeck et al /5/ is compatible with our observations. For this purpose, we have arbitrarily divided our SAGE II extinction coefficient at 385 mm by a factor 2; this lead to an effective radius, r 55 pa at 15 km and ref4. .40 pm at 18—20 km. Figure 8 presents the degree of polarizat~oncomputed using the new size distribution (curves b). It is clear tha.t such a reduction by a factor 2 of the SAGE II extinction at 385 nm leads to a size distribution incompatible with the polarization measurements.
SAGE II Data Inversions
(3)231
Photographies of the limb radiance were made by the Institut d’Aéronomie Spatiale de Belgique (lASS) at Aire sur l’Adour on 22 April, simultaneously with the polarization measurements. The cameras were flown on a separate balloon and they recorded the limb radiance for low sun elevation, at various solar azimuths, and for three wavelengths 840 mm, 440 nm and 375 nm. The extinction is deduced from the radiance measured at 30° scattering angle and the Rayleigh extinction is substracted to obtain the aerosol extinction. At 30° from the sun, and for the tangent height of 20 km, the air mass observed was very close to the SAGE II tangent
point.
A comparison between the balloon and the SAGE II extinction profiles at 440 nra is presented in figure 9. The general agreement is very good, above 22 km. Fine structures of the aerosol layer appear on the balloon profiles, especially at the short wavelengths, which cannot be detected with the SAGE II resolution of 1 km. OZONE AND NITROGEN DIOXIDE
The ozone sounding profiles compared on the same day at different locations, or for successive days at the same location present differences, which can be retrieved 4dation on the SAGE more II profiles except for the experiment a=d perind. mr~kera precisea ~al difficult, when a close zone coincidence can be!4owever found. this Figure 10 presents comparison for April experiment. A profile of NO was obtained on 20 April 1985 at 19.00 GMT; the solar occultation spectrometer was ~‘lownon a balloon launched from Aire sur l’Adour and the tangent point for an altitude of 25 km was 44°59N, l°O6W. The six NO 2 profiles for the SAGE II events (sunsets) over Europe from 20 April to 23 April are almost identical between 22 and 40 km with differences much smaller than the error bars; this give sense to the comparison with a balloon profile which is not in close coincidence with a SAGE II event. Figure 11 presents the NO2 extinction profile at 448 nm retrieved from SAGE II data on 22 April (with the two retrieval algorithms) and the balloon profile on 20 April. The agreement is very good and particularly comforting in the altitude range between 20 and 30 km, where the aerosol contamination is important and make the NO2 data not very reliable. CONCLUSION
The two European correlative experiments of November 1984 and April 1985 have provided data to validate the SAGE II products. Several ozone profile comparisons have been possible; they generally confirm SAGE II profiles above 20 km. However there are not enough comparisons in very close coincidence to get firm conclusions at lower levels, where the profiles are very variable with time and location, and where the SAGE II results are dubious, due to the large aerosols correction. Only one NO2 profile has been obtained, but it is almost in perfect agreement with the SAGE II profiles, which are very stable over the experiment zone. This certainly provides a good validation for SAGE II NO2 data, especially between 20 and 30 km, where the retieval is delicate. Most of the analysis effort has been devoted to the aerosol data validation for the four channels. The April experiment was especially important, because the aerosol layer was stable and homogeneous; but the November results lead to similar conclusions. Different optical observations, lidar backscattering, limb radiances, degree of polarization have been analysed with the SAGE II extinction profiles at four wavelength. All the results are consistent, in terms of profile and size distribution, which seems a good indirect validation of SAGE II aerosol data. It has been checked that a modification of SAGE II short wavelength data as suggested by an American validation experiment would be inconsistent with our observations. ACKNOWLEGMENTS
The different participants were supported by their national organizations. The work done by the Laboratoire d’Optique Atmosphérique de Lille was supported by the Centre National d’Etudes Spatiales under Contracts N°84—1230 and 85—1230. REFERENCES
1— L.E. Mauldin, N.H. Zaun, M.P. Mc Cormick, J.H. Guy, W.R. Vaughn — Stratospheric aerosol and gas experiment II instrument: a functionnal description. Optical Engineering, 24, 307—312 (1985).
2 — J. Lenoble, P. Pruvost — Inference of the aerosol Angstrom coefficient from SAGE short—wavelength data. J. Climate Appl. Meteor. 22, 1717—1725 (1983).
J. Lenoble
(3)232
3 — J.Y. Balois, L. Gonzalez, N. Herman, P. Lecomte, J. Lenoble, R. Santer, C. Verwaerde — Stratospheric aerosol observations from a balloon borne polarimetric experiment. Applied Optics, in press. 4 — Compte—rendu de la campagne MAP/GLOBUS NO 85, tome 1. Rapport N°054 CNES/CT/DRT/IBA/CL (1985). x 5 — V.R. Oberbeck, J. Livingston, R. Pueschel, K. Snetsinger, G. Ferry, W. Fong, S. Verma — Aerosol sampling for the August 7th and 9th, 1985 SAGE II validation experiment. Sixth Conf. on Atm. Rad. AMS Williamburg May 12—16 (1986). Table 1
Coordinator of the European correlative experiments: J. LENOBLE Participants M. Ackerman — Institut d’Aéronomie Spatiale — Bruxelles — Belgique. W. Attmannspacher — Deutscher Wetterdienst Meteorologisches Observatorium — Hohenpeis— senberg— B.R.D.. D. De Muer — Institut Royal Météorologique — Bruxelles — Belgique. G. Fiocco and G.P. Gobbi — Rosa Instituto di Fisica — Roma — Italia. M. Herman and R. Santer — laboratoire doptique Atmospherique — lille — France. G. Mégie and J. Pelon — Service d’Aéronomie — Verrières le Buisson — France. J.P. Pommereau — Service d’Aéronomie — Verrières le Buisson — France. H. Reiter — Institut fUr Atmosphärische Umweltforschung — Garmisch — Partenkirchen — B.R.D.. L. Stefanuti — IROE — CNR — Firenze — Italia. The balloon launches were made by the french Centre National d’Etudes Spatiales (CNES) at its launch site of Aire sur lAdour. Latitude (N) Ground stations
Aire sur l’Adour Garmisch—Partenkirchen Hohenpeissenberg Observatoire de Haute Provence Uccle Frascatti Florence
Longiture (E)
44 47.5 48
0 11 11
44 51 42 44
6 4 13 11
~
a(km-’)
o~ iO~
10—6
Figure la
—
1O—~
3
io—
—.
a(km-1)
1O_2
Comparison of LaRC (dashed line)
5~rLOA (solid line) retrieved profiles for o
(1.02).
0
________________________
10—6
1O~
iO—~
Figure 1~ — Same as figure la for a er( 45)
iO—~
10_2
SAGE II Data Inversions
30
30
___________________________
~
(3)233
___________________________
z(km)~j~~
a(km—1)
0
iO~~
10_6
i0—~
i0—~
10_2
Figure 2 — Average of five SAGE II aerosol extinction profiles at 1.02 pm with the stan— dard deviations: 04—21, 5O°14N, 1°l9E 04—22, 47°3ON, 2l°29E 04—22, 47°O9N, 357°O1E 04—23, 44°O3N, 17°O8E 04—23, 43°8ON, 352°BOE
10_6
~
io—~
iO—~
1O_2
______________________________
z(km)
a(km-’)
0 10_6
3
io—
Figure 3 — Aerosol extinction profiles at 1.02 pm deduced from Garmisch—Partenkirchen (April 21) lidar backacattering coefficient at 0.694 pm with various aerosol LND models: Veff — 0.1, = 0.55 pm Vff = 0.25, rf~ = 0.22 pm V = 0.1, r = 0.15 pm V5 = 0.25, r5 ~ = 0.10 pm eff eff Veff = 0.25, rff = 0.05 pm
30. z(km)
a(km-’)
0
a(kr
0 io—~
io—4
io—~
Figure 4 — Comparison of the average SAGE II aerosol extinction profile at 1.02 pm with the lidar deduced extinction profile, SAGE II profile of figure 2 Lidar profile, converted with an aerosol model: r = 0.35 pm, V = 0.25, a = 1.60, r = O~r~ pm for the lgwer curve; rff = 0.10 pm, V = 0.25, o = 1.60, rm = O.~S~’ pm, for the upper curve.
.—,—,-.-.-,.,1
~
10_6
iO~
10~
1O~
Figure 5 — Comparison of SAGE II profile on November 30 with the lidar deduced extinction profile. Lidar at Frascatti about 100 km from SAGE event. Conversion with LND models (—_r ~~=~3S pm;——--r ~~=•22 pm) a e
(3)234
J. Lenoble
102
_________________________________
28km S
N
25km
20km 15km
100
.3
.4
.5
.6
.7
.8
.9
1.0
Figure 6 — Spectral variation of the aerosol ex5~’(X)— April 22 — 47°3ON— tinction coefficient a 2l°29E.The curves reoresent the best fit aer aer 2 log a (X) — log a (1.0) = a logA — BM(logx) and the points are the measured values.
/_—;f.~
IMP
/
I
.28
22
~
1
0
2
4
Figure 7 — Diagram a — MB (M = Zn 10 = 2.302) for LND aerosol models: solid curves for constant variance: l._V 5ff = .1, 2~ ~ef~ = .25, 3 — Vff = 4V ~ = 1.0; dashec—notted curves for constant effective radius, the number on the curves are rff. The points on the diagram correspond to the average values, with their standard deviations from the five SAGE II events; the number near each point is the altitude in km.
SAGE II Data Inversions 80 ____________________________
____________________________
0
(3)235
0
+180
—180
0
+180
0
+180
—180
0
+180
80
80
35 z(km) 30
u!,,,J,rIrI
t~~/.\ ~cJ~
0pm, 180 +180 Figure Azation (curves), (z = = 850 15.0 8(z in rim, —~ percent; versus km): Comparison on(b)vqf the (a) the measured right reff scattering between = A —180 .37 = (a) (dots) 1650 the pm, vmm. degree and computed On = of .17; curves the polarileft (b) r~. bottom vff = = 0.17; .55 = 21.1 t~m) neff =curves = .17; 0.40 pm, rangle. Vff (~ =0=Top 18.2 0.29 0.17. km), L.~.L~_’ I middle I pm,
.~
25
<
20
“ 15 10_6
.
io-~
iO—~
~
iO~
10_2
Figure 9 — Comparisons of the aerosol extinction profiles of SAGE II with the aerosol extinction profiles retrieved from the balloon limb radiance observations: dashed line, balloon A = 0.44 pm; dotted line SAGE II A = 0.45 pm.
J. Lenoble
(3)236
40
___________________
1z~cm) 30
20~ ,
a(km-1)
—
uu, 4 b-
.
-
—0
-
io~
102
Figure 10 — Comparison of SAGE II ozone profiles (April 22 — 19.05 GMT) retrieved by LaRC (thin solid line), LOA (dotted line), and of ozone sonde profile (thick line) at Aire sur l’Adour (April 22 around 16 GMT); distance between the two profiles is about 500 km.
50 ____________________________________ I z(km) 40
30,
I
_.,,
-
—
V
20
-~ ‘C
‘C
‘C ‘C
‘C
a(km-1) 10.
10~
iO’’
io~
io~
io—~
10_2
Figure 11 — NO extinction coefficient profile at .448 pm: from ~AGE II, April 22, lat. 47.18M, long. 2.93W, LOA inversion (dotted line) and LaRC inversion (solid line); from balloon measurements (X) April 20, lat. 44.59N, long. 1.06W.
0273-1177/87 $0.00 + .50 Copyright © COSPAR
VALIDATION OF SAGE II DATA INVERSIONS BY THE EUROPEAN CORRELATIVE EXPERIMENTS J. Lenoble Laboratoire d’Optique Atmospherique, Université des Sciences et Techniques de Lille Flandres Artois, U.F.R. de Physique, 59655 Villeneuve d’Ascq Cédex, France
ABSTRACT
An European program of correlative experiments has been organized in order to validate SAGE II data during three periods of observation over Europe (November 1984, April 1985, October 1985). About ten groups from France, Belgium, Germany and Italy were participating. The correlative data are lidar aerosol profiles, soundings of ozone profiles, and balloon observations, including limb photographies, polarimetric measurements of the aerosol scattered light and nitrogen dioxide extinction measurements. Results of the comparisons between SAGE II inverted data and correlative data are presented. The analysis of the aerosol correlative observations with the SAGE II four aerosol channel data, in term of profile and size distribution is perfectly consistent and provide a good indirect validation. The NO 2 comparison shows a good agreement between SAGE II and correlative data. INTRODUCTION The Stratospheric Aerosol and Gas Experiment II (SAGE II) is a seven channel occultation experiment /1/. It is expected to provide ozone, nitrogen dioxide, water vapor content profiles, and aerosol extinction profiles at four wavelengths. SAGE II is flown on the Earth Radiation Budget Satellite (ERBS) with a 610 km circular orbit at 57° inclination. It observes sunsets and sunrises, with a tangent point shifting approximately between BO°Sto 80°N in about a month; 15 events per day (sunset or sunrise) distant of about 24° in longitude are recorded in a narrow latitude band. A programme of correlative experiments, aiming at the validation of SAGE II data has been developped in Europe. The three main periods of observations were November 1984, April 1985, September—October 1985.About ten groups from Belgium, France, Germany and Italy were participating in these validations. The first two sections present the analysis of SAGE II products and the organization of the European correlative experiments, with the available data. The third section is devoted to the problem of the aerosol retrieval, including their vertical profile and their size distribution. The fourth section presents the comparison results for the ozone and the nitrogen dioxide profiles. ANALYSIS OF SAGE II DATA The raw radiances are converted into transmittances, averaged over 1 km; they are given with their standard deviation versus the tangent height, on the SAGE II PROFILE tapes provided by NASA to the users. The tapes contain also the meteorological data, which are used to compute and to correct the Rayleigh contribution to the measured transmissions. We will leave out of this discussion the 940 nm channel, because no water vapor measurements have been made during the European experiments, and because its inversion needs a particular treatment for the gaseous line transmission. In the six other channels (1020 nm, 600 nm, 525 nm, 453 nm, 448 nm, 385 nm) the extinction due to aerosols, O3~ or NO2 varies slowly within the filter widths (about 3 nra for 453 and 448 nm, and 20 nm for the other channels); the inversion is straightforward and leads to the vertical profiles of the extinction coefficients a(X) for the six channels. Error bars on o(X) are evaluated from the experimental error on the transmission and from the expected error on the Rayleigh correction /2/. At 1020 nm the extinction is only due to aerosols. In the 600 nm channel, the main contribution is due to the ozone absorption, at least above 20 km; below this level the aerosol correction becomes large and the results are of poor quality. The two narrow channel transmission ratio gives (o(.448) — o(.453)J, which is mainly due to NO , with a small correction for 0 and aerosols, above 25—30 km; at lower levels the aeroso~contribution is too large to al~ow a good retrieval of NO2. The 03 and NO2 extinction profiles can be converted into number density profiles, given the absorption cross sections.
(3)227
(3)228
J. Lenoble
With the necessary 03 and NO
2 corrections, the aerosol extinction coefficient profiles are obtained at 525 nm, 453 ns, and 385 nra; however between 25—30 km, the commanding role in extinction shifts from aerosols to NO2, making the results dubious, for both components. Whereas the aerosol extinction profile at 1020 nra can be retrieved down to 3 km from the ground in cloudless atmospheres, the short wavelength profiles are limited, by the increasing Rayleigh contribution, at respectively about 10, 12 and 14 km. The conversion of aerosol extinction into number density needs the knowledge of the aerosol size distribution n(r), which can be sought from the spectral variation of the extinction c,aer(X). However a direct inversion of the experimental data is not feasible, because of the rather large errors on the three short wavelength channels; a smoothing of the data has been introduced, using the best fit approximation 5~’(X) = 9~ 2 (1) 9~n o 0aer(10) — a ZnX — B(2~nX) This means that we will be able to derive two parameters of the size distribution (to be chosen and related to a and B). An inversion algorithm has been developed at the Laboratoire d’Optique Atmosphérique de Lille (LOA) in order to derive the extinction profiles from the transmission profiles. The comparison of the results with the extinction derived at Langley Research Center (LaRC) and given on the SAGE II PROFILE tapes is generally good (Figures 1—9—10), with some exceptions in the altitude ranges, where the data have to be considered with caution, as explained above. EUROPEAN CORRELATIVE EXPERIMENTS The list of the participants to the European correlative experiments is given in table 1, with the geographical position of the ground stations. The balloon experiments were launched from Aire sur l’Adour by the french Centre National d’Etudes Spatiales. Three major coordinated experiments have been organized for SAGE II validation: i/ in November 1984, during the two periods when SAGE II was observing sunsets at the latitudes of Europe, i.e. 10—14 November and 26—30 November; ii/ in April 1985, from 20 April to 23 April (sunsets); iii/ in September—October 1985, with the MAP—GLOBUS NO experiment starting on 19 September , just after the sunset observations of SAGE II on 15218 September and an aerosol—ozone experiment during the sunrise observations of SAGE II on 12—14 October. A few other individual observations of ozone or aerosol backscattering have been performed during SAGE II passages over Europe and are available for further validations. The balloon polarimetric experiment has been flown again in coincidence with a SAGE II sunset observation on 21 April 1986. Ozone soundings During the three periods ozone Komhyr—ECC sondes were launched from Garmisch— Partenkirchen and Ozone Brewer Mast sondes from Aire sur l’Adour, Hohenpeissenberg, Observatoire de Haute Provence (OHP) and Uccle; from previous comparisons it is expected that the Brewer Mast sondes give values slightly larger in the troposphere and slightly smaller in the stratosphere than the Komhyr—ECC sondes. All the ozone data have been transmitted to the experiment coordina~r~nd converted into extinction coefficients at 600 nm, using a cross section of 4.84.10 cm , for comparison with SAGE II data. Lidar soundings Lidar backscattering aerosol profiles have been obtained during the three main periods with a ruby lidar (694 nm) at Garmish—Partenkirchen and with a Nd YAG lidar (532 nra) at Florence, Frascatti and OHP. In order to compare with the SAGE II extinction profiles at 1020 mm, the aerosol backscattering profiles have to be converted into extinction, using an aerosol model. It has been checked that the conversion is not very sensitive to the exact size distribution, but can be fixed by an effective radius rff defined by reff
=
r3 n(r)dr
/ 1
r2 n(r)dr
(2)
The model chosen, which may vary with altitude, must be compatible with the spectral variation of the SAGE II extinction coefficient and with the other correlative observations.
SAGE II Data Inversions
(3)229
Balloon experiments Three instruments were flown on correlative experiment programme.
balloons
from
Aire
sur
l’Adour
during the
SAGE
II
Limb camera. Photographies of the earth limb at 840 nm, 440 nm and 375 nm were taken with the camera of the Institut d’Aéronomie Spatiale de Belgique (IASB) on 10 November 1984, and 22 April 1985. The radiance profiles at 30°scattering angle were inverted at the lASS in order to provide aerosol extinction profiles at the three wavelengths; the two shortest wavelengths are very close to SAGE II channels 450 ns and 385 nm, allowing a direct comparison. Infrared polarimeter. The radiance and the degree of polarization at 850 mm and 1650 nm are recorded scanning in an horizontal plane for various altitudes. The instrument built by the LOA was flown on 10 and 28 November 1984, on 22 April 1985, and on 12 October 1985. The radiance at 850 nm and 30° scattering angle is inverted to provide the extinction coefficient; the conversion of extinction at 850 nm to extinction at 1020 nm is not very sensitive to the aerosol model. The polarization diagram allows a retrieval of the size distribution /3/. occultation spectrometer. The occultation spectrometer of the Service d’Aéronomie (SA) was flown on 20 April 1985. The data were analysed at the SA, and results provided to the coordinator as a NO 2 number density profile. In order to compare with SAGE II data, they were con~rt~d into an extinction coefficient profile at 448 rim using the cross section 5.73 10 cm . The MAP—GLOBUS NO experiment has been described elsewhere /4/ and the data are presently analysed by the participants. Only the SAGE II data for November 1984 and April 1985 have been received till now, from NASA. The main results of the comparison for these two periods will be presented in the next sections. AEROSOL During the April 1985 experiment the aerosol layer was very homogeneous and stable; the five SAGE II aerosol profiles over the experiment zone were very similar for all channels. The average of these five profiles at 1020 mm is shown in figure 2. This is a very advantageous situation for validation purpose and we will focus most of our discussion on this case. In November 1984, the aerosol layer was more variable, especially in mid—November, and we will present only some typical results. Comparison between SAGE II and lidar data The backscattering profile obtained at Garmisch—Partenkirchen on 21 April is of good quality up to 30 km; it has been converted into extinction coefficient, using various log normal (LND) aerosol size distributio~s: n(r)
1
exp
=
/~ir~no
r~ L
nra 2 2~n o
1
J
the effective radius rff defined previously is related to the mode radius rm by reff
=
r
exp
(
5q2 ~ ~.n o)
;
(4)
we will use also the effective variance 2O) — 1 (5) Vff exp (in Some of the extinction profiles deduced from the lidar profile are presented in figure 3; it appears that the conversion factor from backscatttering to extinction is mainly sensitive to ref and does not depend much on the variance of the size distribution. The extinction profile varies slightly with the model, as long as r is larger than 0.2 I~m, but it becomes strongly model dependent for smaller particles. ~e best agreement between lidar and SAGE II profiles is found for a model with r around 0.35 3~m for altitudes smaller than 20—21 km and for a model with rf around O.X~~Amabove 22—23 km. A transition layer between 20—23 km corresponds apparently a very rapid change of the particle sizes. Figure 4 compares the SAGE II profile averaged from the five profiles (figure 2), to the lidar profile converted into extinction with an aerosol effective radius of 0.35 pm for the lower levels and of 0.10 pm for the higher levels; the error bars on the lidar profiles correspond only to the statistical fluctuations.
(3)230
J. Lenoble
On 30 November 1984 a lidar profile was obtained at Frascatti in very close coincidence to the SAGE II observation; the result of the comparison is presented in figure 5. The aerosol size distribution deduced from the spectral variation of extinction The lidar comparison suggests a decrease of the aerosol size with altitude, wich should reflect on the spectral distribution of the extinction coefficient as observed by SAGE II. For the sake of simplicit~, 0aer(1•02) has been taken as the value at 1.00 pm, and the best fit curve to aer (X)/ae (1.00), defined by equation (1) has been forced to pass by 1; this seems justified because the measure is of better quality in the 1020 mm channel than in the short wavelength channels. As can be seen in figure 6 the experimental points are generally very close to the fitting curve. A rough comparison with LND models shows that the experimental curves correspond approximately to LND size distributions with r ~ = 0.35 pm at 15 km, r ~ = 0.28 pm at 20 km, r ~ between 0.15 and 0.10 pm at 25 km an~r ~ between 0.10 I 0.05 ~m at 28 km. This confiFms the results found previously: in ord~ér to find agreement between the SAGE II profile and the lidar profile, we had to make the conversion of backscattering into extinction using an aerosol model with r ~ decreasing from about O.35pm below 20 km to about 0.10 1jn above 23 km. A more detaile~analysis can be sought, using a diagram of the coefficients a andBof equation (1). Figure 7 exhibits the behaviour of (a,B ) for LND aerosol models with various Vff and rff. For a given variance, a increases when the effective radius decreases, whereas B is mainly sensitive to the variance and decreases for large variances. The knowledge of a arid B from experimental data allows on the diagram of figure 7 an approximate determination of the two parameters of a LND size distribution, i.e. V and r , orG and r • For a bimodal size distribution, more eff and they eff cannot be deauced from the only knowledge of a and 8. parameters are necessary However B decreases very fast when two LND size distributions are mixed together, increasing from zero the contribution of one mode. Therefore very low or even negative values of B could suggest the presence of a bimodal size distribution. The average of a and B~ for the five SAGE II events of April, with their standard deviations at various altitudes, are plotted on figure 7. Despite the large dispersion of the points, the results on figure 7 confirm the general decrease of the aerosol sizes, accompanied by an increase of the variance when the altitude increases: z z z z z
= = = = =
16—18 20—21 22 km 23—24 25—27
km km km km
rff rff reff rff rff
.35 .28 .22 .15 .05
pm pm pm pm to,lO pm
vff Vff
veff Vff Vff
.15 to .20 .15 .17 .30 .30
Balloon borne polarization measurement The infrared polarimeter RADIBAL was flown on a CNES balloon from Aire sur l’Adour on 22 April 1985. Measurements of the degree of polarization at 850 nm and 1650 nm were made during the ascent between 15—22 km and 27—30 km. Unfortunately the instrument broke down at this level and no measurements were recorded during the descent, when the gondolla should have been more stable, and the sun lower on the horizon. In order to reduce the influence of the small oscillations of the gondolla, the data are cumulated for three rotations. The contribution of the solar radiation reflected from the ground and the lower atmosphere, has been taken care of, assuming an albedo of 0.20 at 850 nm and 0.15 at 1650 nm, which were the values measured beginning of May 1984 in the same conditions of clear sky. No direct inversion of the data has been tried, but the measured polarization has been compared with the polarization computed using the SAGE II extinction profile at 1020 nra, and the aerosol size distribution deduced from SAGE II spectral extinction. The results are presented for various altitudes between 15 km and 21.5 km in figure 8, and the agreement is very good; the model used (curves a)are LND with Ve f 0.17 (0=1.48) and reff = 0.37 pm (r5 0.25 pa) at 15 km, r5ff=O.29 pm (rm 0.20 pm) a~ove. During the American SAGE II validation experiment, direct in situ measurements of the aerosol size distribution have been made, and the extinction computed from these size distributions have been compared with the SAGE II extinction values. A good agreement was found at 1020 nra, but at the short wavelengths the SAGE II values seem larger than the computed ones, by approximately a factor 2 at 385 nm /5/. We do not have in situ size distributions available to try the same comparison. But we have checked if the conclusion of Oberbeck et al /5/ is compatible with our observations. For this purpose, we have arbitrarily divided our SAGE II extinction coefficient at 385 mm by a factor 2; this lead to an effective radius, r 55 pa at 15 km and ref4. .40 pm at 18—20 km. Figure 8 presents the degree of polarizat~oncomputed using the new size distribution (curves b). It is clear tha.t such a reduction by a factor 2 of the SAGE II extinction at 385 nm leads to a size distribution incompatible with the polarization measurements.
SAGE II Data Inversions
(3)231
Photographies of the limb radiance were made by the Institut d’Aéronomie Spatiale de Belgique (lASS) at Aire sur l’Adour on 22 April, simultaneously with the polarization measurements. The cameras were flown on a separate balloon and they recorded the limb radiance for low sun elevation, at various solar azimuths, and for three wavelengths 840 mm, 440 nm and 375 nm. The extinction is deduced from the radiance measured at 30° scattering angle and the Rayleigh extinction is substracted to obtain the aerosol extinction. At 30° from the sun, and for the tangent height of 20 km, the air mass observed was very close to the SAGE II tangent
point.
A comparison between the balloon and the SAGE II extinction profiles at 440 nra is presented in figure 9. The general agreement is very good, above 22 km. Fine structures of the aerosol layer appear on the balloon profiles, especially at the short wavelengths, which cannot be detected with the SAGE II resolution of 1 km. OZONE AND NITROGEN DIOXIDE
The ozone sounding profiles compared on the same day at different locations, or for successive days at the same location present differences, which can be retrieved 4dation on the SAGE more II profiles except for the experiment a=d perind. mr~kera precisea ~al difficult, when a close zone coincidence can be!4owever found. this Figure 10 presents comparison for April experiment. A profile of NO was obtained on 20 April 1985 at 19.00 GMT; the solar occultation spectrometer was ~‘lownon a balloon launched from Aire sur l’Adour and the tangent point for an altitude of 25 km was 44°59N, l°O6W. The six NO 2 profiles for the SAGE II events (sunsets) over Europe from 20 April to 23 April are almost identical between 22 and 40 km with differences much smaller than the error bars; this give sense to the comparison with a balloon profile which is not in close coincidence with a SAGE II event. Figure 11 presents the NO2 extinction profile at 448 nm retrieved from SAGE II data on 22 April (with the two retrieval algorithms) and the balloon profile on 20 April. The agreement is very good and particularly comforting in the altitude range between 20 and 30 km, where the aerosol contamination is important and make the NO2 data not very reliable. CONCLUSION
The two European correlative experiments of November 1984 and April 1985 have provided data to validate the SAGE II products. Several ozone profile comparisons have been possible; they generally confirm SAGE II profiles above 20 km. However there are not enough comparisons in very close coincidence to get firm conclusions at lower levels, where the profiles are very variable with time and location, and where the SAGE II results are dubious, due to the large aerosols correction. Only one NO2 profile has been obtained, but it is almost in perfect agreement with the SAGE II profiles, which are very stable over the experiment zone. This certainly provides a good validation for SAGE II NO2 data, especially between 20 and 30 km, where the retieval is delicate. Most of the analysis effort has been devoted to the aerosol data validation for the four channels. The April experiment was especially important, because the aerosol layer was stable and homogeneous; but the November results lead to similar conclusions. Different optical observations, lidar backscattering, limb radiances, degree of polarization have been analysed with the SAGE II extinction profiles at four wavelength. All the results are consistent, in terms of profile and size distribution, which seems a good indirect validation of SAGE II aerosol data. It has been checked that a modification of SAGE II short wavelength data as suggested by an American validation experiment would be inconsistent with our observations. ACKNOWLEGMENTS
The different participants were supported by their national organizations. The work done by the Laboratoire d’Optique Atmosphérique de Lille was supported by the Centre National d’Etudes Spatiales under Contracts N°84—1230 and 85—1230. REFERENCES
1— L.E. Mauldin, N.H. Zaun, M.P. Mc Cormick, J.H. Guy, W.R. Vaughn — Stratospheric aerosol and gas experiment II instrument: a functionnal description. Optical Engineering, 24, 307—312 (1985).
2 — J. Lenoble, P. Pruvost — Inference of the aerosol Angstrom coefficient from SAGE short—wavelength data. J. Climate Appl. Meteor. 22, 1717—1725 (1983).
J. Lenoble
(3)232
3 — J.Y. Balois, L. Gonzalez, N. Herman, P. Lecomte, J. Lenoble, R. Santer, C. Verwaerde — Stratospheric aerosol observations from a balloon borne polarimetric experiment. Applied Optics, in press. 4 — Compte—rendu de la campagne MAP/GLOBUS NO 85, tome 1. Rapport N°054 CNES/CT/DRT/IBA/CL (1985). x 5 — V.R. Oberbeck, J. Livingston, R. Pueschel, K. Snetsinger, G. Ferry, W. Fong, S. Verma — Aerosol sampling for the August 7th and 9th, 1985 SAGE II validation experiment. Sixth Conf. on Atm. Rad. AMS Williamburg May 12—16 (1986). Table 1
Coordinator of the European correlative experiments: J. LENOBLE Participants M. Ackerman — Institut d’Aéronomie Spatiale — Bruxelles — Belgique. W. Attmannspacher — Deutscher Wetterdienst Meteorologisches Observatorium — Hohenpeis— senberg— B.R.D.. D. De Muer — Institut Royal Météorologique — Bruxelles — Belgique. G. Fiocco and G.P. Gobbi — Rosa Instituto di Fisica — Roma — Italia. M. Herman and R. Santer — laboratoire doptique Atmospherique — lille — France. G. Mégie and J. Pelon — Service d’Aéronomie — Verrières le Buisson — France. J.P. Pommereau — Service d’Aéronomie — Verrières le Buisson — France. H. Reiter — Institut fUr Atmosphärische Umweltforschung — Garmisch — Partenkirchen — B.R.D.. L. Stefanuti — IROE — CNR — Firenze — Italia. The balloon launches were made by the french Centre National d’Etudes Spatiales (CNES) at its launch site of Aire sur lAdour. Latitude (N) Ground stations
Aire sur l’Adour Garmisch—Partenkirchen Hohenpeissenberg Observatoire de Haute Provence Uccle Frascatti Florence
Longiture (E)
44 47.5 48
0 11 11
44 51 42 44
6 4 13 11
~
a(km-’)
o~ iO~
10—6
Figure la
—
1O—~
3
io—
—.
a(km-1)
1O_2
Comparison of LaRC (dashed line)
5~rLOA (solid line) retrieved profiles for o
(1.02).
0
________________________
10—6
1O~
iO—~
Figure 1~ — Same as figure la for a er( 45)
iO—~
10_2
SAGE II Data Inversions
30
30
___________________________
~
(3)233
___________________________
z(km)~j~~
a(km—1)
0
iO~~
10_6
i0—~
i0—~
10_2
Figure 2 — Average of five SAGE II aerosol extinction profiles at 1.02 pm with the stan— dard deviations: 04—21, 5O°14N, 1°l9E 04—22, 47°3ON, 2l°29E 04—22, 47°O9N, 357°O1E 04—23, 44°O3N, 17°O8E 04—23, 43°8ON, 352°BOE
10_6
~
io—~
iO—~
1O_2
______________________________
z(km)
a(km-’)
0 10_6
3
io—
Figure 3 — Aerosol extinction profiles at 1.02 pm deduced from Garmisch—Partenkirchen (April 21) lidar backacattering coefficient at 0.694 pm with various aerosol LND models: Veff — 0.1, = 0.55 pm Vff = 0.25, rf~ = 0.22 pm V = 0.1, r = 0.15 pm V5 = 0.25, r5 ~ = 0.10 pm eff eff Veff = 0.25, rff = 0.05 pm
30. z(km)
a(km-’)
0
a(kr
0 io—~
io—4
io—~
Figure 4 — Comparison of the average SAGE II aerosol extinction profile at 1.02 pm with the lidar deduced extinction profile, SAGE II profile of figure 2 Lidar profile, converted with an aerosol model: r = 0.35 pm, V = 0.25, a = 1.60, r = O~r~ pm for the lgwer curve; rff = 0.10 pm, V = 0.25, o = 1.60, rm = O.~S~’ pm, for the upper curve.
.—,—,-.-.-,.,1
~
10_6
iO~
10~
1O~
Figure 5 — Comparison of SAGE II profile on November 30 with the lidar deduced extinction profile. Lidar at Frascatti about 100 km from SAGE event. Conversion with LND models (—_r ~~=~3S pm;——--r ~~=•22 pm) a e
(3)234
J. Lenoble
102
_________________________________
28km S
N
25km
20km 15km
100
.3
.4
.5
.6
.7
.8
.9
1.0
Figure 6 — Spectral variation of the aerosol ex5~’(X)— April 22 — 47°3ON— tinction coefficient a 2l°29E.The curves reoresent the best fit aer aer 2 log a (X) — log a (1.0) = a logA — BM(logx) and the points are the measured values.
/_—;f.~
IMP
/
I
.28
22
~
1
0
2
4
Figure 7 — Diagram a — MB (M = Zn 10 = 2.302) for LND aerosol models: solid curves for constant variance: l._V 5ff = .1, 2~ ~ef~ = .25, 3 — Vff = 4V ~ = 1.0; dashec—notted curves for constant effective radius, the number on the curves are rff. The points on the diagram correspond to the average values, with their standard deviations from the five SAGE II events; the number near each point is the altitude in km.
SAGE II Data Inversions 80 ____________________________
____________________________
0
(3)235
0
+180
—180
0
+180
0
+180
—180
0
+180
80
80
35 z(km) 30
u!,,,J,rIrI
t~~/.\ ~cJ~
0pm, 180 +180 Figure Azation (curves), (z = = 850 15.0 8(z in rim, —~ percent; versus km): Comparison on(b)vqf the (a) the measured right reff scattering between = A —180 .37 = (a) (dots) 1650 the pm, vmm. degree and computed On = of .17; curves the polarileft (b) r~. bottom vff = = 0.17; .55 = 21.1 t~m) neff =curves = .17; 0.40 pm, rangle. Vff (~ =0=Top 18.2 0.29 0.17. km), L.~.L~_’ I middle I pm,
.~
25
<
20
“ 15 10_6
.
io-~
iO—~
~
iO~
10_2
Figure 9 — Comparisons of the aerosol extinction profiles of SAGE II with the aerosol extinction profiles retrieved from the balloon limb radiance observations: dashed line, balloon A = 0.44 pm; dotted line SAGE II A = 0.45 pm.
J. Lenoble
(3)236
40
___________________
1z~cm) 30
20~ ,
a(km-1)
—
uu, 4 b-
.
-
—0
-
io~
102
Figure 10 — Comparison of SAGE II ozone profiles (April 22 — 19.05 GMT) retrieved by LaRC (thin solid line), LOA (dotted line), and of ozone sonde profile (thick line) at Aire sur l’Adour (April 22 around 16 GMT); distance between the two profiles is about 500 km.
50 ____________________________________ I z(km) 40
30,
I
_.,,
-
—
V
20
-~ ‘C
‘C
‘C ‘C
‘C
a(km-1) 10.
10~
iO’’
io~
io~
io—~
10_2
Figure 11 — NO extinction coefficient profile at .448 pm: from ~AGE II, April 22, lat. 47.18M, long. 2.93W, LOA inversion (dotted line) and LaRC inversion (solid line); from balloon measurements (X) April 20, lat. 44.59N, long. 1.06W.