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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. D5, PAGES 9073-9090, MAY 20, 1995

Stratospheric aerosol and gas experiments I and II

comparisons with ozonesondes

Robert E. Veiga

Science Applications International Corporation, Hampton, Virginia

J

Derek M. Cunnold

Georgia Institute of Technology, Atlanta

William P. Chu and M. Patrick McCormick

NASA Langley Research Center, Hampton, Virginia

Abstract. Ozone profiles measured by the Stratospheric Aerosol and Gas Experiments(SAGE) I and II are compared with ozonesonde profiles at 24 stations over the periodextending from 1979 through 1991. Ozonesonde/satellite differences at 21 stations withSAGE II overpasses were computed down to 11.5 km in the midlatitudes, to 15.5 km

in the lower latitudes, and for nine stations with SAGE I overpasses down to 15.5 kin.The set of individual satellite and ozonesonde profile comparisons most closelycolocated in time and space shows mean absolute differences relative to the satellitemeasurement of 6 -- 2% for SAGE II and 8 +- 3% for SAGE I. The ensemble of

ozonesonde/satellite differences, when averaged over all altitudes, shows that forSAGE II, 70% were less than 5%, whereas for SAGE I, 50% were less than 5%. Thebest agreement occurred in the altitude region near the ozone density maximum wherealmost all the relative differences were less than 5%. Most of the statistically significantdifferences occurred below the ozone maximum down to the tropopause in the regionof steepest ozone gradients and typically ranged between 0 and -20%. Correlationsbetween ozone and aerosol extinction in the northern midlatitudes indicate that

aerosols had no discernible impact on the ozonesonde/satellite differences and on theSAGE II ozone retrieval for the levels of extinction encountered in the lower

stratosphere during 1984 to mid-1991.

Introduction

Over the last 3 decades, vertical profiles of ozone extend-ing from the ground into the lower stratosphere have beenroutinely measured by balloon-borne instruments (ozone-sondes) at a number of stations located predominantly in thenorthern hemisphere. With the advent of space-based plat-forms it became possible to measure ozone profiles withexpanded coverage over the Earth. The longest record ofsatellite-based high vertical resolution ozone profiles hasbeen generated by the Stratospheric Aerosol and Gas Ex-periments (SAGE) I and II, both developed at NASALangley Research Center [McCormick et al., 1979; Mauldinet al., 1985]. Both the ozonesonde and the satellite data have

been extensively used to quantify the processes governingatmospheric ozone variation. This paper presents the resultsof a statistical comparison designed to estimate any altitudedependent relative bias between the ozonesonde and thesatellite measurements•

SAGE I and SAGE II are conceptually identical multi-channel spectrophotometers which sense solar intensitythrough a slant path in the atmosphere as the instrumentorbits into (sunset) or out of (sunrise) the Earth's shadow.Ozone measurements are made in the Chappuis region of the

Copyright 1995 by the American Geophysical Union.

Paper number 94JD03251.0148-0227/95/94JD-03251 $05.00

spectrum at 600 nm with a vertical resolution of 1 kmthrough a slant path in the atmosphere approximately 220 kmin length at any given altitude. The quality of the measure-

ment in the lower stratosphere depends primarily on theextent to which interfering species such as aerosols or otherabsorbers can be accurately removed in the ozone retrieval[Chu and McCormick, 1979; Chu et al., 1989]. In addition tothe 600 nm channel, SAGE I utilized transmission measure-ments at 1000, 450, and 385 nm while SAGE II utilizeschannels at 1000, 940, 525,453,448, and 385 nm to charac-

terize other species. The ozone measurement's quality in thetroposphere is impacted by the presence of clouds andaerosols in the instrument field of view. A unique aspect ofthe solar occultation measurement is that long-term sensordrift is effectively removed via an exoatmospheric calibra-tion made during every profile measurement [Watson et al.,1988]. CunnoM et al. [1989] provided the following errorestimates for SAGE I and SAGE II in the altitude region of24-36 km: 7% systematic bias, 5% random error, and refer-ence altitude uncertainties of 0.25 km (SAGE I) and 0.2 km(SAGE II). An analysis of the error budget of the differencebetween SAGE I and SAGE II ozone retrievals over these

altitudes yields an expected systematic error of 6% at 20 kmand 2% between 25 and 30 km [Watson et al., 1988].

One characteristic of the occultation measurements is thatthe instrument makes at most one sunrise and one sunset

profile per orbit. The orbital inclinations of SAGE I and II

9073

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9074 VEIGA ET AL.: SAGE 1 AND II COMPARISONS WITH OZONESONDES

yield patterns of observations whose latitudes vary slowly

with time. The latitudes ranging from 80°S to 80°N are

sampled in a period of about 1.5 months; however, only the

range from 50°S to 50°N are sampled every season of the

year. SAGE I was launched in February 1979 and operated

until November 1981. SAGE II was launched in October

1984 and continues to provide measurements. Studies using

the SAGE II ozone data set have included analyses of the

ozone quasi-biennial and semiannual oscillations (QBO and

SAO), Antarctic and Arctic springtime ozone variabilities,

and global ozone trends [McCormick and Larsen, 1988,

McCormick et al., 1989a,b; Zawodny and McCormick,1991].

Ozonesondes are launched on balloons at various stations

throughout the world at regular intervals. The types of

sondes in most common use are the electrochemical concen-

tration cell (ECC) [Komhyr, 1969; Komhyr and Harris,

1971], the Brewer-Mast (BM) bubbler [Brewer and Milford,

1960], and the carbon-iodine (CI) sonde [Komhyr, t965].

Each of these sondes employs the same method whereby

ozone is measured by pumping ambient air through an

electrolytic cell containing a buffered potassium iodide solu-

tion where ozone oxidizes the iodide into iodine. The result-

ant cell reaction current is directly proportional to the ozone

concentration in the cell. The major differences between

sonde types lie in the design of the cell and the electrolyte

concentrations. All ozonesondes are flown on a balloon with

a radiosonde for pressure and temperature data. After data

reduction the ozone is converted into units of partial pres-sure.

Above the burst altitude of the balloon the upper level

ozone amount must be taken into account if the integral of

the ozonesonde profile is to be used to estimate total ozone

above the station. During data reduction, the residual ozone

above the burst altitude is estimated by extrapolation of the

measured profile along contours of constant mixing ratio.

Furthermore, the ozonesonde output is not an absolute

measurement of the ozone profile, since ozone losses occur

within the instrument, and the instrument has a finite re-

sponse time [De Muer and Malcorps, 1984]. In order to

compensate for these deficiencies it has been general prac-

tice to multiply the measured ozone profile by the ratio of the

total ozone amount measured at the site by a Dobson

spectrophotometer to the total ozone amount derived from

integration of the ozonesonde profile. This ratio, called the

correction factor, is used by almost all stations as an altitude

independent scaling factor which makes the measured

ozonesonde profile consistent with the Dobson measure-

ment. However, in some cases the correction factor is not

available in the ozonesonde data set. A large deviation of the

correction factor from unity is usually indicative of measure-

ment errors in the ozonesonde profile. Tabulated mean

correction factors indicate that correction factor deviations

are, on average, less than 20% and depend on the station

[Logan, 1985]. Some stations exhibit temporal trends in the

correction factors indicating long-term changes in sonde

flight calibration [Tiao et al., 1986].

Systematic errors in the ozonesonde measurement can

arise from altitude-dependent pump efficiency [Komhyr and

Harris, 1965; Torres, 1981; Harder, 1987], background cur-

rent correction [Komhyr and Harris, 1971; Thornton and

Niazy, 1982, 1983], frequency response of the sensor and

air-sampling system [De Muer and Malcorps, 1984], electro-

lyte concentration, extrapolated upper level column amount,

and altitude determination [Schmidlin, 1988]. Tests con-

ducted on ECCs in a controlled laboratory environment

indicate an accuracy of 3--5% positive error from 300 to 50

hPa and 10% from 50 to 15 hPa with precision estimates of

5-6% from 200 to 10 hPa [Barnes et al., 1985]. These results

are in overall agreement with the Balloon Ozone Intercom-

parison Campaign (BOIC) which was designed to assess the

accuracy and precision of atmospheric ozone measuring

instruments [Hilsenrath et al., 1986]. ECC ozonesonde error

assessments performed by Komhyr et al. [1994] indicate 6%

accuracy and 3% precision from 100 to 10 hPa.

Other SAGE I/II Comparisonswith Ozonesondes

Several comparisons between SAGE I/SAGE II and

ozonesondes have been performed largely as satellite instru-

ment validation studies not specifically addressing the pos-

sibility of altitude dependent systematic relative biases be-

tween the two ozone measuring methods [McCormick and

Reiter, 1982; McCormick et al., 1984; Attmannspacher et

al., 1989; Cunnold et al., 1989; Margitan et al., 1989; WMO,

1990; Barnes et al., 1991 ; De Muer et al., 1990; McDermid et

al., 1990]. De Muer et al. [1990], for example, analyzed a

sample of 24 colocated profile pairs (0.3 day and 600 km) at

Uccle. The SAGE II/Brewer-Mast differences over the

altitude range from 10-26 km indicated SAGE II was lower

in column amount by 4% than the sondes. On the other hand,

SAGE II was higher than the sondes by 3.3% between 26 and

31 km. In Barnes et al. [1991], samples of 14 SAGE II

profiles were compared with seven ECC profiles during a

correlative mission at Natal, Brazil, in March and April

1985, and a difference profile was estimated over the altitude

range from 17.5 to 24.5 km. From 20.5 to 24.5 km, SAGE II

was within 0.5% of the ECC measurements. Below 20.5 km

the 95% confidence intervals were large due to atmospheric

variability and included 0%. Cunnold et al. [1989] computed

the relative difference between a sample of five colocated

measurements between SAGE II and ECCs over the altitude

range from 15.5 to 25.5 km, and their results were consistent

with those presented herein. Cunnold and Veiga [1991]

presented a comparison between SAGE I/II and ozone-

sondes which showed larger ozonesonde/SAGE I differences

than ozonesonde/SAGE II differences and general altitude

dependent differences maximizing between 16 and 18 kin.

The work presented herein is an extension of their method

which utilizes an expanded set of ozonesonde and SAGE I/IIdata.

All of the previous published comparisons described

above were performed using a version of the SAGE II data

set earlier than that used here. The version used here

(version 5.9) has improvements in the aerosol correction to

the ozone below 15 km, and a long-term time-varying mirror

reflectivity correction which affects ozone concentration

above 50 km.

Data Description

The fundamental SAGE I/II measurement of ozone is

number density as a function of geometric altitude at 1 km

increments. Transformation to a pressure altitude coordinate

involves using National Meteorological Center (NMC) data

VEIGAETAL.:SAGEI ANDII COMPARISONSWITHOZONESONDES 9075

interpolatedto theSAGEI/II location,aprocedurewhichaddsanunnecessarylevelofuncertainty.Thusthecompar-isonswereperformedon a geometricaltitudescalebytransformingtheozonesondedatafrompressurealtitudetogeometricaltitude.Therationalefor usingthisaltitudecoordinateisthattheozonesondepressureandtemperaturemeasurementsrepresentamoreaccuraterepresentationoflocalconditionsthandothepressureandtemperaturedatainterpolatedfromtheNMC-griddedanalysis.Theozone-sondeprofilesweremappedto a geometricaltitudescaleusingthehypsometricequationwithgravitationalaccelera-tionvariablewith latitudeandaltitude[List, 1951].Nohumiditydatawereavailablefor theozonesondeprofiles,andthusthemeanmolecularweightwasassumedconstant.Ozonesondemeasurementswereconvertedfrompartialpressureto numberdensity.Thereareerrorsinherentinusingthehypsometricequationtoobtaingeometricaltitudeandinconvertingpartialpressureto numberdensityfromradiosondepressureandtemperaturemeasurements.Par-

sons et al. [1984] compared highly accurate radar altitudes

with altitudes constructed through the hypsometric equation

using U.S. radiosonde measurements, and they derived

altitude errors (rms) of up to 600 m at 30 km and 250 m at 25

km. Schmidlin [1988] intercompared radar altitudes with

hypsometric altitudes derived from closely matched multiple

soundings of several well-calibrated radiosonde types in

worldwide use. Their results were inconclusive regarding the

sign of any potential altitude difference. Near 18 km the

radiosonde/radar altitude difference and standard deviation

were both less than approximately 100 m, indicating rela-

tively good agreement among the various sonde types.

However, near 24 km both the altitude difference and

standard deviation ranged from 100 to 500 m among the

sonde types.

Most of the profiles in the ozonesonde database are

corrected for the total ozone amount as part of the standard

data reduction process at the ozonesonde station. Profiles

from stations for which the Dobson correction is not applied

as part of the standard data processing were corrected for

this study. Furthermore, each ozonesonde profile was mul-

tiplied by 0.9743 to account for the currently accepted ozone

cross sections used in the Dobson measurement [Bass and

Paur, 1985; Komhyr, 1980]. Profiles were rejected from the

comparison whenever the correction factors were not in the

range 0.80-1.2. Profiles which had no corresponding Dobson

measurement available were used with no total ozone cor-

rections applied; however, the number of such profiles was

less than 6% of the total sample size of the ozonesonde data

set.

The ozonesonde/satellite sampling was set so that the

satellite-altitude coordinate ranged from cloud top to ap-

proximately 32 km, and the spatial location of the profiles

was taken at the latitude and longitude of the SAGE I/II 20

km tangent point. SAGE I/II profiles were not compared

with ozonesondes if local meteorological data was unavail-

able below 25 km (used for the Rayleigh extinction correc-

tion to the satellite ozone profile). The number of ozone-

sonde/satellite profile pairs (a pair is defined below) used in

computing a difference profile was based on a spatial-

temporal window (STW) which was large enough to make

the length of the 95% confidence interval on the difference

smaller than 20% at some point in the altitude region near the

peak of the ozone number density (21-26 km). Using this

criterion, the STWs for each station ranged from a maximum

of 2 days and 1000 km to 18 hours and 600 km. If more than

one SAGE I/II profile was within the STW, then all the

satellite profiles in the window were compared with the

single colocated sonde profile. Henceforth we shall refer to

the set of ozonesonde/SAGE colocated profiles as the

"paired data."

Table 1 lists the 24 ozonesonde stations for which suffi-

ciently large sample sizes of ozonesonde/SAGE colocations

occurred during the period of 1979-1991. Most stations used

the ECC. The Canadian stations (station numbers 21, 24, 76,

and 77) changed from using BM sondes to ECC sondes in

1979-1980, whereas the Japanese stations (7, 12, 14, 101, and

190) used the CI sonde. Figure 1 shows the distribution of

the ozonesonde station locations (triangles) superposed with

the sampling locations (squares) for the sunset meridional

sweep of SAGE II during March (SAGE I sampling is

similar).The SAGE I and SAGE II data set were provided by the

NASA Langley Research Center, Hampton, Virginia, and

were also available through the National Space Science Data

Center, Greenbelt, Maryland. The ozonesonde data sets

were provided by the World Ozone Data Center (WODC),

Downsview, Ontario; the National Oceanic and Atmo-

spheric Administration (NOAA), Boulder, Colorado; and

the National Institute of Water and Atmospheric Research,

Central Otago, New Zealand.

Difference Profiles

By utilizing the relatively large number of sampling oppor-

tunities available in the paired data, it was possible to

estimate the relative systematic difference between the in

situ electrochemical method and the satellite occultation

method. The underlying assumption was that the effect of

random variation would cancel, as the sample became large.

However, the spatial and temporal separation constraints

tend to keep the sample sizes from growing unlimitedly since

increasing each pair's spatial separation also increases the

probability of geophysically induced differences.

Vertical profiles of the percentage difference between the

ozonesonde measurement and the satellite measurement

referenced to the satellite measurement over the altitude

range of 15.5-32.5 km (SAGE I) and 10.5-32.5 km (SAGE II)

in 1 km increments were computed. The SAGE measure-

ment was chosen as the reference since it represents the

output of a unique self-calibrating instrument with constant

characteristics through time, whereas the ozonesonde pro-

files come from a variety of stations with interunit differ-

ences.The measure of difference chosen to estimate the ozone-

sonde/SAGE difference was the median percentage differ-

ence defined as

A = 100 • median (_-_),

where Y represents the vector of ozonesonde measurements

and X the corresponding vector of SAGE I/for measure-

ments in the colocated sample. Ninety-five percent confi-

dence intervals on A were computed using the bootstrap

technique [Efron, 1982]. As a consistency check, the collec-

tion of sample fractions, (¥ - X)/X, were also modeled with

9076 VEIGA ET AL.: SAGE I AND II COMPARISONS WITH OZONESONDES

Table 1. World Ozone Data Center Ozonesonde Stations

Latitude, Longitude, Elevation,Station deg deg m SAGE I Period SAGE II Period Sonde

12, Sapporo14, Tateno21, Edmonton24, Resolute67, Boulder

76, Goose Bay77, Churchill

99, Hohenpeissenberg101 Syowa107 Wallops Island109 Hilo

132 Sophia156 Payerne174 Lindenberg190 Naha191 Samoa

197 Biscarrosse210 Palestine

215 Garmisch233 Marambio254 Laverton256 Lauder

262 Sodankyla

265, Irene 25S 28E 1524 ECC

43N 141E 19 Oct. 1986 to June 1991 CI

36N 140E 31 Nov. 1984 to April 1991 CI54N I I4W 766 Feb. 1979 to Nov. 1981 Aug. 1985 to June 1991 ECC75N 95W 64 May 1979 to Sept. 1981 Aug. 1985 to April 1991 ECC40N 105W 1743 Jan. 1985 to Feb. 1990 ECC

53N 60W 44 March 1979 to Sept. 1981 Nov. 1984 to June 1991 ECC59N 94W 35 March 1979 to Sept. 1981 Oct. 1984 to June 1981 ECC48N liE 975 Feb. 1979 to Nov. 1981 Oct. 1984 to June 1991 BM69S 40E 21 Dec. 1984 to Oct. 1990 CI

38N 76W 13 March 1979 to Nov. 1981 Nov. 1984 to May 1991 ECC20N 155W 11 Dec. 1984 to Nov. 1990 ECC

43N 23E 58 Nov. 1984 to April 1991 Unknown47N 7E 491 Feb. 1979 to Sept. 1981 Unknown52N 14E 98 May 1979 to Nov. 1981 Oct. 1984 to April 1991 ECC

26N 128E 27 Sept. 1989 to July 1991 CI14S 170W 82 July 1986 to March 1988 ECC

44N IW 18 May 1979 to Nov. 1981 BM

32N 96W 210 May 1985 to May 1985 ECC48N llE 740 Feb. 1979 to Nov. 1981 BM

64S 57W 198 Nov. 1988 to April 1991 ECC38S 144E 21 July 1986 to Oct. 1990 BM45S 170E 370 Sept. 1986 to Dec. 1990 ECC68N 27E 179 March 1989 to April ECC

1991

July 1990 to May 1991

Ozonesonde stations for which SAGE I/II overpassed within a window of 24 hours and 1000 km. CI is Carbon-Iodine; ECC iselectrochemical concentration cell; BM is Brewer-Mast.

90

70

50

30

[

10

SAGE II Locations 26-Feb-1988 to 2-Apr-1988 Sunset

o

D

O []

i i

,iO 0 :

0

o []

Cl [] O O

[] q ......... 0 .........

[] o D 0[] 0 [] []

D [] []D 0 []

[]

0

0 [] []

0 o

::o []

o []

[] £

[]

D 0

o :0o o

io.........o...._ o: [] O i O

0 [] : [][] [] O0 [] []

[]Oi[]:D

o o

[] []

[] []

0 : 0

m rn O

[]

O 0 i O[] 0 [D0 0 [][]

0

D[]

[]

[]

-70

-90

-180 -135 -90 -45 0 45 90 135 180

Figure 1. Ozonesonde locations (triangles) and SAGE II sampling locations for February-April 1988(squares). The circle around the Wallops Island station is 1000 km in radius.

VEIGA ET AL.: SAGE I AND II COMPARISONS WITH OZONESONDES 9077

(a) 35

30

25

I0

5

0

o,1

(c) 35

30

25

10

-14.3 189.4 82 Samoa (191)i

Year 1988

WODC day II ,_.SAGE day I0SAGE profile 4 sunsetDT 38 hoursDS 948 kmCF 0.00WODC

SAGE_

trop

1.0

03 ( xi0 n cm "s )

-25.3 28.2 1524 Irene (265)

I0.0

(b) 35

3O

25

10

5

0

o.1

iYear 1991

WODC day 16SAGE day 18SAGE profile 3 sunriseDT 43 hoursDS 447 kmCF 1.05WODC _------_

SAGE _ trop

I

(d) 35

30

25

15

10

5 5

0 00.1 1.0 10.0 0.1 1.0

0 3 ( xl0 n cm "3) 0 3 ( xl0 _ cm _ )

19.7 204.9 11 Hilo (109)Year 1986 ....... ' ......

WODC day 45SAGE day 45SAGE profile 3 sunsetDT 15 hoursDS 415 kmCF 1.13WODCSAGE m******_ trep

1.0 10.0

03 ( xlO n cm "_)

26.2 127.7 27 Naha (190)

Year 1991 ....... ' .....

WODC day 184SAGE day 184 -'h_SAGE profile 7 sunset "_DT 4 hours DDS 644 km apCF 0.94WODC_----,

SAGE_ tr_

10.0

Figure 2. The closest colocated SAGE II and ozonesonde profiles from the ensemble used in calculatingmedian difference profiles. In the legend at the upper left, DT is the time separation rounded to the nearesthour, DS is the spatial separation, and CF is the correction factor. If CF is 0.0, then no correction factorwas available for the WODC profile. The approximate height of the tropopause is marked along the rightaxis. SAGE II data are shown down to the highest detectable cloud. The ozonesonde station's latitude,longitude, altitude (m), name, and number are written along the top of each plot.

a lognormal distribution. The mean of the lognormal servedas the difference estimator, and standard confidence inter-

vals were computed. The results from using either A or thelognormal approach were in good agreement except in caseswhere large differences caused the Iognormal mean to bebiased. A was chosen as the difference estimator instead of

the lognormal mean because it is a more robust measure ofcentral tendency whenever large deviations occur in the

sample.

Results

Searching the ozonesonde and satellite databases forcolocated profiles meeting the criteria described above pro-duced a set of individual profile pairs at each station withclosest agreement. These closest profile pairs are shown foreach station in Figures 2 and 3 for SAGE II and SAGE I,respectively. Profile pair information appears on the upperleft of each panel, with the NMC-derived height of thetropopause marked near the right axis. Ozonesonde profiles(solid line) are displayed at all available altitudes and havealso been integrated in the 1 km vertical altitudes corre-sponding to the SAGE I/II altitudes (triangles). The SAGEI/II profiles (squares) are plotted from cloud top up along

with the lo-uncertainty (dots). It is clear and very impressive

that when the ozonesonde and SAGE I/II sampled similar

synoptic conditions (Figures 2h, 21, 2p, 2u, and 3f) that both

systems agree remarkably well with respect to the large-scale features of the profile. It is obvious that features with3-5 km vertical extent are detected by the satellite instru-

ment as seen in Figure 2n at 14 km; 2p at 18 kin; 2q at 23 kin;2s at 25 km; 2t at 18 kin; 2u at 25 km; and 3i at 15 km. The

two profiles at Sodankyla in 1990 (Figure 2s) show that

vertically narrow laminar structures, when integrated over 1km in the ozonesonde profile, also agree very well with theSAGE II measurements. For each of the profile pairs in

Figures 2 and 3, the mean absolute difference relative to thesatellite measurement was computed at each altitude. The

average of these differences for the 21 ozonesonde/SAGE IIpairs in Figure 2 was 6 -+ 2% (l_r). For the nine ozonesonde/SAGE I pairs in Figure 3 the difference was 8 -+ 3% and is ingood agreement with the results of a previous SAGE I/ECCcorrelative measurement program [McCormick et al., 1984].

The ozonesonde/satellite median difference profiles, ar-

ranged in increasing distance from the equator, are shown inFigure 4 for the 21 stations with SAGE II overpasses and in

Figure 5 for the nine stations with SAGE I overpasses.

(e) 35

30

25

30

15 _i

10

5

0

0.1

(s) 3s

30

25

i

10

5

Oi

0.1

31.8 264.3 121 Palestine (210)...... i

Year 1985WODC day 136 _.SAGE day 136SAGE prollle 8 sunrise

7 hours

WOi_----_SAGE

trep

1.0 10.0

0 3 ( xl0 u cut _ )

37.8 284.5 13 Wallops Island (i07)

Year 1990WODC day 277SAGE day 278 -_SAGE profile 7 sunrise "_DT 19 hoursDS 784 kmCF 1.00 _ffwoven------,

SAG_

...... trop

1.0 10.0

0 3 ( xlO I=cm "_)

(h) 35

30

25

10

5

0

0.1

(i) 3$

3O

25

30

10

5

00.1

(k) 35

30

25

10

40.0 254.8 1743 Boulder (67)...... i .......

Year 1985

WODC day 211SAGE day 211SAGE profile 8 sunriseDT 4 hoursDS 598 kmCF 0.99WODC _-----_SAGE

trop

1.0

0 3 ( xl0 TMcm "3)

43.0 141.3 19 Sapporo (12) .......

Year i987 ....... '

WODC day 259

SAGE day 259 "_SAGE profile 6 sunsetDT 3 heursDS 337km 1,CF 1.14 ._rwoDc.------_

SAGE_

...o. ..... -."

5

00.1 1.0

0 3 ( xl0 u cm _ )

mtrop

(j) 35

3_

25

• _ 15

10

5

0

10.0 0.1

,0.0

Figure 2.

(I) 35

30

25

10

5

0

0.1

42.8 23.4 588 Sofia (132)....... i

Year 1986

WODC day 141SAGE day 141

SAGE profile 2 sunriseDT 9 hoursDS 687kmCF 1.12WODCSAGE _..***m

trop

1.0 10.0

0 3 ( xl0 u cm "_)

-45. 0 169.7 370 Lander (256! ......Year 1987

WODC day 187SAGE day 187SAGE profile 13 sunriseDT 2 hoursDS 265kmCF 0.99WODCSAGE l******_

. _ trop

t.0 10.0

0 3 ( xlO n cm "3)

36.0 140.1 31 Tateno (14) ........

Year i990 ........

WODC day 206

SAGE day 305SAGE profile 13 sunriseDT 10 hoursDS 514 kmCF 0,99WODCSAGE _****_

trep

(continued)

(m)35

30

25

15

10

5

0

0.1

(o) 35

30

25

]1,10

$

0

0.1

47.8 11.0 975 Hohenpeissenberg (99)

Year i986 ....... ' ........

WODC day 34SAGE day 34SAGE profile 11 sunsetDT 9 hoursDS 383kmCF 1.03WODCt-----tSAGE

I

1.0 10.o

0 3 ( xlO TM cm "s)

53.3 299.6 44 Goose Bay (76)

Year i_0 ...... '

WODC day 318 t_SAGE day 318SAGE profile 11 sunsetDT 10 hoursDS _O lensCF 1.00WODC_------_SAGE m*****_

._ trep

1.0 10.0

0 3 ( xl0 n cm "3)

(n) 35

30

25

10

5

o

0.!

(p) 3S

3O

25

_ 15

10

5

0

0.1

52.2 14.1 98 Lindenberg (174)...... I

Year 1990WODC day 108SAGE day 107SAGE profile 12 suaset

,%.

DT 17 hours "_DS 744 kmCF 1.19WODC t-------tSAGE m***.*_

trep

1.0

03 ( xl0 u cm "3)

53.6 245.9 766 Edmonton (21)...... n ........

Year 1998WODC day 141SAGE day 141SAGE profile 8 sunrise

I hours

WOIN2 _SAGE _,**.*m

10.0

1.0

0 3 ( xl0 n cm "3)

10.0

(q) 35

3O

25

10

5

00.1

(s) 35

3O

25

],,10

5

0

0.1

58.8 265.9 35 Churchill (77)

Year i9S6 ........

WODC day 218SAGE day 218SAGE profile 7 sunriseDT 0 hearsDS 564kmCF 0.98WODC t-------tSAGE m**.**m

trep

1.0

03 ( xl0 u ¢m -_ )

67.5 26.6 179 Sodankyla (262)

Year i_90 ........

WODC day 73SAGE day 73SAGE profile 4 sunriseDT 7 hoursDS 662 kmCF 1.14WODCSAGE

10.0

1.0

0 3 ( xl0 u cm "3)

10.0

(r) 35

3O

25

15

l0

5

0

0.!

(t) 35

M

25

10

5

0

OA

-64.2 303.3 198 Marambio (233)

Year i988 ........ " ....... tWODC day 329 ]SAGE day 325 -_

SAGE profile $ sunrise "_DT 27 hours _ -]DS 594 km =_CF 0.0o "_t twoDc,---_ ]L

S-- l1.0 10.0

0 3 ( xl0 u cm "3)

-69.0 39.6 21 Syowa (101)

Year 1988

WODC day 279 tl_SAGE day 278SAGE profile 11 sunsetDT 17 hoursDS 405 kmCF 0_9WODC Jr----_SAGE

L0

0 3 ( xlO u cm "j)

trop

10.0

Figure 2. (continued)

9080 VEIGA ET AL.: SAGE I AND II COMPARISONS WITH OZONESONDES

(u) 35

30

25

20

,¢

lO mtrop

74.7 265.0 64 Resolute (24),iYear 1988

WODC day 223 __SAGE day 223SAGE profile 6 sunriseDT 2 hoursDS 377 kmCF 0.94WODCSAGE

LO

0 3 ( xl012cm "3)

00.1 10.0

Figure 2. (continued)

Because of the limited data availability, not all years are fully

represented, and the reader is referred to Table 1 for the

dates. Each panel of difference profiles lists the total number

of samples available at each altitude along the right axis.

Ninety-five percent confidence intervals are represented by

the dotted band. Each profile is shown down to only those

altitudes where the length of the 95% confidence interval was

less than 20%. Although difference estimates were computed

below the lowest altitudes shown in Figures 4 and 5, the

combination of small sample sizes along with large variabil-

ity of the median difference precluded the estimation of the

ozonesonde/satellite bias with a high degree of confidence.

For Samoa (Figure 4a), almost all differences are not

significant for the altitudes 21.5-31.5 km. The Hilo data

(Figure 4b) indicate SAGE II ozone is larger by 8% above 17

km. There is no apparent altitude trend in the difference

profile shape, a feature indicative of good altitude registra-

tion in the satellite measurement. A characteristic tendency

for many comparisons (Figures 4c-4h, 4m, and 4q) is good

agreement near the peak of the ozone profile and a subse-

quent divergence to significant negative differences below

the peak. This effect is most pronounced equatorward of 40 °

and may be related to the steep gradient between the ozone

peak and the tropopause at these latitudes. Figure 4e shows

the comparison at Palestine which was organized as part of

a SAGE II correlative measurement program in 1985. Al-

though the sample size is small, there are no significant

differences between 20.5 and 30.5 km. Poleward of 45 °, all

but one comparison had data extending below 14 km (Fig-

ures 41-4u) which showed no significant differences at the

lowest altitudes. The exception is Syowa in Antarctica

where the difference is between - 10 and -5% below 23 km.

This altitude range at Syowa coincides with the ozone

depletion region during Antarctic spring when SAGE II

samples these polar latitudes densely. Ozone gradients as-

sociated with the vortex may have caused the differences in

the Syowa comparison. The greatest number of colocations

per sampling window size occurred at Hohenpeissenberg

(Figure 4m). For this station the difference profile exhibits

negative values up to -10% above 32 km and also below the

ozone density maximum. The negative differences at the

upper altitudes may be due to reduced air pump efficiency of

the Brewer-Mast sonde. The largest ozonesonde/satellite

deviations occur in the Lindenberg comparison (Figure 4n)

above 25 km where the differences reach -20% at 31.5 km.

An assessment of the relative ozonesonde/SAGE II differ-

ence using the difference profiles of Figure 4a-4u was

performed by enumerating the differences less than 5% in

magnitude at each altitude. These "5%" differences are

shown in Figure 4v as the shaded region of a rectangle whose

length is the total number of differences for a given altitude.

Between 21 and 30 km at least 15 stations had absolute

differences less than 5%, with the best count at 24.5 km

where all but Hilo agreed to better than 5%. Between 14.5

and 20.5 km and at 31.5 km about half the ozonesondes

agreed with SAGE II to within 5%. From the combined

stations, differences were estimated at 343 altitudes, and at

240 of those altitudes the median differences were less than 5%.

The comparisons with SAGE I are shown for nine stations

in Figures 5a-5i. 95% confidence intervals of length 20%

were not available below 15 km. Except for the northern-

most station the profiles show increasingly negative values

as the altitude decreases below the ozone maximum, culmi-

nating in differences between -20 and -10% near 15.5 km.

Except for Payerne (Figure 5c), which shows an overall

difference of -10%, all the stations agree well near the

maximum of the ozone density. At all but one station the

differences at the upper altitudes show increasingly negative

values with increasing altitude, the extreme case being

Resolute (Figure 5i) with -16% at 31.5 km but with few

coincident comparisons.

The combined differences for SAGE I are shown in Figure

5j, and are consistent with the SAGE II tabulated differences

(Figure 4v) in the altitude range near the ozone maximum.

However, below 20 km less than half the stations showed

agreement within 5% with SAGE I. No confidence intervals

of 20% in length were available below 15 km. From the

combined stations, differences were estimated at 138 alti-

tudes, and at 71 of those altitudes the median differences

were less than 5%.

The tendency for some of the difference profiles (Figures

4b, 4c, 4d, 4t, 4g, 4h, 4k, 4m, 4p, 4q and Figures 5a-5h) to

exhibit trends toward negative values as the altitude de-

creases below the ozone maximum may, in part, be due to

the ozonesonde measurement. In the region of rapid ozone

increases above the tropopause, the measured ozonesonde

profile is the convolution of the true ozone profile with the

sonde instrument temporal response function. De Muer et

al. [1990] reported better agreement between 24 colocated

ozonesonde and SAGE II profiles at Uccle when the instru-

ment response function was deconvolved from the measured

sonde profile. Comparisons of the measured ozonesonde

profiles at Uccle with their corresponding deconvolved

profiles indicate a mean difference (measured-deconvolved)

of -3 --- 1% at 15 km, whereas at 30 km the mean difference

is 6 -+ !% (D. De Muer, personal communication, 1990). This

positive difference at 30 km contrasts with the ozonesonde/

SAGE II difference profiles shown in Figure 4 where nega-

tive differences appear at 30 km, and may be indicative that

declining pump efficiency has a stronger effect than sonde

response on the ozone measurement. Additional evidence

supporting the sonde temporal response's effect on the

measured profile is found in the BOIC study where differ-

ences of approximately 10% between UV photometers and

ECCs were recorded in the vicinity of 80 hPa with the UV

photometers measuring higher ozone than the sondes. These

VEIGA ET AL.: SAGE 1 AND II COMPARISONS WITH OZONESONDES 9081

(a) 35

30

25

so

lO

o

0.1

(c) 35

30

25

_20

37.8 284.5 13 Wallops Island (107)i

Year 1981WODC day 195 _m,_.SAGE day 196SAGE prof'de 1 sunsetDT 10 hoursDS 540 kmCF 1.01WODCSAGE m..***_

trop ._

1.0

0 3 ( XI012 cm 3 )

46.8 7.0 491 Payerne (156)

Year 1980

WODC day 213SAGE day 213SAGE profile 12 sunsetDT 5 hoursDS 256 kmCF 1.05WODCSAGE

10.0

15

10

5

00.1

Figure 3.

_ trop

\

1.0 10.0

0 3 ( xl0 n em "3)

(b) 35

30

25

_20

._ 15

1o

o

0.1

(d) 35

30

25

20

•= 15

10

44.4 358.8 18 Biscarrosse (197)i

Year 1980WODC day 77SAGE day 77SAGE profile 12 sunsetDT 4 hoursDS 299 kmCF 1.17WODC t-------_SAGE

trop

1.0

0 3 ( xl0 n cm-_ )

47.5 11.1 740 Garmisch (215)

10.0

iYear 1980

WODC day 347SAGE day 347 _.SAGE profile 9 sunsetDT 7 hoursDS 562 kmCF 1.19WODC _-----tSAGE

__t_p

o

0.1 1.0 10.0

0 3 ( xl0 tz cm "3)

The closest colocated SAGE I and ozonesonde profiles from the ensemble used in calculatingmedian difference profiles. In the legend at the upper left, DT is the time separation rounded to the nearesthour, DS is the spatial separation, and CF is the correction factor. If CF is 0.0, then no correction factorwas available for the WODC profile. The approximate height of the tropopause is marked along the rightaxis. SAGE I data are shown down to the highest detectable cloud. The ozonesonde station's latitude,longitude, altitude (m), name, and number are written along the top of each plot.

differences were attributed to the ECCs lagging the photom-

eters in the altitude region of a high ozone gradient

[Hilsenrath et al., 1986]. The difference profiles in Figures 4

and 5 are broadly consistent with those observed in BOIC.

Implications on the SAGE II/SAGE I Difference

The satellite comparisons with the ozonesondes at Wal-lops Island (Figures 4g and 5a), Hohenpeissenberg (Figures4m and 5e), Goose Bay (Figures 4o and 5f), Edmonton

(Figures 4p and 5g), and Churchill (Figures 4q and 5h)

provide an opportunity to address the validity of the lower

stratospheric trends computed using the SAGE I and SAGE

II data over the period of 1979 through 1991 where trends

were computed down to 17.5 km [McCormick et al., 1992].

Implicit here is the assumption that the ozonesonde instru-

ment quality, calibration, and analysis did not change

throughout the time period. Comparing the difference pro-

files at 17.5 km for each of the above stations between the

SAGE I and SAGE II time periods reveals that the 95%

confidence intervals overlap, and thus it cannot be inferred

that the difference between SAGE I and SAGE II ozone at

this altitude was nonzero. However, sampling the Hohen-

peissenberg data using a larger sampling window reduces the

size of the ozonesonde/SAGE I and II difference profile

confidence intervals, and yet the shape and location of the

difference profiles are essentially the same as in Figures 4m

and 5e. At 17.5 km the ozonesonde/SAGE I difference is

-15% while the ozonesonde/SAGE II difference is -9%.

This yields a SAGE I/II difference of 6%, and thus within the

estimated SAGE I/II uncertainty reported by Watson et al.

[1988] for the 20 km altitude. Thus we cannot conclude,

based on the Hohenpeissenberg data alone, that the SAGE

I/II difference at 17.5 km is statistically significant.

Aerosol Correlation and Temporal Stability

The relatively large paired data sample (1 day and 1000km) available at Hohenpeissenberg was used to assess thepotential influence of a wide dynamic range in aerosolextinction on the ozonesonde/sateUite difference. Figure 6shows the 1020 nm SAGE II aerosol extinction coefficient at

18.5 km in a 10° latitude band centered over 48°N, thelatitude of Hohenpeissenberg. Near 18.5 km the extinctionprofile takes on its stratospheric maximum at these latitudes,

and thus the time series in Figure 6 approximates, up to a

scaling constant, the time history of stratospheric optical

depth for this latitude band. It can be seen that the extinction

9082 VEIGAETAL.:SAGE I AND I1 COMPARISONS WITH OZONESONDES

(e) 35

3O

25

J

10

5

0

0.1

(g) 35

30

25

15

I0

5

0

0.1

47.8 11.0 975 Hohenpeissenberg (99)i

Year 1981

WODC day 264SAGE day 263SAGE prellle 9 sunsetDT 15 hoursDS 164 kmCF 1.11WODC*------_SAGE a**-.*.-m

trop

1.0

0 3 ( xl0 TM cm -3)

53.6 245.9 766 Edmonton (21)

10.0

iYear 1980

WODC day 282SAGE day 283SAGE profile I sunsetDT 14 hours!_ 429 lanCF 1.15WODCSAGE

trap

I

1.0

0 3 ( xl012 cm "3)

10.0

(13 35

30

25

15

10

5

0

0.1

(h) 35

30

25

10

5

0

0.!

53.3 299.6 44 Goose Bay (76)i

Year 1980

WODC day 73SAGE day 73SAGE profile 14 sunsetDT 0 hoursDS 595 kmCT 1.09WODCSAGE

_.._----__,_

1.0

0 3 ( xl012 ¢nf 3 )

58.8 265.9 35 Churchill (77)

10.0

iYear 1981

WODC day 259SAGE day 259 :_SAGE profile I sunsetDT 10 hoursDS 547 kmCF 1.13WODC *------_SAGE s******_

1.0

0 3 ( xl0 n cm "3)

10.0

Figure 3. (continued)

time history began a decline from the large values in 1984-

1985, which were predominantly the volcanic aerosol rem-

nants of the 1982 eruption of El Chich6n (18°N), to highly

variable values in early 1986 driven by the Nevado Del Ruiz

(5°N) eruption in late 1985, and subsequently to the low

values in early 1991. Each year was punctuated by large

winter variances induced by the intrusion of polar air masses

and small summer variances. Significant stepwise decreases

in the mean aerosol amount occurred during the springs of

1985, 1988, and 1991 and may be related to QBO modulated

advection to the high latitudes. After mid-1991, the Mount

Pinatubo (15°N) eruption caused large increases in extinction

[McCormick and Veiga, 1992].

To assess the potential impact of less extreme aerosol

loading than that produced by Mount Pinatubo, the ozone-

sonde/SAGE II differences at Hohenpeissenberg were ana-

lyzed in order to determine whether a time dependent

correlation existed between the ozone differences and aero-

sol extinction. The presence of larger correlations during

periods of time when the aerosol extinction was higher than

during periods when the extinction was lower would be

indicative that the SAGE II ozone retrieval contained an

aerosol residual. Several time periods of varying length were

chosen so that each period could be clearly classified as

having high, medium, or low aerosol amount (Figure 6:

1984-1985, 1986--1987, and 1989-1990, respectively). Corre-

lation coefficients of the ozonesonde/SAGE II difference

versus the SAGE II 1020 nm extinction were computed over

the altitude range from 10.5 to 32.5 km, and the resulting set

of three correlation profiles possessed a high degree of

similarity irrespective of the period each represented. The

temporal constancy of the correlation profile indicates that

for the aerosol levels encountered between late 1984 and

mid-1991, the SAGE II ozone retrieval algorithm effectively

accounted for aerosol extinction.

The solid curve in Figure 7 shows the mean of an ensemble

(i) 3S

30

25

128

10

5

0

0.1

Year 1980

WODC day 136SAGE day 136SAGE profile 4 sunset

" 18 hours981 _mCF 1.09WODC _SAGE a******_

74.7 265.0 64 Resolute (24)j .......

1.0 10.0

03 ( xl0 n cm -3 )

Figure 3. (continued)

(a) 35

2s

IO

5

:_,GE,, "i t "M''_ '"".;: ..:

..'/

-40 -20 0 20 40(%)

LSAGE 11 II Max. distance 10tO.0 ken

30 ""'l :'

Iu ,...r ,t"

_. , • • • _ , , , I , , . L , , . , ,

-40 -20 0 20 40(%)

m) 35

30

j2

•< 15

Ill

5

(d) 35

30

20

10

• , , . . , ...... , • . , , •19.7 204.9 I1Hilo (1_) I Max. time 1.10 days

SAGE II "'". . I Max, d_tmsce 1006,0 km

? : I

"'. :: I

:.... .q,"

• , . . . , ...... i . . . , ,

-40 -20 0 20 40(%)

t Ma_ d_mce 10_S kmSAGE El ." , )

"'. (.

• .': . .L..':...... 1

I

I

I

I

I

I

J

, i , , , i , , , I , , , t . . . ,

-40 -20 0 20 40

(%)

(e) 35

30

25

20

10

• , • • • , • • . i . - - , • • • , ,

31.8 264.3 121 _ (210) I Msx. time 2.00 days

SAGE 11 I h'ht_ dfmmnce 1000.0 km

...... :.ii:.L.,.

-40 ._ 0 _ 40(%)

(_ 35

3O

25

2o

10

5

• , . . . , • . . , . • . , . . . , .

36.0 l_t.I 31Tatemo (14) t Mm_ f_N !.00 days

SAGE I1 t MAUL dtbtan_ Im.I ken

• , . . . , . . . i . . . , . . . , .

-40 -20 0 20 40(%)

_) 35

30

25

20]15

10

SAGE II "... _,. _ df_m_ce 1_0.0 Im_

'"i J...... ': ...

-40 .20 0 20 40(%)

_) 3S

3O

10

5

SAGE [] .._.. Max. d_umce IN0.I ken"i" :"'""

..-" ....;

• _ - . . , , , , I , , , i , , , l ,

-40 -20 0 20 40(%)

Figure 4. Median difference profiles for the ensemble of ozonesonde/SAGE II paired data. See Table 1for the applicable dates. The units are in percentage relative to SAGE II. The dotted band represents the95% confidence interval of the median difference. Only confidence intervals whose length is less than 20%are shown. Samples sizes at each altitude are marked along the right axis. Figure 4v is a compilation of thefrequency with which the combined ozonesonde/satellite differences were less than 5%. Each open barrepresents the total number of sample differences available for a given altitude, and the shaded bar is thenumber of sample differences less than 5%.

9084 VEIGA ET AL.: SAGE I AND II COMPARISONS WITH OZONESONDES

o) 35

3O

_ 20

10

5

ZSAGE n

• k-

_:_

-410 -20

Mare dlmaee ¢,N.O tom

, , . i . . . i .

0 2O 4O

(%)

(J) 35

2, 30

UmloN3o1, _ 2019n9 ._

10

i SAGE II t MmL diMmme 1000.0 kmI

• i . . . t . . . t . . . t . . . 1 ,

-40 -20 0 20 40

(%)

(k) 3_ t d_L0'14|'.319_¢e'(12) " ; MaLt_ "lJO_." :

_SAGE H i MmL d_tsace IMI0.0 km i

"'"I "-

j 20 ........

< 15[

lO_-5F......... : .........

-40 -20 0 20 40

(%)

(t) 35

30

_ 2s

_ 20

10

5

• i • ...... ; M_tk. ,..d_,

SAGE II "i_"_'#:[i':'- MImL dlkdmtee 60e.O laa

"::_iI ....

I

I

I

I

-40 -20 0 20 40(%)

(m) 35

3O

25

l0

Co) 35

30

20

15

10

5

....•"7i..: : I

I

I

I

• , - - - , , , , I , , , I , , , 1 ,

-40 -20 0 20 40

(%)

(n) 35

30

_ 20

lO

: SAGE 1, .._.. : Minx. dl_am_ lON.O km•. . _

:j -'_

I

I

I

I

I

L

-40 -20 0 20 40

(%)

," " M", I, 9_

• : I1

" .1" 19: ., _[2• ", 22

". I : 19

-40 -20 0 20 40

(%)

(p) 35

30

25

15

10

SAGE II ..,...'_ MtLv_ dilute 10N.O km

-.. ':

,5 :_.//'

I

I

I

-40 -20 0 20 40

(%)

Figure 4. (continued)

1721

lY/

01

VEIGA ET AL.: SAGE I AND II COMPARISONS WITH OZONESONDES 9085

(q) 35

30

2s

10

5

(.) 35

30

25

20

15

10

I

.ii .... .:

...'"" "1

I

I

I

I

• i . , . i , . , I . • . , • • , l •

-40 -20 0 20 40(%)

(r) 35

3O

25

20

l0

5

SAGE II I Mu. dltn_ Ill00,0 Iluu

,.. ...i..'1

'J • ";:,

'.. "'p....

i

I

-40 .20 0 20 40(%)

_$AGE H I. 4_.., Max. di_ance 14iOOJPkm'. ..""

)" '1..

..' ..J'

I

I

-40 -20 0 20 40(%)

(t) 35

3O

2s_ 2o

10

5

• . - • • i - - - , - - - , - • • i •

-69.0 39,6 21 Syows (101) I Max. time 2.00 daysi

:.. t:

... • "I

""... "".1

"".. :-A

I

I

I

-40 -20 0 20 40(%)

(u> 35

30

15

10

,II

I

I

-40 -20 0 20 40(%)

Figure 4.

(v) 35

186_77?"t788S

8.5

9t

" i91

;tS8836a

10

5

0

(continued)

5 10 15 20

Number of Differences < 5 %

of correlation profiles of SAGE II/ozonesonde ozone differ-ence versus extinction (note this is the negative of the

correlation profile discussed above). It would be expected

that if the satellite and ozonesonde agreed exactly, or if theirdifference were random, the correlation profile would be

zero. The vertical structure in the SAGE II/ozones0nde

difference versus extinction correlation indicates the exis-

tence of a residual bias between the two ozone measurement

systems, or an ozone retrieval effect, or an intrinsic property

of the vertical structure of the stratosphere. To show evi-dence for the latter, the correlation between the SAGE II

ozone and SAGE II extinction for the paired data sampling

over Hohenpeissenberg is shown in Figure 7 as the dotted

curve, and similarly the dashed curve is the correlationbetween ozonesonde ozone and SAGE II extinction_

Clearly, both these correlation profiles have an almost

identical vertical structure although the magnitudes differ.Since the sonde ozone is a measurement independent from

the SAGE II extinction, the vertical structure of the corre-lation of SAGE II ozone and SAGE II extinction cannot be

due solely to satellite ozone retrieval aerosol effects. The

differences in magnitudes between the dashed and dotted

curves can be explained by the fact that the ozonesonde

measurements are not exactly colocated in time and space

with the satellite extinction measurements, and hence the

ozonesonde versus extinction correlation is always less in

magnitude than the satellite ozone versus satellite extinction

correlation. Cunnold and Veiga [1991] proposed that the

vertical structure of the correlation between ozone and

extinction is produced by horizontal and vertical advection

of the constituents.

The ozonesonde/SAGE II difference profiles computed

9086 VEIGAET AL.: SAGE I AND II COMPARISONS WITH OZONESONDES

(,) 35

3O

25

•¢ 15

10

37.8 18d.$13 W_ _ (1_)

SAGE I " •": _-_t

. . .S ['"

Mu. dl_nc¢ tO0_O k_m

(b) 35

30

25

15

10

g

: _('3_iSBbatnmnm(197) ; " "Mu._bu_ "_D0da_u"

.-" I

.." "I

....'

-40 -20 0 20 40 -40 -20 0 20 40(%) (%)

[SAGE ! .. ,it,.. I Mex. dimuee INOJI km

- ;._

_20 -" :" _• ;I I

,o[5/, I , , , i , , , i

-40 -20 0 20 40(%)

(d) 35

30

20

10

5

• , • . . , . . . , . . . , . . . ) •

4%5 !1.1 ?40,ff_ (_1_ ))SAGE I

• . • i

"'F.

MbL tbie I,,N do35

Max. dbmmce 1000JP km

• i . . . i . , , i , , , l . . . i .

-40 -20 0 20 40(%)

(e) 35

3O

| 20i

1o

5

'.. '.'.

i) :,)...." .' I

)

t

I

)

t

-40 -20 0 20 40(%)

35 t ._3.3'_._"c_,,_,,(7g i " u,,._ "_._d_-30 , ..)

20 9 !:

15 I10

-40 -20 0 20 40(%)

(_ 35

30

25

20•_ 15

10

• . • - • , - - . i • . . ) ....• %6 2_.9 ?_ F_tmemlom ( 21 ) I ]MhtL time 1.00 ,a-'y_

SAGE i I _ dimanee 1000.0 km• -. .L.

t

I

I

)

I

-40 -20 0 20 40

(%)

(b) 35[ _'_#'c_hm(_)" ; " M_,._,,_ ",.O0d_y," 1[ SAGE I ) Mm_ d_mm_¢ I_.0 km ]tl

"I ....' 1• " "'.1 14

_ I,'

• ""I ". 18

". 18

20 _0• • ]8

.,* tit

• "f t5L ......... , .........

-40 -20 0 20 40(%)

Figure 5. Median difference profiles for the ensemble of ozonesonde/SAGE I paired data. See Table 1for the applicable dates. The units are in percentage relative to SAGE I. The dotted band represents the95% confidence interval of the median difference. Only confidence intervals whose length is less than 20%are shown. Sample sizes at each altitude are marked along the rightaxis. Figure 5j is the same as in Figure4v.

VEIGA ET AL.: SAGE I AND I1 COMPARISONS WITH OZONESONDES 9087

(. 35

30

25

_ 20

10

sl

- f " . - , • - - , . . • i - • • , .

74.7 26$.0 64 _ate _ 24) I Max. tbae 2.llO drays

_ SAGE l ......... '"'.."'__.. ' !.MMx. d.net.';!:" "'.. t"" "P'..";'"["'r:'( '"",. l..O km

t

i

t

I

• t . . . 1 , , , 1 , , , A , . , i ,

-40 .20 0 20 40(%)

_1) 35

s 30

25

lO

5

' AE• . . i • . • L

2 4 6 8

Number of Differences < 5 %

Figure 5. (continued)

during varying aerosol conditions and seasons are shown in

Figure 8. Figure 8a shows the difference profiles computedfor three periods ranging from high to low aerosol extinction

levels. The shaded band is the envelope of the 95% confi-

dence interval at each altitude. The differences between any

pair of the three profiles shown were not significant at any

altitude, and hence these results indicate that the relativedifference between the SAGE II ozone measurements and

the ozonesondes over Hohenpeissenberg were temporally

constant. Figure 8b shows the difference profiles from sea-

sonal sampling of the period from late 1984 through mid-

1991. Occultation sampling allowed the most overpasses

during the fall and winter, while the summer months were

sampled less frequently, and consequently little data were

available below 15 km during the June through August time

period. The seasonal variation of the mean tropopause isshown by the tropopause altitudes during winter and sum-

mer at this location. Since the 95% confidence intervals for

any given pair of difference profiles overlapped, these data

indicate that there were no significant seasonal biases in the

ozonesonde/SAGE II difference.

It must be emphasized that the results above are derived

from analyzing the data over the midlatitudes between 1984

and mid-1991, and that possible aerosol/ozone correlations

in the SAGE II data may exist at other latitudes. Analysis of

the SAGE II data after the eruption of Mount Pinatubo

indicates that the ozone is not correlated with aerosol

extinction whenever the 1 /xm extinction is less than 0.001km -] . While the midlatitudes never attained extinction

values larger than this prior to the Mount Pinatubo eruption,

;:

_ :":

•L. "i

:!j....i . 'p

!" I: • " .'."

"" ":"'-" i:.lll! ! :-e itl!:li :

ii "- '!: : ':; '! '-•....

• ",! "i , I: i " I i" i_ll'i I

1984 1986 1988 1990

Figure 6. SAGE II 1020 nm extinction at 18.5 km over the latitude band extending from 43°N to 53°N.

9088 VE1GAETAL.:SAGEI ANDII COMPARISONSWITHOZONESONDES

- - - Sonde O, ',

-- (SAGE I1 - Sonde) O

-,5fj _

?

!01 " _

- 1.0 -0.5 0.0 0.5 1.0

Correlation wilh SAGE I1 Extinction

same air mass. Using the statistical sampling criterion, the

ensemble of ozonesonde/SAGE II differences, taken over all

altitudes, agree within 5% for 70% of all the possible

comparisons, while for SAGE I 50% agreed to within 5%.

The largest differences ranged between -5 and -30% and

were found in the lower stratosphere in the region of

maximum ozone gradient between the altitudes from 15 to 20

km. Most of the comparisons with SAGE I showed statisti-

cally significant differences at the lowest altitudes, whereas

SAGE II showed better agreement at these altitudes. At

several stations, differences were large and negative above

the tropopause and decreased in magnitude toward zero at

the ozone maximum, a feature partly ascribable to hysteresis

in the ozonesonde measurement. The best ozonesonde/

satellite comparisons were found in the altitude range near

Figure 7. Mean correlation between SAGE II ozone ver-

sus SAGE II extinction (dots), ozonesonde ozone versus

SAGE II extinction (dashes), and (SAGE II/ozonesonde)

ozone difference versus SAGE II extinction (solid). Each

profile was computed by averaging an ensemble of correla-

tion profiles where each correlation profile in the ensemble

represented a 1-year data sample. The l-year samplingwindow was shifted in 45 day increments from late 1984

through mid-1991 in generating each correlation profile of the

ensemble. The SAGE II and ozonesonde paired data profiles

within each sampling window were colocated to within i dayand 1000 km over Hohenpeissenberg.

there were larger values in the tropics following the eruptionof Nevado del Ruiz.

Conclusions

We have sampled the ozonesonde in situ profile and

SAGE I/II satellite profile databases within a temporal/

spatial coincidence window, whose nominal size is l day and

1000 km, in order to isolate colocated profile pairs from

which to estimate any possible relative differences between

the two ozone measurement systems. We have also assumed

that an acceptable estimator of the relative difference is the

sample median whose 95% confidence interval has a length

less than 20% and used this criterion to select the size of the

temporal/spatial sampling window. Median differences not

satisfying these criteria were not considered in the study.

Profile pairs were colocated at 21 ozonesonde stations

with SAGE II overpasses and at nine stations with SAGE !

overpasses. The magnitude of the median difference aver-

aged over all altitudes was 6 -+ 2%, for the 21 closest possible

coincides with SAGE II, and 8 -+ 3% for the nine closest

coincidences with SAGE I. Using the statistical sampling

criterion above, the lowest altitudes at which comparisons

were possible with SAGE II were between 15.5-20.5 km

equatorward of 45 ° and 11.5-13.5 km poleward of 45 °. For

nine stations with SAGE I overpasses (38°N-75°N) the

lowest altitude at which comparisons were possible was 15.5km.

On the whole, the comparisons between ozonesondes and

SAGE I and II ozone measurements indicated agreement

well within the errors attributable to either system. Individ-

ual profile pairs showed that fine-scale ozone variations were

well resolved by SAGE when both systems sampled the

J

35 -- _ r

lo!

5_-40

__ tropopause

-20 0 20

Median Difference [ 100(sonde-sage)/sage]

35(r _-_ • i t

-- Mar-May (b)

L ....... Jun - Aug30

_- ........... Sep - Nov

............ Dec - Feb4

,L

J40

-40 -20 0 20 40

Median Difference 1100(sonde-sage)/sagel

Figure 8. Ozonesonde/SAGE II difference profiles com-puted from paired profiles colocated to within 1 day and 1000km over Hohenpeissenberg. (a) Difference profiles repre-senting the periods of late 1984 through 1986 (170 profilepairs), 1987 through 1988 (192 profile pairs), and 1989through mid-1991 (175 profile pairs). (b) Seasonal differenceprofiles representing spring (83 pairs), summer (29 pairs),autumn (183 pairs), and winter (179 pairs). The shaded band

represents at each altitude the envelope of the 95% confi-dence interval taken from the enclosed profiles. Too fewdata were available below 15 km in during the summerseason.

VEIGAETAL.:SAGEI AND II COMPARISONS WITH OZONESONDES 9089

the ozone maximum (21-26 km), where essentially all com-

parisons showed differences less than 5%.

The selection of the ozone profile pairs based solely on a

specific temporal/spatial sampling window (up to 2 days and

1000 km) inevitably includes a relatively large number of

cases where the paired profiles represented different synop-

tic conditions. As a consequence the large sizes of the 95%

confidence intervals at lower stratospheric levels shown in

Figures 4, 5, and 8 contain a geophysical component. One

method of accounting for the synoptic component is to use a

back-trajectory analysis to properly compare ozone mea-

surements from similar air masses. This would probably

improve the confidence in the lower stratospheric compari-

sons.

Analysis of the correlation between aerosol extinction and

ozonesonde/SAGE II differences at one northern midlatitude

station revealed that the SAGE II ozone retrieval was not

affected by the levels of aerosol encountered in the lower

stratosphere in the time period between late 1984 and

mid-1991. A temporally invariant vertical structure in the

correlation profile between ozone and extinction appears in

both the SAGE II ozone data and in the ozonesonde data and

is possibly indicative of transport processes in the strato-

sphere. During the time period from late 1984 through

mid-1991 the ozonesonde/SAGE II difference profile showed

insignificant changes in the lower stratosphere (below 20 km)

as the extinction varied by an order of magnitude throughout

the period. No significant seasonal biases in the difference

profiles were detected.

Acknowledgments. We thank S. J. Oltmans for providing theHilo, Samoa, and Boulder ozonesonde data; W. A. Matthews forproviding the Lauder ozonesonde data; D. De Muer for providingthe SAGE II and Uccle comparison profiles; C. Trepte, and J.Zawodny for valuable discussions. R. Veiga was supported byNASA contract (NAS1-19570). D. M. Cunnold was supported byNASA contract (NAS1-19954).

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R. E. Veiga, Science Applications International Corporation, IEnterprise Parkway, Suite 250, Hampton, VA 23666. (e-mail:R.E.Veiga@Larc.nasa.gov.)

(Received June 28, 1994; revised December I, 1994;accepted December 3, 1994.)