SAGE I AND SAM II MEASUREMENTS OF 1 UM AEROSOL EXTINCTION

IN THE FREE TROPOSPHERE

by

G. S. Kent, U. 0. Farrukh , P. H. Wang, and A. Deepak

Science and Technology Corporation

101 Research Drive, Hampton, Virginia 23666

(KASA-CB-1829115) SAGE 1 AND £AK 2 N88-24121

fclASDEEHEKTS OP 1 filCECN AEfiGSOL EXTIUCTICM

JJs TBE FBEE TJO^OSFHEEI - (Sciecce and

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G3/46 0146692

1. Presently at the Electrical Engineering Department, Hampton University,

Hampton, Virginia 23669 with Hampton University
ABSTRACT

The SAGE I and SAM II satellite sensors were designed to measure, with

global coverage, the 1 urn extinction produced by the stratospheric aerosol.

In the absence of high altitude cloud, similar measurements may be made for

the free tropospheric aerosol. Median extinction values in the northern

hemisphere, for altitudes between 5 and 10 km, are found to be one-half to

one order of magnitude greater than values at corresponding latitudes in the

southern hemisphere. In addition, a seasonal increase by a factor of I.5->- 2

is observed in both hemispheres in local spring and summer. Following major

volcanic eruptions, a long-lived enhancement of the aerosol extinction is

observed for altitudes above 5 km.
I. INTRODUCTION

Measurements of the properties of aerosols in the free troposphere at

altitudes greater than a few kilometers are relatively scarce. At these

altitudes, the aerosol, particularly over the ocean, may be derived from

sources many thousands of kilometers distant and not be related to the

underlying surface type. The majority of existing measurements have been

made in the northern hemisphere over or close to continental areas, and our

knowledge of the aerosol characteristics over remote regions, such as the

oceans of the southern hemisphere rests on few in situ or remote

measurements. Although the general latitudinal trends in aerosol

concentration, composition and size distribution have been derived from the

available measurements, little is known about the variability of these

properties. Current interest in the development and deployment of a Global

Wind Measurement Satellite System (WINDSAT) (NOAA 1981), has led to an

awareness of our lack of knowledge of the global characteristics of the free

tropospheric aerosol. WINDSAT, as presently proposed, would use C09 doppler

shift lidar to measure wind velocity from the boundary layer to the lower

stratosphere. It would rely on backscattering from the atmospheric aerosol

for its signal and thus a knowledge of the global behavior of the aerosol

concentration, size distribution and, in particular, the backscattering

function at C0_ laser wavelengths is required.

In this paper, we describe the use of data obtained by the SAGE I and

SAM II satellite sensors to improve our knowledge of the global

characteristics of the free tropospheric aerosol. These satellites are
designed to measure stratospheric aerosol extinction at a wavelength of I

urn. In the absence of high altitude cloud, tropospheric measurements are not

only possible but are available from a significant fraction of the total

number of measurement opportunities. A detailed study made of one year

(March 1979 - February 1980) of satellite data is described. This has been

used to derive the global variation of the J urn aerosol extinction for

altitudes between approximately 5 km above the earth's surface and the

tropopause. In addition to the anticipated dependance upon latitude and

altitude, a seasonal cycle is also clearly evident in the aerosol

- extinction. The period following 1979 is significant for the number of

volcanic eruptions that have injected material into the stratosphere.

Analysis of upper tropospheric extinction data for 1980 and 1981 shows

evidence of volcanic modification of aerosol loading and the results of a

preliminary study of these changes are also presented.
2. SAGE I AND SAM II TROPOSPHERIC OBSERVATIONS

The SAGE I and SAM II satellite experiments contain sun photometers

designed to measure the extinction produced by stratospheric aerosols

(McCormick et al., 1979). SAM II, which was launched in October 1978, and

which is still operational, consists of a single channel sun photometer

centered at a wavelength of 1.0 urn. The orbit of SAM II is such that its

observations, which are made at satellite sunrise and sunset, occur between

latitudes of 64 S - 80 S and 65 N - 80 N, two measurements being made on each

orbit. SAGE I commenced its observations in February 1979 and, owing to a

faulty satellite power supply, these were terminated in November 1981. In

contrast to SAM II, the SAGE I coverage is nearly global, the „ latitude of

observation moving during a six-week period through about 120 of latitude,

the latitude extremes being approximately 74 N & S. SAGE I has four channels

which include an aerosol channel at a wavelength of 0.45 um in addition to

the 1.0 urn aerosol channel. Useful data on the former channel is limited to

altitudes above 10 km and our analysis has been confined to the 1.0 um data

only. The SAGE I data set is also limited by the fact that observations were

confined to sunsets only, after the first few months of observation, in order

to conserve satellite power. The atmospheric attenuation measured by either

satellite is over a path about 300 km in length with a 0.5 km field of view.

The aerosol extinction values thus represent an average over a section of the

atmosphere with these dimensions.

SAGE I and SAM II were designed for the measurement of stratospheric

aerosol extinction and it was anticipated that tropospheric measurements
would be hindered or possibly prevented by the presence of high altitude

cloud. The former is indeed the case but significant tropospheric

penetration does occur. Examples of SAGE I profiles showing such penetration

are shown in Figure 1. Figure I(a) shows the aerosol extinction increasing

smoothly with decreasing altitude, no apparent discontinuity occurring at the

tropopause. Figure l(b) shows a different profile with a strong enhancement

at an altitude of 10 km, presumed to be due to high altitude cloud. Table 1

sTiows the total number of observations made by SAGE I over a 3-month period

and the relative frequency of penetration to various tropospheric altitudes

for three latitude bands. It can be seen that good penetration («-^ 50%) is

obtained down to an altitude of 8 kilometers or less. Greatest frequency of

penetration occurs in the southern hemisphere and, as might be expected,

least occurs in the equatorial zone with its higher tropopause. Table 1

shows that one may obtain a reasonable description of the free troposphere

aerosol, on an average basis, down to an altitude of perhaps 5 or 6 km.

Below this altitude, individual profiles, when available, will be accurate.

Average values, which represent only 20% - 30% of the total potential data

set, may be expected to be biased toward more transparent atmospheres and

lower extinction.
3. THE EXTINCTION PROBABILITY DISTRIBUTION

Examination of the SAGE I and SAM II data shows that whereas, in the

stratosphere, extinction values at a given altitude and latitude are normally

fairly tightly concentrated about a mean level, the same is not true in the

troposphere. In the latter case, extinction values may vary over several

orders of magnitude, the higher values probably being due to attenuation by

thin (sub-visible) cloud. Under such conditions, the use of the mean

extinction as a measure of central tendency is of doubtful value. In order

to obtain a better description, we have examined the probability distribution

of the values of tropospheric extinction for different conditions. Figure 2

shows the results of such a study. Three months data, taken over the

latitude bands 20°-60°S [Fig. 2(a)] and 20°-60°N [Fig. 2(b)] between March

and May 1979, has been binned by altitude and extinction value. The altitude

interval used is 1 km over the range 0 to 30 km and the extinction interval

-5- 1 -3- 1

is 2x10 km over the range 0 to 10 km ; one extra bin has been added at

-3 -1

each altitude which includes all measured values greater than 10 km . This

-2 -1

bin contains extinction values up to about 10 km , values much greater than

this level not being detectable as they reduce the measured solar radiation

below the threshold of the satellite photometers. The contours in Fig. 2

show the probability of an observation falling into a given

altitude-extinction bin. Superimposed on these contours are lines showing

the 50% cumulative probability levels.

In the stratosphere, in both parts of Fig. 2, the extinction values are

tightly bunched at a given altitude and there is no problem about defining
and using a mean level. In contrast, in the troposphere below about 12 km,

the values are widely separated and there is a significant number of very

—3 — 1 high values (extinction > 10 km ) which are shown at the right-hand side of

Figures 2(a) and 2(b). These values probably represent attenuation by

subvisible cloud (Rao, 1975; Uthe & Russell, 1977). Rather than calculating a

mean extinction level at each altitude which would be biased in the

troposphere toward these very high values, that are "not representative of the

background tropospheric aerosol, we have chosen to use the 50% probability

level, or the median, as our measure of central tendency. In the

stratosphere, it approximates very well to the mean level. In the

troposphere, it defines an a.erosol level which is both useful and

meaningful. The numerical value of the median is not appreciably affected by

the inclusion of a few events, of very high extinction, due to thin cloud.

Its relationship to the aerosol extinction probability distribution makes it

compatible with published data on tropospheric aerosol backscatter

measurements at infra-red wavelengths (e.g., Post et al., 1982).

The probability distributions for the extinction values shown in Fig.

2(a) and 2(b) show very clearly a major feature of the satellite data.

Although the extinction values in the stratosphere are very similar in the

two hemispheres, the northern hemisphere tropospheric values at any given

altitude are significantly greater than the values at the same altitude in

the southern hemisphere. This hemispheric asymmetry was a systematic feature

of the data and is discussed in detail in the next section.
4. VARIATION OF EXTINCTION WITH LATITUDE, ALTITUDE, AND SEASON

In order to study the variation of the aerosol extinction with latitude

and season, the SAGE I data were grouped into seven latitude bands and the

SAM II data in four latitude bands, as shown in Table 2. Figure 3(a) shows

the altitude variation of the median SAGE I extinction for the six latitude

bands observed during the period March-May 1979. Apart from data at low

altitudes in the 60N - 75N latitude band, there is a general decrease in

aerosol extinction with increasing altitude. In examining these and other

data presented in this section, it should be remembered that below an

altitude of 5 or 6 km, the fractional penetration is less than 50% and the

data may have a systematic bias. This is particularly likely when the

extinction is high, as in the 60°N - 75°N latitude band, and it is doubtful

if in this case the decrease in median extinction for altitudes below 5 km is

representative of the true aerosol characteristics. It is more likely that

observations are being made down to these altitudes only when the atmosphere

is relatively clean of both aerosol and cloud. A secondary feature of the

variation with altitude is the greater extinction observed in the upper free

troposphere within the equatorial belt (20 S - 20 N) as compared to the other

latitude bands. This reflects the higher tropopause level ("16 km against

H2 km for mid-latitude) and must indicate the effects of convection in

raising the aerosol to the higher levels.

Apart from the variation with altitude, the most important feature is

the marked latitude asymmetry. At an altitude of 6 km, there is a steady

decrease in extinction between 60N - 75N and 40-60S by approximately one
order of magnitude. Although this asymmetry is present at all times of the

year, it is at a maximum in March-May, both in 1979 and in the following

years.

Figures 3(b)-(d) show the equivalent aerosol extinction profiles for

June-August 1979, September-November 1979, and December 1979-February 1980.

The features noted above are present in all these plots, the latitude

asymmetry is, however, less in Figs. 3(c) and (d). The peak in aerosol

extinction visible in the 20S - 20N latitude band in Fig. 3(d) at an altitude

of 19 km is caused by the injection of material from the eruption of the

Sierra Negra volcano on November 13, 1979 (Kent & McCormick, 1984). Analysis

of SAM II tropospheric data for 1979 for latitudes between 60 N and 90 N and

60 S and 90 S shows similar characteristics to the SAGE data. In March-May,

1979, the extinction at an altitude of 6-7 km and 60 -75 N is about an order

of magnitude greater than at the same altitude and latitude in the southern

hemisphere. In September-November 1979, the asymmetry is reduced to about

one-half of an order of magnitude.

Figure 3 shows the seasonal variation in aerosol extinction. In order

to present this variation more clearly, Figure 4 shows the variation of the

SAGE I/SAM II extinction at an altitude of 6 km as a function of latitude;

data are shown for the same four seasons as defined previously. Both Figures

4(a) and 4(b) show the hemispheric asymmetry; in addition, they show a clear

superimposed seasonal variation. In both hemispheres, maximum aerosol

extinction is found in local Spring-Summer and minimum extinction in local

Fall-Winter.
There is a relative lack of published aerosol data for the free

troposphere, as opposed to the boundary layer and the stratosphere, with

which to compare these observations. Many observations (e.g. Blifford, 1970;

Blifford and Ringer, 1969; Cress, 1980) are confined to a limited latitude

band or consist of too few measurements to determine meaningful statistical

averages. The most extensive data set is that of Patterson et al. (1980)

taken on two flight series, undertaken as part of the GAMETAG program, over

the Pacific Ocean in 1977 and 1978. Previously unpublished data from these

flights have recently been included in a NASA Contractors report (Kent et

al., 1985). Data taken on these flights clearly show the latitude gradient in

aerosol concentration and, hence, agrees with optical extinction

characteristics described above. This variation almost certainly reflects

the predominance of aerosol sources in the northern hemisphere and the

relative lack of trans-equatorial transport. Quantitative comparison of

extinction values at an altitude of 6 km calculated from the GAMETAG size

distributions with the direct SAGE I measurements shows good agreement in the

northern hemisphere. In the southern hemisphere, good agreement was obtained

for the 1977 GAMETAG data, while the 1978 data indicated significantly lower

extinction values. The reason for this difference is not clear but appears

to be a sampling variation. It must also be remembered that the sampling

volumes may differ greatly between alternative measurement systems. In the

case of SAGE I/SAM II, the sample volume is approximately 300 km in length

and the measured 1 urn extinction values correspond to an arithmetic average

over the variations along this optical path. This is in contrast to the in

situ aircraft measurements where the horizontal averaging is over at most a

few tens of kilometers.
Information on the seasonal variation of aerosol concentrations is also

scarce but the spring-summer maximum observed in both hemispheres is most

probably related to increased convection over land at that time of year.

Measurements of the infra-red aerosol backscattering function made at

Boulder, Colorado shows a clear seasonal variation, minimum values being

observed in fall and winter (Post, 1983; 1984). A notable feature of the

seasonal variation observed in the satellite data is the very strong I urn

extinction observed in March=-May, 1979 at latitude 60 -75 N and which is

repeated in the following two .years. This is the season at which arctic haze

is observed (Schnell, 1984). This haze originates in northern hemisphere

industrial areas (Raatz and Schnell, 1984) and is transported long distances

into the arctic. Flight measurements show the haze to occur in layers up to

altitudes of about 5 km (Radke et al., 1984). The SAGE I data barely extends

down to these altitudes due to the high extinction levels which cause the

measured solar radiation to fall below the instrument threshold. It is

possible that the increase in extinction observed in northern latitudes in

Spring at altitudes 5-8 km is related to the outer haze layers at lower

altitudes.

10
5. VARIATION OF AEROSOL EXTINCTION WITB SURFACE CHARACTERISTICS

Most of the aerosol in the free troposphere over the remote oceans is

derived, not by convection from the ocean surface, but by long-range

transport of aerosol and precursor gases from over the continental land

masses (WMO, 1980; Jaenicke, 1980). Some modification of the aerosol optical

properties, particularly that due to loss of the largest, optically

significant, particles by sedimentation, might be expected to occur during

this transport. A search was made, using the SAGE I data, for any evidence

of such, a variation. For the purpose of this study, the global surface was

divided into 10 latitude-longitude regions and each region categorized

according to the underlying surface. Five classes of surfaces were defined,

ranging from 100% land surface, to 100% ocean at a distance of at least 3000

km from the nearest continental land mass.

Each SAGE I observation has been classified according to the surface

type beneath the observation position, as well as by season and latitude.

Median extinction values have been calculated for each altitude. The

analysis shows very little significant variation of aerosol extinction with

sub-surface type. In most latitude bands, any systematic difference between

the extinction over land or ocean is less than the error in the median

values. The only positive result to be obtained from the analysis was for

the equatorial region (20°S - 20°N). Within this region, the median

extinction, at an altitude of 6 km, decreased approximately 20% over the

range of sub-surface types from land to remote ocean. This very small change

is consistent with the theory of aerosol injection over land followed by slow

particle sedimentation during horizontal transport.

11
The lack of any systematic dependence, for most of the globe, of the

aerosol extinction at an altitude of 6 km upon the surface characteristics

beneath the observation point indicates that air masses at these altitudes

must be transported from land to ocean in a time short compared with that

required for appreciable modification of aerosol properties. For typical

zonaf wind velocities (Lorenz, 1967), these times would be a few days to a

week. It may also be noted that 6 km is rather above the altitude at which

desert dust is normally transported over the oceans (Prospero and Carlson

1972; Shaw, 1980; Duce e't al., 1980). The small positive result obtained for

the equatorial region may be related to the lower wind velocities there and

possibly also to increased convective activity over land.

12
6. VOLCANIC EFFECTS

It is well known that volcanic eruptions inject solid and gaseous

materials into the stratosphere and that aerosols formed and deposited there

have lifetimes of months or years (Deirmendjian, 1973; Deepak, 1982; Kent and

McCormick, 1984). Solid particles are also injected in the troposphere where

the majority of them are presumed to be fairly quickly removed by

sedimentation and washout. Examination of the SAGE I and SAM II data set

shows that the upper troposphere, as well as the stratosphere, has a

long-lived enhancement in aerosol extinction following a significant volcanic

eruption. An example of this is given in Figure 5 which shows the altitude

variation of the median SAGE I extinction for September-November, 1980. At

this time, the stratospheric aerosol extinction at high northern latitudes

was strongly enhanced by material injected from the eruption of Mt. St.

Helens (latitude 46 N) on May 18, 1980. In addition, the aerosol layer over

equatorial latitudes still showed the effects of the eruption of Sierra Negra

(latitude 1°S) on November 13, 1979.

The profiles in Figure 5 may be compared with those in Figure 3(c) for

the same months in 1979. The stratosphere effects of the volcanic injection

are clear. In addition, in 1980, the aerosol extinction in the free

troposphere down to an altitude of 5 km is profoundly modified for latitude

bands 40 N-60 N and 60 N-75 N. Similar differences are observed within the

same latitude bands for June-August 1980 and in the 40 -60 N latitude band

for December 1980-February 1981 (no data is available for the 60°N-75°N

latitude band during northern winter); in all cases the enhancement appears

13
to occur in the free troposphere down to an altitude of about 5 km. The

stratospheric enhancement during this period and within these latitude bands

is produced by the injection of material from the Mt. St. Helens eruption and

there is little doubt that the free tropospheric enhancement must be related

to the same source. Material injected directly into the free troposphere by

volcanic eruptions may be expected to have a residence time short compared to

those occurring here (Pruppacher and Klett, 1978). It is noticeable that the

enhancement reaches its maximum amplitude close to the tropopause (^10 km at

60 N) and it is likely that the aerosol in the stratosphere is acting as a

reservoir from which material is being fed into the upper troposphere by

sedimentation and stratospheric-tropospheric exchange processes. The data

shows many interesting features which will be the object of future study.

For example, comparison of the profiles in Figure 5 with those in Figure 3(c)

shows that the transfer of aerosol from the stratosphere to the troposphere

occurs at high latitudes, whereas no such transfer is evident at low

latitudes, although volcanic material from Sierra Negra is clearly present in

the stratosphere. These differences may help resolve the relative importance

of sedimentation, stratospheric-tropospheric exchange and general circulation

as mechanisms for transfer of material from stratosphere to troposphere or

vice-versa.

There appears to be no published comparable measurement of free

tropospheric aerosol enhancement following the Mt. St. Helens eruption but

Post (1985) has described similar observations following the eruption of El

Chichon in 1982. Infra-red backscatter measurements showed an enhancement of

the free tropospheric aerosol backscattering function above an altitude of

14
about 6 km. Post (1985) was able to associate lifetimes of 208 days with the

stratospheric volcanic aerosol and of 60 days with the tropospheric aerosol.

He has attributed the tropospheric enhancement to the mixing downward of

stratospheric air containing the volcanic aerosol.

15
7. CONCLUSIONS

The SAGE I/SAM II satellite instruments have been shown to provide

useful data on the extinction produced by the aerosol in the free troposphere

at a wavelength of 1 pm. The satellite provided almost complete global

coverage between February 1979 and November 1981 although, because of

absorption and scattering by tropospheric cloud, the majority of the data are

confined to altitudes above about 5 km. Some data have been obtained at

lower altitudes, but this is only a small fraction of the total data set and

is probably not representative, corresponding as it does to the clearer cloud

and aerosol free occasions. At altitudes above 5 km, the data set is

extensive. Measured extinction values are sometimes very large. Such values

are believed to be to the presence of cloud somewhere along the optical

path. Use of an arithmetic mean to describe the average behavior at a given

altitude results in a value that is biased toward the higher extinction

values which are not representative of the aerosol. For this reason, we

have, after detailed examination of the probability distribution function for

the extinction, decided to use the median level as a relatively unbiased

parameter to describe the average aerosol behavior.

The data has yielded a detailed picture of the variation of the 1 urn

free tropospheric aerosol extinction with latitude, season and altitude, as

well as changes following volcanic injection of material into the

stratosphere. The most obvious characteristic is a pronounced hemispheric

asymmetry with minimum extinction being observed in high southern latitudes.

This behavior agrees with that established by the GAMETAG flight series over

16
the Pacific Ocean in 1977 and 1978. The magnitude of the asymmetry is

seasonally variable as both hemispheres also show a similar antiphase

seasonal oscillation in aerosol extinction. The greatest extinction in

either hemisphere is observed in local spring and summer and least in local

fall and winter. This seasonal variation is in agreement with that observed

by infra-red backscatter from aerosols in the free troposphere. The very

large extinction values observed in the highest northern latitudes coincide

in time with the occurrence of arctic haze and the two phenomena may be

causally related.

A search has been made for any correlation between the magnitude of the

aerosol extinction in the free troposphere and the nature of the underlying

surface. With the exception of the equatorial region, no significant

relationship was found, indicating that aerosols injected into the free

troposphere over land change their characteristics relatively slowly as the

affected air mass travels over the ocean. A more direct study of the

relationship between aerosol extinction and air mass history has not been

made and represents a possible direction for future work.

Significant increases in the aerosol content of the northern hemisphere

free troposphere above an altitude of 5 km were observed following volcanic

injection of material into the stratosphere. At the higher altitudes, this

enhancement was greater than the seasonal variation in aerosol extinction.

The long life-time of the extinction enhancement (many months) indicated that

the aerosol was almost certainly the result of downward transfer from a

stratospheric reservoir rather than that directly injected by the eruption

17
into the free troposphere. Again, this result is in agreement with

observations made using infra-red backscatter on the stratospheric and free

tropospheric aerosol burden following the eruption of El Chichon in 1982.

18
8. ACKNOWLEDGMENTS

We are glad to be able to acknowledge the assistance and interest shown

in this work by Dr. D. E. Fitzjarrald, NASA-Marshall Space Flight Center,

Huntsville, Alabama; and Dr. R. J. Curran, NASA-Headquarters, Washington,

D.C. , as well as that shown by Dr. M. P. McCormick and Mr. L. E. McMaster,

NASA-Langley Research Center, Hampton, Virginia. The work was supported under

NASA Contract NAS8-35594.

19
9. REFERENCES

Blifford, I. H. , 1970: Tropospheric aerosols, J. Geophys. Res., 75,

3099-3103.

Blifford, I. H., and L. D. Ringer 1969: The size and number distribution of

aerosols in the continental troposphere, J. Atmos. Sci., 26, 716-726.

Cress, T. S., 1980: Airborne Measurement of Aerosol Size Distributions over

Northern Europe, Vol. 1. Spring and Fall, 1976, Summer 1977, Air Force

Geophysical Laboratory, Hanscom Field, Massachusetts, Environmental Research

Paper 702.

Deepak, A. (ed.), 1982: Atmospheric Effects-and Potential Climatic Impact of

the 1980 Eruptions of Mount St. Helens, NASA Conference Publication 2240.

Deirmendjian, D., 1973: On volcanic and other particular turbidity anomalies,

Advanced Geophys., Jj>, 267-296.

Duce, R. A., C. K. Unni, B. J. Ray, J. M. Prospero, and J. T. Merrill, 1980:

Long range atmospheric transport of soil dust from Asia to the tropical north

Pacific: temporal variability, Science, 209. 1522-1524.

Jaenicke, R., 1980: Natural aerosols, New York Academy of Science Annals,

338, 317-329.

Kent, G. S. , and M. P. McCbrmick, 1984: SAGE and SAM II measurements of

global stratospheric aerosol optical depth and mass loading, J. Geophys.

Res., 89^ 5303-5314.

Kent, G. S., P. H. Wang, U. 0. Farrukh, A. Deepak, and E. M. Patterson, 1985:

Development of a global model for atmospheric backscatter at CO wavelengths,

Final Report on NASA Contract NAS8-35594, March 1985.

Lorenz, E. N., 1967: The nature and theory of the general circulation of the

atmosphere, World Meteorological Organization, 161 pp.

McCormick, M. P., P. Hamill, T. J. Pepin, W. P. Chu, T. J. Swissler, and L.

R. McMaster, 1979: Satellite studies of the stratospheric aerosol, Bull, of

the Am. Meteor. Soc., 60, 1038-1046.

NOAA, 1981: Global Wind Measuring Satellite System-WINDSAT Final Report for

NOAA Contract NA 79RA COO 127.

Patterson, E. M. , C. S. Kiang, A. C. Delany, A. F. Wartburg, A. C. D. Leslie,

and B. J. Huebert, 1980: Global measurements of aerosols in remote

continental and marine regions: Concentrations, size distributions, and

optical properties, J. Geophys. Res., 85, 7361-7376.

20
Post, M. J., F. F. Hall, R. A. Richter, and T. R. Lawrence, 1982: Aerosol

backscattering profiles at A = 10.6 urn, Appl. Opt., 21, 2442-2446.

Post, M. J., 1983: Atmospehric Aerosol Profiles at CO- Wavelengths, 2nd

Topical Meeting on Coherent Laser Radar, Technology and Applications, August

1-4, 1983, Aspen, Colorado, Technical Digest, pp. Th B4-1 to Th B4-5.

Post, M. J., 1984: Lidar observations of the El Chichon Cloud at A = 10.6 urn,

Geophys. Res. Lett., l_, 846-849.

Post, M. J., 1985: Atmospheric Infrared Backscattering Profiles:

Interpretation of Statistical and Temporal Properties, NOAA Technical

Memorandum, ERL WPL-122, May 1985.

Prospero, J. M., and T. M. Carlson, 1972: Vertical and areal distribution of

Saharan dust over the west equatorial North Atlantic Ocean, J. Geophys. Res.,

77., 5255-5215.

Pruppacher, H. R., and J. D. Klett, 1978: Microphysics of clouds and

precipitation, D. Reidel, Boston, 714 pp. "

Raatz, W. E., and R. C. Schnell, 1984: Aerosol distribution and an Arctic

aerosol front during AGASP: Norwegian Arctic, Geophys. Res. Lett^. , 11,

373-376.

Radke, L. F., J. H. Lyons, D. A. Hegg, and P. V. Hobbs, 1984: Airborne

observations of Arctic aerosols. 1: Characteristics of Arctic haze, Geophys.

Res. Lett., J_I_, 393-396.

Rao, P. K., 1975: Invisible cirrus clouds in NOAA-2 VHRR imagery, Mon.

Weather Rev. , _103, 72-77.

Schnell, R. C., 1984: Arctic haze and the Arctic gas and aerosol sampling

program (GASP), Geophys. Res. Let^t., 11, 361-364.

Shaw, G. E., 1980: Transport of Asian desert aerosol to the Hawaiian Islands,

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Uthe, E. E., and P. B. Russell, 1977: Lidar Observations of Tropical High

Altitude Cirrus Clouds, Proceedings of the Symposium on Radiation in the

Atmosphere, Garmisch-Partenkirchen, FRG, 19-28 August 1976, H. J. Bolle

(ed.), Science Press, 242-244.

World Meteorological Organization Report No. WGP-12, "Aerosols and Climate,"

Report of the meeting of the JSC experts held in Geneva, 27-31 October 1980.

21
Table 1. Relative Frequency of SAGE Observations in the

Troposphere (March - May 1979)

Relative Frequency in Each Latitude Band (%)

Altitude

(km)

20

18

16

14

12

10

8

6

4

2

60° - 20°S

100

100

100

98

89

73

58

44

30

6

20°S - 20°N

100

96

78

61

53

48

45

36

17

0

20°N - 60°N

100

100

99

98

89

68

52

34

15

4

TOTAL NUMBER

OF

OBSERVATIONS 827 290 455
Table 2. Latitude Bands Used in the Analysis of SAGE I

and SAM II Data

(a) SAGE I

(b)

60°N -

40°N -

20 °N -

20°S -

40°S -

. 60°S -

75°S -

SAM II

75 °N -

60°N -

75 °S -

90°S -

75 °N

60°N

40 °N

20°N

20°S

:40°S

60°S

90 °N

75 °N

60°S

75 °S
AEROSOL EXTINCTION (km~)

10

-6

AEROSOL EXTINCTION (km'

Figure L. SAGE I I urn extinction proCiels showing penetration into the troposphere.

(a) March 1, 1979: 37.5°S, 111.3°E. No high-altitude cloud present.

(b) March 2, 1979: 34.8°S, 131.6°W. High-altitude cloud present.

Dashed lines show tropopause altitudes.
(b)

EXTINCTION (10 ~ " km EXTINCTION (10~4 km"1)

Figure 2. Distribution of SAGE I, 1 urn extinction values, March-May, 1979,

(a) 20°-60°S (b) 20°-60°N

i

Probability (%) Pattern Probability (%) Pattern
25]

(b)

10-3

AEROSOL EXTINCTION (km-1)

345678 9

io-2

AEROSOL EXTINCTION (km -')

25 -

(d)

AEROSOL EXTINCTION (km-')

345678 9 2 345676 9

1C"3 10-'

AEROSOL EXTINCTION (km-1)

Figure 3. Median I urn aerosol extinction profiles for SAGE 1 data shown as a

function of latitude band.

(a) March - May, 1979

(b) June - AUgust, 1979

(c) September - November, 1979

(d) December 1979 - February, 1980

LATITUDE BAND

a

O

A

60N-75N

40N-60N

20N-40N

20S-20N

40S-20S

60S-40S

75S-60S
AEROSOL ' AEROSOL

EXTINCTION EXTINCTION

(10-4krr>-1) (10-4km~1)

1

30

20

10

L

A

 6'

..; • ;

2

J

30

j

20

\ *

[ iA **

r T 8*

• * ! • ' :

 ij * •

2

i i i i i i i i i i i i i i i i i

-

0

0

:. n f

! * .f

-

1 1. 1 I, 1 L 1 1

5 80 60 40 20 E 20 40 60 80 N S 80 60 40 20 E 20 40 60 80 h

LATITUDE LATITUDE

Figure 4. SAGE I/SAM II median 1 jim aerosol extinction profiles at an altitude of

(a) Equinoxes. (b) Solstices.

km.

0 SACE. MAR-MAY 7J

0 SAM II. MAR-MAY 79

f SACE. SEP-NOV 79

4 SAM II. SEP-NOV 79

SACE. JUN-;AUG 7»

SAM II.. JUN-AUC 79

SACE. DEC 79-FEB 10

SAM II. DEC 79-FEB 10
r

5678 9

10-3

3 4 5678 9

10-2

AEROSOL EXTINCTION (km-1)

Figure 5. Median 1 urn aerosol extinction profiles for SAGE I data,

September - November, 1980, following the eruptions of

Sierra Negra and Mount St. Helens.

LATITUDE BAND

a 75N-6ON

O 4ON-6ON

A 20N-40N

K 20S-20N

40S -20S

60 S - 40 S

75 S-60S