Several years of satellite observations indicate the presence of enhanced amounts of tropospheric ozone over the tropical South Atlantic during the austral springs. Wide-spread biomass burning is prevalent over Africa and South America during the same time of the year. Another recent satellite technique has identified the locations of fires over the continents. In this study, we present an analysis of the prevailing meteorological conditions when the highest amounts of tropospheric ozone are present

Brackett, V. G.

Fakhruzzaman, K. M.

Fishman, J.

Justice, C. O.

Kendall, J. D.

English

NASA Technical Reports Server

N95-10628
LARGE. SCALE CIRCULATION PATTERNS ASSOCIATED WITH HIGH
CONCENTRATIONS OF TROPOSPHERIC OZONE IN THE TROPICAL
SOUTH ATLANTIC OCEAN
K. M. Fakhruzzaman 1, j. Fishman, and V. G. Brackett 1
Atmospheric Sciences Division (Mail Stop 401A)
NASA Langley Research Center
Hampton, Virginia 23681-0001 U. S. A.
J. D. Kendall 2 and C. O. Justice 3
NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 U.S.A.
ABSTRACT
Several years of satellite observations
indicate the presence of enhanced amounts
of tropospheric ozone over the tropical South
Atlantic during the austral springs. Wide-
spread biomass burning is prevalent over
Africa and South America during the same
time of the year. Another recent satellite
technique has identified the locations of
fires over the continents. In this study, we
present an analysis of the prevailing meteo-
rological conditions when the highest
amounts of tropospheric ozone are present.
1. INTRODUCTION
Recently, a methodology has been
developed at the NASA Langley Research
Center for the indirect measurement of the
tropospheric ozone (known as tropospheric
residual) using observations of two satellite
instruments (Total Ozone Measurement
Spectrometer [TOMS] and Stratospheric
Aerosol and Gas Experiment [SAGE], Fish-
man et al., 1990). The tropospheric resid-
ual ozone was obtained by subtracting
stratospheric ozone measured by SAGE
instruments from the total column of atmo-
spheric ozone measured by TOMS. The
analysis of several years of satellite observa-
tions indicates that large amounts of tropo-
spheric ozone are often present over the trop
1 Science Application International Corporation.
2 Science Systems Application Incorporated.
3 University of Maryland, College Park.
pical South Atlantic Ocean (Fishman et al.,
1991). The highest amounts of ozone are
generally observed during austral spring
(September-November). Based on these
analyses, the figure below shows the annual
average of the global distribution of tropo-
spheric ozone (Fig. 1).
INTEGRATED TROPOSPHERIC OZONE
(1979-1990)
25
-25
.o
-50 _ '/' _ ....... f_
-180 -120 -60 0 80 120 180
(IrEST) LONGITUDE (FAST)
Figure. 1
In this study, we present a case study
analysis of the prevailing meteorological
conditions when high tropospheric amounts
are present. Another technique has been
developed to identify hotspots and thus
anthropogenic origin of greenhouse gases by
using Advanced Very High Resolution Radi-
ometer (AVHRR) satellite imagery. Using
these techniques, we have located the
regions of highest ozone concentration and
their relationship to the source regions
using isentropic trajectory analyses. A case
study of a fire in the Okavango River delta
in northern Botswana is shown below.
Though isobaric surfaces are a conven-
tional way of most meteorological analyses,
the quasi-conservative three-dimensional
158
https://ntrs.nasa.gov/search.jsp?R=19950004216 2020-06-16T11:28:41+00:00Z
airflow takes place quite closely on the sur-
faces of equal potential temperature
(Danelsen, 1961). Therefore, we have chosen
isentropic surfaces for prevailing meteoro-
logical analysis (Haagenson and Shapiro,
1979). The use of an isentropic trajectory
model unveils a complex three-dimensional
flow regime over the tropical South Atlantic
Ocean of continental origin which is typical
during the burning season.
Utilizing all these analyses, we will
determine the relative contributions from
tropospheric sources in both Africa and
South America, as well as attempt to quan-
tify how much ozone in the troposphere had
been recently transported from the lower
stratosphere and upper troposphere. Our
analyses also have utilized observations
from ozonesonde launches (Cros et al., 1992;
Fishman et al., 1992) made simultaneously
at Ascension Island (8 ° S, 15 ° W) and Braz-
zaville, Congo (4 ° S, 150 E).
2. OZONESONDE OBSERVATIONS
AND TRAJECTORIES
The ozonesonde measurements at two
stations reveal high ozone during the burn-
ing season of equatorial southern sub-tropi-
cal Africa. Typically ozone maxima in
Ascension Island are lower in concentration
and at a higher altitude than at Brazzaville,
Congo (Fig. 2).
TYPICAL BURNING SEASON OZONE PROFILE
Ascension Island,(12 Sept., 1990),
and Brazzavllle,Congo, (19Sept., 1990)
45O
.J:[--'l- I I I I I I I I000 _"" """" "- ... _ e
550 : _ CONGO I 6
i
,$
650 v
800 : 2
650 !
900 l
95O
1000
1o5o I I I I I I I 1 I I I I o
15 20 25 30 35 40 45 50 55 50 65 70 715 80
OZONE (nb)
Figure 2
The isentropic trajectories of air par-
cels from equatorial Africa confirmed that
ozone-rich air ascends slowly during west-
ward transit across the Atlantic by the pre-
vailing trade-winds (Fig. 3). The
Montgomery stream functions generated by
the isentropic analyses indicate the flow
pattern of the region on the given potential
temperature surfaces.
Backward Trajectories From Ascension Island
Theta Level = 312 K
Start 00Z Sept 10, 1989
Figure 3
End00Z Sept 17,1989
3. CASE STUDY: OKAVANGO
DELTA FIRE
Our analyses of AVHRR imagery can
be used to identify active fires, smoke, and
the burn scars during the case study (Mat-
son and Dozier, 1981; Thomas and Tag,
1990). For our case of study, we have ana-
lyzed ozone, meteorological and AVHRR
data in conjunction with widespread burn-
ing taking place in near the Okavango River
delta.
The progress of the fire fronts, the
development of the burn scars, and the
plumes of smoke indicated at least three dif-
ferent directions of air flow in this region
during the time of the fire (Fig. 4). The for-
ward trajectories from the delta region con-
firmed the three different directions of
transport of trace gases (Fig. 5). Allowing
the time and suitable condition of photo-
chemical production of ozone, a significant
159
increase in the tropospheric ozone was regime that consists of air originating from
found along the trajectories as shown in fig- South America as well as from southern
ure 6. Africa.
Okavango River Delta Fire, September 3, 1989 Progression of Biomass Burning, Okavango River Delta
A.cA
In" (_0 I_v!_:: :_i,,.O_" a¢_=..
I .............
I _";_ Enlarged--_
Smoke Nn Recent burn area _._ rk
Old burned area _ Active Fires '=' _'_
F]gure 4
Forward Trajectories From Okavango Oelta, Botswana
There Level = 320 K
i
Start O0Z Sep102, 1989
Figure 5
\
End 00Z Sept 11, 1989
4. THREE-DIMENSIONAL FLOW
REGIME
We have constructed a generalized
three-dimensional flow regime of atmo-
spheric circulation over the tropical South
Atlantic Ocean for the month of September,
1989 by calculating bulk isentropic trajecto-
ries of continental air parcels that origi-
nated over the regions of biomass burning
(Fig. 7). This analysis suggests that the
source of ozone-rich air off the coast of
Angola is result of a fairly complex flow
August 31, lS89 i Septsmbslr S, 1989
i September 3, 1909
20° N , , • , , q.lO.h
_o0_._ 's_
60 ° W 40 ° 20 ° O*
Longitude
Residual Ozone Difference
September 3 - August 31, 1989
20 ° 40 ° 60 ° E
Figure 6
5. CONCLUSION
Recent scientific interest on global
warming and pollution highlights the need
to understand atmospheric chemistry and
biomass burning in the tropics. The subse-
quent transport of trace gases is also an
important issue, along with the photochem-
istry. At the present time very little is
known about the tropical meteorology of this
region of the world.
This study of the three dimensional
flow regime in the southern tropics is among
the first of its kind (Fig. 7). These analyses
show that the circulation pattern is more
160
Middle and Lower Tropospheric Flow Regime (September, 1989)
..... i
Figure 7
complex than previously thought. The eleva-
tion of the African landmass and the pres-
ence of a semi-permanent high pressure
system, in addition to the migration of the
Inter-Tropical Convergence Zone (ITCZ) and
subtropical jet stream greatly complicate
the observed circulation pattern. Further
studies are needed to understand fully the
dynamics of this region.
Tropical meteorologists, atmospheric
chemists and environmentalists are now
enthusiastic about the study of this region.
It is expected that considerable insight will
come forth as a result of the upcoming
Transport and Atmospheric Chemistry near
the Equator -- Atlantic (TRACE-A) mission
which is scheduled in August-October,
1992..
5. ACKNOWLEDGMENT
The authors thank P. Haagenson for
developing the NCAR's isentropic trajectory
model which has been used in this study.
6. REFERENCES
Cros, B., D. Nganga, A. Minga, J. Fishman,
and V. Brackett, Distribution of tropo-
spheric ozone at Brazzaville, Congo,
determined from ozonesonde measure-
ments, J. Geophys. Res., 97, 12869-
12876, 1992.
mb
900
800
7OO
60O
50O
40O
Danielsen, E. F., Trajectories: isobaric, isen-
tropic and actual, J. Meteor., 18, 470-
486, 1961.
Fishman, J., C. E. Watson, J. C. Larsen, and
J. A. Logan, The distribution of tropo-
spheric ozone determined from satellite
data, J. Geophys. Res. 95, 3599-3617,
1990.
Fishman, J., K. Fakhruzzaman, B. Cros,
and D. Nganga, Identification of wide-
spread pollution in the southern hemi-
sphere deduced from satellite analyses,
Science, 252, 1693-1696, 1991.
Fishman, J., V. Brackett, and K. Fakhruzza-
man, Distribution of tropospheric ozone
in the tropics from satellite and ozone-
sonde measurements, J. of Atmos. Tern
Phys. 54, 589-597, 1992.
Haagenson, P. and M. Shapiro, Isentropic
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NCAR Technical Note. NCAR / TN-
149+STR, Boulder, CO., 30 pp., 1979.
Matson, M. and J. Dozier, Identification of
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161


Large-scale circulation patterns associated with high concentrations of tropospheric ozone in the tropical South Atlantic Ocean

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