High-altitude aerosol variations associated with stratospheric warmings
High-altitude aerosol variations associated with stratospheric warmings
-20 0 00 o 0 000
w -40 -
-60 -0
000
Mc MURDO, 1984
D.J. HOFMANN and J.M. ROSEN
10
30 m
-80 -
Department of Physics and Astronomy University of Wyoming Laramie, Wyoming 82071
On 27 October 1983, a balloon sounding was conducted to determine to what extent volcanic sulfuric acid aerosol, injected by the eruption of El Chichon in Mexico in April 1982, had affected the antarctic stratosphere. A sizeable layer of aerosol was detected in the 10 to 17 kilometer altitude range, and from the average particle size, this layer was identified as El Chichon debris. In the 20 to 30 kilometer range, absence of the larger (radius greater than 0.15 micrometer) aerosol and an enhancement of the smaller (radius greater than 0.01 micrometer) aerosol was interpreted as possibly being due to evaporation and recondensation, because a stratospheric warming was taking place at these altitudes with temperatures sufficiently high to question the state (liquid or vapor) of the sulfuric acid/water aerosol. These results were reported in the literature (Hofmann and Rosen 1985-a, 1985-b). In 1984, the measurements were repeated, this time with two optical particle counters for better resolution and two balloon soundings, one at McMurdo Station on 1 November 1984 and one at South Pole Station on 10 November 1984. At McMurdo, an 8,000 cubic meter volume polyethylene balloon (largest flown in Antarctica to date) was used to carry the 35-kilogram payload to an altitude of 34.5 kilometers. The two particle detectors simultaneously measured the small particles (radius greater than 0.01 micrometer, called "condensation nuclei") and the larger particles in two size ranges (radius greater than 0.15 and 0.25 micrometer) during balloon ascent and parachute descent. Data was obtained through radio telemetry. The payload was recovered by helicopter about 100 kilometers from McMurdo. Following thorough check of the detectors and preliminary data analysis, our group went to South Pole Station on the ason's second flight into the station. The instruments were teunched on a 7,200 cubic meter volume balloon to an altitude of 32.5 kilometers, again functioning normally. We estimated that the impact of the payload would be 70 to 80 kilometers from the station, and although recovery attempts were made using a Hercules LC-130 airplane on routine McMurdo to South Pole flights, the payload was not located. As in 1983, a stratospheric warming was again underway during our soundings. This can be seen in figure 1 where the temperature versus time at McMurdo and South Pole for the 10 millibar (about 30 kilometers altitude) and 30 millibar (about 23 kilometers altitude) pressure levels, as obtained by radiosonde ascents during this period, are shown. During this period, the wind speeds in the 20 to 30 kilometer altitude region were quite high, peaking at about 70 meters per second at McMurdo on 29 October. These high winds suggested that the aerosol has been in several temperature regimes during a day or two prior to our observing them and resulted in very complicated distributions. 1985 REVIEW
-100 SEPT
I
In
OCT
00 0000
0 000 00 000 00 0 00
60
SOUTH POLE, 1984
m 0 1 50,b
00 0 0 0 80L
SEPT
OCT
NOV
Figure 1. Temperatures at the 10 and 30 millibar pressure levels as determined by radiosonde ascents at McMurdo and South Pole Stations in September to November 1984. Missing data indicate that the balloon did not reach sufficient altitude. Arrows indicate the times of the aerosol soundings at the two stations. ("mb' denotes "millibar." "gm (cm- 1)" denotes "micrometer per cubic centimeter:')
Figure 2 shows the results of the two balloon soundings for both the large and small aerosol. The remnants of the El Chichon eruption can be seen in the larger, optically active aerosol (radius greater than 0.15 micrometer) between about 9 and 18 kilometers altitude. We see that this layer, which is a global feature, is nearly identical at the two stations. The peak concentration is about 3.5 particles per cubic centimeter. One year earlier this concentration was 7.0 particles per cubic centimeter. Thus the layer has decayed by a factor of two in 1 year. For an exponential decay, this suggests a characteristic decay time of about 17 months. However, more data to improve statistics would be required to determine this factor accurately. The latter is currently being done in monthly soundings at Laramie, Wyoming. When we examine the 20 to 30 kilometer altitude range in figure 2, we see variations in aerosol concentration which are quite complicated. They are probably associated with transport from regions having different temperature characteristics. We note in particular that the South Pole Station sounding apparently displays an absence of large aerosol, as compared to the McMurdo sounding, in the 20 to 25 kilometer altitude region. In this same region, the South Pole Station sounding displays an enhancement of small aerosol. This is again reminiscent of a mass-conserving process such as evaporation-recondensation and/or coagulation. These data are currently being analyzed using satellite temperature maps to determine the origin and temperature history of the air parcels encountered during the soundings. It is hoped this will shed light on some of the 217
processes governing high-altitude aerosol distributions. Additional balloon soundings will be conducted in 1985 to increase the data base. D.J. Hofmann, N.T. Kjome, G.L. Olson, and S. Rolf were in the field from 15 October to 15 November. This work was supported in part by National Science Foundation grant DPP 83-14487.
References
Hofmann, D.J., and J.M. Rosen. 1985-a. Antarctic observations of stratospheric aerosol and high altitude condensation nuclei following the El Chichon eruption. Geophysical Research Letters, 12(1), 13 - 16. Hofmann, D.J., and J.M. Rosen. 1985-b. Detection of El Chichon volcanic aerosol in the antarctic stratosphere. Antarctic Journal of the U.S., 19(5), 196 - 199.
1OH
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(1cM)
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18
S 588b
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1808
1888L
182 ir' 18+0 18+' PARTICLE CONCENTRATION RIO. B ye (c13)
18+2
IO 10+1 18+2 18+ PARTICLE CONCENTRATION 118.8l pu (c13)
Figure 2. Profiles of large (left) and small (right) aerosol concentration at McMurdo on 1 November and South Pole (profiles with crosses) on 1( November obtained during balloon soundings in Antarctica in 1984. ("mb" denotes "millibar.")
218
ANTARCTIC JOURNAL
-20 0 00 o 0 000
w -40 -
-60 -0
000
Mc MURDO, 1984
D.J. HOFMANN and J.M. ROSEN
10
30 m
-80 -
Department of Physics and Astronomy University of Wyoming Laramie, Wyoming 82071
On 27 October 1983, a balloon sounding was conducted to determine to what extent volcanic sulfuric acid aerosol, injected by the eruption of El Chichon in Mexico in April 1982, had affected the antarctic stratosphere. A sizeable layer of aerosol was detected in the 10 to 17 kilometer altitude range, and from the average particle size, this layer was identified as El Chichon debris. In the 20 to 30 kilometer range, absence of the larger (radius greater than 0.15 micrometer) aerosol and an enhancement of the smaller (radius greater than 0.01 micrometer) aerosol was interpreted as possibly being due to evaporation and recondensation, because a stratospheric warming was taking place at these altitudes with temperatures sufficiently high to question the state (liquid or vapor) of the sulfuric acid/water aerosol. These results were reported in the literature (Hofmann and Rosen 1985-a, 1985-b). In 1984, the measurements were repeated, this time with two optical particle counters for better resolution and two balloon soundings, one at McMurdo Station on 1 November 1984 and one at South Pole Station on 10 November 1984. At McMurdo, an 8,000 cubic meter volume polyethylene balloon (largest flown in Antarctica to date) was used to carry the 35-kilogram payload to an altitude of 34.5 kilometers. The two particle detectors simultaneously measured the small particles (radius greater than 0.01 micrometer, called "condensation nuclei") and the larger particles in two size ranges (radius greater than 0.15 and 0.25 micrometer) during balloon ascent and parachute descent. Data was obtained through radio telemetry. The payload was recovered by helicopter about 100 kilometers from McMurdo. Following thorough check of the detectors and preliminary data analysis, our group went to South Pole Station on the ason's second flight into the station. The instruments were teunched on a 7,200 cubic meter volume balloon to an altitude of 32.5 kilometers, again functioning normally. We estimated that the impact of the payload would be 70 to 80 kilometers from the station, and although recovery attempts were made using a Hercules LC-130 airplane on routine McMurdo to South Pole flights, the payload was not located. As in 1983, a stratospheric warming was again underway during our soundings. This can be seen in figure 1 where the temperature versus time at McMurdo and South Pole for the 10 millibar (about 30 kilometers altitude) and 30 millibar (about 23 kilometers altitude) pressure levels, as obtained by radiosonde ascents during this period, are shown. During this period, the wind speeds in the 20 to 30 kilometer altitude region were quite high, peaking at about 70 meters per second at McMurdo on 29 October. These high winds suggested that the aerosol has been in several temperature regimes during a day or two prior to our observing them and resulted in very complicated distributions. 1985 REVIEW
-100 SEPT
I
In
OCT
00 0000
0 000 00 000 00 0 00
60
SOUTH POLE, 1984
m 0 1 50,b
00 0 0 0 80L
SEPT
OCT
NOV
Figure 1. Temperatures at the 10 and 30 millibar pressure levels as determined by radiosonde ascents at McMurdo and South Pole Stations in September to November 1984. Missing data indicate that the balloon did not reach sufficient altitude. Arrows indicate the times of the aerosol soundings at the two stations. ("mb' denotes "millibar." "gm (cm- 1)" denotes "micrometer per cubic centimeter:')
Figure 2 shows the results of the two balloon soundings for both the large and small aerosol. The remnants of the El Chichon eruption can be seen in the larger, optically active aerosol (radius greater than 0.15 micrometer) between about 9 and 18 kilometers altitude. We see that this layer, which is a global feature, is nearly identical at the two stations. The peak concentration is about 3.5 particles per cubic centimeter. One year earlier this concentration was 7.0 particles per cubic centimeter. Thus the layer has decayed by a factor of two in 1 year. For an exponential decay, this suggests a characteristic decay time of about 17 months. However, more data to improve statistics would be required to determine this factor accurately. The latter is currently being done in monthly soundings at Laramie, Wyoming. When we examine the 20 to 30 kilometer altitude range in figure 2, we see variations in aerosol concentration which are quite complicated. They are probably associated with transport from regions having different temperature characteristics. We note in particular that the South Pole Station sounding apparently displays an absence of large aerosol, as compared to the McMurdo sounding, in the 20 to 25 kilometer altitude region. In this same region, the South Pole Station sounding displays an enhancement of small aerosol. This is again reminiscent of a mass-conserving process such as evaporation-recondensation and/or coagulation. These data are currently being analyzed using satellite temperature maps to determine the origin and temperature history of the air parcels encountered during the soundings. It is hoped this will shed light on some of the 217
processes governing high-altitude aerosol distributions. Additional balloon soundings will be conducted in 1985 to increase the data base. D.J. Hofmann, N.T. Kjome, G.L. Olson, and S. Rolf were in the field from 15 October to 15 November. This work was supported in part by National Science Foundation grant DPP 83-14487.
References
Hofmann, D.J., and J.M. Rosen. 1985-a. Antarctic observations of stratospheric aerosol and high altitude condensation nuclei following the El Chichon eruption. Geophysical Research Letters, 12(1), 13 - 16. Hofmann, D.J., and J.M. Rosen. 1985-b. Detection of El Chichon volcanic aerosol in the antarctic stratosphere. Antarctic Journal of the U.S., 19(5), 196 - 199.
1OH
10
30 28
30
b
28 25 A
A? L R T F 29 1 s
R F S 50 S
L T
58
28 1 T U
T S U U
D RIOB
188F (mh)
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D
F
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(1cM) (.b)
288
(1cM)
288
H
588
18
18
S 588b
5
1808
1888L
182 ir' 18+0 18+' PARTICLE CONCENTRATION RIO. B ye (c13)
18+2
IO 10+1 18+2 18+ PARTICLE CONCENTRATION 118.8l pu (c13)
Figure 2. Profiles of large (left) and small (right) aerosol concentration at McMurdo on 1 November and South Pole (profiles with crosses) on 1( November obtained during balloon soundings in Antarctica in 1984. ("mb" denotes "millibar.")
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ANTARCTIC JOURNAL
