Lower atmosphere studies_________________ Ozone and aerosol ...
Lower atmosphere studies_________________ Ozone and aerosol measurements in the springtime antarctic ozone hole D.J. HOFMANN, J.M. ROSEN, J.A. HARDER, and S.R. ROLF Department of Physics and Astronomy University of Wyoming Laramie, Wyoming 82071
Since 1972, the University of Wyoming's high-altitude balloon research group has been conducting soundings of stratospheric aerosol concentrations in Antarctica. The primary purpose of these measurements in recent years has been to determine the stratospheric effects in the Southern Hemisphere of the 1982 volcanic eruption of El Chichon. In addition, observations at Laramie, Wyoming since 1979 (Rosen and Hofmann 1983; Hofmann, Rosen, and Cringe! 1985), suggested that stratospheric warming episodes in the north polar region were instrumental in drastically altering the aerosol size distribution in the 30-kilometer region and, if the proposed model of aerosol transformation was valid, should occur in the corresponding season in the antarctic stratosphere. The latter was verified in the 1983 measurements (Hofmann and Rosen 1985a) and study of these events continued in 1984 in Antarctica (Hofmann and Rosen 1985b). These studies suggested that information on the origin of the measured air parcel could be vital in interpreting the data. Since stratospheric ozone can serve as a useful tracer and since ozone measurements in Antarctica have recently revealed that the October minimum in total column ozone has been on the decline, ozone profile measurements were added in 1985. The aerosol measurements were made with optical particle counters, as described previously (Hofmann and Rosen 1982). Ozone measurements were made using commercial electrochemical ozonesondes (Scientific Pump Corp.). Four soundings were conducted from McMurdo Station on 5, 8, 9, and 13 November. All measured ozone, but only the soundings on 5 and 9 November also measured the aerosol distribution. Altitudes in excess of 30 kilometers were achieved on all flights. At the time of the soundings, the stratospheric wind speeds were quite high. In fact, the circumpolar wind maximum or polar jet (region of maximum gradient of height contours at a fixed pressure), which may be used to delineate a hypothetical boundary of the polar vortex region, was generally situated near McMurdo. This resulted in the sampling of air with very different histories over this time period. Figure 1 shows the temperature profiles measured on the four soundings discussed here. The position of the south polar vortex at a height of 23 kilometers, relative to McMurdo and 228
South Pole Stations, from satellite measurements is also shown here. These data suggest that the character of the temperature profiles encountered on 8 and 9 November were decidedly different than those on 5 and 13 November. Examination of the vortex position indicates substantial motion relative to McMurdo Station during this period; for example, the station was inside the 30-millibar, 23-kilometer pressure-height contour on 8 and 9 November but it was outside this contour on 5 and 13 November. The nature of this movement was more that of rotation of an elongated region of low pressure rather than a simple bulk movement of the vortex toward and then away from the station. The temperature profiles in figure 1 show the appearance of the colder vortex region at 15-30 kilometers on 8 and 9 November. The profiles on 5 and 13 November are typical of extra-vortex air during the spring warming period, similar to that observed in 1983 and 1984. Figure 2 shows the ozone profiles measured on these days. It is clear that the nature of these profiles, in the 15-30 kilometer region, is also drastically different for 8 and 9 November as compared to 5 and 13 November. The difference may be characterized as less ozone on days when McMurdo Station was apparently under the influence of the vortex and more or less normal otherwise. The difference in total ozone between 5 and 9 November is nearly a factor of two. Quite remarkable in figure 3 is the observation that on 9 November, ozone was considerably reduced even at altitudes in excess of 30 kilometers, in the region of extremely high temperature. We noted also that the lower stratospheric ozone features (below about 15 kilometers) are quite similar in all surroundings, suggesting a reasonable comparative accuracy among soundings. The soundings on 5 and 9 November also included aerosol measurements, as indicated earlier, obtained with a condensation nuclei counter, which detected particles with radii greater than about 0.01 micrometer, and an optical particles counter which detected particles in two size ranges, radii greater than 0.15 and greater than 0.25 micrometer. Aerosol profiles for the two soundings are shown in figure 3. The remnants of the El Chichon volcanic eruptions of 1982 are still easily observable in the optically active (0.15-micrometer) component between aobut 8 and 18 kilometers. Concentrations of these volcanically produced sulfuric acid droplets have been decreasing by roughly a factor of two each year since 1983. The large tropospheric and small stratospheric condensation-nuclei concentrations are typical of this component worldwide (Rosen, Hofmann, and Kaselau 1978). The aerosol profiles in the 20-35 kilometer region in figure 3 may be characterized as being more or less normal on 5 November (from previous observations in Antarctica) and quite abnormal on 9 November. On the latter sounding, we see essentially a complete absence of optically active aerosol above about 20 kilometers and substantial increases in condensation nuclei (very small particles) in this region. The layered nature of the enhanced condensation nuclei suggests that they probably have ANTARCTIC JOURNAL
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November 1-13, 1985 30mb, (23 km) Height Contour • Vortex Center C McMurdo Station + South Pole
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Figure 1. Temperature profiles measured during balloon ascents and McMurdo Station, Antarctica in 1985 (left) and motion of the south polar vortex during this period (right). Numbers along the constant height curves are dates in November 1985. ("nb" denotes "nanobars?' "mb" denotes "millibars." "km" denotes "kilometers?') I I I I I
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OZONE VOLUME MIXING RATIO (ppm)
Figure 2. Ozone partial pressure (left) and mixing ratio (right) profiles obtained at McMurdo Station, Antarctica. Numbers along the profiles are dates of the soundings in November 1985. ('mb" denotes "millibars?' "km" denotes "kilometers?') 1986 REVIEW
229
McMurdo, Antarctica
10
November, 1985
18
28
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25 A
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I 20 1 U D 15 E (kin)
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PARTICLE CONCENTRATION R8.15 pm (cm-3)
Figure 3. Concentration profiles of condensation nuclei (left) and optically active aerosol (right) obtained at McMurdo Station, Antarctica in November 1985. ("cm " denotes "per cubic centimeter:' "i.m" denotes "micrometer:' "kb" denotes "kilobar.")
not been mixed up from lower (e.g., tropospheric) regions of high condensation-nuclei concentration but are more likely condensation layers formed in situ. Similar events have been observed every year at Laramie since 1979 (Rosen and Hofmann 1983; Hofmann et al. 1985) during intrustions of air from warm arctic regions during stratospheric warmings and in Antarctica since 1983 during the final warming period (Hofmann and Rosen 1985a, 1985b). The aerosol size distribution appears to be highly dependent on its past thermal history, i.e., on its trajectory in and around the polar vortex. Apparent aerosol-ozone correlations are probably brought about by entirely independent processes at this time. It is now quite clear that springtime ozone in the south polar vortex region has been on the decline since about 1975 (Farman, Gardiner, and Shanklin 1985; Stolarski et al. in press). This phenomena has come to be known as the "antarctic ozone hole" and may have important implications for stratospheric chemistry and climate studies. The measurements reported by Stolarski et al. (in press), are from the Nimbus and TOMS satellites. These instruments indicate that south polar vortex ozone levels, which reach a minimum in the month of October, took additional precipitous drop in October 1985 (Stolarski personal communication). In view of this, the most consistent interpretation of the ozone observations reported here, is that the pressure-height contour which swept over McMurdo between 5 and 9 November delineated a "boundary" of the ozone hole region. The ozone deficit problem has created considerable interest in antarctic ozone and aerosol and has spawned an increase in research plans involving these and related species in Antarctica. D.J. Hofmann, J. A. Harder, N. Kjome, and G. L. Olson were in the field from 15 October to 25 November. M. Gelman and W. 230
Komhyr of the National Oceanic and Atmospheric Administration provided the satellite data and ozonesondes, respectively. This work was supported in part by National Science Foundation grant DPP 84-19094. References
Farman, J.C., B.C. Gardiner, and J.D. Shanklin. 1985. Large losses of total ozone in Antarctica reveal seasonal CLO/NO, interaction. Nature, 315, 207-210. Hofman, D.J., and J.M. Rosen. 1982. Balloon-borne observations of stratospheric aerosol and condensation nuclei during the year following the Mt. St. Helens eruption. Journal of Geophysical Research, 87, 11,039-11,061. Hofmann, D.J., and J.M. Rosen. 1985a. Antarctic observations of stratospheric aerosol and high altitude condensation nuclei following the El Chichon eruption. Geophysical Research Letters, 12, 13-16. Hofmann, D.J., and J.M. Rosen. 1985b. High-altitude aerosol variations associated with stratospheric warmings. Antarctic Journal of the U.S., 20(5), 217-218. Hofmann, D.J., J.M. Rosen, and W. Cringe!. 1985. Delayed production of sulfuric acid condensation nuclei in the polar stratosphere from El Chichon volcanic vapors. Journal of Geophysical Research, 90, 2341-2354. Rosen, J. M., D.J. Hofmann, and K. H. Kaselau. 1978. Vertical profiles of condensation nuclei. Journal of Applied Meteorology, 17, 1737-1740. Rosen, J.M., and D.J. Hofmann. 1983. Unusual behavior in the condensation nuclei concentration at 30 km. Journal of Geophysical Research, 88, 3725-3731. Stolarski, R.S. 1986. Personal communication. Stolarski, R.S., A.J. Krueger, M.R. Schoeberl, R.D. Peters, P.A. Newman, and J.C. Alpert. In press. Nimbus 7sBuv/ToMs measurements of the springtime Antarctic ozone hole. Nature.
ANTARCTIC JOURNAL
Since 1972, the University of Wyoming's high-altitude balloon research group has been conducting soundings of stratospheric aerosol concentrations in Antarctica. The primary purpose of these measurements in recent years has been to determine the stratospheric effects in the Southern Hemisphere of the 1982 volcanic eruption of El Chichon. In addition, observations at Laramie, Wyoming since 1979 (Rosen and Hofmann 1983; Hofmann, Rosen, and Cringe! 1985), suggested that stratospheric warming episodes in the north polar region were instrumental in drastically altering the aerosol size distribution in the 30-kilometer region and, if the proposed model of aerosol transformation was valid, should occur in the corresponding season in the antarctic stratosphere. The latter was verified in the 1983 measurements (Hofmann and Rosen 1985a) and study of these events continued in 1984 in Antarctica (Hofmann and Rosen 1985b). These studies suggested that information on the origin of the measured air parcel could be vital in interpreting the data. Since stratospheric ozone can serve as a useful tracer and since ozone measurements in Antarctica have recently revealed that the October minimum in total column ozone has been on the decline, ozone profile measurements were added in 1985. The aerosol measurements were made with optical particle counters, as described previously (Hofmann and Rosen 1982). Ozone measurements were made using commercial electrochemical ozonesondes (Scientific Pump Corp.). Four soundings were conducted from McMurdo Station on 5, 8, 9, and 13 November. All measured ozone, but only the soundings on 5 and 9 November also measured the aerosol distribution. Altitudes in excess of 30 kilometers were achieved on all flights. At the time of the soundings, the stratospheric wind speeds were quite high. In fact, the circumpolar wind maximum or polar jet (region of maximum gradient of height contours at a fixed pressure), which may be used to delineate a hypothetical boundary of the polar vortex region, was generally situated near McMurdo. This resulted in the sampling of air with very different histories over this time period. Figure 1 shows the temperature profiles measured on the four soundings discussed here. The position of the south polar vortex at a height of 23 kilometers, relative to McMurdo and 228
South Pole Stations, from satellite measurements is also shown here. These data suggest that the character of the temperature profiles encountered on 8 and 9 November were decidedly different than those on 5 and 13 November. Examination of the vortex position indicates substantial motion relative to McMurdo Station during this period; for example, the station was inside the 30-millibar, 23-kilometer pressure-height contour on 8 and 9 November but it was outside this contour on 5 and 13 November. The nature of this movement was more that of rotation of an elongated region of low pressure rather than a simple bulk movement of the vortex toward and then away from the station. The temperature profiles in figure 1 show the appearance of the colder vortex region at 15-30 kilometers on 8 and 9 November. The profiles on 5 and 13 November are typical of extra-vortex air during the spring warming period, similar to that observed in 1983 and 1984. Figure 2 shows the ozone profiles measured on these days. It is clear that the nature of these profiles, in the 15-30 kilometer region, is also drastically different for 8 and 9 November as compared to 5 and 13 November. The difference may be characterized as less ozone on days when McMurdo Station was apparently under the influence of the vortex and more or less normal otherwise. The difference in total ozone between 5 and 9 November is nearly a factor of two. Quite remarkable in figure 3 is the observation that on 9 November, ozone was considerably reduced even at altitudes in excess of 30 kilometers, in the region of extremely high temperature. We noted also that the lower stratospheric ozone features (below about 15 kilometers) are quite similar in all surroundings, suggesting a reasonable comparative accuracy among soundings. The soundings on 5 and 9 November also included aerosol measurements, as indicated earlier, obtained with a condensation nuclei counter, which detected particles with radii greater than about 0.01 micrometer, and an optical particles counter which detected particles in two size ranges, radii greater than 0.15 and greater than 0.25 micrometer. Aerosol profiles for the two soundings are shown in figure 3. The remnants of the El Chichon volcanic eruptions of 1982 are still easily observable in the optically active (0.15-micrometer) component between aobut 8 and 18 kilometers. Concentrations of these volcanically produced sulfuric acid droplets have been decreasing by roughly a factor of two each year since 1983. The large tropospheric and small stratospheric condensation-nuclei concentrations are typical of this component worldwide (Rosen, Hofmann, and Kaselau 1978). The aerosol profiles in the 20-35 kilometer region in figure 3 may be characterized as being more or less normal on 5 November (from previous observations in Antarctica) and quite abnormal on 9 November. On the latter sounding, we see essentially a complete absence of optically active aerosol above about 20 kilometers and substantial increases in condensation nuclei (very small particles) in this region. The layered nature of the enhanced condensation nuclei suggests that they probably have ANTARCTIC JOURNAL
.
- ,t1
18
U
39
, 0
28
0^0 1`
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25
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November 1-13, 1985 30mb, (23 km) Height Contour • Vortex Center C McMurdo Station + South Pole
A L T
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Ii
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8 (
15 E IL
P (
(Mb)
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Antarctica
tictitzrdc,
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November, 1985
10
-
-
I
-88 -68 -48 -28 8 +29 TEMPERATURE (CC)
Figure 1. Temperature profiles measured during balloon ascents and McMurdo Station, Antarctica in 1985 (left) and motion of the south polar vortex during this period (right). Numbers along the constant height curves are dates in November 1985. ("nb" denotes "nanobars?' "mb" denotes "millibars." "km" denotes "kilometers?') I I I I I
10-
'
1
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T r r
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10
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18861-
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5
186 268 369 9
OZONE PARTIAL PRESSURE (oh)
5
19
OZONE VOLUME MIXING RATIO (ppm)
Figure 2. Ozone partial pressure (left) and mixing ratio (right) profiles obtained at McMurdo Station, Antarctica. Numbers along the profiles are dates of the soundings in November 1985. ('mb" denotes "millibars?' "km" denotes "kilometers?') 1986 REVIEW
229
McMurdo, Antarctica
10
November, 1985
18
28
28
25 A
P B E S 50 S U H 108 E (mh)
I 20 1 U D 15 E (kin)
B S 50 S U B 108 E
30
25 A
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(mb)
L I 20 1 I U D 15 E (km)
200
208
18
10 500 1886 18+8 iø+1 102 1+3 PARTICLE CONCENTRATION R6.61 pm (cm- 3 )
1888
18 18-2
i-11810
PARTICLE CONCENTRATION R8.15 pm (cm-3)
Figure 3. Concentration profiles of condensation nuclei (left) and optically active aerosol (right) obtained at McMurdo Station, Antarctica in November 1985. ("cm " denotes "per cubic centimeter:' "i.m" denotes "micrometer:' "kb" denotes "kilobar.")
not been mixed up from lower (e.g., tropospheric) regions of high condensation-nuclei concentration but are more likely condensation layers formed in situ. Similar events have been observed every year at Laramie since 1979 (Rosen and Hofmann 1983; Hofmann et al. 1985) during intrustions of air from warm arctic regions during stratospheric warmings and in Antarctica since 1983 during the final warming period (Hofmann and Rosen 1985a, 1985b). The aerosol size distribution appears to be highly dependent on its past thermal history, i.e., on its trajectory in and around the polar vortex. Apparent aerosol-ozone correlations are probably brought about by entirely independent processes at this time. It is now quite clear that springtime ozone in the south polar vortex region has been on the decline since about 1975 (Farman, Gardiner, and Shanklin 1985; Stolarski et al. in press). This phenomena has come to be known as the "antarctic ozone hole" and may have important implications for stratospheric chemistry and climate studies. The measurements reported by Stolarski et al. (in press), are from the Nimbus and TOMS satellites. These instruments indicate that south polar vortex ozone levels, which reach a minimum in the month of October, took additional precipitous drop in October 1985 (Stolarski personal communication). In view of this, the most consistent interpretation of the ozone observations reported here, is that the pressure-height contour which swept over McMurdo between 5 and 9 November delineated a "boundary" of the ozone hole region. The ozone deficit problem has created considerable interest in antarctic ozone and aerosol and has spawned an increase in research plans involving these and related species in Antarctica. D.J. Hofmann, J. A. Harder, N. Kjome, and G. L. Olson were in the field from 15 October to 25 November. M. Gelman and W. 230
Komhyr of the National Oceanic and Atmospheric Administration provided the satellite data and ozonesondes, respectively. This work was supported in part by National Science Foundation grant DPP 84-19094. References
Farman, J.C., B.C. Gardiner, and J.D. Shanklin. 1985. Large losses of total ozone in Antarctica reveal seasonal CLO/NO, interaction. Nature, 315, 207-210. Hofman, D.J., and J.M. Rosen. 1982. Balloon-borne observations of stratospheric aerosol and condensation nuclei during the year following the Mt. St. Helens eruption. Journal of Geophysical Research, 87, 11,039-11,061. Hofmann, D.J., and J.M. Rosen. 1985a. Antarctic observations of stratospheric aerosol and high altitude condensation nuclei following the El Chichon eruption. Geophysical Research Letters, 12, 13-16. Hofmann, D.J., and J.M. Rosen. 1985b. High-altitude aerosol variations associated with stratospheric warmings. Antarctic Journal of the U.S., 20(5), 217-218. Hofmann, D.J., J.M. Rosen, and W. Cringe!. 1985. Delayed production of sulfuric acid condensation nuclei in the polar stratosphere from El Chichon volcanic vapors. Journal of Geophysical Research, 90, 2341-2354. Rosen, J. M., D.J. Hofmann, and K. H. Kaselau. 1978. Vertical profiles of condensation nuclei. Journal of Applied Meteorology, 17, 1737-1740. Rosen, J.M., and D.J. Hofmann. 1983. Unusual behavior in the condensation nuclei concentration at 30 km. Journal of Geophysical Research, 88, 3725-3731. Stolarski, R.S. 1986. Personal communication. Stolarski, R.S., A.J. Krueger, M.R. Schoeberl, R.D. Peters, P.A. Newman, and J.C. Alpert. In press. Nimbus 7sBuv/ToMs measurements of the springtime Antarctic ozone hole. Nature.
ANTARCTIC JOURNAL
