Quantifying transport between the tropical and mid-latitude lower stratosphere

Science

Volumn 272, Issue 5269, 1996, Pages 1763-1768

  Volk, C M ^a,b   Elkins, J W ^c   Fahey, D W ^c   Salawitch, R J ^d   Dutton, G S ^a,b   Gilligan, J M ^a,b,g   Proffitt, M H ^b,c   Loewenstein, M ^e   Podolske, J R ^e   Minschwaner, K ^f   Margitan, J J ^d   Chan, K R ^e  

^a EARTH SYSTEM RESEARCH LABORATORY   (United States)

^b UNIVERSITY OF COLORADO   (United States)

^c NOAA EARTH SYSTEM RESEARCH LABORATORY   (United States)

^d CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^e NASA AMES RESEARCH CENTER   (United States)

^f NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY   (United States)

^g VANDERBILT UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

AIR MONITORING; AIR QUALITY; ARTICLE; OZONE LAYER; PRIORITY JOURNAL; STRATOSPHERE; TRANSPORT KINETICS; TROPICS;

MID LATITUDE; OZONE; STRATOSPHERE; TRANSPORT; TROPICAL TRACER MODEL;

EID: 0029663011     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.272.5269.1763     Document Type: Article

References (68)

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30. During the flight campaign [the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA)] the ER-2 sampled air from 60°N to 70°S up to 21 km.
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35. 3 is a good tracer for tropical air. The latitudinal range of the selected tropical data vaned from flight to flight and between the two seasons sampled. The tropical observations span 10°N to 26°S in late March-early April 1994 and 19°N to 14°S in late October 1994; most of the data fall within 12° of the equator.
36. As used here, "exchange" between the tropics and mid-latitudes and related terms therefore refer to isentropic (that is, adiabatic) processes.
37. 5 Pa, Potential temperature is a conserved quantity for isentropic air motions and is a monotonically increasing function of altitude in the stratosphere. Its use as a vertical coordinate in Eq 1 is convenient because isentropic mixing occurs horizontally in this coordinate system. The tropical profile of potential temperature versus pressure altitude adopted in the model is based on temperature data from the U.K. Meteorological Office data assimilation system. The data were averaged from 10°N to 10°S over a 24-month period (November 1993 to October 1994).
38. If potential temperature θ is used as a vertical coordinate, a vertical displacement implies diabatic gain or loss of heat.
39. K. H. Rosenlof, J. Geophys. Res. 100, 5173 (1995) Ascent rates were averaged from 10°N to 10°S and over a 24-month penod (September 1992 to August 1994). The uncertainty of these calculations in the lower stratosphere is estimated as ∼50% above 18 km and even more just above the tropopause.
40. J. Eluszkiewicz et al., J. Atmos. Sci. 53, 217, 1996 Results were averaged as described above (28). Uncertainties are estimated as ∼50%. The averaged tropical heating rates agree with those obtained from (28) within the estimated uncertainties
41. 3 from a climatology (based on satellite, sonde, and in situ measurements) that was scaled to match total column measurements from the Total Ozone Mapping Spectrometer and by vertical profiles for temperature and aerosol extinction from the National Meteorological Center and the Stratospheric Aerosol and Gas Experiment II, respectively. We averaged photolysis rates calculated for winter, summer, and the equinox, and for latitudes from 10°N to 10°S. Uncertainties in the photolysis rates are ∼20% for most species.
42. R. J. Salawitch et al , Geophys. Res Lett. 21, 2551 (1994)
43. Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling, Evaluation No. 11, JPL Publ. 94-26 (NASA, Jet Propulsion Laboratory, Pasadena, CA, 1994).
44. S. A. Montzka et al., Science, in press, J. W Elkins and E J Dlugokencky, unpublished data from the NOAA/CMDL global network. Methods and trend analysis are described in J. W. Elkins et al., Nature 364, 780 (1993), and E. J Dlugokencky, L P Steele, P M. Lang, K A. Masarie, J. Geophys. Res. 99, 17021 (1994). Only data from tropical stations were used. Although the growth rates are less than a few percent per year, they are generally of the same order as photochemical loss rates near the tropical tropopause.
45. S. A. Montzka et al., Science, in press, J. W Elkins and E J Dlugokencky, unpublished data from the NOAA/CMDL global network. Methods and trend analysis are described in J. W. Elkins et al., Nature 364, 780 (1993), and E. J Dlugokencky, L P Steele, P M. Lang, K A. Masarie, J. Geophys. Res. 99, 17021 (1994). Only data from tropical stations were used. Although the growth rates are less than a few percent per year, they are generally of the same order as photochemical loss rates near the tropical tropopause.
46. S. A. Montzka et al., Science, in press, J. W Elkins and E J Dlugokencky, unpublished data from the NOAA/CMDL global network. Methods and trend analysis are described in J. W. Elkins et al., Nature 364, 780 (1993), and E. J Dlugokencky, L P Steele, P M. Lang, K A. Masarie, J. Geophys. Res. 99, 17021 (1994). Only data from tropical stations were used. Although the growth rates are less than a few percent per year, they are generally of the same order as photochemical loss rates near the tropical tropopause.
47. S. A. Montzka et al., Science, in press, J. W Elkins and E J Dlugokencky, unpublished data from the NOAA/CMDL global network. Methods and trend analysis are described in J. W. Elkins et al., Nature 364, 780 (1993), and E. J Dlugokencky, L P Steele, P M. Lang, K A. Masarie, J. Geophys. Res. 99, 17021 (1994). Only data from tropical stations were used. Although the growth rates are less than a few percent per year, they are generally of the same order as photochemical loss rates near the tropical tropopause.
48. The unmixed case corresponds to the "tropical pipe" model in (16)
49. C. M. Volk et al , data not shown.
50. Much of the mid-latitude air in the lower stratosphere has at one time been lofted to higher altitudes in the tropics before descending in the downward branch of the stratospheric circulation cell. Because of the increasing intensity of ultraviolet radiation with altitude, this air has "photochemically aged," resulting in lower mixing ratios for the species displayed in Fig. 1 at mid-latitudes than in the tropics.
51. A. E. Dessler et al., J. Atmos. Chem. 23, 209 (1996).
52. This approach is pursued in (20).
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54. 3), again from a loess fit versus θ, is then used to transform the coordinate system from θ to X. Finally, Eq 2 is solved as a differential equation of Y in X to calculate the tropical correlation Y(X) Initial (tropical tropopause) mixing ratios are obtained by averaging of all measurements taken in the upper tropicai troposphere during the flight campaign
55. in as function of altitude determined by direct inversion of Eq 2 depends sensitively on the choice of functional fit to the tropical data to determine ∂Y/∂X versus altitude; its geophysical meaning is therefore questionable.
56. in. The weighted mean is thus equivalent to a weighted geometric mean and its uncertainty is best expressed as an uncertainty factor that evaluated to 1 2.
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58. K. A. Boering et al , Geophys Res Lett. 21, 2567 (1991); E. J. Hintsa et al., ibid., p 2559; K. A. Boering et al , ibid 22, 2737 (1995).
59. K. A. Boering et al , Geophys Res Lett. 21, 2567 (1991); E. J. Hintsa et al., ibid., p 2559; K. A. Boering et al , ibid 22, 2737 (1995).
60. Based on the ascent rates from (28, 29), ascent of tropical air from the tropopause to 21 km takes ∼8 months Hence, the two observational snapshots in March/April and October 1994 combine air influenced by mixing during the time span of at least a full seasonal cycle. Differences between the March/April and October tropical observations on a given potential temperature level were generally smaller than flight-to-flight variability.
61. 3 satellite measurements (29)
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63. M. K. W Ko, personal communication. The model calculated the decadal change in the ozone column between 1980 and 1990, as well as the transient ozone change in response to increased aerosol loading after the eruption of Mount Pinatubo in June 1991. A description of the model is given in M. K. W. Ko, K. K Tung, D K. Weisenstein, and N. D. Sze [J. Geophys. Res, 90, 2313 (1985)]; restricted mixing was achieved by a decrease in the horizontal diffusion coefficient within the tropical lower stratosphere as described in D. K. Weisenstein, M. K. W. Ko. N. D. Sze, and J. M. Rodnguez [Geophys. Res. Lett. 23, 161 (1996)]. Restriction of mixing across the tropics also resulted in an ∼20% decrease of the calculated lifetimes of tropospheric source gases.
64. M. K. W Ko, personal communication. The model calculated the decadal change in the ozone column between 1980 and 1990, as well as the transient ozone change in response to increased aerosol loading after the eruption of Mount Pinatubo in June 1991. A description of the model is given in M. K. W. Ko, K. K Tung, D K. Weisenstein, and N. D. Sze [J. Geophys. Res, 90, 2313 (1985)]; restricted mixing was achieved by a decrease in the horizontal diffusion coefficient within the tropical lower stratosphere as described in D. K. Weisenstein, M. K. W. Ko. N. D. Sze, and J. M. Rodnguez [Geophys. Res. Lett. 23, 161 (1996)]. Restriction of mixing across the tropics also resulted in an ∼20% decrease of the calculated lifetimes of tropospheric source gases.
65. M. K. W Ko, personal communication. The model calculated the decadal change in the ozone column between 1980 and 1990, as well as the transient ozone change in response to increased aerosol loading after the eruption of Mount Pinatubo in June 1991. A description of the model is given in M. K. W. Ko, K. K Tung, D K. Weisenstein, and N. D. Sze [J. Geophys. Res, 90, 2313 (1985)]; restricted mixing was achieved by a decrease in the horizontal diffusion coefficient within the tropical lower stratosphere as described in D. K. Weisenstein, M. K. W. Ko. N. D. Sze, and J. M. Rodnguez [Geophys. Res. Lett. 23, 161 (1996)]. Restriction of mixing across the tropics also resulted in an ∼20% decrease of the calculated lifetimes of tropospheric source gases.
66. W. S. Cleveland, J. Am Stat Assoc. 74, 829 (1979).
67. -1 + γ). T is the relevant time scale for the combined effects of local growth and photochemical loss that determine the vertical profile of the tropical abundance in the absence of mixing. Because photochemical loss is the dominant factor (above ∼18 km) for the species considered here, we refer to T simply as lifetime or photochemical lifetime.
68. We thank K H. Rosenlof and J. Eluszkiewicz for providing data for tropical ascent rates and suggestions, R. A. Plumb, M. K. W Ko, and F. L Moore for discussions; P. J. Fraser, L. P. Steele, M. P Lucarelli, and S A. Montzka for support during the field deployments in New Zealand; and our many colleagues of the 1994 ASHOE/MAESA campaign, especially the pilots of the ER-2 aircraft. Supported in part by NASA's Upper Atmospheric Research Program, the Atmospheric Effects of Stratospheric Aircraft component of the NASA High-Speed Research Program, and the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program.