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  • 1
    Online Resource
    Online Resource
    The distribution of hydrogen, nitrogen, and chlorine radicals in the lower stratosphere: Implications for changes in O 3 due to emission of NO y from supersonic aircraft
    American Geophysical Union (AGU) ; 1994
    In:  Geophysical Research Letters Vol. 21, No. 23 ( 1994-11-15), p. 2547-2550
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 21, No. 23 ( 1994-11-15), p. 2547-2550
    Abstract: In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained in the lower stratosphere during SPADE are compared to results from a photochemical model that assimilates measurements of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N 2 O 5 agree well with measured concentrations of NO and ClO, but concentrations of HO 2 and OH are underestimated by 10 to 25%, concentrations of NO 2 are overestimated by 10 to 30%, and concentrations of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO 2 ] are reduced if we allow for higher yields of O( 1 D) from O 3 photolysis and for heterogeneous production of HNO 2 . The data suggest more efficient catalytic removal of O 3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using recommended rates and cross sections. Increases in [O 3 ] in the lower stratosphere may be larger in response to inputs of NO y from supersonic aircraft than estimated by current assessment models.
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/94GL02781
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1994
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  • 2
    Online Resource
    Online Resource
    The diurnal variation of hydrogen, nitrogen, and chlorine radicals: Implications for the heterogeneous production of HNO 2
    American Geophysical Union (AGU) ; 1994
    In:  Geophysical Research Letters Vol. 21, No. 23 ( 1994-11-15), p. 2551-2554
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 21, No. 23 ( 1994-11-15), p. 2551-2554
    Abstract: In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N 2 O 5 on sulfate aerosols agree with measured concentrations of NO, NO 2 , and ClO throughout the day, but fail to account for high concentrations of OH and HO 2 observed near sunrise and sunset. The morning burst of [OH] and [HO 2 ] coincides with the rise of [NO] from photolysis of NO 2 , suggesting a new source of HO x that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HNO 2 results in an excellent simulation of the diurnal variations of [OH] and [HO 2 ].
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/94GL02782
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1994
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  • 3
    Online Resource
    Online Resource
    Mixing of polar vortex air into middle latitudes as revealed by tracer‐tracer scatterplots
    American Geophysical Union (AGU) ; 1997
    In:  Journal of Geophysical Research: Atmospheres Vol. 102, No. D11 ( 1997-06-20), p. 13119-13134
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 102, No. D11 ( 1997-06-20), p. 13119-13134
    Abstract: The occurrence of mixing of polar vortex air with midlatitude air is investigated by examining the scatterplots of insitu measurements of long‐lived tracers from the NASA ER‐2 aircraft during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE, April, May 1993; northern hemisphere) and the Airborne Southern Hemisphere Ozone Experiment / Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA, March‐October 1994; southern hemisphere) campaigns. The tracer‐tracer scatterplots from SPADE form correlation curves which differ from those measured during previous aircraft campaigns (Airborne Antarctic Ozone Experiment (AAOE), Airborne Arctic Stratospheric Experiments I (AASE I) and II (AASE II)). It is argued that these anomalous linear correlation curves are “mixing lines” resulting from the recent mixing of polar vortex air into the middle latitude environment. Further support for this mixing scenario is provided by contour advection calculations and calculations with a simple one‐dimensional strain‐diffusion model. The scatterplots from the midwinter deployments of ASHOE/MAESA are consistent with those from previous midwinter measurements (i.e., no mixing lines), but the spring CO 2 :N 2 O scatterplots form altitude‐dependent mixing lines which indicate that air from the vortex edge region (but not from the inner vortex) is mixing with midlatitude air during this period. These results suggest that at altitudes above about 16 km the mixing of polar vortex air into middle latitudes varies with season: in northern and southern midwinter this mixing rarely occurs, in southern spring mixing of vortex‐edge air occurs, and after the vortex breakup mixing of inner vortex air occurs.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/96JD03715
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1997
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  • 4
    Online Resource
    Online Resource
    Comparison between DC‐8 and ER‐2 species measurements in the tropical middle troposphere: NO, NO y , O 3 , CO 2 , CH 4 , and N 2 O
    American Geophysical Union (AGU) ; 1998
    In:  Journal of Geophysical Research: Atmospheres Vol. 103, No. D17 ( 1998-09-20), p. 22087-22096
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 103, No. D17 ( 1998-09-20), p. 22087-22096
    Abstract: We compare measurements of six species taken aboard NASA DC‐8 and ER‐2 aircraft during two flight legs in the tropical middle troposphere near Hawaii. NO, NO y , O 3 , CH 4 , and N 2 O measurements agree to within the limits set by the known systematic errors. For CO 2 , which can be measured with better relative precision than the other five species, differences in measured values from the two platforms are slightly larger than expected if the air masses sampled by the two aircraft were indeed similar in CO 2 composition to better than 0.08%.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/98JD01421
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1998
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  • 5
    Online Resource
    Online Resource
    Mean ages of stratospheric air derived from in situ observations of CO 2 , CH 4 , and N 2 O
    American Geophysical Union (AGU) ; 2001
    In:  Journal of Geophysical Research: Atmospheres Vol. 106, No. D23 ( 2001-12-16), p. 32295-32314
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 106, No. D23 ( 2001-12-16), p. 32295-32314
    Abstract: Accurate mean ages for stratospheric air have been derived from a spatially and temporally comprehensive set of in situ observations of CO 2 , CH 4 , and N 2 O obtained from 1992 to 1998 from the NASA ER‐2 aircraft and balloon flights. Errors associated with the tropospheric CO 2 seasonal cycle and interannual variations in the CO 2 growth rate are 〈 0.5 year throughout the stratosphere and 〈 0.3 year for air older than 2 years (N 2 O 〈 275 ppbv), indicating that the age spectra are broad enough to attenuate these influences over the time period covered by these observations. The distribution of mean age with latitude and altitude provides detailed, quantitative information about the general circulation of the stratosphere. At 20 km, sharp meridional gradients in the mean age are observed across the subtropics. Between 20 and 30 km, the average difference in mean age between the tropics and midlatitudes is ∼2 years, with slightly smaller differences at higher and lower altitudes. The mean age in the midlatitude middle stratosphere (∼25–32 km) is relatively constant with respect to altitude at 5±0.5 years. Comparison with earlier balloon observations of CO 2 dating back to the 1970s indicates that the mean age of air in this region has remained within ±1 year of its current value over the last 25 years. A climatology of mean age is derived from the observed compact relationship between mean age and N 2 O. These characteristics of the distribution of mean age in the stratosphere will serve as critically needed diagnostics for models of stratospheric transport.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2001JD000465
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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  • 6
    Online Resource
    Online Resource
    Estimates of total organic and inorganic chlorine in the lower stratosphere from in situ and flask measurements during AASE II
    American Geophysical Union (AGU) ; 1995
    In:  Journal of Geophysical Research: Atmospheres Vol. 100, No. D2 ( 1995-02-20), p. 3057-3064
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 100, No. D2 ( 1995-02-20), p. 3057-3064
    Abstract: Aircraft sampling has provided extensive in situ and flask measurements of organic chlorine species in the lower stratosphere. The recent Airborne Arctic Stratospheric Expedition II (AASE II) included two independent measurements of organic chlorine species using whole air sample and real‐time techniques. From the whole air sample measurements we derive directly the burden of total organic chlorine (CCl y ) in the lower stratosphere. From the more limited real‐time measurements we estimate the CCl y burden using mixing ratios and growth rates of the principal CCl y species in the troposphere in conjunction with results from a two‐dimensional photochemical model. Since stratospheric chlorine is tropospheric in origin and tropospheric mixing ratios are increasing, it is necessary to establish the average age of a stratospheric air parcel to assess its total chlorine (Cl Total ) abundance. Total inorganic chlorine (Cl y ) in the parcel is then estimated by the simple difference, Cl y = Cl Total ‐ CCl y . The consistency of the results from these two quite different techniques suggests that we can determine the CCl y and Cl y in the lower stratosphere with confidence. Such estimates of organic and inorganic chlorine are crucial in evaluating the photochemistry controlling chlorine partitioning and hence ozone loss processes in the lower stratosphere.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/94JD02744
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1995
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  • 7
    Online Resource
    Online Resource
    Three‐dimensional simulations of long‐lived tracers using winds from MACCM2
    American Geophysical Union (AGU) ; 1997
    In:  Journal of Geophysical Research: Atmospheres Vol. 102, No. D17 ( 1997-09-20), p. 21493-21513
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 102, No. D17 ( 1997-09-20), p. 21493-21513
    Abstract: Three‐dimensional simulations of the stratospheric constituents CH 4 , N 2 O, O 3 , SF 6 , and CO 2 over an annual cycle have been performed using a semiLagrangian chemical transport model [ Rasch and Williamson , 1990; Rasch et al ., 1994] driven by archived wind data from the Middle Atmosphere version of the National Center for Atmospheric Research Community Climate Model version 2 (MACCM2) general circulation model. The constituents undergo chemical production and loss at rates calculated by two‐dimensional photochemical models. We compare these “off‐line” simulations of CH 4 and N 2 O with “on‐line” simulations in which the trace constituent distributions are computed interactively within the MACCM2 general circulation model and find good agreement even when daily averaged wind data and no subgrid scale parameterized mixing are used in the off‐line simulations. We also compare the model simulations to satellite, aircraft, and balloon measurements. In most regions and seasons, the zonally averaged model CH 4 , N 2 O, and O 3 fields agree well with observations. Notable discrepancies are (1) a lack of a “double peak” structure in the zonally averaged mixing ratios of model CH 4 and N 2 O at equinox, (2) an overall underestimate of CH 4 and N 2 O in the upper stratosphere, and (3) an underestimate of the height of the mixing ratio peak in O 3 , particularly at high latitudes. We find good agreement between modeled CO 2 and SF 6 and recent aircraft observations in the lower stratosphere, and balloon measurements in the lower and middle stratosphere. From the SF 6 distribution we determine the mean age of air in the model stratosphere, with values as old as 10 years in the wintertime polar upper stratosphere. In addition, we simulate the annual cycle of CO 2 , a stringent test of model transport, which supplements the mean age. We obtain good agreement with aircraft measurements in phase and magnitude at the tropical tropopause, and the vertical profiles of CO 2 are similar to those observed. However, the amplitude of the cycle attenuates too rapidly with height in the model stratosphere, suggesting the influence of midlatitude air and/or the vertical diffusion are too large in the model tropics.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/97JD00793
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1997
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