A. R. Douglass

Loyola University Maryland, Baltimore, Maryland, United States

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Publications (261)423.46 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Chemistry climate models (CCMs) are used to project future evolution of stratospheric ozone as concentrations of ozone-depleting substances (ODSs) decrease and GHGs increase, cooling the stratosphere. CCM projections exhibit many common features, but also a broad range of values for quantities such as year of ozone-return-to-1980 and global ozone level at the end of the 21st century. Multiple linear regression is applied to each of fourteen CCMs to separate ozone response to ODS concentration change from that due to climate change. We show that the sensitivity of lower stratospheric ozone to chlorine change ΔO3/ΔCly is a near linear function of partitioning of total inorganic chlorine (Cly) into its reservoirs; both Cly and its partitioning are largely controlled by lower stratospheric transport. CCMs with best performance on transport diagnostics agree with observations for chlorine reservoirs and produce similar ozone responses to chlorine change. After 2035 differences in ΔO3/ΔCly contribute little to the spread in CCM projections as the anthropogenic contribution to Cly becomes unimportant. Differences among upper stratospheric ozone increases due to temperature decreases are explained by differences in ozone sensitivity to temperature change ΔO3/ΔT due to different contributions from various ozone loss processes, each with its own temperature dependence. Ozone decrease in the tropical lower stratosphere caused by a projected speed-up in the Brewer-Dobson circulation may or may not be balanced by ozone increases in the middle and high latitude lower stratosphere and upper troposphere. This balance, or lack thereof, contributes most to the spread in late 21st century projections.
    Journal of Geophysical Research: Atmospheres. 04/2014;
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    ABSTRACT: Measurements from the Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS), both onboard the Aura spacecraft, have been used to produce daily global maps of column and profile ozone since August 2004. Here we compare and evaluate three strategies to obtain daily maps of tropospheric and stratospheric ozone from OMI and MLS measurements: trajectory mapping, direct profile retrieval, and data assimilation. Evaluation is based on an assessment that includes validation using ozonesondes and comparisons with the Global Modeling Initiative (GMI) chemical transport model (CTM). We investigate applications of the three ozone data products from near-decadal and inter-annual timescales to day-to-day case studies. Inter-annual changes in zonal mean tropospheric ozone from all of the products in any latitude range are of the order 1-2 Dobson Units while changes (increases) over the 8-year Aura record investigated vary by 2-4 Dobson Units. It is demonstrated that all of the ozone products can measure and monitor exceptional tropospheric ozone events including major forest fire and pollution transport events. Stratospheric ozone during the Aura record has several anomalous inter-annual events including split stratospheric warmings in the Northern Hemisphere extra-tropics that are well captured using the data assimilation ozone profile product. Data assimilation with continuous daily global coverage and vertical ozone profile information is the best of the three strategies at generating a global tropospheric and stratospheric ozone product for science applications.
    Journal of Geophysical Research: Atmospheres. 04/2014;
  • Luke D. Oman, Anne R. Douglass
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    ABSTRACT: The evolution of ozone is examined in the latest version of the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) using old and new ozone depleting substances (ODS) scenarios. This version of GEOSCCM includes a representation of the Quasi-Biennial Oscillation, a more realistic implementation of ozone chemistry at high solar zenith angles, an improved air/sea roughness parameterization, and an extra 5 ppt of CH3Br to account for brominated very short-lived substances. Together these additions improve the representation of ozone compared to observations. This improved version of GEOSCCM was used to simulate the ozone evolution for the A1 2010 and the new SPARC 2013 ODS scenario derived using the SPARC Lifetimes Report 2013. This new ODS scenario results in a maximum Cltot increase of 65 pptv, decreasing slightly to 60 pptv by 2100. Approximately 72% of the increase is due to the longer lifetime of CFC-11. The quasi-global (60°S-60°N) total column ozone difference is relatively small and less than 1 DU on average and consistent with the 3-4% larger 2050-2080 average Cly in the new SPARC 2013 scenario. Over high latitudes, this small change in Cly compared to the relatively large natural variability makes it not possible to discern a significant impact on ozone in the 2nd half of the 21st century in a single set of simulations.
    Journal of Geophysical Research: Atmospheres. 04/2014;
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    ABSTRACT: We examine the seasonal behavior of ozone by using measurements from various instruments including ozonesondes, Aura MLS, and SAGE II. We find that the magnitude of the annual variation in ozone, as a percentage of the mean ozone, exhibits a maximum at or slightly above the tropical tropopause. The maximum is larger in the northern tropics than in the southern tropics, and the annual maximum of ozone in the southern tropics occurs two months later than that in the northern tropics, in contrast to usual assumption that the tropics can be treated as a horizontally homogeneous region. The seasonal cycles of ozone and other species in this part of the lower stratosphere result from a combination of the seasonal variation of the Brewer-Dobson Circulation and the seasonal variation of tropical and mid-latitude mixing. In the northern hemisphere, the impacts of upwelling and mixing between the tropics and midlatitudes on ozone are in phase and additive. In the southern hemisphere, they are not in phase. We apply a tropical leaky pipe model independently to each hemisphere to examine the relative roles of upwelling and mixing in the northern and southern tropical regions. Reasonable assumptions of the seasonal variation of upwelling and mixing yield a good description of the seasonal magnitude and phase in both the southern and northern tropics. The differences in the tracers and transport between the northern and southern tropical stratosphere suggest that the paradigm of well-mixed tropics needs to be revised to consider latitudinal variations within the tropics.
    Journal of Geophysical Research: Atmospheres. 04/2014;
  • Douglas R. Allen, Anne R. Douglass, Susan E. Strahan
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    ABSTRACT: [1] The 2011 Arctic stratospheric final warming was characterized by a large-scale frozen-in anticyclone (FrIAC) that rapidly displaced the winter polar vortex, establishing unusually strong polar easterlies. A comprehensive overview of the 2011 FrIAC is provided using meteorological analyses, Microwave Limb Sounder (MLS) N2O observations, and N2O simulations from the Global Modeling Initiative (GMI) 3-D chemistry and transport model and the Van Leer Icosahedral Triangular Advection (VITA) 2-D (latitude × longitude) isentropic transport model. A vortex edge diagnostic is used to determine the FrIAC boundary, allowing quantification of several FrIAC properties. The 2011 FrIAC originated over North Africa in late March and traveled eastward and poleward over 2 weeks, forming a strong anticyclone that extended from ~580–2100 K potential temperature (~25–50 km). Low potential vorticity (PV) was transported to the pole with the FrIAC in early April; during May, most of the PV signature decayed due to diabatic processes. A small remnant negative PV anomaly persisted near the pole until mid-June. Tracer equivalent latitude was low initially and remained low throughout the summer. GMI, VITA, and MLS showed elevated N2O in the FrIAC, although the peak value was smaller in GMI due to a subtropical low bias. The high-resolution (~20 km) VITA filamentary structure quantitatively matched most of the features observed by MLS when smoothed to match the MLS resolution. The high-N2O anomaly persisted in the middle stratosphere over 4 months until late August, when it was destroyed by horizontal and vertical shearing, combined with photochemical processes.
    Journal of Geophysical Research: Atmospheres. 03/2013; 118(6).
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    ABSTRACT: Observations have shown that the mass of nitrogen dioxide decreased at both southern and northern midlatitudes in the year following the eruption of Mt. Pinatubo, indicating that the volcanic aerosol had enhanced nitrogen dioxide depletion via heterogeneous chemistry. In contrast, the observed ozone response showed a northern midlatitude decrease and a small southern midlatitude increase. Previous simulations that included an enhancement of heterogeneous chemistry by the volcanic aerosol but no other effect of this aerosol produce ozone decreases in both hemispheres, contrary to observations. The authors' simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and Southern Hemisphere extratropical downwelling. This enhanced extratropical downwelling, combined with the time of the eruption relative to the phase of the Brewer–Dobson circulation, increased Southern Hemisphere ozone via advection, counteracting the ozone depletion due to heterogeneous chemistry on the Pinatubo aerosol.
    Journal of the Atmospheric Sciences 03/2013; 70:894-900. · 2.67 Impact Factor
  • S. E. Strahan, A. R. Douglass, P. A. Newman
    Journal of Geophysical Research: Atmospheres. 02/2013; 118(3).
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    ABSTRACT: The El Niño-Southern Oscillation (ENSO) is the dominant mode of inter-annual variability in the tropical ocean and troposphere. Its impact on tropospheric circulation causes significant changes to the distribution of ozone. Here we derive the lower tropospheric to lower stratospheric ozone response to ENSO from observations by the Tropospheric Emission Spectrometer (TES) and the Microwave Limb Sounder (MLS) instruments, both on the Aura satellite, and compare to the simulated response from the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Measurement ozone sensitivity is derived using multiple linear regression to include variations from ENSO as well as from the first two empirical orthogonal functions of the quasi-biennial oscillation. Both measurements and simulation show features such as the negative ozone sensitivity to ENSO over the tropospheric tropical Pacific and positive ozone sensitivity over Indonesia and the Indian Ocean region. Ozone sensitivity to ENSO is generally positive over the midlatitude lower stratosphere, with greater sensitivity in the Northern Hemisphere. GEOSCCM reproduces both the overall pattern and magnitude of the ozone response to ENSO obtained from observations. We demonstrate the combined use of ozone measurements from MLS and TES to quantify the lower atmospheric ozone response to ENSO and suggest its possible usefulness in evaluating chemistry-climate models.
    Journal of Geophysical Research 01/2013; 118(2):965-976. · 3.17 Impact Factor
  • Mark A. Olsen, Anne R. Douglass, Trevor B. Kaplan
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    ABSTRACT: The extratropical stratosphere-troposphere exchange (STE) of ozone from 2005 to 2010 is estimated by combining Microwave Limb Sounder ozone observations and MERRA reanalysis meteorological fields in an established direct diagnostic framework. The multiyear mean ozone STE is 275 Tg yr-1 and 214 Tg yr-1 in the Northern and Southern Hemispheres, respectively. The year-to-year variability is greater in the Northern Hemisphere, where the difference between the highest and the lowest annual flux is 15% of the multiyear mean compared with 6% in the Southern Hemisphere. Variability of lower stratospheric ozone and variability of the net mass flux both contribute to interannual variability in the Northern Hemisphere ozone flux. The flux across the extratropical 380 K surface determines the amount of flux across the extratropical tropopause, and the greatest seasonal variability of the 380 K ozone flux occurs in the late winter/early spring, around the time of greatest flux. Both the mass flux and the ozone mixing ratios on the 380 K surface show recurring spatial patterns, but interannual variability of these quantities and their alignment contribute to the ozone flux variability. The spatial and temporal variability are not well represented when zonal and/or monthly mean fields are used to calculate the ozone STE, although this results in a small high bias of the seasonal amplitude and annual magnitude. If the climatological variability over these 6 years is representative, the estimated number of years required to detect a 2 - 3% decade-1 trend in ozone STE using this diagnostic is 35 - 39 years.
    Journal of Geophysical Research 01/2013; 118(2):1090-1099. · 3.17 Impact Factor
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    ABSTRACT: The impact of changes in the abundance of greenhouse gases (GHGs) on the evolution of tropospheric ozone (O3) between 1960 and 2005 is examined using a version of the Goddard Earth Observing System chemistry-climate model (GEOS CCM) with a combined troposphere-stratosphere chemical mechanism. Simulations are performed to isolate the relative role of increases in methane (CH4) and stratospheric ozone depleting substances (ODSs) on tropospheric O3. The 1960 to 2005 increases in GHGs (CO2, N2O, CH4, and ODSs) cause increases of around 1-8% in zonal-mean tropospheric O3 in the tropics and northern extratropics, but decreases of 2-4% in most of the southern extratropics. These O3 changes are due primarily to increases in CH4 and ODSs, which cause changes of comparable magnitude but opposite sign. The CH4-related increases in O3are similar in each hemisphere (˜6%), but the ODS-related decreases in the southern extratropics are much larger than in northern extratropics (10% compared to 2%). This results in an interhemispheric difference in the sign of past O3 change. Increases in the other GHGs (CO2 and N2O) and SSTs have only a small impact on the total burden over this period, but do cause zonal variations in the sign of changes in tropical O3 that are coupled to changes in vertical velocities and water vapor.
    Journal of Geophysical Research 12/2012; 117(D23):23304-. · 3.17 Impact Factor
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    ABSTRACT: Projections of future ozone levels are made using models that couple a general circulation model with a representation of atmospheric photochemical processes, allowing interactions among photochemical processes, radiation, and dynamics. Such models are known as coupled chemistry-climate models (CCMs). Although developed from common principles and subject to the same boundary conditions, simulated ozone time series vary among models for scenarios for ozone depleting substances (ODSs) and greenhouse gases. Photochemical processes control the upper stratospheric ozone level, and there is broad agreement among CCMs in that ozone increases as ODSs decrease and temperature decreases due to greenhouse gas increase. There are quantitative differences in the ozone sensitivity to chlorine and temperature. We obtain insight into differences in sensitivity by examining the relationship between the upper stratospheric seasonal cycles of ozone and temperature as produced by fourteen CCMs. All simulations conform to expectation in that ozone is less sensitive to temperature when chlorine levels are highest because chlorine catalyzed loss is nearly independent of temperature. Analysis reveals differences in simulated temperature, ozone and reactive nitrogen that lead to differences in the relative importance of ozone loss processes and are most obvious when chlorine levels are close to background. Differences in the relative importance of loss processes underlie differences in simulated sensitivity of ozone to composition change. This suggests 1) that the multimodel mean is not a best estimate of the sensitivity of upper stratospheric ozone to changes in ODSs and temperature; and 2) that the spread of values is not an appropriate measure of uncertainty.
    Journal of Geophysical Research 08/2012; 117(D16):16306-. · 3.17 Impact Factor
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    ABSTRACT: During the 2011 stratospheric final warming (SFW), a large anticyclone rapidly encompassed the pole, displacing the polar vortex and establishing strong summer easterlies. Tracer Equivalent Latitude (TrEL) maps indicate low latitude air was transported by the anticyclone into the summer polar vortex. MLS nitrous oxide was anomalously high throughout the following summer, confirming the TrEL results. A 33-year (1979-2011) TrEL simulation at 850 K potential temperature reveals a number of similar low-TrEL events, which are often, but not always, associated with Frozen-In Anticyclone (FrIAC) formation. The summertime TrEL values are highly correlated with zonal wind speed in the polar stratosphere following the SFW, suggesting that strong post-SFW circulation favors polar trapping of low-TrEL air. The 2011 event, classified as a large-scale FrIAC, was unusual in having the lowest TrEL values and the strongest easterly vortex within the past three decades.
    Geophysical Research Letters 06/2012; 39(12):12801-. · 3.98 Impact Factor
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    ABSTRACT: We use data from the Nimbus-7 Limb Infrared Monitor of the Stratosphere (LIMS) for the 1978-1979 period together with data from the Upper Atmosphere Research Satellite Microwave Limb Sounder (UARS MLS) for the years 1993 to 1999, the Aura MLS for the years 2004 to 2011, and the Aura High Resolution Infrared Limb Sounder (HIRDLS) for the years 2005 to 2007 to examine ozone-temperature correlations in the upper stratosphere. Our model simulations indicate that the sensitivity coefficient of the ozone response to temperature (Δln(O3)/Δ(1/T)) decreases as chlorine has increased in the stratosphere and should increase in the future as chlorine decreases. The data are in agreement with our simulation of the past. We also find that the sensitivity coefficient does not change in a constant-chlorine simulation. Thus the change in the sensitivity coefficient depends on the change in chlorine, but not on the change in greenhouse gases. We suggest that these and future data can be used to track the impact of chlorine added to the stratosphere and also to track the recovery of the stratosphere as chlorine is removed under the provisions of the Montreal Protocol.
    Journal of Geophysical Research 05/2012; 117(D10):10305-. · 3.17 Impact Factor
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    ABSTRACT: We present analysis of simulations using the NASA GEOS-5 chemistry and transport model to quantify contributions from different continents to the Western Arctic pollution, to investigate pollution sources and to identify transport pathways. We compare DC-8 airborne measurements of CO, SO2, BC and SO4 from the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaigns (spring and summer, 2008) and observations from the AIRS instrument on NASA's Aqua satellite to demonstrate the strengths and limitations of our simulations and to support this application of the model. Comparisons of measurements along the flight tracks with regional averages show that the along-track measurements are representative of the region in April but not in July. Our simulations show that most Arctic pollutants are due to Asian anthropogenic emissions during April. Boreal biomass burning emissions and Asian anthropogenic emissions are of similar importance in July. European sources make little contribution to pollution in the campaign domain during either period. The most prevalent transport pathway of the tracers is from Asia to the Arctic in both April and July, with the transport efficiency stronger in spring than in summer.
    Atmospheric Chemistry and Physics 04/2012; 12(4):8823-8855. · 4.88 Impact Factor
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    ABSTRACT: The stratospheric age spectrum is the probability distribution function of the transit times since a stratospheric air parcel had last contact with a tropospheric boundary region. Previous age spectrum studies have focused on its annual mean properties. Knowledge of the age spectrum's seasonal variability is very limited. In this study, we investigate the seasonal variations of the stratospheric age spectra using the pulse tracer method in the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM). The relationships between the age spectrum and the boundary impulse response (BIR) are reviewed, and a simplified method to reconstruct seasonally varying age spectra is introduced. The age spectra in GEOSCCM have strong seasonal cycles, especially in the lowermost and lower stratosphere and in the subtropical overworld. These changes reflect the seasonal evolution of the Brewer-Dobson circulation, isentropic mixing, and transport barriers. We also investigate the seasonal and interannual variations of the BIRs. Our results clearly show that computing an ensemble of seasonally dependent BIRs is necessary in order to capture the seasonal and annual mean properties of the stratospheric age spectrum.
    Journal of Geophysical Research 03/2012; 117(D5):5134-. · 3.17 Impact Factor
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    ABSTRACT: In this study we investigate long-term variations in the stratospheric age spectra using a 21st century simulation with the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Our purposes are to characterize the long-term changes in the age spectra, and identify processes that cause the decrease of the mean age in a changing climate. Changes in the age spectra in the 21st century simulation are characterized by decreases in the modal age, the mean age, the spectral width, and the tail decay timescale throughout the stratosphere. Our analyses show that the decrease in the mean age is caused by two processes: the acceleration of the residual circulation that increases the young air masses in the stratosphere, and the weakening of the recirculation that leads to a decrease of the tail of the age spectra and a decrease of the old air masses. Weakening of the stratospheric recirculation is also strongly correlated with the increase of the residual circulation. One important result of this study is that the decrease of the tail of the age spectra makes an important contribution to the decrease of the mean age. Long-term changes in the stratospheric isentropic mixing are also investigated. Mixing increases in the subtropical lower stratosphere, but its impact on the age spectra is smaller than the increase of the residual circulation. The impacts of the long-term changes in the age spectra on long-lived chemical tracers are also investigated.
    Journal of Geophysical Research 01/2012; 117. · 3.17 Impact Factor
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    ABSTRACT: The El Nino-Southern Oscillation (ENSO) is the dominant mode of tropical variability on interannual time scales. ENSO appears to extend its influence into the chemical composition of the tropical troposphere. Recent results have revealed an ENSO induced wave-1 anomaly in observed tropical tropospheric column ozone. This results in a dipole over the western and eastern tropical Pacific, whereby differencing the two regions produces an ozone anomaly with an extremely high correlation to the Nino 3.4 Index. We have successfully reproduced this result using the Goddard Earth Observing System Version 5 (GEOS-5) general circulation model coupled to a comprehensive stratospheric and tropospheric chemical mechanism forced with observed sea surface temperatures over the past 25 years. An examination of the modeled ozone field reveals the vertical contributions of tropospheric ozone to the column over the western and eastern Pacific region. We will show targeted comparisons with SHADOZ ozonesondes over these regions to provide insight into the vertical structure, along with comparisons of observations from NASA's Aura satellite Microwave Limb Sounder (MLS), the Tropospheric Emissions Spectrometer (TES), and other appropriate data sets. We are also investigating the water vapor response to ENSO to help illuminate its role relative to dynamics in impacting ozone concentrations. These results indicate that the tropospheric ozone response to ENSO is potentially a very useful chemistry-climate diagnostic and should be considered in future modeling assessments.
    AGU Fall Meeting Abstracts. 12/2011;
  • M. A. Olsen, A. R. Douglass, J. C. Witte, T. Kaplan
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    ABSTRACT: The transport of ozone from the stratosphere to the extratropical troposphere is an important boundary condition to tropospheric chemistry. However, previous direct estimates from models and indirect estimates from observations have poorly constrained the magnitude of ozone stratosphere-troposphere exchange (STE). In this study we provide a direct diagnosis of the extratropical ozone STE using data from the Microwave Limb Sounder on Aura and output of the MERRA reanalysis over the time period from 2005 to the present. We find that the mean annual STE is about 275 Tg/yr and 205 Tg/yr in the NH and SH, respectively. The interannual variability of the magnitude is about twice as great in the NH than the SH. We find that this variability is dominated by the seasonal variability during the late winter and spring. A comparison of the ozone flux to the mass flux reveals that there is not a simple relationship between the two quantities. This presentation will also examine the magnitude and distribution of ozone in the lower stratosphere relative to the years of maximum and minimum ozone STE. Finally, we will examine any possible signature of increased ozone STE in the troposphere using sonde and tropospheric ozone residual (TOR) data, and output from the Global Modeling Initiative Chemistry Transport Model (GMI CTM).
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: We have run multi-year ensembles of one-year simulations with GEOS CCM to study both annual average and seasonal effects of NOx emissions by aviation. GEOS CCM is an atmospheric GCM with interactive stratospheric and tropospheric chemistry. Hourly aircraft NOx emissions over the globe for the year 2006 were provided by courtesy of the US Department of Transportation. All simulations were forced by historical SSTs and sea ice with constant greenhouse gases for 2005, and climatological lightning NOx, aerosols and dust were prescribed in monthly fields. On average, the perturbation response in NOx is positive and predominantly in the upper troposphere and lower stratosphere of the Northern Hemisphere where the bulk of the emissions lie, reaching values over 50 pptv at ~10 km on an annual average basis. The concomitant ozone response extends over a deeper layer in the troposphere with statistically significant mid-tropospheric increases of more than 5% and 8% in mid-latitudes and at the northern polar regions. Seasonal differences in the responses are striking, with the largest perturbations of NOx during January at the tropopause near the core of the emissions at 40°N, while in July perturbations over 50 pptv spread throughout the Arctic. These differences are reflected in ozone, which shows perturbations of 50 ppbv and greater in July at the summer polar tropopause while in January the tropospheric response throughout the middle and polar latitudes is limited to ~10 ppbv. We compare these seasonal variations in response to aviation NOx emissions in GEOS CCM with those from GMI, a chemical transport model that shares the COMBO chemistry scheme with GEOS CCM . Finally, we examine the radiative impacts of these seasonal perturbations in ozone and methane.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: A new version of the Goddard Earth Observing System chemistry-climate model (GEOS CCM) with a combined troposphere-stratospheric chemical mechanism is used to examine the impact of stratospheric changes on the evolution of tropospheric ozone. Time-slice integrations were performed for 1960, 2005 and 2100. These simulations differ in values of prescribed ozone depleting substances (ODSs), greenhouse gases (GHGs) and sea-surface temperatures (SSTs). The past decline and projected future recovery in stratospheric ozone lead that the influx of stratospheric ozone into the troposphere decreased between 1960 and 2005 and increases between 2005 and 2100. An increase in mass transport into the troposphere, due primarily to increases in GHGs and SSTs, further enhances the stratospheric contribution in the future. The net stratospheric impact in the past is the largest in the southern extratropics (10-15% decrease in tropospheric burden and surface ozone, compared to 1-3% decrease in northern hemisphere). However, for the scenario considered, the impact in the future is similar in both hemispheres (~10-15% increase in tropospheric burden).
    AGU Fall Meeting Abstracts. 12/2011;

Publication Stats

4k Citations
423.46 Total Impact Points

Institutions

  • 2001–2002
    • Loyola University Maryland
      Baltimore, Maryland, United States
    • University of Maryland, Baltimore County
      Baltimore, Maryland, United States
  • 1990
    • Universities Space Research Association
      Houston, Texas, United States