Publications (55)5.45 Total impact
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Article: The Response of Ozone and Nitrogen Dioxide to the Eruption of Mt. Pinatubo at Southern and Northern Midlatitudes
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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. · 2.56 Impact Factor -
Article: Modeling the Frozen-In Anticyclone in the 2005 Arctic summer stratosphere
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ABSTRACT: Immediately following the breakup of the 2005 Arctic spring stratospheric vortex, a tropical air mass, characterized by low potential vorticity (PV) and high nitrous oxide (N2O), was advected poleward and became trapped in the easterly summer polar vortex. This feature, known as a "Frozen-In Anticyclone (FrIAC)", was observed in Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) data to span the potential temperature range from ~580 to 1100 K (~25 to 40 km altitude) and to persist from late March to late August 2005. This study compares MLS N2O observations with simulations from the Global Modeling Initiative (GMI) chemistry and transport model, the GEOS-5/MERRA Replay model, and the Van Leer Icosahedral Triangular Advection (VITA) isentropic transport model to elucidate the processes involved in the lifecycle of the FrIAC, which is here divided into three distinct phases. During the "spin-up phase" (March to early April), strong poleward flow resulted in a tight isolated anticyclonic vortex at ~70–90° N, marked with elevated N2O. GMI, Replay, and VITA all reliably simulated the spin-up of the FrIAC, although the GMI and Replay peak N2O values were too low. The FrIAC became trapped in the developing summer easterly flow and circulated around the polar region during the "anticyclonic phase" (early April to the end of May). During this phase, the FrIAC crossed directly over the pole between the 7 and 14 April. The VITA and Replay simulations transported the N2O anomaly intact during this crossing, in agreement with MLS, but unrealistic dispersion of the anomaly occurred in the GMI simulation due to excessive numerical mixing of the polar cap. The vortex associated with the FrIAC was apparently resistant to the weak vertical shear during the anticyclonic phase, and it thereby protected the embedded N2O anomaly from stretching. The vortex decayed in late May due to diabatic processes, leaving the N2O anomaly exposed to horizontal and vertical wind shears during the "shearing phase" (June to August). The observed lifetime of the FrIAC during this phase is consistent with timescales calculated from the ambient horizontal and vertical wind shear. Replay maintained the horizontal structure of the N2O anomaly similar to MLS well into August. The VITA simulation also captured the horizontal structure of the FrIAC during this phase, but VITA eventually developed fine-scale N2O structure not observed in MLS data.Atmospheric Chemistry and Physics Discussions. 01/2011; -
Article: Finding the missing stratospheric Br<sub>y</sub>: a global modeling study of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub>
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ABSTRACT: Recent in situ and satellite measurements suggest a contribution of ~5 pptv to stratospheric inorganic bromine from short-lived bromocarbons. We conduct a modeling study of the two most important short-lived bromocarbons, bromoform (CHBr<sub>3</sub>) and dibromomethane (CH<sub>2</sub>Br<sub>2</sub>), with the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to account for this missing stratospheric bromine. We derive a "top-down" emission estimate of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub> using airborne measurements in the Pacific and North American troposphere and lower stratosphere obtained during previous NASA aircraft campaigns. Our emission estimate suggests that to reproduce the observed concentrations in the free troposphere, a global oceanic emission of 425 Gg Br yr<sup>−1</sup> for CHBr<sub>3</sub> and 57 Gg Br yr<sup>−1</sup> for CH<sub>2</sub>Br<sub>2</sub> is needed, with 60% of emissions from open ocean and 40% from coastal regions. Although our simple emission scheme assumes no seasonal variations, the model reproduces the observed seasonal variations of the short-lived bromocarbons with high concentrations in winter and low concentrations in summer. This indicates that the seasonality of short-lived bromocarbons is largely due to seasonality in their chemical loss and transport. The inclusion of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub> contributes ~5 pptv bromine throughout the stratosphere. Both the source gases and inorganic bromine produced from source gas degradation (Br<sub>y</sub><sup>VSLS</sup>) in the troposphere are transported into the stratosphere, and are equally important. Inorganic bromine accounts for half (2.5 pptv) of the bromine from the inclusion of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub> near the tropical tropopause and its contribution rapidly increases to ~100% as altitude increases. More than 85% of the wet scavenging of Br<sub>y</sub><sup>VSLS</sup> occurs in large-scale precipitation below 500 hPa. Our sensitivity study with wet scavenging in convective updrafts switched off suggests that Br<sub>y</sub><sup>VSLS</sup> in the stratosphere is not sensitive to convection. Convective scavenging only accounts for ~0.2 pptv (4%) difference in inorganic bromine delivered to the stratosphere.Atmospheric Chemistry and Physics. 01/2010; -
Article: Finding the missing stratospheric Br<sub>y</sub>: a global modeling study of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub>
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ABSTRACT: Recent in situ and satellite measurements suggest a contribution of ~5 pptv to stratospheric inorganic bromine from short-lived bromocarbons. We conduct a modeling study of the two most important short-lived bromocarbons, bromoform (CHBr<sub>3</sub>) and dibromomethane (CH<sub>2</sub>Br<sub>2</sub>), with the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to account for this missing stratospheric bromine. We derive a "top-down" emission estimate of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub> using airborne measurements in the Pacific and North American troposphere and lower stratosphere (LS) obtained during previous NASA aircraft campaigns. Our emission estimate suggests that to reproduce the observed concentrations in the free troposphere, a global oceanic emission of 425 Gg Br yr<sup>−1</sup> for CHBr<sub>3</sub> and 57 Gg Br yr<sup>−1</sup> for CH<sub>2</sub>Br<sub>2</sub> is needed, with 60% of emissions from open ocean and 40% from coastal regions. Although our simple emission scheme assumes no seasonal variations, the model reproduces the observed seasonal variations of the short-lived bromocarbons with high concentrations in winter and low concentrations in summer. This indicates that the seasonality of short-lived bromocarbons is largely due to seasonality in their chemical loss and transport. The inclusion of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub> contributes ~5 pptv bromine throughout the stratosphere. Both the source gases and inorganic bromine produced from the source gas degradation (Br<sub>y</sub><sup>VSLS</sup>) in the troposphere are transported into the stratosphere, and are equally important. Inorganic bromine accounts for half (2.5 pptv) of the bromine from the inclusion of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub> near the tropical tropopause and its contribution rapidly increases to ~100% as altitude increases. More than 85% of the wet scavenging of Br<sub>y</sub><sup>VSLS</sup> occurs in large-scale precipitation below 500 hPa and Br<sub>y</sub><sup>VSLS</sup> in the stratosphere is not sensitive to convection.Atmospheric Chemistry and Physics Discussions. 01/2009; -
Article: Sensitivity of polar stratospheric ozone loss to uncertainties in chemical reaction kinetics
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ABSTRACT: The impact and significance of uncertainties in model calculations of stratospheric ozone loss resulting from known uncertainty in chemical kinetics parameters is evaluated in trajectory chemistry simulations for the Antarctic and Arctic polar vortices. The uncertainty in modeled ozone loss is derived from Monte Carlo scenario simulations varying the kinetic (reaction and photolysis rate) parameters within their estimated uncertainty bounds. Simulations of a typical winter/spring Antarctic vortex scenario and Match scenarios in the Arctic produce large uncertainty in ozone loss rates and integrated seasonal loss. The simulations clearly indicate that the dominant source of model uncertainty in polar ozone loss is uncertainty in the Cl2O2 photolysis reaction, which arises from uncertainty in laboratory-measured molecular cross sections at atmospherically important wavelengths. This estimated uncertainty in JCl2O2 from laboratory measurements seriously hinders our ability to model polar ozone loss within useful quantitative error limits. Atmospheric observations, however, suggest that the Cl2O2 photolysis uncertainty may be less than that derived from the lab data. Comparisons to Match, South Pole ozonesonde, and Aura Microwave Limb Sounder (MLS) data all show that the nominal recommended rate simulations agree with data within uncertainties when the Cl2O2 photolysis error is reduced by a factor of two, in line with previous in situ ClOx measurements. Comparisons to simulations using recent cross sections from Pope et al. (2007) are outside the constrained error bounds in each case. Other reactions producing significant sensitivity in polar ozone loss include BrO + ClO and its branching ratios. These uncertainties challenge our confidence in modeling polar ozone depletion and projecting future changes in response to changing halogen emissions and climate. Further laboratory, theoretical, and possibly atmospheric studies are needed.Atmospheric Chemistry and Physics. 01/2009; -
Article: Impacts of climate change on stratospheric ozone recovery
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ABSTRACT: 1] The impact of increasing greenhouse gases (GHGs) on the ''recovery'' of stratospheric ozone is examined using simulations of the Goddard Earth Observing System Chemistry-Climate Model. In this model, GHG-induced climate change has a large impact on the ozone evolution and when O 3 recovery milestones are reached. The two distinct milestones of ''O 3 returning to historical values'' and ''O 3 being no longer significantly influenced by ozone depleting substances (ODSs)'' can be reached at very different dates, and which occurs first varies between regions. GHG-induced cooling in the upper stratosphere causes O 3 to increase, and O 3 returns to 1980 or 1960 values several decades before O 3 is no longer significantly influenced by ODSs. In contrast, transport changes in the tropical and southern mid-latitude lower stratosphere cause O 3 to decrease. Here O 3 never returns to 1980 values, even when anthropogenic ODSs have been removed from the atmosphere. O 3 returning to 1960 (or 1980) values should not necessarily be interpreted as O 3 recovery from the effects of ODSs. Citation: Waugh, D.Geophys. Res. Lett. 01/2009; 36. -
Article: What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated?
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ABSTRACT: Ozone depletion by chlorofluorocarbons (CFCs) was first proposed by Molina and Rowland in their 1974 Nature paper. Since that time, the scientific connection between ozone losses and CFCs and other ozone depleting substances (ODSs) has been firmly established with laboratory measurements, atmospheric observations, and modeling studies. This science research led to the implementation of international agreements that largely stopped the production of ODSs. In this study we use a fully-coupled radiation-chemical-dynamical model to simulate a future world where ODSs were never regulated and ODS production grew at an annual rate of 3%. In this "world avoided" simulation, 17% of the globally-averaged column ozone is destroyed by 2020, and 67% is destroyed by 2065 in comparison to 1980. Large ozone depletions in the polar region become year-round rather than just seasonal as is currently observed in the Antarctic ozone hole. Very large temperature decreases are observed in response to circulation changes and decreased shortwave radiation absorption by ozone. Ozone levels in the tropical lower stratosphere remain constant until about 2053 and then collapse to near zero by 2058 as a result of heterogeneous chemical processes (as currently observed in the Antarctic ozone hole). The tropical cooling that triggers the ozone collapse is caused by an increase of the tropical upwelling. In response to ozone changes, ultraviolet radiation increases, more than doubling the erythemal radiation in the northern summer midlatitudes by 2060.Atmospheric Chemistry and Physics. 01/2009; -
Article: Laminar Structures in Lower Stratospheric Middle Latitude Ozone as Observed by HIRDLS and Represented in a Chemistry Climate Model
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ABSTRACT: During late winter and spring both vertical transport and quasi-horizontal isentropic transport from the lower tropical stratosphere contribute to ozone variability in the lower middle latitude stratosphere. Since ozone in this region is an important greenhouse gas, it is important that the mean and variability of the ozone distribution are realistically represented in chemistry climate models (CCMs). The High Resolution Dynamic Limb Sounder (HIRDLS), one of the instruments on NASA's Aura satellite, measures profiles of temperature and ozone with about 1 km vertical resolution. Profiles at middle latitudes are separated by less than a degree in latitude. HIRDLS commonly observes layered structures in the lower stratosphere that sometimes persist for a week or more. These layered structures are produced by horizontal transport that is sometimes reversible. The evolution of these layers also gives evidence of mixing. In other regions, HIRDLS profiles show ozone enhancement (i.e., ozone greater than the temporal mean) for a 3-4 km vertical range. Separate approaches are used to quantify the importance of these processes to variability in the lower stratosphere. The structures with broad vertical range are identified using the covariance between levels. The frequency of vertical structures is computed over the winter and spring seasons, and results are compared with a similar analysis applied to output from simulations using the NASA Goddard CCM. The contributions of the layered structures to variability and the importance of mixing are examined by computing the distributions of ozone values on potential temperature surfaces for specified intervals of potential vorticity. Ozone is often correlated with potential vorticity, and the aim of this analysis is to explore the mixing processes that are observed by HIRDLS to understand their importance to the breakdown in the pv-ozone correlation. The behavior of the pv-ozone relationship as observed by HIRDLS can be contrasted with that derived from a parallel analysis of the output of the CCM.AGU Fall Meeting Abstracts. 11/2008; -1:04. -
Article: Comparison of lower stratospheric tropical mean vertical velocities
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ABSTRACT: 1] We have analyzed 13 years (1993–2005) of tropical stratospheric water vapor data from the Halogen Occultation Experiment and over 3 years of data (October 2004 through November 2007) from the Aura Microwave Limb Sounder. By correlating the phase lag of the water vapor ''tape recorder'' signal between levels we estimate the time mean vertical velocity. Our estimated vertical velocity compares well with calculations from the Goddard Earth Observing System (GEOS) chemistry-climate model (CCM) and from the GEOS data assimilation system. Between 18 and 26 km both the GEOS CCM simulations and water vapor observations agree that the vertical velocity is below 0.04 cm/s, with a minimum near 20 km of 0.03 cm/s. Vertical velocities deduced from water vapor observations are higher than those from the GEOS CCM in the region 16–18 km (0.04 cm/s) and above 26–30 km (up to 0.07 cm/s). These estimates are close to earlier estimates from a shorter water vapor record and radiative transfer models. No evidence is found for velocities as high as 0.15 cm/s as was recently estimated from aircraft CO 2 measurements in the upper troposphere/lower stratosphere. Further diagnosis of the aircraft CO 2 data and model simulations of CO 2 show that while the CO 2 data give an apparent upward transport velocity of $0.06 cm/s, about half of this is due to vertical and horizontal eddy transport. Accounting for the eddy terms gives a CO 2 -based estimate of the vertical velocity of $0.03 cm/s, in much closer agreement with that estimated from water vapor.J. Geophys. Res. 01/2008; 113. -
Article: Introduction to special section on Aura Validation
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ABSTRACT: 1] Aura, the last of the large EOS observatories, was launched on 15 July 2004 and has now been operating for several years. Aura is designed to make comprehensive stratospheric, mesospheric, and tropospheric constituent measurements from its four instruments HIRDLS, MLS, OMI, and TES. All of the instruments are performing well and observations of stratospheric and tropospheric trace gases and aerosols are revolutionizing our understanding of stratospheric chemistry and transport processes, ozone depletion, air quality, and the hydrological cycle. In this special section, the instrument teams and collaborators report on the validation of the released Aura data products.J. Geophys. Res. 01/2008; 113:15-1. -
Article: The Quasi-biennial Oscillation and annual variations in tropical ozone from SHADOZ and HALOE
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ABSTRACT: We examine the tropical ozone mixing ratio perturbation fields generated from a monthly ozone climatology using 1998 to 2006 ozonesonde data from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network and the 13 year satellite record from 1993 to 2005 obtained from the Halogen Occultation Experiment (HALOE). The lengthy time series and high vertical resolution of the ozone and temperature profiles from the SHADOZ sondes coupled with good tropical coverage north and south of the equator gives a detailed picture of the ozone structure in the lowermost stratosphere down through the tropopause where the picture obtained from HALOE measurements is blurred by coarse vertical resolution. Ozone perturbations respond to annual variations in the Brewer-Dobson Circulation (BDC) in the region just above the cold-point tropopause to around 20 km. Strong annual signals of alternating positive and negative ozone anomalies are observed and correlate well with temperature anomalies. Above 20 km, ozone and temperature perturbations are dominated by the Quasi-biennial Oscillation (QBO). Both satellite and sonde records show good agreement between positive and negative ozone mixing ratio anomalies and alternating QBO easterly and westerly wind shears from the Singapore rawinsondes with a mean periodicity of 26 months for SHADOZ and 25 months for HALOE. There is a temporal offset of one to three months with the ozone QBO preceding the wind shear. Horizontal length scales for the annual cycle and the QBO, obtained using the temperature anomalies and wind shears in the thermal wind equation, compare well with theoretical calculations.Atmospheric Chemistry and Physics Discussions. 01/2008; -
Article: The governing processes and timescales of stratosphere-to-troposphere transport and its contribution to ozone in the Arctic troposphere
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ABSTRACT: We used the seasonality of a combination of atmospheric trace gases and idealized tracers to examine stratosphere-to-troposphere transport and its influence on tropospheric composition in the Arctic. Maximum stratosphere-to-troposphere transport of CFCs and O3 occurs in April as driven by the Brewer-Dobson circulation. Stratosphere-troposphere exchange (STE) occurs predominantly between 40° N to 80° N with stratospheric influx in the mid-latitudes (30–70° N) accounting for 67–81% of the air of stratospheric origin in the Northern Hemisphere extratropical troposphere. Transport from the lower stratosphere to the lower troposphere (LT) takes three months on average, one month to cross the tropopause, the second month to travel from the upper troposphere (UT) to the middle troposphere (MT), and the third month to reach the LT. During downward transport, the seasonality of a trace gas can be greatly impacted by wet removal and chemistry. A comparison of idealized tracers with varying lifetimes suggests that when initialized with the same concentrations and seasonal cycles at the tropopause, trace gases that have shorter lifetimes display lower concentrations, smaller amplitudes, and earlier seasonal maxima during transport to the LT. STE contributes to O3 in the Arctic troposphere directly from the transport of O3 and indirectly from the transport of NOy. Direct transport of O3 from the stratosphere accounts for 78% of O3 in the Arctic UT with maximum contributions occurring from March to May. The stratospheric contribution decreases significantly in the MT/LT (20–25% of total O3) and shows a very weak March–April maximum. Our NOx budget analysis in the Arctic UT shows that during spring and summer, the stratospheric injection of NOy-rich air increases NOx concentrations above the 20 pptv threshold level, thereby shifting the Arctic UT from a regime of net photochemical ozone loss to one of net production with rates as high as +16 ppbv/month.Atmospheric Chemistry and Physics Discussions. 01/2008; -
Chapter: Early Data from Aura and Continuity from UARS and Toms
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ABSTRACT: Aura, the last of the large EOS observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from its four instruments, HIRDLS, MLS, OMI and TES. These four instruments work in synergy to provide data on ozone trends, air quality and climate change. The instruments observe in the nadir and limb and provide the best horizontal and vertical resolution ever achieved from space. After over one year in orbit the instruments are nearly operational and providing data to the scientific community. We summarize the mission, instruments, and initial results and give examples of how Aura will provide continuity to earlier chemistry missions.12/2006: pages 417-430; -
Article: Overview of the EOS aura mission
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ABSTRACT: Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from its four instruments, the High Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), and the Tropospheric Emission Spectrometer (TES). With the exception of HIRDLS, all of the instruments are performing as expected, and HIRDLS will likely be able to deliver most of their planned data products. We summarize the mission, instruments, and synergies in this paper.IEEE Transactions on Geoscience and Remote Sensing 06/2006; · 2.89 Impact Factor -
Article: Sensitivity of Arctic ozone loss to polar stratospheric cloud volume and chlorine and bromine loading in a chemistry and transport model
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ABSTRACT: 1] The sensitivity of Arctic ozone loss to polar stratospheric cloud volume (V PSC) and chlorine and bromine loading is explored using chemistry and transport models (CTMs). One simulation uses multi-decadal winds and temperatures from a general circulation model (GCM). Winter polar ozone loss depends on both equivalent effective stratospheric chlorine (EESC) and polar vortex characteristics (temperatures, descent, isolation, polar stratospheric cloud amount). The simulation reproduces a linear relationship between ozone loss and V PSC in agreement with that derived from observations for 1992–2003. The relationship holds for EESC within $85% of its maximum ($1990–2020). For lower EESC the ozone loss varies linearly with EESC unless V PSC $ 0. A second simulation recycles a single year's winds and temperatures from the GCM so that polar ozone loss depends only on changes in EESC. This simulation shows that ozone loss varies linearly with EESC for the entire EESC range for constant, high V PSC ., Sensitivity of Arctic ozone loss to polar stratospheric cloud volume and chlorine and bromine loading in a chemistry and transport model, Geophys. Res. Lett., 33, L17809, doi:10.1029/2006GL026492.01/2006; -
Article: Polar Processes in a 50-year Simulation of Stratospheric Chemistry and Transport
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ABSTRACT: The unique chemical, dynamical, and microphysical processes that occur in the winter polar lower stratosphere are expected to interact strongly with changing climate and trace gas abundances. Significant changes in ozone have been observed and prediction of future ozone and climate interactions depends on modeling these processes successfully. We have conducted an off-line model simulation of the stratosphere for trace gas conditions representative of 1975-2025 using meteorology from the NASA finite-volume general circulation model. The objective of this simulation is to examine the sensitivity of stratospheric ozone and chemical change to varying meteorology and trace gas inputs. This presentation will examine the dependence of ozone and related processes in polar regions on the climatological and trace gas changes in the model. The model past performance is base-lined against available observations, and a future ozone recovery scenario is forecast. Overall the model ozone simulation is quite realistic, but initial analysis of the detailed evolution of some observable processes suggests systematic shortcomings in our description of the polar chemical rates and/or mechanisms. Model sensitivities, strengths, and weaknesses will be discussed with implications for uncertainty and confidence in coupled climate chemistry predictions.02/2004; -
Article: Interannual variability of stratospheric trace gases: Role of extratropical wave driving
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ABSTRACT: The interannual variability of methane and ozone from a 35-year middle atmosphere climate model simu-lation with no interannual variations in external forcing or chemistry is examined. The internal dynamics in the model produces large tracer interannual variability, particularly in polar regions. During winter and spring the interannual standard deviation in the polar lower-middle stratosphere is about 30% of the climatological mean for methane and 15% for ozone. Global-scale, coherent interannual variations in temperature, residual circulation, and tracers are correlated with variability in the extratropical wave forcing. Statistically significant positive corre-lations between wave driving and polar tracer tendencies, including column ozone, occur from autumn to spring in both hemispheres. These positive correlations imply that interannual variations in polar tracers are dominated by variations in the horizontal eddy transport and not by variations in residual mean descent rates.01/2004; 130:2459-2474. -
Article: N2O and NOy
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ABSTRACT: The principal loss processes for ozone in the stratosphere are either directly or indirectly closely coupled to the abundance and distribution of reactive oxides of nitrogen (NOy). The main source of NOy in the stratosphere is N2O, a trace gas that is changing significantly as a result of anthropogenic forcing. Thus diagnosis of the distributions of N2O, NOy, and their coupling is required to evaluate any chemistry-climate model aspiring to accurately simulate ozone change. In the NASA Assessment of the Effects of High-speed Aircraft in the Stratosphere: 1998 we found that the sensitivity of various models ozone to perturbation did correspond consistently with their background NOy distribution. Coordinated NOy and N2O mixing ratio distributions are available from observations: ER-2 aircraft in the lower stratosphere and ATMOS and balloon profiles to higher altitudes at a subset of latitudes and seasons. Although close comparison to these diagnostics is crucial, unfortunately the distributions are due to a combination of transport and chemical processes, and isolating the source of differences is not always simple. However, in combination with other transport and photochemical diagnostics, comparison with N2O and NOy can be very instructive in evaluation of model processes and performance.02/2003; -
Article: The 2002 Antarctic Ozone Hole
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ABSTRACT: Since 1979, the ozone hole has grown from near zero size to over 24 Million km2. This area is most strongly controlled by levels of inorganic chlorine and bromine oncentrations. In addition, dynamical variations modulate the size of the ozone hole by either cooling or warming the polar vortex collar region. We will review the size observations, the size trends, and the interannual variability of the size. Using a simple trajectory model, we will demonstrate the sensitivity of the ozone hole to dynamical forcing, and we will use these observations to discuss the size of the ozone hole during the 2002 Austral spring. We will further show how the Cly decreases in the stratosphere will cause the ozone hole to decrease by 1-1.5% per year. We will also show results from a 3-D chemical transport model (CTM) that has been continuously run since 1999. These CTM results directly show how strong dynamics acts to reduce the size of the ozone hole.02/2003; -
Article: Stratospheric Ozone: Transport, Photochemical Production and Loss
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ABSTRACT: Observations from various satellite instruments (e.g., Total Ozone Mapping Spectrometer (TOMS), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS)) specify the latitude and seasonal variations of total ozone and ozone as a function of altitude. These seasonal variations change with latitude and altitude partly due to seasonal variation in transport and temperature, partly due to differences in the balance between photochemical production and loss processes, and partly due to differences in the relative importance of the various ozone loss processes. Comparisons of modeled seasonal ozone behavior with observations test the following: the seasonal dependence of dynamical processes where these dominate the ozone tendency; the seasonal dependence of photochemical processes in the upper stratosphere; and the seasonal change in the balance between photochemical and dynamical processes.02/2003;
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2001
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Loyola University Maryland
Baltimore, MD, USA -
University of Maryland, Baltimore County
Baltimore, MD, USA
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