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  • 1
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    Signature of a tropical Pacific cyclone in the composition of the upper troposphere over Socorro, NM (2015)
    Wiley
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    Publication Date: 2015-10-14
    Description: We present a case study based on balloon-borne ozone measurements during SEACIONS (SouthEast American Consortium for Intensive Ozonesonde Network Study) in August-September 2013. Data from Socorro, NM (34 o N, 107 o W) show a layer of anomalously low ozone in the upper troposphere (UT) during 8-14 August. Back trajectories, UT jet analyses, and data from the Microwave Limb Sounder (MLS) on the Aura satellite indicate that this feature originated from the marine boundary layer in the eastern/central tropical Pacific, where several disturbances and one hurricane (Henriette) formed within an active region of the Intertropical Convergence Zone in early August 2013. The hurricane and nearby convection pumped boundary layer air with low ozone (20-30 ppbv) into the UT. This outflow was advected to North America 3-5 days later by a strong subtropical jet, forming a tongue of low ozone observed in MLS fields and a corresponding layer of low ozone in Socorro vertical profiles.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    A study of the Arctic NOy budget above Eureka, Canada (2011)
    Wiley
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    Publication Date: 2011-12-08
    Description: Four years of trace gas measurements have been acquired using the Bruker 125HR Fourier Transform Infrared (FTIR) spectrometer installed at the Polar Environment Atmospheric Research Laboratory (PEARL) in the Canadian high Arctic. These have been compared with data from three models, namely the Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS), the Global Environmental Multiscale stratospheric model with the online Belgium Atmospheric CHemistry package (GEM-BACH), and the off-line 3D chemical transport model SLIMCAT to assess the total reactive nitrogen, NOy, budget above Eureka, Nunavut (80.05°N, 86.42°W). The FTIR data have been also compared with satellite measurements by the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS). The FTIR is able to measure four of the five primary species that form NOy: NO, NO2, HNO3, and ClONO2, while the fifth, N2O5, was obtained using the N2O5/(NO + NO2) ratio derived from the models and ACE-FTS. Combining these results, a four-year time series of NOy 15–40 km partial columns was calculated. Comparisons with each model were made, revealing mean differences (± standard error of the mean) relative to the FTIR of (−16.0 ± 0.6)%, (5.5 ± 1.0)%, and (−5.8 ± 0.4)% for CMAM-DAS, GEM-BACH, and SLIMCAT, respectively. The mean difference between the ACE-FTS and FTIR NOy partial columns was (5.6 ± 2.3)%. While we found no significant seasonal and interannual differences in the FTIR NOy stratospheric columns, the partial columns display nearly twice as much variability during the spring compared to the summer period.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 3
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    Evaluation of Whole Atmosphere Community Climate Model simulations of ozone during Arctic winter 2004-2005 (2013)
    Wiley
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    Publication Date: 2013-02-16
    Description: [1]  The work presented here evaluates polar stratospheric ozone simulations from the Whole Atmosphere Community Climate Model (WACCM) for the Arctic winter of 2004-2005. We use the Specified Dynamics version of WACCM (SD-WACCM), in which temperatures and winds are nudged to meteorological assimilation analysis results. Model simulations of ozone and related constituents generally compare well to observations from the Earth Observing System Microwave Limb Sounder (MLS). At most times modeled ozone agrees with MLS data to within ~10%. However a systematic high biasin ozone in the model of ~18% is found in the lowermost stratosphere in March. We attribute most of this ozone bias to too little heterogeneous processing of halogens late in the winter. We suggestthat the model under-predicts ClONO 2 early in the winter, which leads to less heterogeneous processing and too little activated chlorine. Model HCl could also be overestimated due to an underestimation of HCl uptake into supercooled ternary solution (STS) particles. In late winter, the model overestimates gas-phase HNO 3 , and thus NO y , which leads to an over-prediction of ClONO 2 (under-prediction of activated chlorine). A sensitivity study in which temperatures for heterogeneous chemistry reactions were reduced by 1.5 K shows significant improvement of modeled ozone. Chemical ozone loss is inferred from the MLS observations using the pseudo-passive subtraction approach. The inferred ozone loss using this method is in agreement with or less than previous independent results for the Arctic winter of 2004-2005, reaching 1.0 ppmv on average and up to 1.6 ppmv locally in the polar vortex.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 4
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    Methyl Chloride from the Aura Microwave Limb Sounder: First Global Climatology and Assessment of Variability in the Upper Troposphere and Stratosphere (2013)
    Wiley
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    Publication Date: 2013-10-25
    Description: [1]  Methyl chloride (CH 3 Cl) is by far the largest natural carrier of chlorine to the stratosphere. Its importance in stratospheric ozone chemistry is expected to increase in the coming decades as emission controls alter the relative contributions from natural and anthropogenic halogen sources. The Microwave Limb Sounder (MLS) on NASA's Aura satellite provides the first daily global observations of CH 3 Cl. Here we quantify the quality of the MLS version 3 CH 3 Cl data (single-profile precision of ±100 pptv; accuracy of 30–45%; vertical and horizontal resolution of 4–5 km and 450–600 km, respectively) and demonstrate their utility for scientific studies over the vertical range from 147 to 4.6 hPa. We exploit the unmatched scope of the 8-year MLS data set to investigate the spatial, seasonal, and interannual variations in the distribution of CH 3 Cl in the upper troposphere / lower stratosphere (UTLS). Like carbon monoxide, CH 3 Cl is a marker of pollution from biomass burning that can be lofted to the UTLS very rapidly by deep convection. The climatological seasonal cycle in CH 3 Cl reflects variability in regional fire activity and other surface sources as well as convection, and anomalous CH 3 Cl enhancements in the tropical upper troposphere are linked to specific episodes of intense burning. Methyl chloride is shown to be very useful as a tracer of large-scale dynamical processes, such as diabatic descent inside the stratospheric winter polar vortices, quasi-isentropic cross-tropopause transport associated with the summer monsoon circulations, and effects related to the quasi-biennial oscillation and the tropical “tape recorder”.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    Trace gas evolution in the lowermost stratosphere from Aura Microwave Limb Sounder measurements (2011)
    Wiley
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    Publication Date: 2011-09-24
    Description: Daily global measurements from NASA's Aura Microwave Limb Sounder (MLS) allow comprehensive investigation of interhemispheric and interannual variations in chemical and transport processes throughout the lowermost stratosphere (LMS). We analyze nearly seven years of MLS O3, HNO3, HCl and ClO measurements along with meteorological analyses to place chemical processing in and dispersal of processed air from the winter polar lowermost vortex and subvortex in a global context. The MLS data, the first simultaneous observations of HCl and ClO covering much of the LMS, reveal that chlorine activation is widespread in the Antarctic subvortex and can occur to a significant degree in the Arctic subvortex. Unusually low temperatures and strong, prolonged chlorine activation in the lowermost vortex and subvortex promoted large ozone losses there in the 2006 (and 2008) Antarctic and 2004/2005 Arctic winters, consistent with reported record low column ozone. Processed air dispersing from the decaying vortex in spring induces rapid changes in extravortex trace gas abundances. After vortex breakdown, the subtropical jet/tropopause becomes the major transport barrier in the LMS. Quasi-isentropic transport of tropical tropospheric air into the LMS, associated with the summer monsoon circulations, leads to decreases in extratropical O3, HNO3, and HCl in both hemispheres. Strong mixing in the summertime LMS homogenizes extratropical trace gas fields. MLS measurements in the tropics show signatures of monsoon-related cross-equatorial stratosphere-to-troposphere transport. Observed seasonal and interannual variations in trace gas abundances in the LMS are consistent with variations in the strength of transport barriers diagnosed from meteorological analyses.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    Climatology and variability of trace gases in extratropical double-tropopause regions from MLS, HIRDLS and ACE-FTS measurements (2014)
    Wiley
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    Publication Date: 2014-12-31
    Description: Upper tropospheric and lower stratospheric (UTLS) measurements from the Aura Microwave Limb Sounder (MLS), the Aura High Resolution Dynamics Limb Sounder (HIRDLS), and the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) are used to present the first global climatological comparison of extratropical, non-polar trace gas distributions in double tropopause (DT) and single tropopause (ST) regions. Stratospheric tracers, O 3 , HNO 3 and HCl, have lower mixing ratios ~2–8 km above the primary (lowermost) tropopause in DT than in ST regions in all seasons, with maximum Northern Hemisphere (NH) differences near 50% in winter and 30% in summer. Southern Hemisphere (SH) winter differences are somewhat smaller, but summer differences are similar in the two hemispheres. H 2 O in DT regions of both hemispheres shows strong negative anomalies in November through February and positive anomalies in July through October, reflecting the strong seasonal cycle in H 2 O near the tropical tropopause. CO and other tropospheric tracers examined have higher DT than ST values 2–7 km above the primary tropopause, with the largest differences in winter. Large DT-ST differences extend to high NH latitudes in fall and winter, with longitudinal maxima in regions associated with enhanced wave activity and subtropical jet variations. Results for O 3 and HNO 3 agree closely between MLS and HIRDLS, and differences from ACE-FTS are consistent with its sparse and irregular midlatitude sampling. Consistent signatures in climatological trace gas fields provide strong evidence that transport from the tropical upper troposphere into the layer between double tropopauses is an important pathway for stratosphere-troposphere exchange.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 7
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    Nitric acid enhancements in the mesosphere during the January 2005 and December 2006 solar proton events (2011)
    Wiley
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    Publication Date: 2011-09-02
    Description: We investigate enhancements of mesospheric nitric acid (HNO3) in the Northern Hemisphere polar night regions during the January 2005 and December 2006 solar proton events (SPEs). The enhancements are caused by ionization due to proton precipitation, followed by ionic reactions that convert NO and NO2 to HNO3. We utilize mesospheric observations of HNO3 from the Microwave Limb Sounder (MLS/Aura). Although in general MLS HNO3 data above 50 km (1.5 hPa) are outside the standard recommended altitude range, we show that in these special conditions, when SPEs produce order-of-magnitude enhancements in HNO3, it is possible to monitor altitudes up to 70 km (0.0464 hPa) reliably. MLS observations show HNO3 enhancements of about 4 ppbv and 2 ppbv around 60 km in January 2005 and December 2006, respectively. The highest mixing ratios are observed inside the polar vortex north of 75°N latitude, right after the main peak of SPE forcing. These measurements are compared with results from the one-dimensional Sodankylä Ion and Neutral Chemistry (SIC) model. The model has been recently revised in terms of rate coefficients of ionic reactions, so that at 50–80 km it produces about 40% less HNO3 during SPEs compared to the earlier version. This is a significant improvement that results in better agreement with the MLS observations. By a few days after the SPEs, HNO3 is heavily influenced by horizontal transport and mixing, leading to its redistribution and decrease of the SPE-enhanced mixing ratios in the polar regions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    Unprecedented Arctic ozone loss in 2011 (2011)
    Nature Publishing Group (NPG)
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    Publication Date: 2011-10-04
    Description: Chemical ozone destruction occurs over both polar regions in local winter-spring. In the Antarctic, essentially complete removal of lower-stratospheric ozone currently results in an ozone hole every year, whereas in the Arctic, ozone loss is highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over the Arctic in early 2011 was--for the first time in the observational record--comparable to that in the Antarctic ozone hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18-20 kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or exceeded.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Manney, Gloria L -- Santee, Michelle L -- Rex, Markus -- Livesey, Nathaniel J -- Pitts, Michael C -- Veefkind, Pepijn -- Nash, Eric R -- Wohltmann, Ingo -- Lehmann, Ralph -- Froidevaux, Lucien -- Poole, Lamont R -- Schoeberl, Mark R -- Haffner, David P -- Davies, Jonathan -- Dorokhov, Valery -- Gernandt, Hartwig -- Johnson, Bryan -- Kivi, Rigel -- Kyro, Esko -- Larsen, Niels -- Levelt, Pieternel F -- Makshtas, Alexander -- McElroy, C Thomas -- Nakajima, Hideaki -- Parrondo, Maria Concepcion -- Tarasick, David W -- von der Gathen, Peter -- Walker, Kaley A -- Zinoviev, Nikita S -- England -- Nature. 2011 Oct 2;478(7370):469-75. doi: 10.1038/nature10556.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. Gloria.L.Manney@jpl.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21964337" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Arctic Regions ; Atmosphere/*chemistry ; Chlorine/chemistry ; *Environmental Monitoring ; History, 20th Century ; History, 21st Century ; Ozone/*analysis/chemistry/history ; Seasons ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 9
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    Interhemispheric Differences in Polar Stratospheric HNO3, H2O, CIO, and O3 (1995)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1995-02-10
    Description: Simultaneous global measurements of nitric acid (HNO(3)), water (H(2)O), chlorine monoxide (CIO), and ozone (O(3)) in the stratosphere have been obtained over complete annual cycles in both hemispheres by the Microwave Limb Sounder on the Upper Atmosphere Research Satellite. A sizeable decrease in gas-phase HNO(3) was evident in the lower stratospheric vortex over Antarctica by early June 1992, followed by a significant reduction in gas-phase H(2)O after mid-July. By mid-August, near the time of peak CIO, abundances of gas-phase HNO(3) and H(2)O were extremely low. The concentrations of HNO(3) and H(2)O over Antarctica remained depressed into November, well after temperatures in the lower stratosphere had risen above the evaporation threshold for polar stratospheric clouds, implying that denitrification and dehydration had occurred. No large decreases in either gas-phase HNO(3) or H(2)O were observed in the 1992-1993 Arctic winter vortex. Although CIO was enhanced over the Arctic as it was over the Antarctic, Arctic O(3) depletion was substantially smaller than that over Antarctica. A major factor currently limiting the formation of an Arctic ozone "hole" is the lack of denitrification in the northern polar vortex, but future cooling of the lower stratosphere could lead to more intense denitrification and consequently larger losses of Arctic ozone.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Santee, M L -- Read, W G -- Waters, J W -- Froidevaux, L -- Manney, G L -- Flower, D A -- Jarnot, R F -- Harwood, R S -- Peckham, G E -- New York, N.Y. -- Science. 1995 Feb 10;267(5199):849-52.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17813911" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    Using FTIR measurements of stratospheric composition to identify mid-latitude polar vortex intrusions over Toronto (2013)
    Wiley
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    Publication Date: 2013-11-14
    Description: [1]  Using eleven years of trace gas measurements made at the University of Toronto Atmospheric Observatory (TAO, 43.66°N, 79.40°W), and Environment Canada's Centre for Atmospheric Research Experiments (CARE, 44.23°N, 79.78°W), along with derived meteorological products, we identify a number of polar intrusion events, which are excursions of the polar vortex or filaments from the polar vortex extending down to mid-latitudes. These events are characterized by enhanced stratospheric columns (12-50 km) of hydrogen fluoride (HF) and diminished stratospheric columns of nitrous oxide (N 2 O), and by a scaled potential vorticity above 1.2 × 10 −4  s −1 . The events comprise 16% of winter/spring (November to April inclusive) Fourier transform infrared (FTIR) spectroscopic measurements from January 2002 to March 2013, and we find at least two events per year. The events are corroborated by Modèle Isentrope du transport Méso-échelle del'Ozone Stratosphérique par Advection (MIMOSA) and Modern-Era Retrospective Analysis for Research and Applications (MERRA) potential vorticity (PV) maps, and Global Modeling Initiative (GMI) N 2 O maps. During polar intrusion events, the stratospheric ozone (O 3 ) columns over Toronto are usually greater than when there is no event. Our O 3 measurements agree with the Optical Spectrograph and InfraRed Imaging System (OSIRIS) satellite instrument, and are further verified with the Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS) and Ozone Monitoring Instrument (OMI) satellite observations. We find six cases out of 53 for which chemical O 3 depletion within the polar vortex led to a reduction in stratospheric O 3 columns over Toronto. We have thus identified a dynamical cause for most of the winter/spring variability of stratospheric trace gas columns observed at our mid-latitude site. While there have been a number of prior polar intrusion studies, this is the first study to report in the context of eleven years of ground-based FTIR column measurements, providing insight into the frequency of mid-latitude polar vortex intrusions, and observations of upper-stratospheric (25–50 km) intrusions. It is also the first to present HF measurements during multiple polar intrusions, which provided an excellent tracer for their identification.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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