Attribution of Antarctic ozone recovery to the Montreal protocol requires evidence that (1)Antarctic chlorine levels are declining and (2) there is a reduction in ozone depletion in response to ...achlorine decline. We use Aura Microwave Limb Sounder measurements of O3, HCl, and N2O to demonstratethat inorganic chlorine (Cly) from 2013 to 2016 was 223 ± 93 parts per trillion lower in the Antarctic lowerstratosphere than from 2004 to 2007 and that column ozone depletion declined in response. The mean Clydecline rate, ~0.8%/yr, agrees with the expected rate based on chlorofluorocarbon lifetimes. N2Omeasurements are crucial for identifying changes in stratospheric Cly loading independent of dynamicalvariability. From 2005 to 2016, the ozone depletion and Cly time series show matching periods of decline,stability, and increase. The observed sensitivity of O3 depletion to changing Cly agrees with the sensitivitysimulated by the Global Modeling Initiative chemistry transport model integrated
Past studies have suggested that ozone in the troposphere has increased globally throughout much of the 20th century due to increases in anthropogenic emissions and transport. We show, by combining ...satellite measurements with a chemical transport model, that during the last four decades tropospheric ozone does indeed indicate increases that are global in nature, yet still highly regional. Satellite ozone measurements from Nimbus-7 and Earth Probe Total Ozone Mapping Spectrometer (TOMS) are merged with ozone measurements from the Aura Ozone Monitoring Instrument/Microwave Limb Sounder (OMI/MLS) to determine trends in tropospheric ozone for 1979–2016. Both TOMS (1979–2005) and OMI/MLS (2005–2016) depict large increases in tropospheric ozone from the Near East to India and East Asia and further eastward over the Pacific Ocean. The 38-year merged satellite record shows total net change over this region of about +6 to +7 Dobson units (DU) (i.e., ∼15 %–20 % of average background ozone), with the largest increase (∼4 DU) occurring during the 2005–2016 Aura period. The Global Modeling Initiative (GMI) chemical transport model with time-varying emissions is used to aid in the interpretation of tropospheric ozone trends for 1980–2016. The GMI simulation for the combined record also depicts the greatest increases of +6 to +7 DU over India and East Asia, very similar to the satellite measurements. In regions of significant increases in tropospheric column ozone (TCO) the trends are a factor of 2–2.5 larger for the Aura record when compared to the earlier TOMS record; for India and East Asia the trends in TCO for both GMI and satellite measurements are ∼+3 DU decade(exp −1) or greater during 2005–2016 compared to about +1.2 to +1.4 DU decade(exp −1) for 1979–2005. The GMI simulation and satellite data also reveal a tropospheric ozone increases in ∼+4 to +5 DU for the 38-year record over central Africa and the tropical Atlantic Ocean. Both the GMI simulation and satellite-measured tropospheric ozone during the latter Aura time period show increases of ∼+3 DU decade−1 over the N Atlantic and NE Pacific.
The lifetime of nitrous oxide, the third‐most‐important human‐emitted greenhouse gas, is based to date primarily on model studies or scaling to other gases. This work calculates a semiempirical ...lifetime based on Microwave Limb Sounder satellite measurements of stratospheric profiles of nitrous oxide, ozone, and temperature; laboratory cross‐section data for ozone and molecular oxygen plus kinetics for O(1D); the observed solar spectrum; and a simple radiative transfer model. The result is 116 ± 9 years. The observed monthly‐to‐biennial variations in lifetime and tropical abundance are well matched by four independent chemistry‐transport models driven by reanalysis meteorological fields for the period of observation (2005–2010), but all these models overestimate the lifetime due to lower abundances in the critical loss region near 32 km in the tropics. These models plus a chemistry‐climate model agree on the nitrous oxide feedback factor on its own lifetime of 0.94 ± 0.01, giving N2O perturbations an effective residence time of 109 years. Combining this new empirical lifetime with model estimates of residence time and preindustrial lifetime (123 years) adjusts our best estimates of the human‐natural balance of emissions today and improves the accuracy of projected nitrous oxide increases over this century.
Key Points
Nitrous oxide lifetime is computed empirically from MLS satellite data
Empirical N2O lifetimes compared with models including interannual variability
Results improve values for present anthropogenic and preindustrial emissions
Tropospheric trends in long-lived source gases N2O and the chlorofluorocarbons (CFCs) cause trends in O3 through changes in their reactive product gases. Transport affects the product gases because ...it controls the distribution of the long-lived source gases. We find that large changes in tropical upwelling 10-5 hPa since 2012 have strengthened the northern branch of the upper stratospheric (UpS) transport circulation, dramatically altering the abundances of N2O and its odd nitrogen product gases, NOx and HNO3. Increased upwelling is connected to stronger and more frequent Quasi-Biennial Oscillation easterly winds at 10 hPa and above. We use simulations with and without time varying MERRA2 meteorology to quantify the impact of dynamical changes on O3 loss via the NOx and ClOx cycles. We find that dynamical impacts on these cycles explain the mid-stratospheric tropical O3 increase and Arctic UpS O3 decrease since 2005.
Links between the stratospheric thermal structure and the ozone distribution are explored in the Goddard Earth Observing System chemistry‐climate model (CCM). Ozone and temperature fields are ...validated using estimates based on observations. An experimental strategy is used to explore sensitivities of temperature and ozone using the CCM alongside the underlying general circulation model (GCM) with ozone specified from either observations or from a chemistry‐transport model (CTM), which uses the same chemical modules as the CCM. In the CTM, upper stratospheric ozone is biased low compared to observations; GCM experiments reveal that using CTM ozone reduces a warm temperature bias near the stratopause in the GCM, and this improvement is also seen in the CCM. Near 5 hPa, the global‐mean ozone profile is biased low in the CTM but is close to observations in the CCM, which suggests that the temperature feedbacks are important in simulating the ozone distribution in the middle stratosphere. In the low stratosphere there is a high bias in simulated ozone, which forces a warm bias in the CCM. The high ozone also leads to an overestimate in total column ozone of several tens of Dobson units in the polar regions. In the late part of the twentieth century the seasonal activation of chlorine, especially over Antarctica, destroys ozone as expected, so that chlorine‐induced ozone decreases are overestimated in the CCM compared to the real atmosphere. Ozone‐change experiments reveal that the thermal structures of the GCM and CCM respond in a similar manner to ozone differences between 1980 and 2000, with a peak ozone‐induced temperature change of about 1.5 K (over 20 years) near the stratopause, which is at the low end of the range computed by other models. Greenhouse‐gas‐induced cooling increases with altitude and, near the stratopause, contributes an additional 1.3 K to the cooling near 1 hPa between 1980 and 2000. In the Antarctic, the ozone hole is simulated with some success by the CCM. As with many other models, the polar vortex is too persistent in late winter, but counteracting this, the CCM undergoes too much midwinter variability, meaning the ozone hole is more variable than it is in the real atmosphere. Temperature decreases associated with the ozone hole in the CCM are similar to those computed with other models.
Eight years of ozone measurements retrieved from the Ozone Monitoring Instrument and the Microwave Limb Sounder, both on the EOS Aura satellite, have been assimilated into the Goddard Earth Observing ...System Version 5 (GEOS‐5) data assimilation system. This study evaluates this assimilated product, highlighting its potential for science. The impact of observations on the GEOS‐5 system is explored by examining the spatial distribution of the observation‐minus‐forecast statistics. Independent data are used for product validation. The correlation of the lower stratospheric (the tropopause to 50 hPa) ozone column with ozonesondes is 0.99 and the (high) bias is 0.5%, indicating the success of the assimilation in reproducing the ozone variability in that layer. The upper tropospheric (500 hPa to the tropopause) assimilated ozone column is about 10% lower than the ozonesonde column, but the correlation is still high (0.87). The assimilation is shown to realistically capture the sharp cross‐tropopause gradient in ozone mixing ratio. Occurrence of transport‐driven low ozone laminae in the assimilation system is similar to that obtained from the High Resolution Dynamics Limb Sounder (HIRDLS) above the 400 K potential temperature surface, but the assimilation produces fewer laminae than seen by HIRDLS below that surface. Although the assimilation produces about 25% fewer occurrences per day during the 3 years of HIRDLS data, the interannual variability is captured correctly. This data‐driven assimilated product is complementary to ozone fields generated from chemistry and transport models. Applications include study of the radiative forcing by ozone and tracer transport near the tropopause.
Key Points
Ozone observations from OMI and MLS are assimilated into GEOS‐5
Very good agreement with ozonesondes in the lower stratosphere
Representation of transport‐driven ozone structures in the UTLS
Overview of the EOS aura mission Schoeberl, M.R.; Douglass, A.R.; Hilsenrath, E. ...
IEEE transactions on geoscience and remote sensing,
05/2006, Letnik:
44, Številka:
5
Journal Article
Recenzirano
Odprti dostop
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.
Stratospheric ozone depletion plays a major role in driving climate change in the Southern Hemisphere. To date, many climate models prescribe the stratospheric ozone layer’s evolution using monthly ...and zonally averaged ozone fields. However, the prescribed ozone underestimates Antarctic ozone depletion and lacks zonal asymmetries. This study investigates the impact of using interactive stratospheric chemistry instead of prescribed ozone on climate change simulations of the Antarctic and Southern Ocean. Two sets of 1960–2010 ensemble transient simulations are conducted with the coupled ocean version of the Goddard Earth Observing System Model, version 5: one with interactive stratospheric chemistry and the other with prescribed ozone derived from the same interactive simulations. The model’s climatology is evaluated using observations and reanalysis. Comparison of the 1979–2010 climate trends between these two simulations reveals that interactive chemistry has important effects on climate change not only in the Antarctic stratosphere, troposphere, and surface, but also in the Southern Ocean and Antarctic sea ice. Interactive chemistry causes stronger Antarctic lower stratosphere cooling and circumpolar westerly acceleration during November–January. It enhances stratosphere–troposphere coupling and leads to significantly larger tropospheric and surface westerly changes. The significantly stronger surface wind stress trends cause larger increases of the Southern Ocean meridional overturning circulation, leading to year-round stronger ocean warming near the surface and enhanced Antarctic sea ice decrease.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Observations from long‐term ozonesonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Réunion Island (21.1°S, 55.5°E) in ...June–August. Here we examine possible causes of the observed ozone variation at Réunion Island using hindcast simulations by the stratosphere‐troposphere Global Modeling Initiative chemical transport model for 1992–2014, driven by assimilated Modern‐Era Retrospective Analysis for Research and Applications meteorological fields. Réunion Island is at the edge of the subtropical jet, a region of strong stratospheric‐tropospheric exchange. Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Réunion is driven by the large IAV of the stratospheric influence. The IAV of the large‐scale, quasi‐horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Réunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited to the lower troposphere near the surface in August–September.
Key Points
The GMI‐CTM Model simulated the main features of the observed ozone IAV over Réunion
Stratospheric input plays an important role in the tropospheric ozone IAV over Réunion
Changes in emissions have little influence on middle and upper tropospheric ozone over Réunion
We use the Goddard Earth Observing System Chemistry‐Climate Model, a contributor to both the 2010 and 2014 World Meteorological Organization Ozone Assessment Reports, to show that inclusion of 5 ...parts per trillion (ppt) of stratospheric bromine (Bry) from very short lived substances (VSLS) is responsible for about a decade delay in ozone hole recovery. These results partially explain the significantly later recovery of Antarctic ozone noted in the 2014 report, as bromine from VSLS was not included in the 2010 Assessment. We show multiple lines of evidence that simulations that account for VSLS Bry are in better agreement with both total column BrO and the seasonal evolution of Antarctic ozone reported by the Ozone Monitoring Instrument on NASA's Aura satellite. In addition, the near‐zero ozone levels observed in the deep Antarctic lower stratospheric polar vortex are only reproduced in a simulation that includes this Bry source from VSLS.
Key Points
Including 5 ppt of Br from VSLS reduces biases with observed ozone and BrO
Resolves a discrepancy with an observational derived parametric model
Causes a decade later recovery of Antarctic ozone to 1980 levels
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