416 research outputs found
Data used to produce figures in the manuscript ‘Maximizing Ozone Signals Among Chemical, Meteorological, and Climatological Variability’ by Brown-Steiner et al. (2018)
No full textData used to produce figures in the manuscript ‘Maximizing Ozone Signals Among Chemical, Meteorological, and Climatological Variability’ by Brown-Steiner, B.; Selin, N. E.; Prinn, R. G.; Monier, E.; Tilmes, S.; Emmons, L.; Garcia-Menendez, F
Sensitivity of the Methane Lifetime to Sulfate Geoengineering: Results from the Geoengineering Model Intercomparison Project (GeoMIP)
No full textSulfate geoengineering, made by sustained injection of SO2 in the tropical lower stratosphere, may impact the abundance of tropospheric methane through several photochemical mechanisms affecting the tropospheric OH abundance and hence the methane lifetime. Geoengineered sulfate aerosols in the stratosphere are responsible of important radiative and chemical effects: (a) solar radiation scattering increases the planetary albedo and cools the surface, with a tropospheric water vapor decrease as a response to this cooling: less OH. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D): less OH. (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-upper troposphere, thus reducing the amount of NOx and tropospheric O3 production: less OH. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rates perturbation are strongly latitude dependent, producing a significant change of the pole-to-equator temperature gradient and mean zonal wind distribution, with a net increase of tropical upwelling. A stronger meridional component of the Brewer-Dobson circulation may affect the abundance of mid-upper tropospheric sulfate aerosols, NOy, and O3 (all possibly affecting the budget of tropospheric OH), as well as CH4 transport directly. Three climate-chemistry coupled models are used here to explore the above radiative, chemical and dynamical mechanisms affecting the methane lifetime (ULAQ-CCM, CCSM4, GEOSCCM). First results show that the CH4 lifetime may become significantly longer (Fig.1) with a sustained injection of 2.5 Tg-S/yr started in year 2020 (exp. G4), which implies an increase of tropospheric CH4 (Fig. 2) and a positive indirect RF of sulfate geoengineering due to CH4 changes, of the order of 10% the aerosols direct forcing, but with opposite sign
Data used to produce figures in the manuscript 'Evaluating Simplified Chemical Mechanisms within Present-Day Simulations of CESM Version 1.2 CAM-chem (CAM4): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast Chemistry' by Brown-Steiner et al. (2018)
No full textData used to produce figures in the manuscript Evaluating Simplified Chemical Mechanisms within Present-Day Simulations of CESM Version 1.2 CAM-chem (CAM4): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast Chemistry by Brown-Steiner, B.; Selin, N. E.; Prinn, R.; Tilmes, S.; Emmons, L.; Lamarque, J.-F.; and Cameron-Smith, P
Chemical ozone loss in the Arctic winter 1991–1992
No full textChemical ozone loss in winter 1991–1992 is recalculated based on observations of the HALOE satellite instrument, Version 19, ER-2 aircraft measurements and balloon data. HALOE satellite observations are shown to be reliable in the lower stratosphere below 400 K, at altitudes where the measurements are most likely disturbed by the enhanced sulfate aerosol loading, as a result of the Mt.~Pinatubo eruption in June 1991. Significant chemical ozone loss (13–17 DU) is observed below 380 K from Kiruna balloon observations and HALOE satellite data between December 1991 and March 1992. For the two winters after the Mt. Pinatubo eruption, HALOE satellite observations show a stronger extent of chemical ozone loss towards lower altitudes compared to other Arctic winters between 1991 and 2003. In spite of already occurring deactivation of chlorine in March 1992, MIPAS-B and LPMA balloon observations indicate that chlorine was still activated at lower altitudes, consistent with observed chemical ozone loss occurring between February and March and April. Large chemical ozone loss of more than 70 DU in the Arctic winter 1991–1992 as calculated in earlier studies is corroborated here
A new Geoengineering Model Intercomparison Project (GeoMIP) experiment designed for climate and chemistry models
No full textA new Geoengineering Model Intercomparison Project (GeoMIP) experiment “G4 specified
stratospheric aerosols” (short name: G4SSA) is proposed to investigate the impact of stratospheric
aerosol geoengineering on atmospheric composition, climate, and the environment. In contrast
to the earlier G4 GeoMIP experiment, which requires an emission of SO2 into the model, a
prescribed aerosol forcing file is provided to the community, to be consistently 5 applied to future
model experiments between 2020 and 2100. This stratospheric aerosol distribution, with a total burden
of about 2 Tg S has been derived using the ECHAM5-HAM microphysical model, based on a
continuous annual tropical emission of 8 Tg SO2. A ramp-up of geoengineering in 2020 and a rampdown
in 2070 over a period of two years are included in the distribution, while a background aerosol
10 burden should be used for the last 3 decades of the experiment. The performance of this experiment
using climate and chemistry models in a multi-model comparison framework will allow us to better
understand the significance of the impact of geoengineering and the abrupt termination after 50 years
on climate and composition of the atmosphere in a changing environment. The zonal and monthly
mean stratospheric aerosol input dataset is available at https://www2.acd.ucar.edu/gcm/geomip-g4-
15 specified-stratospheric-aerosol-data-set
Sensitivity of Methane Lifetime and Transport to Sulfate Geoengineering
No full textSulfate geoengineering, made by sustained injection of SO2 in the tropical lower stratosphere, may impact the abundance of tropospheric methane through several photochemical mechanisms affecting the tropospheric OH abundance and hence the methane lifetime. Changes of the stratospheric Brewer-Dobson circulation also play a role in the upper tropospheric CH4 transport. Three mechanisms lead to lower OH concentrations and a longer CH4 lifetime: (a) solar radiation scattering increases the planetary albedo and cools the surface, with a tropospheric water vapor decrease as a response to this cooling. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D). (c) The extra-tropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-upper troposphere, thus reducing the amount of NOx and tropospheric O3 production. On the other hand, the tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rates perturbation are strongly latitude dependent, producing a significant change of the pole-to-equator temperature gradient and mean zonal wind distribution, with a net increase of tropical upwelling. A stronger meridional component of the Brewer-Dobson circulation increases the extra-tropical stratosphere to troposphere transport of CH4 poorer air, resulting in less CH4 transported in the UTLS. The net effect on tropospheric OH may be positive or negative depending on the net result of different superimposed species perturbations in the UTLS, i.e. CH4 (negative), NOy and O3 (positive). Three climate-chemistry coupled models are used here to explore the above radiative, chemical and dynamical mechanisms affecting the methane lifetime (ULAQ-CCM, GEOSCCM, CCSM-CAM4). First results show that the CH4 lifetime may become significantly longer (by about 10%) with a sustained injection of 2.5 Tg-S/yr started in year 2020, which implies an increase of tropospheric CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH4 changes (+0.1 W/m2 in the 2045)
Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)
No full textSulfate geoengineering (SG), made by sustained injection of SO2 in the
tropical lower stratosphere, may impact the CH4 abundance through several
photochemical mechanisms affecting tropospheric OH and hence the methane
lifetime. (a) The reflection of incoming solar radiation increases the
planetary albedo and cools the surface, with a tropospheric H2O decrease.
(b) The tropospheric UV budget is upset by the additional aerosol scattering
and stratospheric ozone changes: the net effect is meridionally not uniform,
with a net decrease in the tropics, thus producing less tropospheric
O(1D). (c) The extratropical downwelling motion from the lower
stratosphere tends to increase the sulfate aerosol surface area density
available for heterogeneous chemical reactions in the mid-to-upper troposphere,
thus reducing the amount of NOx and O3 production. (d) The tropical
lower stratosphere is warmed by solar and planetary radiation absorption by
the aerosols. The heating rate perturbation is highly latitude dependent,
producing a stronger meridional component of the Brewer–Dobson circulation.
The net effect on tropospheric OH due to the enhanced
stratosphere–troposphere exchange may be positive or negative depending on
the net result of different superimposed species perturbations (CH4,
NOy, O3, SO4) in the extratropical upper troposphere and lower
stratosphere (UTLS). In addition, the atmospheric stabilization resulting
from the tropospheric cooling and lower stratospheric warming favors an
additional decrease of the UTLS extratropical CH4 by lowering the
horizontal eddy mixing. Two climate–chemistry coupled models are used to
explore the above radiative, chemical and dynamical mechanisms affecting
CH4 transport and lifetime (ULAQ-CCM and GEOSCCM). The CH4 lifetime may
become significantly longer (by approximately 16 %) with a sustained
injection of 8 Tg-SO2 yr−1 starting in the year 2020, which implies an increase of tropospheric
CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate
geoengineering due to CH4 changes (+0.10 W m−2 in the 2040–2049
decade and +0.15 W m−2 in the 2060–2069 decade)
Stratospheric Ozone Response to Sulfate Geoengineering: Results from the Geoengineering Model Intercomparison Project (GeoMIP)
No full textGeoengineering with stratospheric sulfate aerosols has been proposed as a means of temporarily cooling the planet, alleviating some of the side effects of anthropogenic CO2 emissions. However, one of the known side effects of stratospheric injections of sulfate aerosols under present-day conditions is a general decrease in ozone concentrations mainly via changes in photolysis rates, tropical upwelling of ozone-poor air, and an increase in available surfaces for heterogeneous chemistry. Here we present the effects that increased amounts of sulfate aerosol have on stratospheric meteorology and/or ozone concentrations, as simulated by two general circulation models and two coupled chemistry-climate models within the experiments G3 and G4 of the Geoengineering Model Intercomparison Project (GeoMIP). On average, the models simulate in G4 a factor of 20-40 increase in sulfate aerosol surface area density at 50 hPa in the tropics with respect to unperturbed background conditions and a factor of 3-10 increase at mid- and high latitudes, similar to conditions a year after the Mt. Pinatubo eruption. The net effect on ozone concentrations during the central decade of the experiment (2040-2049) is a decrease in globally averaged ozone by 1.1-2.1 DU. Enhanced heterogeneous chemistry on sulfate aerosols leads to an ozone increase in low and mid-latitudes, whereas enhanced heterogeneous reactions in polar regions (both on sulfate and polar stratospheric cloud particles) and increased tropical upwelling lead to a reduction of stratospheric ozone. The increase in UV-B radiation at the surface due to ozone depletion is offset by the screening due to the aerosols in the tropics and mid-latitudes, while in polar regions the UV-B radiation is increased by 5% on average, with 12% peak increases during springtime. The contribution of ozone changes to the tropopause radiative forcing during 2040-2049 is found to be less than -0.1 W m-2 in all the experiments. After 2050, because of decreasing ClOx concentrations, the suppression of the NOx cycle becomes more important than destruction of ozone by ClOx, causing an increase in total stratospheric ozone
Reply to comment by Rolf Müller and Simone Tilmes on ‘‘Middle atmospheric O3, CO, N2O, HNO3, and temperature profiles during the warm Arctic winter 2001–2002’’
No full textReply to comment by Rolf Müller and Simone Tilmes on "Middle atmospheric O3, CO, N2O, HNO3, and temperature profiles during the warm Arctic winter 2001–2002"[1] Muscari et al. [2007] (hereafter referred to as M07) analyzed Arctic winter stratospheric conditions for 2001–2002 by means of ground-based measurements of stratospheric
trace gases and temperature from Thule Air Base, Greenland (76.5°N, 68.7°W). The paper characterized stratospheric air masses observed over Thule from 20 January to
5 March 2002. Topics that were discussed included: the passage of both the polar vortex and the Aleutian high over Thule, with significant changes in ozone mixing ratio and
temperature values; variations of measured O3 total column; vertical descent of air masses observed by means of CO measurements; observations of "ozone pockets" [Manney
et al., 1995]; the correlation between illumination fraction and ozone mixing ratio at 900 K, indicating the relative significance of dynamics and photochemistry on ozone concentration at this altitude; the complete absence of polar stratospheric clouds, as concurrently monitored with a lidar system at Thule; and a qualitative (not quantitative) estimation of local ozone deficiency by means of N2O/O3 correlations.
Müller and Tilmes [2008] (hereafter referred to as MT08) question the significant ozone deficiencies reported by M07 inside the vortex, which, as also pointed out by M07, are difficult to explain by heterogeneous chemistry during the warm winter 2001–2002. Nonetheless, M07 did speculate that heterogeneous activation of halogen compounds
during mid-December and early January could have been the origin of the substantial ozone deficiency observed at the end of January/beginning of February in the small
portion of the vortex core sampled by the Ground-Based Millimeter-Wave Spectrometer (GBMS). MT08 question this claim, as it "cannot be reconciled with the current
understanding of halogen driven chemical ozone destruction in the Arctic." They suggest flaws in the N2O selection criteria used by M07 in order to identify intravortex N2O/O3 correlations, arising from their contention that GBMS measurements of N2O do not have the necessary spatial resolution needed for the task. MT08 favor instead the use of Potential Vorticity (PV) fields from European Centre Medium-Range Weather Forecasts (ECMWF) analyses.
[2] As a result of the criticism of MT08, we have looked at N2O/O3 correlations from independent measurements carried out by the Odin Sub-Millimeter Radiometer (Odin/SMR) [Murtagh et al., 2002] and have also reprocessed the GBMS O3 measurements using a different deconvolution technique. The GBMS O3 reanalysis furnishes a significantly
smaller qualitative estimate of local ozone loss (here and in the following we use "ozone loss" specifically to indicate an ozone deficiency due to heterogeneous activation of
halogen compounds) and is consistent with the Odin/SMR data (section 2). This has resulted in a corrected and enriched version of Figure 9a of M07 (see Figure 2 in section 2).
Although we value the comments of MT08 which prompted us to reanalyze GBMS ozone data, correcting and improving Figure 9 of M07 and the related discussion, we do reject some of the comments of MT08 concerning the N2O
selection criteria used by M07, and reiterate the choice of GBMS N2O measurements rather than ECMWF PV values to separate air masses located inside, outside, or at the edge
of the polar vortex (section 3). Furthermore, we stress that the use of N2O/O3 correlation curves to determine ozone loss inside the vortex, in particular near its edge (a region
often called "the outer vortex"), can indeed cause an overestimation of local ozone loss near the vortex edge region and possibly also an overestimation of the vortex averaged loss (section 4).PublishedD183041.8. Osservazioni di geofisica ambientaleJCR Journalreserve
U.S. Global Change Research Program National Climate Assessment Global Change Information System
No full textThe program: a) Coordinates Federal research to better understand and prepare the nation for global change. b) Priori4zes and supports cutting edge scientific work in global change. c) Assesses the state of scientific knowledge and the Nation s readiness to respond to global change. d) Communicates research findings to inform, educate, and engage the global community
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