313 research outputs found
Upper tropospheric ice sensitivity to sulfate geoengineering
No full textAside from the direct surface cooling sulfate geoengineering (SG) would produce, the investigation on possible sideeffects
of this method is still ongoing, as for instance on upper tropospheric cirrus cloudiness. Goal of the present study is to
better understand the SG thermo-dynamical effects on the homogeneous freezing ice formation process. This is done by comparing
SG model simulations against a RCP4.5 reference case: in one case the aerosol-driven surface cooling is included and
coupled to the 5 stratospheric warming resulting from aerosol absorption of longwave radiation. In a second SG perturbed case,
surface temperatures are kept unchanged with respect to the reference RCP4.5 case. Surface cooling and lower stratospheric
warming, together, tend to stabilize the atmosphere, thus decreasing turbulence and water vapor updraft velocities (-10% in
our modeling study). The net effect is an induced cirrus thinning, which may then produce a significant indirect negative radiative
forcing (RF). This would go in the same direction as the direct effect of solar radiation scattering by the aerosols, thus
10 influencing the amount of sulfur needed to counteract the positive RF due to greenhouse gases. In our study, given a 8 Tg-SO2
equatorial injection in the lower stratosphere, an all-sky net tropopause RF of -2.13 W/m2 is calculated, of which -0.96 W/m2
(45%) from the indirect effect on cirrus thinning (7.5% reduction in ice optical depth). When the surface cooling is ignored, the
ice optical depth reduction is lowered to 5%, with an all-sky net tropopause RF of -1.45 W/m2, of which -0.21 W/m2 (14%)
from cirrus thinning. Relatively to the clear-sky net tropopause RF due to SG aerosols (-2.06 W/m2), the cumulative effect of
15 background clouds and cirrus thinning accounts for -0.07 W/m2, due to close compensation of large positive shortwave (+1.85
W/m2) and negative longwave adjustments (-1.92 W/m2). When the surface cooling is ignored, the net cloud adjustment becomes
+0.71 W/m2, with the shortwave contribution (+1.97 W/m2) significantly larger in magnitude than the longwave one
(-1.26 W/m2). This highlights the importance of including all dynamical feedbacks of SG aerosols
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)
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
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
Assessing GFDL‐ESM4.1 Climate Responses to a Stratospheric Aerosol Injection Strategy Intended to Avoid Overshoot 2.0°C Warming
No full textAbstract In this work, we apply the GFDL Earth System Model (GFDL‐ESM4.1) to explore the climate responses to a stratospheric aerosol injection (SAI) scenario that aims to restrict global warming to 2.0°C above pre‐industrial levels (1850–1900) under the CMIP6 overshoot scenario (SSP5‐34‐OS). Simulations of this SAI scenario with the CESM Whole Atmosphere Community Climate Model (CESM2‐WACCM6) showed nearly unchanged interhemispheric and pole‐to‐Equator surface temperature gradients relative to present‐day conditions around 2020, and reduced global impacts, such as heatwaves, sea ice melting, and shifting precipitation patterns (Tilmes et al., 2020, https://doi.org/10.5194/esd‐11‐579‐2020). However, model structural uncertainties can lead to varying climate projections under the same forcing. Implementing identical stratospheric aerosol radiative properties in GFDL‐ESM4.1, which has a much lower Effective Climate Sensitivity compared to CESM2‐WACCM6, resulted in a decrease in global‐mean surface temperature by more than 1.5°C and a corresponding reduction in precipitation responses. Two major reasons contribute to the different temperature response between the two models: first, GFDL‐ESM4.1 has less warming in the SSP534‐OS scenario; second, GFDL‐ESM4.1 has shown more pronounced cooling in response to the same stratospheric AOD perturbation. Notably, the Southern Hemisphere experiences substantial cooling compared to the Northern Hemisphere, accompanied by a northward shift of the Intertropical Convergence Zone (ITCZ). Furthermore, our analysis reveals that spatially heterogeneous forcing within the SAI scenario results in diverse climate feedback parameters in the GFDL‐ESM4.1 model, through varying surface warming/cooling patterns. This research highlights the importance of considering model structural uncertainties and forcing spatial patterns for a comprehensive evaluation of future scenarios and geoengineering strategies
Chemical Ozone Loss in the Arctic Polar Stratosphere : an analysis of twelve years of satellite observations
No full textIn this thesis, the chemical ozone loss in the Arctic stratosphere was investigated for twelve years between 1991-92 and 2002-03. The accumulated local ozone loss and the column ozone loss were consistently derived using the ozone-tracer correlation (TRAC) technique. This technique considers the relation between ozone and a long-lived tracer during the lifetime of the polar vortex. Results are presented on the basis of observations obtained from two solar occultation satellite instruments: ILAS (Improved Limb Atmospheric Spectrometer) aboard the ADEOS satellite (Advanced Earth Observing Satellite) and HALDE (Halogen Occultation Experiment) aboard the UARS satellite (Upper Atmosphere Research Satellite). The HALDE observations used in the present work have been available since October 1991. The instrument made measurements during a period of a few days every two or three months in high northern latitudes during the entire period between 1991 and 2003. The ILAS instrument performed mear surements continuously from November 1996 to June 1997 in the high latitude region of both hemispheres. In the present work, the TRAC method was confirmed against criticism raised in the past. The improved and extended method permits both a reduction and a better quantification of uncertainties. New procedures implemented in the method allow the ozone loss for the winter to be calculated, in case where no results could have been derived in the past. Therefore, a consistent analysis is possible for the twelve winters. An intensive analysis of chemical ozone loss is performed considering as an example the winter 1996-97, for which measurements from both HALDE and ILAS are available. The ILAS observations allow a detailed analysis of the temporal evolution of the ozone-tracer correlation inside the polar vortex for the first time and in particular of the development of the early vortex. Especially the influence of mixing between vortex air and air from outside the vortex is discussed. The evolution of significant PSC-related chemical ozone loss can be followed over the entire lifetime of the vortex, from mid-February to May 1997 from ILAS observations. HALDE measurements are available between March and May 1997. Partly large differenced between the two data sets are analysed. Both data sets consistently show a distinct inhomogeneity in the derived ozone loss inside the vortex in spring 1997, which is a specific feature in comparison to the other observed winters between 1991-92 and 2002-03. During these twelve winters the ozone loss was consistently derived mainly on the basis of HALDE observations. With the use of the ozone-tracer [...
Chemical ozone loss in the arctic polar stratosphere derived from satellite observations
No full textIn dieser Arbeit wurde der chemische Ozonverlust in der arktischen Stratosphäre über elf Jahre hinweg, zwischen 1991 und 2002, mit Hilfe der so genannten "Ozon-Tracer Korrelationstechnik" (TRAC), untersucht. Bei dieser Methode werden Korrelationen zwischen Ozon und langlebigen Spurenstoffen im Verlauf des Winters im Polarwirbels beobachtet und so der jährliche akkumulierte Ozonverlust berechnet. Die Ergebnisse dieser Arbeit basieren im wesentlichen auf Messdaten der Satelliteninstrumente: HALOE (Halogen Occultation Experiment) auf UARS (Upper Atmosphere Research Satellite) und ILAS (Improved Limb Atmospheric Spectrometer) Instrument auf ADEOS (Advanced Earth Observing Satellite). Das HALOE Instrument misst seit Oktober 1991 kontinuierlich alle zwei bis drei Monate für einige Tage in höheren nördlichen Breiten. ILAS lieferte ausschließlich für den Winter 1996-97 Messungen, die über sieben Monate hinweg in hohen Breiten aufgenommen wurden. Aufgrund der eingeführten Erweiterungen und Verbesserungen der Methode in dieser Arbeit, konnte die Methode anhand einer detaillierten Studie für den Winter 1996-97 validiert werden. Die ILAS Messreihe wurde dazu verwendet, erstmals die Untersuchung der zeitlichen Entwicklung von Ozon-Tracer Korrelationen kontinuierlich für die gesamte Lebensdauer des Polarwirbels durchzuführen. Dabei wurden auch Korrelationen während der Bildung des Wirbels untersucht und im Besonderen mögliche Mischungsvorgänge zwischen Wirbelluft und Luftmassen außerhalb des Wirbels. Ausserdem wurde ein Vergleich der Ergebnisse von ILAS und HALOE Messdaten durchgeführt und Unterschiede in den Ergebnissen tiefgreifend analysiert. Basierend auf HALOE Messungen konnte die erweiterte TRAC Methode über elf Jahren hinweg angewendet werden. Damit war erstmals eine konsistente Analyse von Ozonverlust und Chloraktivierung über diesen Zeitraum möglich. Die Erweiterungen führten zu einer Verringerung und genauen Quantifizierung von Unsicherheiten der Ergebnisse. Ein deutlicher Zusammenhang zwischen meteorologischen Bedingungen, Chloraktivierung und dem chemischen Ozonverlust wurde deutlich. Weiterhin zeigte sich eine Abhängigkeit zwischen den meteorologischen Bedingungen und der Homogenität des Ozonverlustes innerhalb eines Winters, sowie der mögliche Einfluss von horizontaler Mischung auf Luftmassen in einem schwach ausgeprägten Polarwirbel. In dieser Arbeit wurde eine positive Korrelation zwischen den über die gesamte Lebensdauer des Wirbels auftretenden möglichen PSC-Flächen und den akkumulierten Ozonverlusten für die elf untersuchten Jahre deutlich. Es konnte darüber hinaus gezeigt werden, dass der Ozonverlust von deutlich mehr Einflüssen als nur von der Fläche möglichen PSC Auftretens bestimmt wird, sondern zum Beispiel von der Stärke der Sonneneinstrahlung abhängt. Außerdem lassen sich Auswirkungen von Vulkanausbrüchen, wie zum Beispiel im Jahr 1991 der des Mount Pinatubo, identifizieren
Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer
No full text© 2020. American Geophysical Union. The authors thank the reviewers for their comments and suggestions. The authors acknowledge the constructive discussion with scientists at the Atmospheric Chemistry Observations and Modeling Lab at NCAR, especially Bill Randel, Laura Pan, and Mijeong Park at the early stage of this work. Y. W. would like to thank Li Song, Joowan Kim, and Walter Robinson for helpful discussions. The computations were carried out with high-performance computing support provided by NCAR's Computational and Information Systems Laboratory, which is sponsored by the National Science Foundation (NSF). The data produced for and analyzed in this paper are available through the IRI/LDEO Climate Data Library (http://kage.ldeo.columbia.edu:81/SOURCES/.LDEO/.ClimateGroup/.PROJECTS/.PublicationsData/.Wu_ etal_JGR_2019). Y. W. and X. W. are supported by NSF Award AGS-1802248. M. A. acknowledges funding from the Program Atracción de Talento Comunidad de Madrid (2016-T2/AMB-1405).This study identifies the fast (i.e., ∼ days–weeks) transport pathways that connect the Northern Hemisphere surface to the upper troposphere and lower stratosphere (UTLS) during northern summer by integrating a large (90 member) ensemble of Boundary Impulse Response tracers in the Whole Atmosphere Community Climate Model version 5. We show that there is a fast transport pathway that occurs over the southern slope of the Tibetan Plateau, northern India, the Arabian Sea, and Saudi Arabia; furthermore, we show that during July this pathway connects the Northern Hemisphere surface to the UTLS on a modal time scale of 5–10 days. A less efficient transport pathway is also identified over the western Pacific. A detailed budget analysis reveals that, while convective processes are responsible for transport to 200–300 hPa, the resolved dynamics, specifically the vertical eddy flux, dominate at 100–150 hPa. Transport variations are analyzed on weekly, monthly, and interannual time scales and are largely related to differences in the resolved dynamics in the UTLS.National Science Foundation (NSF)Comunidad de MadridDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu
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