Effects of the PDO Phase on the Tropical Belt Width

Recent studies have shown that the tropical belt (TB) has progressively expanded since at least the late 1970s. This trend has been largely attributed to the radiative forcing due to greenhouse gas (GHG) increase and stratospheric ozone depletion, even if an influence of sea surface temperature (SST) anomalies has been also suggested. The impact of the Pacific decadal oscillation (PDO) on the TB width is investigated in this work. The study is performed by using both Atmospheric Model Intercomparison Project (AMIP) and idealized simulations, produced by the NCAR Community Atmosphere Model, version 3 (CAM3) GCM and reanalysis data [40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), ERA-Interim, and Modern-Era Retrospective Analysis for Research and Applications (MERRA)]. Reanalyses show that a switch of the PDO from a positive to a negative phase can lead to a significant TB expansion during the equinoxes. This effect, indicating a possible PDO contribution to the widening that characterized the TB width during the last decades, is not correctly reproduced by model simulations. Deficiencies in the sensitivity of model-simulated convective processes to SST anomalies are suggested as a possible cause of the TB widening underestimation.

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Exploring the uncertainties in the aviation soot–cirrus effect

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-17267-2021 ◽

2021 ◽

Vol 21 (23) ◽

pp. 17267-17289

Author(s):

Mattia Righi ◽

Johannes Hendricks ◽

Christof Gerhard Beer

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Internal Variability ◽

Reanalysis Data ◽

Ice Nucleation ◽

Cirrus Clouds ◽

Model Studies ◽

Model Dynamics ◽

Analogous Model ◽

The Impact

Abstract. A global aerosol–climate model, including a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to assess the uncertainties in this effect related to (i) the assumptions on the ice nucleation abilities of aviation soot, (ii) the representation of vertical updrafts in the model, and (iii) the use of reanalysis data to relax the model dynamics (the so-called nudging technique). Based on the results of the model simulations, a radiative forcing from the aviation soot–cirrus effect in the range of −35 to 13 mW m−2 is quantified, depending on the assumed critical saturation ratio for ice nucleation and active fraction of aviation soot but with a confidence level below 95 % in several cases. Simple idealized experiments with prescribed vertical velocities further show that the uncertainties on this aspect of the model dynamics are critical for the investigated effect and could potentially add a factor of about 2 of further uncertainty to the model estimates of the resulting radiative forcing. The use of the nudging technique to relax model dynamics is proved essential in order to identify a statistically significant signal from the model internal variability, while simulations performed in free-running mode and with prescribed sea-surface temperatures and sea-ice concentrations are shown to be unable to provide robust estimates of the investigated effect. A comparison with analogous model studies on the aviation soot–cirrus effect show a very large model diversity, with a conspicuous lack of consensus across the various estimates, which points to the need for more in-depth analyses on the roots of such discrepancies.

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Impact of biogenic very short-lived bromine on the Antarctic ozone hole during the 21st century

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-1673-2017 ◽

2017 ◽

Vol 17 (3) ◽

pp. 1673-1688 ◽

Cited By ~ 20

Author(s):

Rafael P. Fernandez ◽

Douglas E. Kinnison ◽

Jean-Francois Lamarque ◽

Simone Tilmes ◽

Alfonso Saiz-Lopez

Keyword(s):

21St Century ◽

Stratospheric Ozone ◽

Montreal Protocol ◽

Ozone Hole ◽

Community Atmosphere Model ◽

Hole Area ◽

Photochemical Decomposition ◽

Antarctic Ozone ◽

The Impact ◽

Antarctic Ozone Hole

Abstract. Active bromine released from the photochemical decomposition of biogenic very short-lived bromocarbons (VSLBr) enhances stratospheric ozone depletion. Based on a dual set of 1960–2100 coupled chemistry–climate simulations (i.e. with and without VSLBr), we show that the maximum Antarctic ozone hole depletion increases by up to 14 % when natural VSLBr are considered, which is in better agreement with ozone observations. The impact of the additional 5 pptv VSLBr on Antarctic ozone is most evident in the periphery of the ozone hole, producing an expansion of the ozone hole area of ∼ 5 million km2, which is equivalent in magnitude to the recently estimated Antarctic ozone healing due to the implementation of the Montreal Protocol. We find that the inclusion of VSLBr in CAM-Chem (Community Atmosphere Model with Chemistry, version 4.0) does not introduce a significant delay of the modelled ozone return date to 1980 October levels, but instead affects the depth and duration of the simulated ozone hole. Our analysis further shows that total bromine-catalysed ozone destruction in the lower stratosphere surpasses that of chlorine by the year 2070 and indicates that natural VSLBr chemistry would dominate Antarctic ozone seasonality before the end of the 21st century. This work suggests a large influence of biogenic bromine on the future Antarctic ozone layer.

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Investigation of strongly enhanced methane Part I: Chemical feedbacks and rapid adjustments.

10.5194/egusphere-egu2020-9786 ◽

2020 ◽

Author(s):

Franziska Winterstein ◽

Patrick Jöckel ◽

Martin Dameris ◽

Michael Ponater ◽

Fabian Tanalski ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Model ◽

Numerical Study ◽

Stratospheric Ozone ◽

Lower Boundary ◽

Tropospheric Chemistry ◽

Substantial Part ◽

Mixing Ratios ◽

The Impact

Methane (CH4) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities and currently on a sharp rise. We present a study with numerical simulations using a Chemistry-Climate-Model (CCM), which are performed to assess possible consequences of strongly enhanced CH4 concentrations in the Earth's atmosphere for the climate.Our analysis includes experiments with 2xCH4 and 5xCH4 present day (2010) lower boundary mixing ratios using the CCM EMAC. The simulations are conducted with prescribed oceanic conditions, mimicking present day tropospheric temperatures as its changes are largely suppressed. By doing so we are able to investigate the quasi-instantaneous chemical impact on the atmosphere. We find that the massive increase in CH4 strongly influences the tropospheric chemistry by reducing the OH abundance and thereby extending the tropospheric CH4 lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O3) column increases overall, but SWV induced stratospheric cooling also leads to enhanced ozone depletion in the Antarctic lower stratosphere. Regional&#160; patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport&#160; towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH4 experiment to be 0.69 W m-2 and for the 5xCH4 experiment to be 1.79 W m-2. A substantial part of the RI is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates and is for the first time splitted and spatially asigned to its chemical contributors.This numerical study using a CCM with prescibed oceanic conditions shows the rapid responses to significantly enhanced CH4 mixing ratios, which is the first step towards investigating the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

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Three-dimensional visualization of ensemble weather forecasts – Part 1: The visualization tool Met.3D (version 1.0)

Geoscientific Model Development ◽

10.5194/gmd-8-2329-2015 ◽

2015 ◽

Vol 8 (7) ◽

pp. 2329-2353 ◽

Cited By ~ 17

Author(s):

M. Rautenhaus ◽

M. Kern ◽

A. Schäfler ◽

R. Westermann

Keyword(s):

Visual Analysis ◽

Weather Forecasting ◽

Spatial Perception ◽

Three Dimensional ◽

Atmospheric Model ◽

Weather Forecasts ◽

Research And Teaching ◽

Grid Topology ◽

Ensemble Visualization ◽

The Impact

Abstract. We present "Met.3D", a new open-source tool for the interactive three-dimensional (3-D) visualization of numerical ensemble weather predictions. The tool has been developed to support weather forecasting during aircraft-based atmospheric field campaigns; however, it is applicable to further forecasting, research and teaching activities. Our work approaches challenging topics related to the visual analysis of numerical atmospheric model output – 3-D visualization, ensemble visualization and how both can be used in a meaningful way suited to weather forecasting. Met.3D builds a bridge from proven 2-D visualization methods commonly used in meteorology to 3-D visualization by combining both visualization types in a 3-D context. We address the issue of spatial perception in the 3-D view and present approaches to using the ensemble to allow the user to assess forecast uncertainty. Interactivity is key to our approach. Met.3D uses modern graphics technology to achieve interactive visualization on standard consumer hardware. The tool supports forecast data from the European Centre for Medium Range Weather Forecasts (ECMWF) and can operate directly on ECMWF hybrid sigma-pressure level grids. We describe the employed visualization algorithms, and analyse the impact of the ECMWF grid topology on computing 3-D ensemble statistical quantities. Our techniques are demonstrated with examples from the T-NAWDEX-Falcon 2012 (THORPEX – North Atlantic Waveguide and Downstream Impact Experiment) campaign.

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Organic pollutants from tropical peatland fires: regional influences and its impact on lower stratospheric ozone

10.5194/acp-2020-1130 ◽

2020 ◽

Author(s):

Simon Rosanka ◽

Bruno Franco ◽

Lieven Clarisse ◽

Pierre-François Coheur ◽

Andreas Wahner ◽

...

Keyword(s):

Biomass Burning ◽

El Niño ◽

El Nino ◽

Stratospheric Ozone ◽

Lower Troposphere ◽

Atmospheric Model ◽

Chemical Production ◽

Global Models ◽

Upward Transport ◽

The Impact

Abstract. The particularly strong dry season in Indonesia in 2015, caused by an exceptional strong El Niño, led to severe peatland fires resulting in high volatile organic compound (VOC) biomass burning emissions. At the same time, the developing Asian monsoon anticyclone (ASMA) and the general upward transport in the intertropical convergence zone (ITCZ) efficiently transported the resulting primary and secondary pollutants to the upper troposphere/lower stratosphere (UTLS). In this study, we assess the importance of these VOC emissions for the composition of the lower troposphere and the UTLS, and we investigate the effect of in-cloud oxygenated VOC (OVOC) oxidation during such a strong pollution event. This is achieved by performing multiple chemistry simulations using the global atmospheric model ECHAM/MESSy (EMAC). By comparing modelled columns of the biomass burning marker hydrogen cyanide (HCN) to spaceborne measurements from the Infrared Atmospheric Sounding Interferometer (IASI), we find that EMAC properly captures the exceptional strength of the Indonesian fires. In the lower troposphere, the increase in VOC levels is higher in Indonesia compared to other biomass burning regions. This has a direct impact on the oxidation capacity, resulting in the largest regional reduction in hydroxyl radicals (OH) and nitrogen oxides (NOx). Even though an increase in ozone (O3) is predicted close to the peatland fires, particular high concentrations of phenols lead to an O3 depletion in eastern Indonesia. By employing the detailed in-cloud OVOC oxidation scheme Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC), we find that the predicted changes are dampened and that by ignoring these processes, global models tend to overestimate the impact of such extreme pollution events. In the ASMA and the ITCZ, the upward transport leads to elevated VOC concentrations in the UTLS region, which results in a depletion of lower stratospheric O3. We find that this is caused by a high destruction of O3 by phenoxy radicals and by the increased formation of NOx reservoir species, which dampen the chemical production of O3. The Indonesian peatland fires regularly occur during El Niño years and contribute to the depletion of O3. In the time period from 2001 to 2016, we find that the lower stratospheric O3 is reduced by about 0.38 DU and contributes to about 25 % to the lower stratospheric O3 reduction observed by remote sensing. By not considering these processes, global models might not be able to reproduce this variability in lower stratospheric O3.

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Combined assimilation of IASI and MLS observations to constrain tropospheric and stratospheric ozone in a global chemical transport model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-21455-2013 ◽

2013 ◽

Vol 13 (8) ◽

pp. 21455-21505

Author(s):

E. Emili ◽

B. Barret ◽

S. Massart ◽

E. Le Flochmoen ◽

A. Piacentini ◽

...

Keyword(s):

Tropospheric Ozone ◽

Radiative Forcing ◽

Transport Model ◽

Stratospheric Ozone ◽

Chemical Transport ◽

Free Troposphere ◽

Chemical Transport Model ◽

Ozone Monitoring Instrument ◽

Global Chemical Transport Model ◽

The Impact

Abstract. Accurate and temporally resolved fields of free-troposphere ozone are of major importance to quantify the intercontinental transport of pollution and the ozone radiative forcing. In this study we examine the impact of assimilating ozone observations from the Microwave Limb Sounder (MLS) and the Infrared Atmospheric Sounding Interferometer (IASI) in a global chemical transport model (MOdèle de Chimie Atmosphérique à Grande Échelle, MOCAGE). The assimilation of the two instruments is performed by means of a variational algorithm (4-D-VAR) and allows to constrain stratospheric and tropospheric ozone simultaneously. The analysis is first computed for the months of August and November 2008 and validated against ozone-sondes measurements to verify the presence of observations and model biases. It is found that the IASI Tropospheric Ozone Column (TOC, 1000–225 hPa) should be bias-corrected prior to assimilation and MLS lowermost level (215 hPa) excluded from the analysis. Furthermore, a longer analysis of 6 months (July–August 2008) showed that the combined assimilation of MLS and IASI is able to globally reduce the uncertainty (Root Mean Square Error, RMSE) of the modeled ozone columns from 30% to 15% in the Upper-Troposphere/Lower-Stratosphere (UTLS, 70–225 hPa) and from 25% to 20% in the free troposphere. The positive effect of assimilating IASI tropospheric observations is very significant at low latitudes (30° S–30° N), whereas it is not demonstrated at higher latitudes. Results are confirmed by a comparison with additional ozone datasets like the Measurements of OZone and wAter vapour by aIrbus in-service airCraft (MOZAIC) data, the Ozone Monitoring Instrument (OMI) total ozone columns and several high-altitude surface measurements. Finally, the analysis is found to be little sensitive to the assimilation parameters and the model chemical scheme, due to the high frequency of satellite observations compared to the average life-time of free-troposphere/low-stratosphere ozone.

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Implication of extreme atmospheric methane concentrations for chemistry-climate connections

10.5194/acp-2019-41 ◽

2019 ◽

Author(s):

Franziska Winterstein ◽

Fabian Tanalski ◽

Patrick Jöckel ◽

Martin Dameris ◽

Michael Ponater

Keyword(s):

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Model ◽

Numerical Study ◽

Stratospheric Ozone ◽

Tropospheric Chemistry ◽

Substantial Part ◽

Atmospheric Concentration ◽

Regional Patterns ◽

The Impact

Abstract. Methane (CH4) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities. In this study, numerical simulations with a chemistry-climate model (CCM) are performed aiming to assess possible consequences of significantly enhanced CH4 concentrations in the Earth's atmosphere for the climate. We analyze experiments with 2xCH4 and 5xCH4 present day (2010) mixing ratio and its quasi-instantaneous chemical impact on the atmosphere. The massive increase in CH4 strongly influences the tropospheric chemistry by reducing the hydroxyl radical (OH) abundance and thereby extending the CH4 lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O3) column increases overall, but SWV induced stratospheric cooling also leads to a enhanced ozone depletion in the Antarctic lower stratosphere. Regional patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH4 experiment to be 0.69 W/m2 and for the 5xCH4 experiment to be 1.79 W/m2. A substantial part of the RI is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates. To our knowledge this is the first numerical study using a CCM with respect to two/fivefold CH4 concentrations and it is therefore an overdue analysis as it emphasizes the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

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Role of Sea Surface Temperatures in Forcing Circulation Anomalies Driving U.S. Great Plains Pluvial Years

Journal of Climate ◽

10.1175/jcli-d-18-0726.1 ◽

2019 ◽

Vol 32 (20) ◽

pp. 7081-7100 ◽

Cited By ~ 1

Author(s):

Paul X. Flanagan ◽

Jeffrey B. Basara ◽

Jason C. Furtado ◽

Elinor R. Martin ◽

Xiangming Xiao

Keyword(s):

Great Plains ◽

Reanalysis Data ◽

Tropical Pacific ◽

Specific Pattern ◽

Sea Surface ◽

Northern Great Plains ◽

The Pacific ◽

Precipitation Anomalies ◽

Circulation Anomalies ◽

Sst Anomalies

Abstract In the U.S. Great Plains (GP), diagnosing precipitation variability is key in developing an understanding of the present and future availability of water in the region. Building on previous work investigating U.S. GP pluvial years, this study uses ERA twentieth century (ERA-20C) reanalysis data to investigate key circulation anomalies driving GP precipitation anomalies during a subset of GP pluvial years (called in this paper Pattern pluvial years). With previous research showing links between tropical Pacific sea surface temperature (SST) anomalies and GP climate variability, this study diagnoses the key circulation anomalies through an analysis of SSTs and their influence on the atmosphere. Results show that during Pattern southern Great Plains (SGP) pluvial years, central tropical Pacific SST anomalies are coincident with key atmospheric anomalies across the Pacific basin and North America. During northern Great Plains (NGP) Pattern pluvial years, no specific pattern of oceanic anomalies emerges that forces the circulation anomaly feature inherent in specific NGP pluvial years. Utilizing the results for SGP pluvial years, a conceptual model is developed detailing the identified pathway for the occurrence of circulation patterns that are favorable for pluvial years over the SGP. Overall, results from this study show the importance of the identified SGP atmospheric anomaly signal and the potential for predictability of such events.

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Exploring the uncertainties in the aviation soot-cirrus effect

10.5194/acp-2021-329 ◽

2021 ◽

Author(s):

Mattia Righi ◽

Johannes Hendricks ◽

Christof Gerhard Beer

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Internal Variability ◽

Reanalysis Data ◽

Ice Nucleation ◽

Cirrus Clouds ◽

Model Studies ◽

Model Dynamics ◽

Analogous Model ◽

The Impact

Abstract. A global aerosol-climate model, including a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to assess the uncertainties in this effect related to (i) the assumptions on the ice nucleation abilities of aviation soot; (ii) the representation of vertical updrafts in the model; and (iii) the use of reanalysis data to relax the model dynamics (the so-called nudging technique). Based on the results of the model simulations, a radiative forcing from the aviation soot-cirrus effect in the range of −35 mW m−2 to 13 mW m−2 is quantified, depending on the assumed critical saturation ratio for ice nucleation and active fraction of aviation soot, but with a confidence level below 95 % in several cases. Simple idealized experiments with prescribed vertical velocities further show that the uncertainties on this aspect of the model dynamics are critical for the investigated effect and could potentially add a factor of about two of further uncertainty to the model estimates of the resulting radiative forcing. The use of the nudging technique to relax model dynamics is proved essential in order to identify a statistically significant signal from the model internal variability, while simulations performed in free-running mode and with prescribed sea-surface temperatures and sea-ice concentrations are shown to be unable to provide robust estimates of the investigated effect. A comparison with analogous model studies on the aviation-soot cirrus effect show a very large model diversity, with a conspicuous lack of consensus across the various estimates, which points to the need for more in-depth analyses on the roots of such discrepancies.

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Radiative forcing of climate change from the Copernicus reanalysis of atmospheric composition

Earth System Science Data ◽

10.5194/essd-12-1649-2020 ◽

2020 ◽

Vol 12 (3) ◽

pp. 1649-1677 ◽

Cited By ~ 2

Author(s):

Nicolas Bellouin ◽

Will Davies ◽

Keith P. Shine ◽

Johannes Quaas ◽

Johannes Mülmenstädt ◽

...

Keyword(s):

Climate Change ◽

Carbon Dioxide ◽

Tropospheric Ozone ◽

Radiative Forcing ◽

Stratospheric Ozone ◽

Atmospheric Composition ◽

Global Average ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions ◽

The Impact

Abstract. Radiative forcing provides an important basis for understanding and predicting global climate changes, but its quantification has historically been done independently for different forcing agents, has involved observations to varying degrees, and studies have not always included a detailed analysis of uncertainties. The Copernicus Atmosphere Monitoring Service reanalysis is an optimal combination of modelling and observations of atmospheric composition. It provides a unique opportunity to rely on observations to quantify the monthly and spatially resolved global distributions of radiative forcing consistently for six of the largest forcing agents: carbon dioxide, methane, tropospheric ozone, stratospheric ozone, aerosol–radiation interactions, and aerosol–cloud interactions. These radiative-forcing estimates account for adjustments in stratospheric temperatures but do not account for rapid adjustments in the troposphere. On a global average and over the period 2003–2017, stratospherically adjusted radiative forcing of carbon dioxide has averaged +1.89 W m−2 (5 %–95 % confidence interval: 1.50 to 2.29 W m−2) relative to 1750 and increased at a rate of 18 % per decade. The corresponding values for methane are +0.46 (0.36 to 0.56) W m−2 and 4 % per decade but with a clear acceleration since 2007. Ozone radiative-forcing averages +0.32 (0 to 0.64) W m−2, almost entirely contributed by tropospheric ozone since stratospheric ozone radiative forcing is only +0.003 W m−2. Aerosol radiative-forcing averages −1.25 (−1.98 to −0.52) W m−2, with aerosol–radiation interactions contributing −0.56 W m−2 and aerosol–cloud interactions contributing −0.69 W m−2 to the global average. Both have been relatively stable since 2003. Taking the six forcing agents together, there is no indication of a sustained slowdown or acceleration in the rate of increase in anthropogenic radiative forcing over the period. These ongoing radiative-forcing estimates will monitor the impact on the Earth's energy budget of the dramatic emission reductions towards net-zero that are needed to limit surface temperature warming to the Paris Agreement temperature targets. Indeed, such impacts should be clearly manifested in radiative forcing before being clear in the temperature record. In addition, this radiative-forcing dataset can provide the input distributions needed by researchers involved in monitoring of climate change, detection and attribution, interannual to decadal prediction, and integrated assessment modelling. The data generated by this work are available at https://doi.org/10.24380/ads.1hj3y896 (Bellouin et al., 2020b).

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