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Mineral dust contributes significantly to the global atmospheric aerosol burden and is an important climate factor. Its model-based description of the atmospheric life cycle and impacts largely depends on an accurate parameterization of dust emissions. The large variability of near-source dust distribution in current forecast and aerosol-climate models is an indication that accurate simulation of dust emissions remains problematic. The occurrence and strength of dust emissions depends on both surface properties and surface winds. While satellite remote sensing offers great potential for determining relevant surface properties such as surface roughness and land use, model simulations of surface winds remain problematic in resolving strong wind events that occur on small spatial and temporal scales. The peak wind speeds of such events have the potential to cause strong dust emissions, but are unlikely to be captured in model simulations with parameterized convection. Advances in high-resolution convection atmospheric modelling are a major opportunity for overcoming these limitations. Convection permitting simulations and multi-scale model approaches become feasible with the new ICON model framework which has been developed jointly by the German Weather Service (DWD) and the Max Planck Institute for Meteorology in Hamburg. Results of dust simulations with the HAM aerosol model coupled to ICON will be presented. The new model system will advance the flexibility and possibilities to work on understanding the role of mineral dust aerosol and their interactions within the changing climate. The new model system will improve the ability to understand the role of mineral dust aerosols and their interactions with the climate system.

The uncertain climate impact of extreme wildfires not only unfolds because of the emitted carbon dioxide, but also due to smoke aerosol. In the present study, we address the global impact caused by the exceptionally strong and high-reaching smoke emissions from the Australian wildfires using simulations with a global aerosol-climate model. We show that the absorption of solar radiation by the black carbon contained in the emitted smoke led to a shortwave radiative forcing of more than +5 W m−2 in the southern mid-latitudes of the lower stratosphere. Subsequent adjustment processes in the stratosphere slowed down the diabatically driven meridional circulation, thus redistributing the heating perturbation on a global scale. As a result of these stratospheric adjustments, a positive temperature perturbation developed in both hemispheres leading to additional longwave radiation emitted back to space. The changes in the lower stratosphere also affected the upper troposphere through a thermodynamic downward coupling mechanism in the model. Subsequently, increased temperatures were also obtained in the upper troposphere, causing a decrease in relative humidity, cirrus amount, and the ice water path. As a result, surface precipitation also decreased, which was accompanied by a weakening of the tropospheric circulation due to the given energetic constraints. In general, it appears that the radiative effects of smoke from single extreme wildfire events can lead to global impacts that affect the interplay of tropospheric and stratospheric cycles in complex ways. This emphasizes that future changes in extreme wildfires need to be included in projections of aerosol radiative forcing., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

More than 1 Tg smoke aerosol was emitted into the atmosphere by the exceptional 2019-2020 southeastern Australian wildfires. Triggered by the extreme fire heat, several deep pyroconvective events carried the smoke directly into the stratosphere. Once there, smoke aerosol remained airborne considerably longer than in lower atmospheric layers. The thick plumes traveled eastward, thereby being distributed across the high and mid-latitudes in the Southern Hemisphere, enhancing the atmospheric opacity. Due to the increased atmospheric lifetime of the smoke plume, its radiative effect increased compared to smoke that remains in lower altitudes. Global models describing aerosol-climate impacts lack adequate descriptions of the emission height of aerosols from intense wildfires. Here, we demonstrate, by a combination of aerosol-climate modeling and lidar observations, the importance of the representation of those high-altitude fire smoke layers for estimating the atmospheric energy budget. Through observation-based input into the simulations, the Australian wildfire emissions by pyroconvection are explicitly prescribed to the lower stratosphere in different scenarios. Based on our simulations, the 2019-2020 Australian fires caused a significant top-of-atmosphere (TOA) hemispheric instantaneous direct radiative forcing signal that reached a magnitude comparable to the radiative forcing induced by anthropogenic absorbing aerosol. Up to +0.50Wm(-2) instantaneous direct radiative forcing was modeled at TOA, averaged for the Southern Hemisphere (+0.25Wm (-2) globally) from January to March 2020 under all-sky conditions. At the surface, on the other hand, an instantaneous solar radiative forcing of up to 0.81Wm(-2) was found for clear-sky conditions, with the respective estimates depending on the model configuration and subject to the model uncertainties in the smoke optical properties. Since extreme wildfires are expected to occur more frequently in the rapidly changing climate, our findings suggest that high-altitude wildfire plumes must be adequately considered in climate projections in order to obtain reasonable estimates of atmospheric energy budget changes., Atmospheric Chemistry and Physics, 22 (15), ISSN:1680-7375, ISSN:1680-7367

The oxidation of dimethyl sulfide (DMS) is key for the natural sulfate aerosol formation and its climate impact. Multiphase chemistry is an important oxidation pathway but neglected in current chemistry���climate models. Here, the DMS chemistry in the aerosol���chemistry���climate model ECHAM���HAMMOZ is extended to include multiphase methane sulfonic acid (MSA) formation in deliquesced aerosol particles, parameterized by reactive uptake. First simulations agree well with observed gas���phase MSA concentrations. The implemented formation pathways are quantified to contribute up to 60% to the sulfate aerosol burden over the Southern Ocean and Arctic/Antarctic regions. While globally the impact on the aerosol radiative forcing almost levels off, a significantly more positive solar radiative forcing of up to +0.1 W m���2 is computed in the Arctic (>60��N). The findings imply the need of both further laboratory and model studies on the atmospheric multiphase oxidation of DMS., Plain Language Summary: The emission of dimethyl sulfide (DMS) represents the largest natural reduced sulfur source into the atmosphere. There, DMS can be oxidized to sulfur dioxide, sulfuric acid, or methane sulfonic acid modifying the radiative properties of aerosol particles and clouds. DMS oxidation is represented in chemistry���climate models by a limited number of very simplified reactions. Small changes in the parameter settings can have large effects, that's why these should be as accurate as possible. In this study, the DMS chemistry in ECHAM���HAMMOZ was upgraded. Sensitivity simulations show variations in the natural aerosol radiative forcing due to the different schemes tested in this study. Further laboratory and process studies with models are therefore essential., Key Points: Dimethyl sulfide (DMS) chemistry in chemistry���climate simulations extended by multiphase methane sulfonic acid (MSA) formation provides more realistic MSA gas���phase concentrations. Formation of MSA is very sensitive toward reactive uptake on deliquesced aerosol particles. In the Arctic, the extended DMS chemistry leads to a significantly less negative effective radiative forcing of sulfate aerosol., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Record wildfires affected Australia from December 2019 to early 2020. Massive plumes of fire pollutants were lifted into the upper troposphere and even into the stratosphere by pyro-convection triggered by the intense heat of the fires. Subsequently the smoke aerosol was transported over thousands of kilometres eastwards at above 20 km altitude as Lidar observations in South America and satellite imagery show. Space and ground-based remote sensing of aerosol optical thickness indicate a temporary substantial increase in aerosol loading over large parts of the Southern Hemisphere, which offset the usual hemispheric contrast in aerosol. In addition to the massive impact on air quality at Australia’s east coast, this had important effects on the hemisphere-wide radiation budget.We investigate the dispersal of the fire smoke aerosol and its radiative effects with the global aerosol-climate model ECHAM6.3-HAM2.3. Biomass burning emissions are prescribed by daily satellite-based estimates from the Global Fire Assimilation System (GFAS). As the horizontal model resolution is too coarse to explicitly resolve convection, the injection height of Australian fire smoke is set to heights between 5 and 15 km and varied in terms of sensitivity studies. The model results for late 2019 and early 2020 are evaluated with ground and satellite remote sensing measurements, as well as contrasted with smoke results for years with low Australian wildfire emissions. The sensitivity results show how the fire injection heights affect the evolution of the smoke plume but also what role radiatively induced self-lifting plays. According to the model, the 2019/20 Australian wildfires considerably perturbed the radiation budget of the Southern Hemisphere. Due to large transport heights relative to clouds and a long lifetime of smoke particles in the stratosphere, the solar irradiance at ground averaged from January to March 2020 decreased by more than 1 W m-2 for the Southern Hemisphere, which corresponds roughly to the short-term cooling caused by a large volcanic eruption, while the elevated smoke layers experienced significant absorptive heating.Considering the recent series of extreme wildfires globally and their probably further increasing occurance in a changing climate, these results indicate a need for larger attention to pyro-convection in global climate modelling.

The meridional circulation of the stratosphere, or Brewer-Dobson circulation (BDC), is projected to accelerate with increasing greenhouse gas (GHG) concentrations. The acceleration is typically quantified by changes in the tropical upward mass flux (Ftrop) across a given pressure surface. Simultaneously, models project a lifting of the entire atmospheric circulation in response to GHGs; notably, the tropopause rises about a kilometer over this century. In this study, it is shown that most of the BDC trend is associated with the rise in the circulation. Using a chemistry-climate model (CCM), Ftrop trends across 100 hPa are contrasted with those across the tropopause: while Ftrop at 100 hPa increases 1–2 %/decade, the mass flux entering the atmosphere above the tropopause actually decreases. Similar results are found for other CCMs, suggesting that changes in the BDC may better be described as an upward shift of the circulation, as opposed to an increase, with implications for the mechanism and stratosphere-troposphere exchange.

Using multidecadal simulations with the European Centre/Hamburg–Modular Earth Submodel System Atmospheric Chemistry (EMAC) model, the role of changing concentrations of ozone-depleting substances (ODSs) and greenhouse gases (GHGs) on Arctic springtime ozone was examined. The focus is on potential changes in the meteorological conditions relevant for Arctic ozone depletion. It is found that with rising GHG levels the lower Arctic stratosphere will cool significantly in early winter, while no significant temperature signal is identified later in winter or spring. A seasonal shift of the lowest polar minimum temperatures from late to early winter in the second part of the 21st century occurs. However, Arctic lower stratosphere temperatures do not seem to decline to new record minima. The future Arctic lower stratosphere vortex will have a longer lifetime, as a result of an earlier formation in autumn. No extended vortex persistence is found in spring due to enhanced dynamical warming by tropospheric wave forcing. Because of the dominant early winter cooling, largest accumulated polar stratospheric cloud (PSC) areas (APSC) are projected for the middle of the 21st century. A further increase of APSC toward the end of the 21st century is prevented by increased dynamical polar warming. EMAC suggests that in the near future, there is a chance of low Arctic springtime ozone in individual years; however, there is no indication of a formation of regular Arctic ozone holes. Toward the end of the 21st century, when ODSs will be close to the 1960 levels, further rising GHG levels will cause increased Arctic springtime ozone.

[1] Future changes in the occurrence rates of major stratospheric warmings (MSWs) have recently been identified in chemistry-climate model (CCM) simulations, but without reaching a consensus, potentially due to the competition of different forcings. We examine future variations in the occurrence rates of MSWs in transient and timeslice simulations of the ECHAM/MESSy atmospheric chemistry (EMAC) CCM, with a focus on the individual effect of different external factors. Although no statistically significant variation is found in the decadal-mean frequency of MSWs, a shift of their timing toward midwinter is detected in the future. The strengthening of the polar vortex in early winter is explained by recovering ozone levels following the future decrease in ozone-depleting substances. In midwinter, a stronger dynamical forcing associated with changes in tropical sea surface temperatures will lead to more MSWs, through a similar mechanism that explains the stratospheric response to El Nino-Southern Oscillation (ENSO).

Future projections of tropical total column ozone (TCO) are challenging, as its evolution is affected not only by the expected decline of ozone depleting substances but also by the uncertain increase of greenhouse gas (GHG) emissions. To assess the range of tropical TCO projections, we analyze simulations with a chemistry-climate model forced by three different GHG scenarios (Representative Concentration Pathway (RCP) 4.5, RCP6.0, and RCP8.5). We find that tropical TCO will be lower by the end of the 21st century compared to the 1960s in all scenarios with the largest decrease in the medium RCP6.0 scenario. Uncertainties of the projected TCO changes arise from the magnitude of stratospheric column decrease and tropospheric ozone increase which both strongly vary between the scenarios. In the three scenario simulations the stratospheric column decrease is not compensated by the increase in tropospheric ozone. The concomitant increase in harmful ultraviolet irradiance reaches up to 15% in specific regions in the RCP6.0 scenario.

Monthly averaged surface erythemal solar irradiance (UV-Ery) for local noon from 1960 to 2100 has been derived using radiative transfer calculations and projections of ozone, temperature and cloud change from 14 chemistry climate models (CCM), as part of the CCMVal-2 activity of SPARC. Our calculations show the influence of ozone depletion and recovery on erythemal irradiance. In addition, we investigate UV-Ery changes caused by climate change due to increasing greenhouse gas concentrations. The latter include effects of both stratospheric ozone and cloud changes. The derived estimates provide a global picture of the likely changes in erythemal irradiance during the 21st century. Uncertainties arise from the assumed scenarios, different parameterizations – particularly of cloud effects on UV-Ery – and the spread in the CCM projections. The calculations suggest that relative to 1980, annually mean UV-Ery in the 2090s will be on average ~12 % lower at high latitudes in both hemispheres, ~3 % lower at mid latitudes, and marginally higher (~1 %) in the tropics. The largest reduction (~16 %) is projected for Antarctica in October. Cloud effects are responsible for 2–3 % of the reduction in UV-Ery at high latitudes, but they slightly moderate it at mid-latitudes (~1 %). The year of return of erythemal irradiance to values of certain milestones (1965 and 1980) depends largely on the return of column ozone to the corresponding levels and is associated with large uncertainties mainly due to the spread of the model projections. The inclusion of cloud effects in the calculations has only a small effect of the return years. At mid and high latitudes, changes in clouds and stratospheric ozone transport by global circulation changes due to greenhouse gases will sustain the erythemal irradiance at levels below those in 1965, despite the removal of ozone depleting substances. At northern high latitudes (60°–90°), the projected decreases in cloud transmittance towards the end of the 21st century will reduce the yearly average surface erythemal irradiance by ~5 % with respect to the 1960s.

Previous research shows that blocking highs (BHs) influence wintertime polar stratospheric variability through the modulation of the climatological planetary waves (PWs) depending on the BH location. BHs over the Euro-Atlantic sector tend to enhance the upward PW propagation, and those over the northwestern Pacific Ocean tend to reduce it. Future changes are examined in the response of the wave activity flux to the BH location and their relationship with wintertime stratospheric variability in transient simulations of ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC). After it is verified that EMAC can reproduce qualitatively well the geographical dependence of the BH influence on PW activity injection, it is shown that this dependence does not change in the future. However, an eastward shift of the pattern of the BH influence on PW propagation over the Pacific, a farther eastward extension of the pattern over the Atlantic Ocean, and an intensification of the wavenumber-1 component of the interaction between climatological and anomalous waves are detected. Changes in the upper-tropospheric jet and an intensification of the wavenumber-1 climatological wave due to a strengthening of the Aleutian low agree with these variations. The spatial distribution of future BHs preceding extreme polar vortex events is also affected by the slight modifications in the wave activity pattern. Hence, future BHs preceding strong vortex events tend to be more concentrated over the Pacific than in the past, where BHs interfere negatively with wavenumber-1 climatological waves. Future BHs prior to major stratospheric warmings are located in a broader area than in the past, predominantly over an extended Euro-Atlantic sector.

In the Project on Solar Effects on Chemistry and Climate Including Ocean Interactions (ProSECCO) fundamental questions of the impact of solar variability on Earth have been investigated with improved climate system models and observations. On the decadal time scale, the atmospheric signature of the 11-year Schwabe cycle and the underlying mechanisms have been studied. This included the impact of variations in UV radiation and particle precipitation on stratospheric chemistry and ozone, as well as on the solar signal in the troposphere and on climate. On the centennial to millennium time scale, effects of solar variability on climate of different pre-industrial periods, focusing on the Maunder Minimum and the mid-Holocene, have been addressed.

Heating rate calculations with the FUBRad shortwave (SW) radiation parameterization have been performed to examine the effect of prescribed spectral solar fluxes from the NRLSSI, MPS and IUP data sets on SW heating rates over the 11 year solar cycle 22. The corresponding temperature response is derived from perpetual January General Circulation Model (GCM) simulations with prescribed ozone concentrations. The different solar flux input data sets induce clear differences in SW heating rates at solar minimum, with the established NRLSSI data set showing the smallest solar heating rates. The stronger SW heating in the middle and upper stratosphere in the MPS data warms the summer upper stratosphere by 2 K. Over the solar cycle, SW heating rate differences vary up to 40% between the irradiance data sets, but do not result in a significant change of the solar temperature signal. Lower solar fluxes in the newer SIM data lead to a significantly cooler stratosphere and mesosphere when compared to NRLSSI data for 2007. Changes in SW heating from 2004 to 2007 are however up to six times stronger than for the NRLSSI data. Key Points: - Solar minimum and solar cycle differences in SW heating rates and temperature - Comparison of three spectral solar input data sets for solar cycle 22 - Comparison of the newly compiled SORCE-data with the commonly used NRLSSI-data

[1] The results from two simulations with the coupled chemistry climate model (CCM) ECHAM5/MESSy (EMAC-FUB) are analyzed for the effect of solar variability at the 27 day rotational time scale on ozone. One simulation is forced with constant spectral irradiances at the top of the atmosphere and the other one with daily varying irradiances using data of 1 year for solar maximum conditions. Consistent changes are applied to the photolysis scheme of the model. The model results show the main features of observed correlations between ozone and solar irradiance variability with a maximum positive correlation in the upper stratosphere and an anticorrelation in the mesosphere. The relative sensitivity of upper stratospheric ozone to changes in the solar ultraviolet flux is estimated to be 0.3 to 0.4% per 1% change in 205 nm flux. During periods of strong 27 day variability, a similar upper stratospheric ozone sensitivity is derived. However, when the daily solar irradiance variability is weak and dominated by the 13.5 day period, the ozone sensitivity is reduced in the subtropics. The modeled temperature response is consistent with the ozone signal. When averaged over one rotational cycle, the ozone and temperature response to a neglect of the 27 day cycle is weak and statistically insignificant in the stratosphere but of nonnegligible magnitude and statistically significant in the equatorial mesosphere. Our results suggest that ignoring daily solar flux variations on the 27 day time scale in transient CCM simulations does not lead to a significant degradation of the time mean ozone response in the stratosphere, while in the tropical mesosphere, significant errors of up to 3% may occur. This result does not exclude potential additional effects of 27 day solar cycle variability on stratospheric dynamics in winter which were, however, not the subject of this study.

International audience; Coupled chemistry-climate model simulations covering the recent past and continuing throughout the 21st century have been completed with a range of different models. Common forcings are used for the halogen amounts and greenhouse gas concentrations, as expected under the Montreal Protocol (with amendments) and Intergovernmental Panel on Climate Change A1b Scenario. The simulations of the Antarctic ozone hole are compared using commonly used diagnostics: the minimum ozone, the maximum area of ozone below 220 DU, and the ozone mass deficit below 220 DU. Despite the fact that the processes responsible for ozone depletion are reasonably well understood, a wide range of results is obtained. Comparisons with observations indicate that one of the reasons for the model underprediction in ozone hole area is the tendency for models to underpredict, by up to 35%, the area of low temperatures responsible for polar stratospheric cloud formation. Models also typically have species gradients that are too weak at the edge of the polar vortex, suggesting that there is too much mixing of air across the vortex edge. Other models show a high bias in total column ozone which restricts the size of the ozone hole (defined by a 220 DU threshold). The results of those models which agree best with observations are examined in more detail. For several models the ozone hole does not disappear this century but a small ozone hole of up to three million square kilometers continues to occur in most springs even after 2070.

This repository contains the data from ECHAM6-HAMMOZ simulations. The monthly mean model outputs for several parameters during spring 2020 are made available.